000
FXUS66 KSTO 172218
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
330 PM PDT WED MAR 17 2010

.DISCUSSION...
AREA OF HIGH CLOUDINESS (BASES ~20 KFT ACCORDING TO KDAX VWP) NOW
GENERALLY ALONG AND SOUTH OF I-80. THE CLOUDS ARE GENERALLY SOUTH OF
THE DEFORMATION OR STRETCHING AXIS LOCATED ACROSS NORCAL...NEWD INTO
THE LOW CENTER OVER THE SRN CANADIAN PROVINCES. ALONG THIS
DEFORMATION AXIS...WATER VAPOR IMAGERY SHOWS A LITTLE ENHANCEMENT OF
MOISTURE ALONG I-80 WHERE IT IS CONCEIVABLE A SPRINKLE/MTN FLURRY
MAY OCCUR THROUGH THE EARLY EVENING. OTHERWISE... SKIES WILL BE
CLEARING TONIGHT AS THE CLOUDINESS WILL BE SHUNTED SWD BY THE
INCOMING SHORT WAVE THAT WILL BE MOVING ACROSS ORE. THIS NRN SHORT
WAVE WILL ALSO BE SHUNTING THE INCOMING SHORT WAVE TROF OFF THE
SOCAL COAST TO THE S OF NORCAL OVERNITE. THUS...SKIES ARE EXPECTED
TO CLEAR OVER THE SRN HALF OF NORCAL OVERNIGHT. IT WAS A SEASONABLY
WARM DAY TODAY WITH TEMPS IN THE 70S IN THE VLY...60S TO LOW 70S
MOUNTAINS AND LOWER FOOTHILLS...AND 50S HIGHER ELEVATIONS. THESE
TEMPS ARE ABOUT 10-15 DEG ABOVE NORMAL...WITH THE POSSIBILITY THAT
RDD/RBL MAY TOUCH 80.

IT APPEARS IT WILL BE TURNING BREEZIER/WINDIER OVER NORCAL ON THU
AND THU NITE INTO FRI AS THE MODELS CONTINUE TO FORECAST THE
INTENSIFICATION OF THE TROF/VORT MAX MOVING ACROSS ORE TONIGHT AND
SLIDING SSEWD OVER NORCAL ON THU. THIS FEATURE IS SLIDING SEWD ON
THE E SIDE OF THE AMPLIFYING RIDGE OFF THE W COAST...AND SW OF THE
MAIN LOW SPILLING OVER THE RIDGE FROM B.C. AND FORECAST TO TRACK
TOWARDS THE 4-CORNERS. TODAY`S GFS/NAM SHOW THE ORE VORT MAX
TRACKING MAINLY OVER THE SIERNEV ON THU...FOLLOWED BY AN AMPLIFYING
RIDGE ALONG THE W COAST REACHING NWD TOWARDS THE ARCTIC CIRCLE FOR
FRI. SO AFTER SOME INITIAL COOLING ON THU DUE TO THE STRONG MID
LEVEL CAA...TEMPS ARE EXPECTED TO REBOUND WELL ABOVE NORMAL ON FRI
AND INTO THE WEEKEND.

GIVEN THE TRACK OF THE VORT MAX...VERY STRONG MID LEVEL CAA...
STRONGER CYCLONIC FLOW AND ALBEIT WEAK UPPER LEVEL DIVERGENCE...WE
DO BELIEVE SOME CONVECTION/SHOWERS IS/ARE POSSIBLE OVER THE SIERNEV
ON THU. MOISTURE WITH THIS SYSTEM IS EXPECTED TO BE VERY SPARSE WITH
ONLY .30 TO .50 INCH PWS AHEAD OF THE VORT MAX/FRONT AND VERY LOW PW
AIR /LESS THAN .20 INCH/ ADVECTED SWD ON THU BEHIND THE VORT MAX/
FRONT AND CONTINUING INTO THE WEEKEND. THE VORT MAX MAY BE STRONG
ENOUGH TO SQUEEZE OUT SOME LIGHT PCPN OR RESULT IN SOME SMALL...
SCATTERED AND RELATIVELY HIGH-BASED STRATOCUMULUS OR ALTOCUMULUS IN
THE VALLEY UNTIL FROPA. THE GFS CROSS SECTIONS INDICATE THAT
SYNOPTIC SCALE DOWNSLOPE FLOW WILL PREVAIL ON THE W SIDE OF THE
SIERNEV ESPECIALLY AFTER TROF/FRONTAL PASSAGE WHICH WILL ALSO
PRECLUDE SHOWER DEVELOPMENT IN OUR FORECAST AREA. BELIEVE THE SHOWER
ACTIVITY WILL BE CONFINED MORE TO THE CREST AND UNLIKELY TO REACH
THE FOOTHILLS. N TO NE PRESSURE GRADIENTS WILL INCREASE BEHIND THE
LOW CENTER THU AND INTO FRI MORNING FOR BREEZY/WINDY N TO E WINDS AT
TIMES OVER PORTIONS OF OUR FORECAST AREA. THESE WILL BE DRYING/
SUBSIDING WINDS. ALREADY...THE MFR-RDD GRADIENT HAS INCREASED TO
OVER 8 MBS AND NLY WINDS SHOULD INCREASE AND BECOME GUSTY AFTER TROF
PASSAGE OVER THE NRN MTN ZONES AND NRN SAC VLY BY EARLY THU MORNING.
THE NAM 925 MBS WINDS SHOW THE NLY WINDS INCREASING TO OVER 30 KTS
IN THE NRN SAC VLY BY THU MORNING...WITH THE CORE OF THE WINDS
SPREADING SWD BY MID MORNING. A POSSIBLE NLY BARRIER JET EVENT IS
SHAPING UP THU NITE AND FRI MORNING AS PRESSURES RISE OVER THE GREAT
BASIN IN THE WAKE OF THE VORT MAX. AT THIS TIME...IT LOOKS LIKE A
50/50 CHANCE THAT WIND ADVSRY CRITERIA WILL BE REACHED IN THE
CENTRAL AND SRN SAC VLY...MAINLY ALONG AND W OF I-5 ON THU AS THE
NLY WINDS DEVELOP AND WORK SWD. THE 35 KT SPEED MAX AT 925 MBS IS
RIGHT AT THE CUSP OF THE 40 MPH MINIMUM GUST CRITERIA. WE WILL BE
MONITORING THIS FOR A POSSIBLE WIND ADVSRY IN UPCOMING FORECAST
PACKAGES.

AS THIS SYSTEM PHASES WITH THE MAIN LOW HEADING TOWARDS THE 4
CORNERS...A HIGHLY AMPLIFIED RIDGE WILL DEVELOP ALONG THE COAST AND
EXTENDING WELL NWD TOWARDS THE ARCTIC CIRCLE ON FRI. LOOKS AS IF
THIS RIDGE WILL DOMINATE OUR WX THROUGH THE WEEKEND...THEN BREAKING
DOWN EARLY NEXT WEEK. MAX TEMPS ARE FORECAST TO BE 10-15 DEG ABOVE
NORMAL FOR FRI AND INTO THE WEEKEND...BEFORE COOLING TO NORMAL EARLY
IN THE WEEK.       JHM


.EXTENDED DISCUSSION (SUNDAY THROUGH WEDNESDAY)...
UPPER RIDGE SHIFTS EAST SUNDAY ALLOWING A WEAK PACIFIC FRONT AND
ASSOCIATED UPPER TROUGH TO MOVE THROUGH INTERIOR NORTHERN CALIFORNIA
EARLY NEXT WEEK. MODELS DIFFER ON TRACK/TIMING AND AMOUNT OF
ASSOCIATED PRECIP BUT MAIN THEME APPEARS TO BE A SLIGHT CHANCE OF
SHOWERS OVER THE COASTAL AND NORTHERN INTERIOR MOUNTAINS AND WEST
SLOPES OF THE SIERRA NEVADA MONDAY INTO TUESDAY MORNING.  MORE
SIGNIFICANT EFFECTS LIKELY TO BE COOLING MON/TUE WITH BREEZY
NORTHERLY WIND. UPPER RIDGE MOVES OVER INTERIOR NORCAL WEDNESDAY
WITH MINOR WARMING AND LESS WIND.

&&

.AVIATION...
VFR CONDS CONTINUE. PRIMARY AVN CONCERN WILL BE STRONG SURFACE WINDS
FOR MUCH OF THURSDAY INTO FRIDAY. NORTHERLY WINDS WILL START TO
STRENGTHEN AFT 12Z FOR THE NRN SAC VLY AND ADJACENT FOOTHILLS WITH
DOWNSLOPE FLOW...PEAKING BTWN 16-22Z WITH SUSTAINED WINDS 13-18
KTS...GUSTS 20-30 KTS. LLWS POSSIBLE FOR KRDD/KRBL APPROX 12-18Z.
ENHANCED WINDS WILL SPREAD INTO THE REST OF THE SAC VLY AFT 18Z
THOUGH NOT AS STRONG...SUSTAINED WINDS UP TO 15 KTS AND LCL GUSTS
POSSIBLE UP TO 20 KTS. WINDS WILL LESSEN VALLEY WIDE NEAR 02Z.
STRONG EAST TO NORTHEASTERLY RIDGETOP WINDS WILL BEGIN 22Z WITH
WINDS UP TO 40 KTS...WINDS GETTING STRONGER AND PEAK EXPECTED BTWN
02-10Z FRIDAY. WINDS ALF BACKING TO NRLY AROUND 06Z.  JBB

&&

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

&&

$$

NWS STO Office Area Forecast Discussion

Site Affiliations

Weather Underground

weatherforyou.com

Anything Weather.com

Mesowest