000
FXUS66 KSTO 241055
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
355 AM PDT THU MAY 24 2012

.DISCUSSION...
CENTER OF THE UPPER LEVEL LOW ALONG THE WESTERN CANADIAN
COASTLINE IS MORE EVIDENT ON THE INFRARED IMAGERY THAN ON WATER
VAPOR AT THIS TIME DUE TO LACK OF ENHANCED CLOUDS. THE LOW WILL
TRACK SOUTHWARD TODAY INTO NRN AND CENTRAL CA AS THE UPSTREAM ERN
PAC RIDGE AMPLIFIES THE LONGWAVE PATTERN AND MOVES THE BASE OF THE
TROUGH WITH THE WESTERLY JETSTREAM OVER NORCAL. THIS WILL RESULT
IN SOME GUSTY WINDS OVER HIGHER TERRAIN AND THE TIGHT W-E PRESSURE
GRADIENT WILL BRING BREEZY WINDS INTO THE VALLEY AS WELL. THE
1000-500MB THICKNESS WILL DECREASE TODAY BUT THE LOW LEVEL AND MID
LEVEL THICKNESSES DON`T DROP MUCH, SO WE DIDN`T COOL TEMPS TOO
MUCH TODAY. IT WILL COOL TEMPS MORE SO IN THE MOUNTAINS THAN THE
CENTRAL VALLEY. TEMPS ACROSS OUR CWA COOLING UP TO 5 DEGREES WITH
A SLIGHT CHANCE TO CHANCE OF SHOWERS IMPACTING THE NORTHERN
MOUNTAINS THIS AFTERNOON AND SPREADING SOUTHWARD TONIGHT.

THE MAIN IMPACTS FROM THE STORM OCCUR FRIDAY AS THE CENTER OF THE
UPPER LOW WILL MOVE DIRECTLY OVER NORCAL. EXPECT CHANCE OF SHOWERS
THROUGHOUT THE VALLEY WITH SHOWERS LIKELY ALONG THE SIERRA. THE
COMBINATION OF THE JETSTREAM OVERHEAD AND THE COLD POOL ALOFT MAY
TRIGGER SOME THUNDERSTORM ACTIVITY FRI AFTERNOON AND EVENING FROM
ABOUT A SOUTHERN LAKE TO PLUMAS COUNTY LINE AND SOUTHWARD. PLEASE
KEEP IN MIND THAT LOCALLY GUSTY WINDS AND BRIEF PERIODS OF HEAVY
SHOWERS WITH SMALL HAIL ARE POSSIBLE DURING THUNDERSTORMS.
TEMPERATURES WILL BE ABOUT 15 DEGREES BELOW NORMAL ACROSS OUR CWA
WITH UPPER 60S TO LOW 70S IN THE VALLEY AND UPPER 30S AND 40S OVER
HIGHER TERRAIN. THE COLD POOL WILL DROP SNOW LEVELS TO ABOUT
4500-5500 FEET RESULTING IN 3 TO 5 INCHES OF SNOWFALL ALONG THE
HIGHER ELEVATIONS OF THE SIERRA...HOWEVER MOST ACCUMULATIONS
SHOULD BE LIGHT WITH UP TO 1-2 INCHES OF SNOW. MOST ROADWAYS WILL
NOT SEE AS MUCH SNOW ACCUMULATION DUE TO THE WARM SURFACE TEMPS WE
HAVE BEEN HAVING AND THE FACT THAT THERE ARE MORE DAYLIGHT HOURS
TO KEEP TEMPS RELATIVELY WARMER DESPITE THE COLD POOL ALOFT.

THE CENTER OF THE LOW SHOULD TRACK TO THE EAST OF OUR CWA ON
SATURDAY WHICH WILL ALLOW LINGERING SHOWERS ALONG THE SIERRA.
OTHERWISE, THE REST OF INTERIOR NORCAL SHOULD BEGIN A WARMING AND
DRYING TREND.

SUN THROUGH THU IS DOMINATED BY WEAK RIDGES AND TROUGHS IN THE
MEAN WESTERLY FLOW ALOFT, RESULTING IN DRY WEATHER. TEMPS WILL
WARM INTO THE UPPER 80S TO NEAR 90 IN THE VALLEY BY THU.
JCLAPP

&&

.AVIATION...
VFR ALL TAF SITES TODAY WITH NORTHERLY WINDS 5 TO 15 MPH. COLD
UPPER LOW DROPPING SOUTHWARD INTO NORCAL WILL BRING PRECIP THREAT
NORTHERN MOUNTAINS TONIGHT WITH SHOWER THREAT INTO THE SACRAMENTO
VALLEY BY FRIDAY MORNING. CIGS REMAINING ABOVE 05O THROUGH 12Z
FRIDAY. GENERALLY NORTHWEST WINDS TONIGHT TO 10 MPH.

&&

.STO WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$