SoCal Possible Rainfall Discussion - November 8-11?, 2005

[wxmann_91]

Opinions?

SHOWERS COULD EVENTUALLY DEVELOP DURING THE DAY TUE AND CONTINUING INTO THE NIGHT...HOWEVER CONFIDENCE REMAINS LOW AND CHANCE POPS IS PROBABLY THE BEST WAY TO GO FOR NOW.

...AN APPROACHING PACIFIC STORM WILL BRING UNSETTLED WEATHER TUESDAY
AND TUESDAY NIGHT..

UPPER LEVEL LOW PRESSURE APPROACHING FROM THE NORTHWEST WILL BRING A
CHANCE OF SHOWERS TUESDAY AND TUESDAY NIGHT. THE CHANCE OF RAIN WILL
INCREASE DURING THE DAY TUESDAY AND LINGER INTO TUESDAY NIGHT.
HOWEVER...THE EXACT TIMING AND STRENGTH OF THE STORM ARE STILL
UNCERTAIN SO PEOPLE SHOULD STAY UPDATED ON THE LATEST FORECAST.

PRELIMINARY RAINFALL ESTIMATES ARE FOR GENERALLY LESS THAN HALF AN
INCH IN THE COASTAL AND VALLEY AREAS WITH UP TO ONE INCH ON THE
SOUTHWEST FACING MOUNTAIN SLOPES. ABOUT A QUARTER OF AN INCH OF RAIN
IS EXPECTED IN THE HIGH DESERTS WITH LESS IN THE LOWER DESERTS.
THERE COULD LOCAL SNOW ACCUMULATIONS OF THREE TO SIX INCHES AT THE
HIGHER ELEVATIONS ABOVE 7500 FEET. GUSTY WINDS WILL ACCOMPANY THIS
STORM...MAINLY IN THE MOUNTAINS AND HIGH DESERTS. THERE WILL ALSO BE
A SLIGHT CHANCE OF THUNDERSTORMS TUESDAY AFTERNOON AS COLD UNSTABLE
AIR ALOFT MOVES INTO SOUTHWESTERN CALIFORNIA.

IF THE RAIN DEVELOPS AS EXPECTED THEN THERE COULD BE LOCAL URBAN
FLOODING OF POORLY DRAINED LOW LYING AREAS. MUD SLIDES AND DEBRIS
FLOW WILL BE POSSIBLE IN AND BELOW RECENTLY BURNED AREAS OR ON STEEP
TERRAIN. PEOPLE SHOULD BE PREPARED FOR WINTER WEATHER CONDITIONS AT
THE HIGHER ELEVATIONS OF THE SAN BERNARDINO AND RIVERSIDE COUNTY
MOUNTAINS. MOTORISTS SHOULD USE EXTRA CAUTION ON RAIN SLICK ROADS.
THE SHOWERS ARE EXPECTED TO END WEDNESDAY MORNING AS DRIER FLOW
ALOFT DEVELOPS.

[weatherlover427]

I looked some at the latest GFS models for this storm and it appears to me that this won't be as big as some of the ones we had last year; however it will be the biggest storm we have had so far this year. The GFS shows a 40+ vort at the height of the storm, with 500mb temps below -20C (very cold for early November here). 700mb VV is high (well past 10 on the latest run); and there is even some 850mb speed (aka orographic enhancement) which should help to raise the rainfall totals.

[wxmann_91]

NWS has considerbly backed off on POPS, looks like the ULL will stall too far offshore to bring us rain, but once it moves inland Thursday it could.

We will see...Stay Tuned.

[aveosmth]

Not so fast...This from the LA NWS

.SHORT TERM...CLOSED LOW OFF THE COAST CURRENTLY CENTERED NEAR 33N/126W
WILL BE THE MAIN WEATHER STORY DURING THE NEXT COUPLE OF DAYS. THE
MAIN CONCERN WITH THIS WEATHER SYSTEM IS THE ENTRAINMENT OF
SUBTROPICAL MOISTURE INTO SOUTHERN CALIFORNIA...WITH A LARGE
PRECIPITABLE WATER PLUME OF 1.2 TO 1.5 INCHES TO OUR SOUTHWEST.
AS THIS SYSTEM BEGINS TO TAKE ON MORE OF A NEGATIVE TILT...THERE
WILL BE INCREASING UPPER LEVEL DIFFLUENCE...WHICH IS ALWAYS A KEY
FACTOR FOR HEAVIER RAINFALL POTENTIAL AND POSSIBLE CONVECTION.
18Z NAM CONTINUES TO SHOW A STRONG UPPER LEVEL JET WITH
THIS SYSTEM WITH A 135 KNOT JET CORE TO OUR SOUTHWEST TONIGHT.
THIS WOULD PLACE OUR FORECAST AREA IN THE FAVORABLE LEFT FRONT
QUADRANT TONIGHT...WITH ASSOCIATED UPPER LEVEL DIVERGENCE. WITH
THIS TYPE OF UPPER LEVEL DYNAMICS...WILL HAVE HEIGHTENED CONCERN FOR
HIGHER INTENSITY RAINFALL. AS A RESULT...A FLASH FLOOD WATCH IS IN
EFFECT FOR ALL BURN AREAS OF SANTA BARBARA...VENTURA...AND
LOS ANGELES COUNTIES. FOR MORE INFORMATION ON THE FLOODING POTENTIAL...
PLEASE REFER TO THE LATEST FLASH FLOOD WATCH PRODUCT (LAXFFALOX).

WHILE SCATTERED LIGHT SHOWERS MAY PRECEDE THE MAIN FRONTAL BAND...
TIMING OF HEAVIER RAINFALL IS EXPECTED TO MOVE INTO SAN LUIS OBISPO AND
SANTA BARBARA COUNTIES LATER THIS AFTERNOON AND TONIGHT. ACROSS
VENTURA AND LOS ANGELES COUNTIES...HEAVIER RAINFALL IS EXPECTED TO
MOVE IN OVERNIGHT AND WEDNESDAY. WITH SOME COLDER TEMPERATURES
ALOFT AND STRONG UPPER LEVEL DYNAMICS...WILL HAVE TO BE CONCERNED
WITH THUNDERSTORM POTENTIAL. HAVE INCREASED THUNDERSTORM PROBABILITY
TO CHANCE CATEGORY WITH AFTERNOON PACKAGE. SOME OF THESE STORMS
COULD PRODUCE STRONG WIND GUSTS...LOCALLY APPROACHING SEVERE LEVELS
DUE TO THE FACT STRONG WINDS ALOFT COULD BE PULLED DOWN TO LOWER
ELEVATIONS. WITH THE COLDER AIR ALOFT...SOME STORMS COULD PRODUCE
SMALL HAIL. DUE TO THE VIGOROUS UPPER LEVEL CIRCULATION AND LOW
LEVEL SHEAR PROFILE...COULD NOT RULE OUT LOCALIZED ROTATION IN THE
FORM OF WATERSPOUTS OR SMALL TORNADOS. FOR MORE INFORMATION ON
THE THUNDERSTORM POTENTIAL...PLEASE REFER TO THE LATEST SPECIAL
WEATHER STATEMENT (LAXSPSLOX) AND MARINE WEATHER STATEMENT
(LAXMWSLOX).

WITH THE THREAT OF HEAVIER RAINFALL AND POSSIBLE CONVECTION...
RAINFALL TOTALS HAVE BEEN INCREASED. TOTAL RAINFALL ESTIMATES
WITH THIS STORM THROUGH THURSDAY ARE (0.50) TO (1.50) INCHES ACROSS
LOWER ELEVATIONS WITH LOCAL AMOUNTS UP TO (2.00) INCHES NEAR THUNDERSTORMS.
WITH FAIRLY HIGH PRECIPITABLE WATER VALUES AND UPPER LEVEL DYNAMICS...HIGH
RAINFALL INTENSITIES WILL CERTAINLY BE POSSIBLE. IN ADDITION TO THE FLASH
FLOOD POTENTIAL FOR THE BURN AREAS...WE WILL LIKELY SEE SOME FLOOD ADVISORIES
POSTED FOR OTHER AREAS. MODEL CROSS SECTIONS ARE SHOWING A MORE PRONOUNCED
SOUTH TO SOUTHEAST FLOW IN THE LOWER LEVELS OF THE ATMOSPHERE WHICH
WILL PROVIDE SOME OROGRAPHIC ENHANCEMENT OF RAINFALL TOTALS ACROSS
SOUTH AND SOUTHEAST MOUNTAIN SLOPES AND FOOTHILL AREAS. CURRENT
VANDENBERG VAD WIND PROFILE ALREADY CONFIRMING THIS WITH SOUTHEAST
WINDS UP TO 35 KNOTS IN THE LOWER LEVELS OF THE ATMOSPHERE. ONE TO
THREE INCHES OF RAIN CAN BE EXPECTED ACROSS THE FOOTHILLS AND
MOUNTAINS...WITH LOCAL AMOUNTS UP TO FOUR INCHES POSSIBLE. LATEST MODEL
GUIDANCE HAS PERIODS OF RAIN OCCURRING THROUGH WEDNESDAY EVENING...WITH
SCATTERED SHOWERS POSSIBLY CONTINUING INTO THURSDAY NIGHT.

Sounds like this storm could be nasty if everything comes together.

[wxmann_91]

Maybe in areas to the north, but the San Diego AFD remains conservative:

DECENT COLD FRONT SEEN ON SATELLITE IMAGES. GFS SHOWS FRONT MOVING
INTO SOCAL WED THROUGH EARLY WED NIGHT WITH ANOTHER FRONT DEVELOPING
FROM VORT MAX MOVING THROUGH LATE THU THROUGH FRI MORNING. MODELS
SEEM TO BE MORE CONSISTENT BUT WHERE THE UPPER LEVEL LOW WILL
ACTUALLY MOVE THROUGH IS STILL SOMEWHAT IN DOUBT. LATEST GFS SHOWS
THE LOW MOVING OVER THE BORDER WITH MEXICO AND THEN SHIFT SLIGHTLY
NORTHEAST AS IT EXITS THE AREA FRIDAY MORNING. UPPER LOW STILL COULD
MOVE MORE INTO NORTHERN BAJA AND COULD EVEN BE FARTHER SOUTH. BUT
COLD FRONT LOOKS SOLID AND COULD MOVE THROUGH...BUT THAT FEATURE IS
STARTING TO STRAIGHTEN OUT NORTH TO SOUTH AND COULD SPLIT OFF WITH
THE SYSTEM MOSTLY AVOIDING THE AREA. WILL KEEP GFS FORECAST GOING
WITH CHANCE RAIN MOST AREAS WED AND THEN POSSIBLE SHOWERS AND
THUNDERSTORMS LATE THU INTO FRI. IT APPEARS THE RAIN WILL BE OUT OF
HERE BY FRI AFTERNOON OR POSSIBLY EVEN EARLIER BUT WILL KEEP SLIGHT
CHANCE THROUGH FRI AFTERNOON DUE TO UNCERTAINTY. DYNAMICS LOOK GOOD
FOR WED INTO WED NIGHT. BUT DYNAMICS HEAD SOUTH INTO NORTHERN BAJA
LATE THU INTO FRI MORNING. PRECIPITATION AMOUNTS LOOK TO BE ABOUT
ONE QUARTER TO ONE HALF INCH IN THE COASTAL AREAS TO AROUND AN INCH
IN THE MOUNTAINS. SNOW LEVEL IS FORECAST TO BE RATHER HIGH...NEAR
8000 FEET WEDNESDAY...THEN DROP TO NEAR 7000 FEET THURSDAY. POSSIBLY
3 TO 5 INCHES OF SNOW AT THE HIGHEST ELEVATIONS. HIGH PRESSURE ALOFT
BEGINS TO INCREASE OVER THE AREA LATE FRI. RIDGE BUILDS INTO CENTRAL
CALIFORNIA SAT WITH NORTHEAST FLOW ALOFT. RIDGE CONTINUES TO BUILD
WITH NORTH TO NORTHEAST FLOW ALOFT THROUGH MON WITH LITTLE CHANGE
TUE. A WEAK OFFSHORE FLOW AT THE SURFACE IS FORECAST FOR SUN MORNING
AND CONTINUES IT THROUGH TUE.

Note: changed title to reflect the possible long duration of this event

[weatherlover427]

I think the San Diego NWS always plays it on the "down low" so to speak, until they get slammed then it's like "oops we messed up" ... I remember many times last season they said we would get 1-2 inches of rain along the coast and I ended up having to empty my 4" rain gauge due to the fact that it went over the top!

Also this summer and early fall they underestimated the coastal temps with the Santa Ana winds a few times ... here we got to about 105° or so (even at John Wayne Airport; where the main OC readings are taken) but yet the San Diego NWS never forecasted such high temps.

[weatherlover427]

Well it finally decided to rain last night and this morning - not much but every little bit helps right?

Currently raining as I type. The low center has yet to move onshore; so we may see some heavier rain from that later today.

(btw sorry for double posting)

[aveosmth]

I would say from about Costa Mesa to the San Diego will get the worst of the moisture from the low coming onshore. LI's are in the -2 range offshore, so a chance of T-storms is a good bet as well.

[wxmann_91]

It rained this morning and now it is sunny. With the ULL moving in I'm expecting some thunderstorms with all this destablization that has been going on since late morning.

Also, if you check the NWS San Diego disco, you'll see that they expect heaviest amounts in SD County. Guess this time it was smart to play "down low".

[wxmann_91]

Three words can sum up this rain event:






BIGGEST BUST EVER.

Period. I hope the story of the rainy season isn't going to be continued busts like this one.

[weatherlover427]

My grand total was 0.22"; less than I was hoping for but largely boosted by the passage of the upper low late last night. It brought some moderate rains for about 20-30 minutes at my location in Costa Mesa.