Warning Description: Special Weather Statement

Warning Date: 2:41 PM PST on February 8, 2010

WarningSum:...A Very Cold And Vigorous Storm System Will Affect Southwestern 
California Tuesday Through Early Wednesday...

Warning Message:A strong and very cold upper low off the Pacific northwest coast 
this afternoon is forecast to drop southward along or just off the 
California coast tonight and Tuesday...tracking right across 
southwestern California Tuesday night. This system will threaten the 
region with a variety of weather hazards...including possibly heavy 
showers...thunderstorms...gusty winds and moderate to heavy snow 
accumulations with very low snow levels.
Clouds will increase across the region tonight. Showers will 
likely develop north of Point Conception early Tuesday morning..then 
become likely in all areas Tuesday afternoon and evening. Showers 
will begin to decrease from northwest to southeast across the region 
late Tuesday night. Scattered showers will linger into 
Wednesday...especially across north facing slopes of the Los Angeles 
and Ventura County mountains and the Antelope Valley.
While moisture will initially be fairly limited with this system... 
it may begin to tap into some deeper Pacific moisture as it moves 
into southwestern California late Tuesday and Tuesday night. Very 
cold air aloft associated with the approaching upper low will cause 
increasing instability through the atmosphere Tuesday afternoon into 
Tuesday night...leading to a chance of thunderstorms...some of which 
could produce small hail...very heavy downpours and gusty winds. 
It is not out of the question that some hail could approach severe 
limits...and some waterspouts in the coastal waters could come 
ashore as weak tornados. 
Since the precipitation will be showery in nature...rainfall totals 
Tuesday through early Wednesday will be highly variable...but will 
average one half inch to one inch in coastal and valley areas...with 
up to 1.50 inches in the foothills and mountains. Any areas that
receive thunderstorms may receive higher rainfall totals. It 
appears that the highest rainfall totals will occur across Los 
Angeles County...especially across eastern sections...including the 
station and Morris burn areas. These areas will also have the best 
chance of receiving thunderstorms with high intensity rainfall. 
Residents in and below the recent burn areas should be prepared for 
the potential for very heavy downpours. Flash flood watches may need 
to be issued for the recent burn areas of Los Angeles County... 
especially if the system takes a more over-water trajectory.
Due to the cold nature of this storm...snow will likely fall at very 
low elevations across the region...impacting travel on many major 
routes into and through the mountains. Snow levels are expected to 
start out between 3500 and 4000 feet on Tuesday...then will lower 
to between 2000 and 2500 feet Tuesday night. This would bring 
accumulating snows into portions of the Antelope Valley and
Cuyama valleys...where up to 4 inches are possible...especially in 
the foothills. An inch or two of snow may even fall over the
higher elevations of the Santa Monica Mountains and the interior 
valleys of San Luis Obispo County. Snow may even occasionally fall
in the higher foothills above the Los Angeles and Ventura County 
valleys...but no snow accumulations are expected there. 
In the mountains of Los Angeles and Ventura counties...snow 
accumulations of 6 to 12 inches are expected...with local totals as 
high as 16 inches in the san Gabriels. In the mountains of San Luis 
Obispo and Santa Barbara counties...3 to 6 inches of snow are 
expected. Please refer to (laxwswlox) for more details.
Residents of southwest California are urged to stay tuned to the 
latest National Weather Service statements and possible watches and 
warnings as this weather situation continues to develop.
        

####018005344####
FXUS63 KFSD 082245
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
445 PM CST MON FEB 8 2010

.DISCUSSION...
OCNL LGT SNOW AND BLOWING SNOW SHUD CONT INTO TNGT OVER WRN PART OF 
FCST AREA WITH THE FALLING SNOW DECREASING SLWLY FROM LATE EVE ON. 
SOME BLOWING SNOW WILL CONT THRU THE NGT AND WILL ACCORDINGLY KEEP 
ADVY THRU THE NGT. FRTHR E...AND ESPLY FAR ERN FCST AREA...LGT SNOW 
AND BLOWING SNOW WILL INCREASE FROM THE N THIS EVE WITH SWD PASSAGE 
OF SFC TROF WHICH IS AN UNCOMMON SORT OF WARMFNT. SNOW...WINDS...AND 
TEMPS WILL ALL INCREASE WITH PASSAGE OF THIS TROF...SO ADVY LOOKS 
GOOD FOR AT LEAST THE BLOWING SNOW...XCP WILL KEEP OUT OF FAR SRN 
FCST AREA FROM SPRINGFIELD/YKN TO SUX. BEST UPPER SUPPORT FOR 
SNOWFALL BRUSHES FAR ERN FCST AREA AND UP TO 3 INCHES OF NEW SNOW 
SEEMS PSBL TNGT ALONG ERN BORDER OF FCST AREA...ESPLY ERN PART OF 
SWRN MN. WITH A RATHER SUDDEN INCREASE OF WINDS EXPECTED BY LATE EVE 
FROM CURRENTLY TRANQUIL CONDS...BLOWING SNOW WILL INCREASE 
RPDLY...AND WINTER STORM OR BLIZZARD CONDS NOT COMPLETELY OUT OF THE 
QSTN. WILL KEEP A STG ADVY FOR NOW WITH RIPEST POTENTIAL FOR DECENT 
SNOW AND WHITEOUTS JUST E OF FCST AREA. BASICALLY CONDS WILL BE 
DETERIORATING E AS THEY BEGIN TO IMPROVE OUT W. TEMPS WILL BE GOING 
UP. FOR NOW EXPECT THAT THE WARMING WILL BE SMOOTHED OUT 
SOMEWHAT...ENUF TO PREVENT TEMPS FROM RISING INTO THE 20S AS WE HAVE 
NOW N OF FCST AREA. IN ANY EVENT TEMPS WILL BE TRICKY TNGT./WILLIAMS

THE FINAL WRAP AROUND SHOULD SLOWLY EXIT THE EASTERN HALF OF THE CWA 
THROUGHOUT THE DAY...WITH POSSIBLE ANOTHER HALF AN INCH OR SO OF 
SNOW IN PARTS OF SW MN AND NW IA. WILL STILL SEE SOME AREAS OF 
BLOWING SNOW AS WELL...SO KEEPING THE ADVISORY IN PLACE FOR THESE 
AREAS SEEMS REASONABLE. OTHERWISE...A MODIFIED COLD AIR MASS WILL BE 
IN PLACE WITH HIGHS MAINLY IN THE TEENS ACROSS THE CWA. HIGH 
PRESSURE WILL WORK INTO THE AREA DURING THE DAY...SO WINDS WILL 
DECREASE FROM WEST TO EAST.

BY TUESDAY NIGHT...CLOUDS WILL DECREASE AND WINDS WILL LIGHTEN 
SIGNIFICANTLY...ESPECIALLY WEST OF I29...AS HIGH PRESSURE MOVES 
OVERHEAD. MODEL SOUNDINGS ARE HINTING THAT A LITTLE FOG COULD BE 
POSSIBLE...BUT WITH THE LOWEST LAYER AT ABOUT -13 DEGREES C OR 
COLDER...WOULD SUSPECT MAINLY ICE CRYSTALS SO FOG WOULD BE LESS OF A 
THREAT. OTHERWISE...THIS SHOULD BE THE COLDEST NIGHT OF THE 
WEEK...WITH LOWS RANGING FROM AROUND ZERO FROM SUX TO SLB TO AROUND 
10 BELOW FROM HON TO BKX.

WEDNESDAY WILL SEE A SLOW PROGRESSION OF THE COLD SFC HIGH PRESSURE 
TO THE EAST. THIS WILL KEEP WINDS LIGHT...WITH A SOUTHEAST WIND 
CREEPING UP TO AROUND 10 MPH FROM THE JAMES VALLEY WEST BY 
AFTERNOON. BECAUSE WE WILL BE SHAKING OFF THIS COLD AIR MASS...HIGHS 
WILL REMAIN A BIT CHILLY...RANGING FROM THE MID TEENS TO LOWER 20S.

WEDNESDAY NIGHT INTO THURSDAY WILL SEE THE AIR MASS MODIFY WITH LOWS 
AND HIGHS BOTH ABOUT 10 DEGREES WARMER THAN ON WEDNESDAY. ALBEIT 
WITH LESS SUNSHINE AND MORE WIND. MORNING LOWS WILL RANGE FROM ABOUT 
ZERO TO 5 BELOW IN SW MN AND NW IA TO 5 TO 10 ABOVE IN SC SD. HIGHS 
ON THURSDAY WILL MAINLY BE IN THE 20S. A WEAK PIECE OF ENERGY WILL 
MOVE THROUGH THE SOUTHERN CWA...SO HAVE PLACED A SMALL POP ALONG THE 
MO RIVER FOR LIGHT SNOW. 

IN THE LATTER PERIODS(FRI/MON)...THIS PERIOD LOOKS TO BE DOMINATED 
BY A STRONG EAST COAST TROF...WHICH WILL LIKELY KEEP THE NORTHERN 
PLAINS IN A MODIFIED NORTH TO NORTHWEST FLOW ALOFT. OF COURSE...WITH 
A RELATIVELY FAST NORTHWEST FLOW AT TIMES...WEAK WAVES FORECAST BY 
THE MODELS HAVE BEEN VARYING FROM DAY TO DAY ON TIMING AND 
PLACEMENT...SO NO MAJOR PRECIPITATION THREATS EXPECTED AT THIS TIME. 
WILL CONTINUE A SMALL CHANCE FOR LIGHT SNOW OVER THE EASTERN CWA ON 
FRIDAY WITH A LITTLE BETTER AGREEMENT AMONGST THE MODELS. 
OTHERWISE...THE NEXT POTENTIAL MAY COME SUNDAY...BUT AGREEMENT AND 
THE FACT THAT IT COULD REMAIN EAST OF US WILL KEEP ANY MENTION OF IT 
OUT OF THE FORECAST. OTHERWISE...TEMPERATURES WILL MODIFY BACK 
TOWARDS SEASONAL NORMALS...BUT LIKELY REMAIN JUST BELOW...MAINLY 
WITH RESPECT TO DAYTIME HIGHS. /08

&&