OWS/NWS discussions - same section of the night.

Southern California and far-away places. Hiking, wildlife, cycling etc.

OWS/NWS discussions - same section of the night.

Postby OntarioWeatherService » Wed Sep 19, 2007 6:13 am

I'm not in it for who is better at temperatures. I am in it for these types of events. Who is the most accurate. I'll compare Forecast Discussions. Here is what they have against me.

NWS Area Forecast Discussion.

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES.

LARGE COLD 554 UPPER LOW CENTERED OVER OREGON HAS INCREASED ONSHORE
FLOW AND HAS DEEPENED THE MARINE LAYER TO 4000 FEET. A STRONG SURFACE
LOW PRESSURE WILL DEVELOP AHEAD OF THE LOW OVER NEVADA THIS AFTERNOON
CAUSING GUSTY WEST WINDS OVER THE MOUNTAINS AND DESERTS. WINDS
ALOFT WILL CAUSE THE GUSTY WINDS ON THE THE MOUNTAIN RIDGES AND DOWN
THE DESERT SLOPES THURSDAY AND FRIDAY. THE LOW IS NOW PROGGED TO MOVE
SLOWLY...SO THE BEST CHANCE FOR RAIN AND THUNDERSTORMS WILL WAIT
UNTIL FRIDAY AFTERNOON THROUGH SATURDAY. HOWEVER...THERE WILL REMAIN
A SLIGHT CHANCE OF LIGHT SHOWERS OR DRIZZLE TONIGHT AND THURSDAY
NIGHT DUE TO A 6000 FOOT DEEP MARINE LAYER CAUSED BY THE UPPER LOW.
THE VERY COLD AIR ALOFT WILL CAUSE THE CHANCE OF THUNDERSTORMS AS
THE 560 UPPER LOW CENTER SLOWLY DRIFTS ACROSS SOUTHERN CALIFORNIA
FROM SW TO NE. THE COLD AIR WILL ALLOW SNOW LEVEL TO DROP TO 6000
FEET FRIDAY NIGHT AND SATURDAY. THE LOW DOES NOT HAVE A BIG SOURCE OF
MOISTURE...SO RAINFALL TOTALS WILL BE QUITE VARIABLE RANGING FROM
LIGHT TO UP 3/4 INCH IN ISOLATED LOCATIONS. HEAVIER AMOUNTS ARE
POSSIBLE UNDER ANY THUNDERSTORMS...AND THAT COULD SPELL A PROBLEM FOR
RECENT BURN AREAS IN SBD AND SAN DIEGO MTS. THE LOW EJECTS RAPIDLY
EASTWARD ON SUNDAY...AND VALLEY TEMPS REBOUND INTO THE 80S SUNDAY
THRU WEDNESDAY UNDER HIGH PRESSURE.

.SGX WATCHES/WARNINGS/ADVISORIES...

DENSE FOG ADVISORY IN EFFECT UNTIL 9 AM PDT THIS MORNING...
AND WIND ADVISORY IN EFFECT FROM NOON TODAY TO 11 AM PDT FRIDAY FOR
SAN BERNARDINO COUNTY MOUNTAINS-
RIVERSIDE COUNTY MOUNTAINS-
SAN DIEGO COUNTY MOUNTAINS-

DENSE FOG ADVISORY IN EFFECT UNTIL 9 AM PDT THIS MORNING FOR
SANTA ANA MOUNTAINS AND FOOTHILLS-

WIND ADVISORY IN EFFECT FROM NOON TODAY TO 11 AM PDT FRIDAY FOR
APPLE AND LUCERNE VALLEYS-
COACHELLA VALLEY-
SAN DIEGO COUNTY DESERTS-


OWS Weather Forecast Discussion.

Category - Dynamics include Heavy Rain, Major Winds, and Severe Thunderstorms possible. Upgraded from Category 4 to Category 5 storm. This is a dangerous situation and must not be taken lightly. Flood watches will be issued with this so stay to OWS.

Winter Storm Avery is still very much on track to nail the forecast area Thursday and Friday. I will start out with Thursday. On Thursday Morning before sunrise the center of Avery would be Northwest of San Luis Obispo area. This would put the area under the mid level jet which would aid in shower developments. Thunderstorms are very possible in the area from a -24C 500mb temperature which would create the instability needed. Vorticy advection will add a bonus to this and I don't see how thunderstorms will not form. They should. Small hail is possible with these storms so driving conditions will be hazardous. Areas East of Los Angeles should remain rather dry however some mid level clouds will be with the mid level moisture ahead of Avery and associated jet dynamics.
By Thursday Night Avery would look like a tropical system with structure such as that on satellite. It will look pretty neat and I'll have some archives of those on the post storm discussion of this storm. We will be seeing a major enhancement of vorticy advection for the areas West of Los Angeles after Midnight however with the mid level moisture putting the Inland Empire areas under a dryslot it looks like they will be between moisture fields. Also the vertical velocity patterns would not be strong enough for much of anything but watching this very closely on the next forecast which could alter this. The rest of the forecast area such as Santa Barbara and Vandenberg will have low level vertical velocity/ vort advection / and instability would create thunderstorms in the areas, especially South, and offshore.
By Friday Avery takes a negative tilt which is always good for wicked weather. By the Morning, Avery looks to lose some of it's low level rotation. This would be good for a spiral like band to come into the forecast area from the Channel Islands Vicinity. What I am trying to say is it looks a bit more than just hit and miss showers and thunderstorms. It looks like a full on spiral band type event like a hurricane. Certainly very impressive if this unfolds this way. This band would make it into the Ventura area by the Afternoon bringing showers and thunderstorms to the area with heavy rain. Tehachapi areas would stay drier than the coastal areas as moisture is not very plentiful there at this time but will be later. Being the southerly flow and jet dynamics would be over the areas East of Los Angeles there will be the chance for your action to start there during the Afternoon and increase into the Evening as more moisture and dynamics work their way in.
Snow level Friday would be around 9,000 Feet for the Ventura County Mountains, 8,000 - 7,500 Feet for Big Bear for the dry air in place, 8,000 Feet over the rim, 7,000 Feet Los Angeles County Mountains, 8,000 to 7,000 Feet for the Tehachapi Mountains areas, and 10,000 to 9,000 Feet over the Riverside County Mountains.
By Friday Night the fun really starts for the Los Angeles, Orange County, Inland Empire and Mountain areas nearby as the main dynamics of Avery come in. The main show will be the spiral like band ejecting out which would be in the Los Angeles area by 9pm. This band will satisfy the want for thunderstorms as it will be associated with a very good chance of a light show. These thunderstorms will be driven by a vorticy advection almost too powerful for this area and at this time of year. Same goes with the cold air aloft. I've never in my 10 years of forecasting seen such cold temperatures in September at 18,000 Feet here. The mid level jet will be East of the area however the upper jet will be over the area. A jet streak North of the Inland Empire would make the areas South of the High Desert into the coastal LA/OC/SD areas having thunderstorms as they will be in the upper divergence section of this storm. Favorable jet dynamics and instability will be enough for the mention of tornadoes into Southern California. Yes, I know it sounds crazy but right now it looks like the chance of tornadoes are there. A rare upper level jet will aid the shear positive enough for tornadoes. Waterspouts will be a very good bet as well and all boaters must take this note. It is possible that the OWS Tornado and Severe Thunderstorm Watch will be issued with is so stay tuned. Too much to talk about now so I'll leave it there. For the Vandenberg areas, subsidence on the backside of the storm system would clear out showers and thunderstorms over the night. Thunderstorms will increase over the LA/OC/IE/SD/Mountain/Desert areas night into sunrise Saturday Morning where after then we should clear out the showers and thunderstorms to the Northeast forecast area.
Snow Level Friday Night be 8,000 Feet over the Ventura County Mountains, 7,500 Feet Tehachapi Mountains, 8,000 Feet for the Los Angeles County Mountains, 8,000 Feet for the San Bernardino Mountains, and 8,000 Feet for the Riverside County Mountains. Snow levels can lower a couple thousand to a few thousand feet in the more powerful thunderstorms so take note of the elevation when hitting one overnight. Because of the path of this and associated band, I am inclined to say amounts at this time. The amounts are usually given a day before the event so it will probably be given on Thursday for the areas West of Los Angeles but stay tuned.


Winds The approaching Winter Storm Avery is going to produce the Northerly winds offshore Central California. This would create a 10mb difference from the ocean to the deserts. These winds will drive through the Cajon Pass and jet out in the form of advisory level winds during the Afternoon, Evening for the High Deserts. These winds usually die down overnight but do not count on it. OWS formula indicates winds gusting 45-50mph in the High Desert locations based on Avery's mid level jet moving in. Winds will likely be gusting over 50 mph near 55+ mph for the Antelope Valley sections and Tehachapi Mountains. I have issued a High Wind Warning for this cause for strong Southwesterly winds tonight in those areas. Going to add a Wind Advisory for the Riverside/San Bernardino/and San Diego County Mountains as well overnight tonight. The jet would orient itself much better for Mountain Waves to also surface into the lower deserts including the Coachella Valley as 40-50mph gusts.
Thursday Afternoon Avery's mid level jet sticks over the San Diego and Riverside County Mountain for the strongest winds from 40-50 mph in gusts there with stronger gusts surfacing in the deserts and Eastern Mountain slopes known as Mountain Waves. This will need to be monitored for updates so stay in tune to OWS. Wind Advisory level 35-45+ mph gusts will be in the High Desert during this time as well, along with the San Bernardino County Mountains. Take note.
By Thursday Night, the jet decreases a bit as Avery makes it's transition phase toward a negative tilt. This would make the winds drop in gusts 10-15 mph in all areas mentioned above.
By Friday this transition phase would be completed and the jet would be allowed to speed up. This jet is very strong for this time of year. 55-60 mph gusts will be possible across the San Diego, Riverside, and San Bernardino Mountains, with Mountain waves surfacing in the Northern slopes and adjacent Valleys and Desert areas to the orientation of the Mountains.
By Friday Night - Winds will decrease with the Jet moving East of the forecast area.

ONTARIO WEATHER SERVICE...WATCHES / WARNINGS / ADVISORIES = FOUR

High Wind Warnings -
Tehachapi town - OWS High Wind Warning Issued for 50+ mph gusts in spots favored for Southwest winds overnight tonight. Wind advisory level winds would start of your night and end it with stronger winds in OWS warning level as the mid level jet parks overhead.

Antelope Valley including the Eastern slopes of the Tehachapi Mountains - OWS High Wind Warning Issued for 50+ mph gusts overnight tonight as the mid level jet parks overhead. Mountain Waves surfacing near the Northern slopes looks good right now so keeping it at that.

Wind Advisories -
High Desert - OWS Wind Advisory Issued for 30-45 mph gusts starting on the weak advisory level side in the Afternoon and Evening, increasing to the higher Advisory level overnight. Mountain Waves are possible to surface with a bit stronger gusts at times. Mountain Waves would be for the Lucerne Valley areas.

San Diego County Mountains - OWS Wind Advisory Issued for 30-45 mph gusts starting on the weak advisory level side in the Evening, increasing to the higher Advisory level overnight. Mountain Waves are possible to surface with a bit stronger gusts at times. Mountain Waves would be for the Eastern slopes and adjacent low desert areas.

San Bernardino County Mountains - OWS Wind Advisory Issued for 30-45 mph gusts starting on the weak advisory level side in the Evening, increasing to the higher Advisory level overnight. Residents in Southwest wind favored locations will see these winds, and anyone on the peaks will definitely see them.

Riverside County Mountains - OWS Wind Advisory Issued for 30-45 mph gusts starting on the weak advisory level side in the Evening, increasing to the higher Advisory level overnight. Mountain Waves are possible to surface with a bit stronger gusts at times. Mountain Waves would be for North and Eastern slopes including the Coachella Valley.

Coachella Valley - OWS Wind Advisory Issued for 30-45 mph winds at advisory level overnight. Mountain Waves are possible to surface from the Riverside County Mountains with a bit stronger gusts at times in spots.

Blowing Dust Advisory - Blowing Dust Advisory Issued for the fact the winds will be advisory and warning levels for the High/Low Desert areas including the Coachella Valley The Afternoon/Evening/Overnight. Drivers in the Desert can prepare for visibility drop with most of it dropping in the Antelope Valley Overnight. Be careful.

Fire Weather Watch Issued - While humidity and temps will be down, the main concern is the High Winds OWS is forecasting over the night tonight into tomorrow. These will come without precipitation during that period so I am very concerned about the fire situation. If the winds provide a boost of it it's not going to be too good. I have cautioned and issued an Extreme Risk Fire Watch for this chance. For the San Bernardino Mountains and San Diego Mountains fires. Both are at a risk here.

PENDING WATCHES : TORNADO, SEVERE THUNDERSTORM, FLOOD, BLOWING SNOW ADVISORY.




FINAL THOUGHTS: I think they will bust their 35 mph gust forecast on the fawnskin area tonight. SB Mountains would see 40-50mph gusts or so with this system depending where you are. So we will see.

Kevin
www.ontarioweatherservice.com

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Postby Perry » Wed Sep 19, 2007 10:42 am

Cool! I notice you predict higher snow levels than NWS. That is something we can easily check.

Here's what I found this morning on NWS on
http://www.wrh.noaa.gov/sgx/display_pro ... GX&pil=AFD

AREA FORECAST DISCUSSION

FXUS66 KSGX 191547 AFDSGX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN DIEGO CA 930 AM PDT WED SEP 19 2007 .SYNOPSIS... AN UNUSUALLY STRONG STORM FOR THIS TIME OF YEAR WILL LIKELY BRING SHOWERS WITH POSSIBLE THUNDERSTORMS FRIDAY AND SATURDAY. A DEEP MARINE LAYER AND STRONG ONSHORE FLOW WILL CONTINUE LOW CLOUDS...PATCHY FOG AND DRIZZLE WEST OF THE MOUNTAINS IN THE NIGHTS AND MORNINGS WITH PARTIAL AFTERNOON CLEARING. LOCAL STRONG GUSTY WINDS IN THE MOUNTAINS AND DESERT TODAY INTO SATURDAY. COOL WEATHER...BECOMING WELL BELOW SEASONAL FRIDAY AND SATURDAY. FAIR AND WARMER EARLY NEXT WEEK UNDER HIGH PRESSURE. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES. .SHORT TERM (TODAY-SAT)... DEEP MARINE LAYER THIS MORNING WITH LOW CLOUDS...LOCAL FOG AND ISOLATED DRIZZLE INTO THE COASTAL MOUNTAIN SLOPES. CLEAR AT THE HIGHER ELEVATIONS AND DESERTS. THE 12Z NKX SOUNDING HAD AN INVERSION BASED NEAR 3700 FT WITH DRY WSW WINDS ALOFT. ONSHORE GRADIENTS AND STRONG ONSHORE TRENDS TO THE NE WITH ABOUT 8 MB SAN-TPH AND 6 MB SAN-IPL. A COLD UPPER LOW CURRENTLY OVER THE OR COAST IS EXPECTED TO MOVE S TO OFF THE SRN CA COAST BY FRI. THE SYSTEM WILL THEN MOVE ONSHORE TO THE NE LATE FRI AND EARLY SAT AND THIS WILL BE THE BEST TIME FOR PRECIP. WHILE THE CORE OF COLDEST AIR ALOFT WILL REMAIN JUST TO OUR N...IT WILL BE COLD ENOUGH ALOFT FOR A CHANCE OF THUNDERSTORMS FRI INTO SAT. THERE COULD ALSO BE FUNNEL CLOUDS OR WATERSPOUTS AS THE COLD AIR ALOFT MOVES OVER THE RELATIVELY WARM COASTAL WATERS. THE SNOW LEVEL WILL LOWER TO AROUND 6000 FT FRI NIGHT. A DEEP MARINE LAYER WILL CONTINUE LOW CLOUDS...PATCHY FOG AND LOCAL DRIZZLE W OF THE MOUNTAINS DURING THE NIGHTS AND MORNINGS THROUGH THU NIGHT. ONSHORE GRADIENTS AND INCREASING WINDS ALOFT WILL CAUSE LOCAL GUSTY WINDS IN THE MOUNTAINS AND DESERTS AT TIMES INTO SAT...ESPECIALLY ACROSS THE RIDGES AND INTO THE NRN DESERTS. MOISTURE IS SOMEWHAT LIMITED WITH THE APPROACHING STORM BUT THERE WILL BE A DEEP MARINE LAYER IN PLACE AND GOOD OVER WATER TRAJECTORY WHICH WILL CONTRIBUTE TO AVAILABLE MOISTURE. RAINFALL TOTALS WILL BE QUITE VARIABLE AND SHOULD RANGE FROM VERY SMALL AMOUNTS IN THE DESERTS TO AROUND AN INCH ON W AND SW FACING MOUNTAIN SLOPES. HOWEVER...THERE COULD BE LOCAL LARGER AMOUNTS IN CONVECTION AND ON THE SW FACING SAN BERNARDINO MOUNTAINS WITH LOCAL TOTALS OF 2 TO 3 INCHES POSSIBLE. EVEN SMALL AMOUNTS OF RAIN COULD CAUSE DEBRIS FLOW IN AND BELOW THE RECENTLY BURNED AREAS IN THE SAN BERNARDINO AND SAN DIEGO COUNTY MOUNTAINS. SHOWERS SHOULD TAPER OFF SAT AFTERNOON. && .LONG TERM (SUN-WED)... RESIDUAL MOISTURE WILL CAUSE A FEW CLOUDS SUN AND THE MARINE LAYER WILL REDEVELOP EARLY NEXT WEEK. OTHERWISE...GENERALLY FAIR AND WARMER WEATHER WILL PREVAIL UNDER HIGH PRESSURE. && .AVIATION... 191415Z...MDCRS SOUNDINGS AND MORNING TOP REPORTS PUT THE MARINE LAYER DEPTH AROUND 4500 FEET. STRATOCU WITH BASES BETWEEN 2500 AND 3000 FEET MSL COVERS MOST OF THE AREA WEST OF THE MOUNTAINS. MARINE LAYER IS DEEP ENOUGH THAT THERE COULD BE A REVERSE CLEARING PATTERN THIS AFTERNOON...BREAKUP OVER THE COASTAL WATERS AND ALONG THE IMMEDIATE COAST BUT REMAINING BROKEN OVER THE INTERIOR. STRATOCU SHOULD FILL IN OVER THE COASTAL WATERS AGAIN THIS EVENING. RAIN AND/OR DRIZZLE WILL DEVELOP OVER THE COASTAL SLOPES TO THE COASTAL WATERS TONIGHT THROUGH THURSDAY MORNING. GUSTY SOUTHWEST TO WEST WINDS ACROSS THE MOUNTAINS COULD DEVELOP SOME MOUNTAIN WAVE/ROTOR ACTIVITY OVER THE ADJACENT DESERT AREAS SUCH AS VICINITY KPSP LATER THIS AFTERNOON AND TONIGHT. HORTON && .SGX WATCHES/WARNINGS/ADVISORIES... WIND ADVISORY IN EFFECT FROM NOON TODAY TO 11 AM PDT FRIDAY FOR THE HIGHER MOUNTAINS AND DESERTS. SEE LAXNPWSGX. SPECIAL WEATHER STATEMENT. SEE LAXSPSSGX. && -------------------------------------------------------------------------------- PUBLIC...DVA AVIATION...HORTON

And Special Weather Statement from
http://www.wrh.noaa.gov/sgx/display_pro ... GX&pil=SPS

SPECIAL WEATHER STATEMENT

WWUS86 KSGX 191147 SPSSGX SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE SAN DIEGO CA 500 AM PDT WED SEP 19 2007 CAZ042-043-048-050-055>058-060>062-201300- ORANGE COUNTY COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS- SAN BERNARDINO AND RIVERSIDE COUNTY VALLEYS-THE INLAND EMPIRE- SAN DIEGO COUNTY VALLEYS-SAN BERNARDINO COUNTY MOUNTAINS- RIVERSIDE COUNTY MOUNTAINS-SANTA ANA MOUNTAINS AND FOOTHILLS- SAN DIEGO COUNTY MOUNTAINS-APPLE AND LUCERNE VALLEYS- COACHELLA VALLEY-SAN DIEGO COUNTY DESERTS- 500 AM PDT WED SEP 19 2007 ...STRONG SEPTEMBER STORM LATE THURSDAY THROUGH EARLY SATURDAY... A PACIFIC STRONG STORM FOR SEPTEMBER MAY MOVE THROUGH SOUTHERN CALIFORNIA LATE THURSDAY THROUGH EARLY SATURDAY. THIS STORM HAS THE POTENTIAL TO PRODUCE WEATHER VERY RARELY SEEN IN SOUTHERN CALIFORNIA IN SEPTEMBER. THIS COULD BE THE STRONGEST MID LATITUDE SEPTEMBER STORM FOR SOUTHERN CALIFORNIA IN AROUND 20 YEARS. SEPTEMBER STORMS WITH SOME SIMILARITY TO THIS STORM OCCURRED IN 1986 AND IN 1963. THE STORM WILL MOVE SLOWLY EASTWARD ACROSS SOUTHERN CALIFORNIA THURSDAY NIGHT THROUGH EARLY SATURDAY. THERE ARE STILL SOME DIFFERENCES IN THE TRACK FORECAST AND TIMING FOR THURSDAY THROUGH SATURDAY AND ESPECIALLY FOR THE POTENTIAL IMPACTS TO SOUTHERN CALIFORNIA. STRONG SOUTHWEST WINDS WILL OCCUR IN ADVANCE OF THIS STORM IN THE MOUNTAINS AND DESERTS THIS AFTERNOON INTO FRIDAY. THIS STORM SHOULD BRING MUCH COOLER TEMPERATURES FOR THURSDAY AND FRIDAY WITH COOLEST TEMPERATURES FRIDAY. DEPENDING UPON THE EVENTUAL TRACK AND TIMING OF THIS STORM...THERE IS THE POTENTIAL FOR LOCALLY HEAVY PRECIPITATION AT TIMES FROM LATE THURSDAY THROUGH LATE FRIDAY. THIS STORM WILL BE QUITE COLD FOR SEPTEMBER WITH THE POSSIBILITY OF THUNDERSTORMS AND EVEN FOR SNOWFALL IN THE MOUNTAINS ABOVE 6000 FEET. THERE IS ALSO THE POSSIBILITY OF WATERSPOUTS OVER THE COASTAL WATERS AND TORNADOES OVER ADJACENT LAND AREAS. ANY HEAVY RAINS WILL BRING THE THREAT FOR FLASH FLOODING AND DEBRIS FLOWS OVER THE RECENT BURN AREAS OF THE ANGEL AND BUTLER FIRES. STAY TUNED THE NEXT FEW DAYS FOR LATER UPDATES ON THIS DEVELOPING STORM.
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Postby Perry » Wed Sep 19, 2007 10:45 am

Okay, I notice the NWS does archive their general forecasts, so we can easily verify that Kevin did copy and paste the forecast from 4:30am this morning:
http://www.wrh.noaa.gov/sgx/display_pro ... &version=2
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Re: OWS/NWS discussions - same section of the night.

Postby Perry » Wed Sep 19, 2007 3:30 pm

This part is vague:

OntarioWeatherService wrote:Snow levels can lower a couple thousand to a few thousand feet in the more powerful thunderstorms so take note of the elevation when hitting one overnight. Because of the path of this and associated band, I am inclined to say amounts at this time. The amounts are usually given a day before the event so it will probably be given on Thursday for the areas West of Los Angeles but stay tuned.


because you haven't specified where the "powerful thunderstorms" will be. On Saturday morning, when hikers ride the tram up at 8:00 am, at what elevation will they see snow?

NWS predicts a snow level of 6,000 feet Friday night:
http://www.nws.noaa.gov/alerts/ca.html# ... SGX.175400

Special Weather Statement
Riverside County Mountains (California)
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SAN DIEGO CA
1100 AM PDT WED SEP 19 2007
CAZ042-043-048-050-055>058-060>062-201300-
ORANGE COUNTY COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS-
SAN BERNARDINO AND RIVERSIDE COUNTY VALLEYS-THE INLAND EMPIRE-
SAN DIEGO COUNTY VALLEYS-SAN BERNARDINO COUNTY MOUNTAINS-
RIVERSIDE COUNTY MOUNTAINS-SANTA ANA MOUNTAINS AND FOOTHILLS-
SAN DIEGO COUNTY MOUNTAINS-APPLE AND LUCERNE VALLEYS-
COACHELLA VALLEY-SAN DIEGO COUNTY DESERTS-
1100 AM PDT WED SEP 19 2007
...STRONG SEPTEMBER STORM FRIDAY AND SATURDAY...
A STRONG PACIFIC STORM FOR SEPTEMBER IS EXPECTED TO MOVE THROUGH
SOUTHERN CALIFORNIA LATE FRIDAY AND EARLY SATURDAY. THIS STORM HAS
THE POTENTIAL TO PRODUCE WEATHER RARELY SEEN IN SOUTHERN CALIFORNIA
IN SEPTEMBER. RAIN COULD BEGIN AS EARLY AS THURSDAY WITH SHOWERS
INTO FRIDAY BUT THE HEAVIEST PRECIPITATION IS EXPECTED FRIDAY NIGHT
INTO EARLY SATURDAY MORNING.
RAINFALL TOTALS WILL BE QUITE VARIABLE DUE TO THE SHOWERY NATURE OF
THE RAIN. PRELIMINARY RAINFALL ESTIMATES ARE FOR ABOUT A QUARTER TO
HALF AN INCH NEAR THE COAST TO ONE INCH ON THE COASTAL MOUNTAIN
SLOPES AND FOOTHILLS WITH UP TO A QUARTER INCH IN THE DESERTS. THERE
COULD BE LOCAL LARGER AMOUNTS OF ONE AND A HALF TO TWO AND A HALF
INCHES ON THE WEST AND SOUTHWEST FACING MOUNTAIN SLOPES OR IN
CONVECTION. ANY SIGNIFICANT RAIN WILL BRING THE THREAT OF FLASH
FLOODING AND DEBRIS FLOW IN AND BELOW RECENT BURN AREAS.
THE COLD AIR ALOFT WILL CAUSE ENOUGH INSTABILITY FOR A CHANCE OF
THUNDERSTORMS. THE SNOW LEVEL WILL LOWER TO NEAR 6000 FEET LATE
FRIDAY NIGHT. LOCAL STRONG GUSTY WINDS WILL PRECEDE AND ACCOMPANY
THIS STORM...MAINLY IN THE MOUNTAINS AND DESERTS. THERE IS ALSO THE
POSSIBILITY OF WATERSPOUTS OVER THE COASTAL WATERS AND FUNNEL CLOUDS
OR EVEN A TORNADO.
SHOWERS WILL TAPER OFF SATURDAY AFTERNOON AS THE STORM MOVES
NORTHEAST. PEOPLE SHOULD STAY INFORMED ON THIS DEVELOPING STORM.
$$
DVA
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Postby OntarioWeatherService » Wed Sep 19, 2007 5:07 pm

Perry with any strong thunderstorm it can lower, but I'll just stick with my higher snow levels without the drop. I do think it's higher than most were forecasting at the time I pasted.
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Postby Perry » Wed Sep 19, 2007 8:59 pm

Great! Even if NWS is more accurate this time, I admire the fact that you are willing to try this experiment. For those not familiar, Mt. San Jacinto is in Riverside County, so Kevin's prediction is a snow level around 9,000 to 10,000 feet, and NWS predicts 6,000 feet. This will be interesting to see on Saturday....
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Round 2

Postby OntarioWeatherService » Thu Sep 20, 2007 6:15 am

NWS FORECAST DISCUSSION EARLY THURSDAY MORNING 9/20/07

STRONG 12 MB ONSHORE FLOW TO A 1000 MB LOW OVER NEVADA WILL CAUSE A
6000 FT DEEP MARINE LAYER AND GUSTY SW WINDS. THIS WILL DRAG SOME
MARINE LAYER STRATUS INTO THE UPPER DESERTS...AND CAUSE SCATTERED
LIGHT RAIN SHOWERS OR DIRZZLE WEST OF THE MTS TODAY. WAD WINDS WILL
CONTINUE IN THE MTS AND DES.

FRIDAY WILL BE A HEAVY WEATHER DAY. THE 550 UPPER LOW WILL BE JUST
WEST OF THE CHANNEL ISLANDS FRI MORNING. LIGHT PRECIP WILL LIKELY BE
SQUEEZED OUT OF THE DEEP MARINE LAYER THROUGH THE MORNING WEST OF THE
MOUNTAINS. RAIN SHOULD INCREASE MID DAY AS A WARM FRONT DEVELOPS
AHEAD OF THE UPPER LOW. AS THE LOW CONTINUES MOVING IN FROM THE WEST
A STRONG COLD FRONT WILL COME IN BETWEEN 4 PM AND MIDNIGHT FRIDAY.
IMPRESSIVE 1 INCH BULLSEYE WITH THIS FRONT. COLD UNSTABLE AIR WITH -3
LIFTED INDEX WILL LIKELY CAUSE THUNDERSTORMS WITH GUSTY WINDS...SMALL
HAIL...AND PERIODS OF HEAVY RAIN. LOTS OF VORTICITY AND SHEAR...SO
PERHAPS EVEN A TORNADO COULD OCCUR. WATERSPOUTS NEAR COAST POSSIBLE.
STRONG SOUTH WINDS UNDER THE LEFT FRONT QUADRANT OF THE CYCLONCALLY
CURVED 125 KT JET COULD CAUSE FLASH FLOODING IN THE SAN BERNADINO
MOUNTAINS FRIDAY AFTERNOON THROUGH FRIDAY NIGHT. THE SNOW LEVEL WILL
ABOVE 7000 FEET FRIDAY...LOWERING TO 6000 FEET FRIDAY NIGHT. MOST
MOUNTAIN PRECIP WILL BE RAIN...BUT THE HIGHER RIDGES COULD END UP
WITH A PATCHY 6 INCH SNOW CAP.

THE STORM SHOULD LET UP EARLY SAT MORNING...BUT A BURST OF SCATTERED
SHOWERS AND THUNDERSTROMS WILL ARRIVE LATER SAT MORNING AS THE 558
CENTER OF THE UPPER LOW ACCLERATES NE ACROSS THE AREA. THE LOW WILL
BE OVER NEVADA BY LATE SAT PM. GUSTY WEST WINDS WILL ENSUE...WHICH
MAY EXTEND THE WAD FOR THE MTS AND DES. THE ONSHORE FLOW WILL CAUSE
A DEEP MARINE LAYER AND CLOUDY SKIES SAT PM.

SGX WATCHES/WARNINGS/ADVISORIES...

WIND ADVISORY
REMAINS IN EFFECT UNTIL 11 AM PDT FRIDAY FOR
SAN BERNARDINO COUNTY MOUNTAINS-
RIVERSIDE COUNTY MOUNTAINS-
SAN DIEGO COUNTY MOUNTAINS-
APPLE AND LUCERNE VALLEYS-
COACHELLA VALLEY-
SAN DIEGO COUNTY DESERTS-


----

OWS FORECAST DISCUSSION EARLY THURSDAY MORNING 9/20/07

Ontario Weather Service
Winter Storm Avery
Category 5
Storm Forecast Discussion
September 20, 2007 - 6:00amPDT
Forecast took about 6-7 hours to complete.



Category - Dynamics include Heavy Rain, Moderate Winds, and Severe Thunderstorms possible. Category 5 storm. This is a dangerous situation and must not be taken lightly.

Winter Storm Avery as of 1am 9/20/07 was moving down the Central California coastline. On Thursday I expect thunderstorms into the San Luis Obispo area as Avery's moisture field and instability dynamics come into the area. Vandenberg personal must be on alert with this system as thunderstorms look very probable with a -22C 500MB temperature and warm enough lower levels for instability needed for this. some of which could contain waterspouts and hail in spots. This area will be off pure instability dynamics as the mid/upper level jets will be over the Los Angeles and Inland Empire areas where I believe we will be in a dry slot so other than some clouds in the area from the marine layer and a some mid level clouds not expecting much of anything there. Same goes with San Diego areas. Most action will happen in the areas East of Los Angeles by this point as this is the area of the deepest moisture field. Increasing activity in those areas into the Afternoon and Evening hours.
By Thursday Night Avery is going to start spinning up more and more on itself as warmer low level air interacts with it further from the coast. This is similar to a tropical system but it is not even close to the definition so don't take my word for it and run for the hills because it's a tropical system. The thing about Avery is it will have spiral bands visible on satellite at this time. I will be going by sections to get you the best information possible. The San Luis Obispo areas will not be in jet dynamic influences so the thunderstorms will again be driven on instability in the area where a -22C 500MB temp will still exist along with that warmer low level air. This is more than enough ins tability for thunderstorms. The moisture field will be deepest over the Southern Vandenberg areas as it ejects later on in the night from Avery's core. This will come ashore as showers and thunderstorms, some of which could contain waterspouts and hail in spots so watch out driving. This goes for Santa Barbara and Ventura as well. Flood watches will likely be needed.
This spiral band will be coming toward the LA/OC areas as well around this time but nothing looks like it will happen till Early Friday Morning there.
I will say this though and it will put my forecasting to the test. National Weather Service says Marine Layer tonight for the same areas as last night with deep and drizzle or light rain from it. I am taking it out of my forecast during this time and leaving it out because of the the dry air in place in the boundary layer looks interesting to me. Not to mention the sinking air ahead of Avery's spiral arms would destroy it by mixing in some dry air. Going on a limb like I always do but I will keep the Marine Layer out of the forecast and leave some clouds along the Northern Mountain slopes in from compression.
By Friday Early morning is where Avery will release it's spiral band outward. I expect this to be around 1am where it will look like a spiral shape crescent moon. By sunrise this area should be just Offshore of the LA/OC areas. This spiral band will be entering an area of extreme jet dynamics in the upper levels. The orientation of the jet would make a strong vortices area in the offshore vicinity which would enhance this entire band further over as the sun rises. This will look rather odd on satellite and radar for this area of the country but it will be worth waiting all the years of forecasting to see something like this. Vort advection in the area would allow this to have some embedded thunderstorms with it. Just before Noon on Friday a low level jet would set up offshore Orange County and San Diego. This would allow the convergence line to be setup enough to blow this up into a major rain event offshore so Catalina Island will need to watch out with this one. Because of the upper level jet speed orientation to the low level jet I would say an OWS Tornado Watch will be pending for this event across the Coastal areas of San Diego / Orange / Los Angeles / Ventura Counties for Waterspouts and this will be mentioned as well in the Ocean Forecast Center for sailor's to take note and watch out. Severe Thunderstorm Watch will likely be needed so pending that as well in the same areas for this time of day. Flood watches issued. It should be starting to rain in the Afternoon and the action will be just starting for the LA/OC/IE areas.
Snow level Friday would be around 6,000 Feet for the Ventura County Mountains, 7,000 Feet for Big Bear for the dry air in place, 6,500 Feet over the rim, 6,500 Feet Los Angeles County Mountains, 7,000 Feet for the Teach Mountains areas, and 7,000 Feet over the Riverside County Mountains.
By Friday Evening/Night during the dinner hour most of you will be out as it is indeed a Friday Night so I'll get right to the goods. By the Evening Avery would have ejected this waiting batch of showers and thunderstorms across the Riverside/ Orange/Los Angeles/ Ventura / San Bernardino County areas dropping heavy rains and thunderstorms in the areas. These thunderstorms would be aided by a 120 mph upper level jet and associated vort advection dynamics. These storms look more numerous across the LA/OC/IE/Ventura areas and less numerous across the San Diego area as you look to be pretty much in a minor intrusion of dry air known as a weak dry slot. I would say areas in the San Bernardino areas would get them around oh say just before sunset. The profile of the atmosphere over the Inland Empire is more unstable than the one of over the coastal area due to the warmer air that would be in place so I wouldn't see how thunderstorms and a tornado watch wouldn't be needed there as well and that will be pending. Same with a Severe Thunderstorm Watch . After sunset toward the 11pm hour the low level moisture increases and so do the storm chances for the Los Angeles areas Eastward. At this point I do not see any reason thunderstorms wouldn't form in this system and it is very tough to forecast. Because of the upper level jet orientation vs instability axis I would say the Tornado Watch would go into this time as well from Los Angeles to San Diego, and through the Inland Empire areas. Same with the Severe Thunderstorm Watch. Will pend those on the final forecast. Worth a note the transition to negative tilt storm would be maximized by this time. Hail is possible and waterspouts in the ocean. If everything stays on forecast we could still be seeing what I want to call a light show.
Everything should calm down by Saturday Morning. There is indication of a small front down the San Luis Obispo areas coast Saturday Night but at this time I don't think much would come from it.
Snow Level Friday Evening/Night be 7,500 Feet over the Ventura County Mountains, 8,000 Feet Tehachapi Mountains, 8,500 Feet for the Los Angeles County Mountains, 8,500 Feet for the San Bernardino Mountains, and 8,000 Feet for the Riverside County Mountains. Snow levels can lower a couple thousand to a few thousand feet in the more powerful thunderstorms so take note of the elevation when hitting one overnight. Because of the path of this and associated band, I am inclined to say amounts at this time. The amounts are usually given a day before the event so it will probably be given on Thursday for the areas West of Los Angeles but stay tuned.

Winds
Thursday Afternoon Avery's mid level jet would develop Advisory level winds in the Mountains and Deserts from 30-35 mph gusts with slight higher near 40mph in the San Diego County Mountains due to mid level jet orientation.
By Thursday Night, Winds would stay advisory level in the Mountains and Deserts.
By Friday Negative tilt would be on the way with 30-45 mph gusts from the Riverside County Mountains to the High Deserts on down to the San Diego Mountains from a speed up of the Mid level Jet. Increasing onshore gradients would make stronger winds in the Inland Empire as well, and downsloping down the Eastern side of the Santa Ana Mountains.
By Friday Night - Winds will decrease with the Jet moving East of the forecast area.



Forecasted Storm Rain Amounts : In Inches , First number is calculated, Second is leeway.
San Luis Obispo - 0.25 - Tops to 0.50
Santa Barbara - 0.40 - Tops to 0.80
Los Angeles - 0.30 - Tops to 0.60
Burbank - 0.50 - Tops to 1.00
John Wayne International - 0.50 - Tops to 1.00
Orange County Foothills - 0.60 - Tops to 1.10
San Diego - 0.25 - Tops to 0.50
San Diego Mountains - 0.75 - Tops to 1.25
Ontario International Airport - 0.30 - Tops to 0.60
High Desert - 0.20 - Tops to 0.40
Cajon Summit - 0.40 - Tops to 0.60


Forecasted Snow Amounts
Check this link here.
http://www.ontarioweatherservice.com/snowforecast.html

CURRENT OWS WATCHES OUT :
Flood Watch
http://www.ontarioweatherservice.com/fw.html

Blowing Snow Advisory
http://www.ontarioweatherservice.com/bsa.html

Wind Advisory
http://www.ontarioweatherservice.com/wfc.html

Severe Thunderstorm Watch Pending
http://www.ontarioweatherservice.com/stw.html

Tornado Watch Pending
http://www.ontarioweatherservice.com/tw.html

Kevin Martin
OntarioWeatherService.Com
www.ontarioweatherservice.com

Admin note: This is a private weather forecasting service and is not associated with National Weather Service or Ontario International Airport.
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Postby Perry » Fri Sep 21, 2007 12:54 am

I noticed you changed your snow level estimate to 7,000 feet Friday and 8,000 feet Friday night. National Weather Service still says 6,000 feet.
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Postby Perry » Fri Sep 21, 2007 1:46 am

You've posted a lot of text. Could you point out some key differences between OWS and NWS that we can compare to observations and see which is more accurate?
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Postby OntarioWeatherService » Fri Sep 21, 2007 4:44 am

Perry, NWS just said this.

"THIS STORM DOES NOT HAVE AS MUCH COLD AIR AS EARLIER THOUGHT...ESPECIALLY SINCE SOME WARM AIR ADVECTION AT 700 MB COULD LIFT THE FREEZING LEVEL FRI NIGHT/SAT. THE SNOW LEVEL WILL PROBABLY NOT GO BELOW 7000 FEET AT ANY TIME THROUGH SAT. SOME SNOW COULD STILL OCCUR SINCE THE MOIST LAYER WILL EXTEND UP TO ABOUT 10000 FEET IN THE SBD COUNTY MTNS...SO A FEW INCHES COULD FALL ABOVE 7000 FEET."


The difference between OWS and NWS is the Tornado Watch I just issued, and the Snow Levels. The snow levels for them was 6,000 Feet when I had the highest all along out of Mike,Ben,and NWS per this article.
http://www.rimoftheworld.net/columns/straley/bizarre

NWS just now upped the levels when I've had the highest all along
Questions?

We will see when the storm is over. My snow forecast formula indicated higher than everyone thought. The formula is a very good thing I developed for snow levels.

Kevin
www.ontarioweatherservice.com

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