000
FXUS66 KSTO 280517
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
920 PM PST MON DEC 27 2010
.DISCUSSION...
LIGHT RAIN MOVING INTO NORCAL THIS EVENING AS THE REGION PREPARES
FOR ANOTHER WET SYSTEM TUESDAY AND WEDNESDAY. SO FAR ONLY A
HUNDREDTH OF AN INCH HAS FALLEN IN REDDING AND RED BLUFF WITH JUST A
FEW HUNDREDTHS FALLING ACROSS THE NORTHERN MOUNTAINS IN SHASTA
COUNTY. LIGHT PRECIPITATION WILL CONTINUE OVERNIGHT OVER NORCAL AS
SNOW LEVELS REMAIN HIGH AROUND 4000-6000 FEET FROM NORTH TO SOUTH.
CONDITIONS WORSEN TOMORROW AS THE FRONTAL SYSTEM MOVES INLAND. RAIN
WILL SPREAD SOUTHWARD AND EASTWARD ON TUESDAY WITH THE BULK OF
PRECIPITATION OCCURRING IN THE AFTERNOON AND EVENING. SOUTHERLY
WINDS EXPECTED TO INCREASE JUST AHEAD OF THE FRONTAL PASSAGE CAUSING
BREEZY CONDITIONS DURING STORM PASSAGE. WITH VALLEY RAIN AMOUNTS
EXPECTED NEAR 1/2 TO 1 INCH...AND FOOTHILL RAIN AMOUNTS UP TO A
COUPLE OF INCHES...RESIDENTS SHOULD BE AWARE OF POSSIBLE IMPACTS
ESPECIALLY GIVEN THE WET WEATHER THIS PAST SATURDAY. DURING THE
FRONTAL PASSAGE THERE COULD BE SHORT BOUTS OF MODERATE TO HEAVY RAIN
WHICH COULD RENEW RISES IN CREEKS AND STREAMS AS WELL AS CAUSE
PONDING ON ROADWAYS. BREEZY WINDS WILL CONTRIBUTE TO LOCALIZED
FLOODING BY BLOWING LOOSE LEAVES THAT COULD PLUG UP STORM DRAINS AND
GUTTERS. WINDS COULD ALSO CAUSE DOWNED TREES AND BRANCHES WHICH MAY
LEAD TO LOCAL POWER OUTAGES. ALONG THE FOOTHILLS...SATURATED SOILS
COULD CREATE ROCK/MUD SLIDES.
SNOW LEVELS WILL INITIALLY REMAIN BETWEEN 4000-6000 TOMORROW DURING
THE ONSET OF THE STORM THEN LOWER TUESDAY NIGHT BETWEEN 3000-5000
FROM NORTH TO SOUTH. HEAVY SNOW ACCUMULATIONS EXPECTED ABOVE 4500
FEET ACROSS WESTERN PLUMAS COUNTY AND THE LASSEN PARK REGION ALONG
WITH THE WESTERN SIERRA SLOPES. STORM TOTALS COULD BE UP TO A COUPLE
FEET OF NEW SNOW...LOCALLY HIGHER NEAR RIDGETOPS. WINTER STORM
WARNING IS IN EFFECT INTO WEDNESDAY FOR THESE REGIONS.
A MUCH COLDER AIRMASS IS PROGGED TO MOVE OVER OUR REGION WEDNESDAY
MORNING AND PERSIST THROUGH THE DAY...700 MB TEMPS RANGING -13 TO
-17 DEGREES C. THIS WILL NOTABLY DROP SNOW LEVELS ON
WEDNESDAY...DOWN AROUND 2000-3000 FEET...LOCALLY LOWER ACROSS
PORTIONS OF THE NORTHERN MOUNTAINS. RAIN AND SNOW SHOWERS ARE
EXPECTED TO TAPER OFF BY WEDNESDAY MORNING SO ONLY LIGHT
PRECIPITATION SHOULD BE OCCURRING WHEN SNOW LEVELS DROP. JBB
BEHIND THIS SYSTEM BREEZY NORTHERLY FLOW AND A VERY COLD AIRMASS
SETTLE OVER THE REGION AS A RIDGE AMPLIFIES OVER THE WEST COAST.
AT THIS TIME IT LOOKS LIKE MANY PLACES FOR THE CENTRAL VALLEY
THURSDAY MORNING WILL BE NEAR OR BELOW FREEZING. COLD OVERNIGHT
TEMPERATURES WILL LIKELY CONTINUE INTO FRIDAY MORNING.
.EXTENDED DISCUSSION (FRIDAY THROUGH MONDAY)...
SOME DISCREPANCY EXISTS IN THE MODELS FOR THE LONG TERM. GFS
MAINTAINS THE RIDGING PATTERN INTO SATURDAY MORNING WHILE THE ECMWF
MODEL DEVELOPS A CLOSED LOW JUST OFFSHORE OF THE NORCAL COASTLINE.
THE GFS DOES SHOW A DISTURBANCE MOVING SOUTHWARD INTO THE GREAT
BASIN ON SATURDAY AFTERNOON...EAST OF THE SIERRAS. MEANWHILE THE
ECMWF EDGES THE CLOSED LOW INTO NORCAL. BY SUNDAY...THE PROGRESSIVE
GFS MOVES THE LOW EASTWARD PUTTING OUR REGION BACK UNDER THE
INFLUENCE OF RIDGING WHILE THE ECMWF SHOWS NORCAL GETTING WET FROM
THE CLOSED LOW. EXTENDED FORECAST WAS TRENDED TOWARDS THE GFS
KEEPING A SLIGHT CHANCE TO CHANCE OF RAIN/SNOW SHOWERS OVER THE NEW
YEAR'S WEEKEND.
&&
.AVIATION...
EVEN THOUGH VFR CONDITIONS STILL CONTINUE TO PREVAIL THIS
EVENING...A FEW LIGHT SHOWERS ARE DEVELOPING OVER THE NORTH END OF
THE VALLEY AND SURROUNDING FOOTHILLS AND MOUNTAINS. THESE VFR
CONDITIONS WILL GIVE WAY TONIGHT THOUGH TO MVFR CONDITIONS WITH
AREAS OF IFR CONDITIONS POSSIBLE...AS MORE WIDESPREAD PRECIPITATION
SPREADS ACROSS NORTHERN CALIFORNIA. IN THE MEANTIME THOUGH...SOME
PATCHY FOG AND LOW CLOUDS ARE TRYING TO FORM ACROSS THE EASTERN
PORTIONS OF THE NORTHERN SAN JOAQUIN AND SOUTHERN SACRAMENTO
VALLEYS. THEREFORE...EXPECT PREDOMINATELY MVFR/IFR CONDITIONS TO
DEVELOP IN THE VALLEY...WITH LOW LIFR CONDITIONS POSSIBLE IN FOG
BETWEEN 08Z AND 16Z. IN THE MOUNTAINS...EXPECT IFR/LIFR CONDITIONS
TO DEVELOP LATE TONIGHT...WITH SNOW LEVELS INITIALLY STARTING OUT
RANGING BETWEEN 4000 AND 5000 FEET TONIGHT. SNOW LEVELS WILL RISE
BETWEEN 1000 AND 1500 FEET TOMORROW...WITH THE WARM AIR
ADVECTION....BUT FALL ONCE AGAIN WITH THE COLD FRONT TUESDAY
EVENING. THE COLD FRONT WILL BRING PERIODS OF GUSTY SOUTH WINDS AS
WELL AS A BRIEF PERIOD OF MODERATE TO HEAVY PRECIPITATION TUESDAY
EVENING.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM 2 PM TUESDAY TO 10 AM PST WEDNESDAY
ABOVE 4500 FEET FOR THE WESTERN PLUMAS COUNTY/LASSEN PARK.
WINTER STORM WARNING FROM 4 PM TUESDAY TO 4 PM PST WEDNESDAY
ABOVE 5000 FEET FOR THE WEST SLOPE NORTHERN SIERRA NEVADA.
WINTER WEATHER ADVISORY FROM 10 AM TUESDAY TO 4 AM PST WEDNESDAY
ABOVE 4000 FEET FOR THE BURNEY BASIN / EASTERN SHASTA COUNTY...
MOUNTAINS SOUTHWESTERN SHASTA COUNTY TO NORTHERN LAKE COUNTY...
SHASTA LAKE AREA / NORTHERN SHASTA COUNTY.
&&
$$
