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FXUS66 KSTO 101223
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
420 AM PST WED FEB 10 2010
.DISCUSSION...
MOSTLY CLEAR SKIES ACROSS INTERIOR NORTHERN CALIFORNIA UNDER THE
INFLUENCE OF A SHORTWAVE RIDGE. A LIGHT OFFSHORE BREEZE HAS KEPT
MOST AREAS FOG FREE...THOUGH IN THE LAST HOUR OR SO A FINGER OF FOG
HAS BEGUN TO CREEP UP THE WIND-SHELTERED AREAS OF THE EASTERN
NORTHERN SAN JOAQUIN AND SOUTHERN SACRAMENTO VALLEYS. WILL NEED TO
KEEP AN EYE ON THINGS TO SEE IF A DENSE FOG ADVISORY MAY BE NEEDED
LATER THIS MORNING FOR THESE AREAS. GOOD RADIATIONAL COOLING AND A
COOL AIRMASS HAS ALLOWING FOR TEMPERATURES TO CREEP DOWN INTO THE
30S TO LOWER 40S IN MOST AREAS...GOOD FOR A 6 TO 12 DEGREE DROP FROM
24 HOURS AGO. CERTAINLY COULD SEE PATCHY FROST DEVELOP IN SOME OF
THE RURAL AREAS OF THE VALLEY THIS MORNING.
EXPECT INCREASING CLOUDINESS TODAY ACROSS THE FORECAST AREA AS THE
NEXT TROUGH APPROACHES THE COAST. THIS TROUGH IS EXPECTED TO TAKE A
MORE NORTHERLY TRACK THAN THE LAST SEVERAL STORMS...MOVING TOWARDS
THE PACIFIC NORTHWEST LATER TODAY. OUTSIDE OF THE CHANCE OF SOME
OVERRUNNING PRECIPITATION TOWARDS THE SHASTA COUNTY MOUNTAINS
TONIGHT INTO TOMORROW...SHOULD SEE LITTLE IMPACT FROM THIS WAVE.
EXPECT TEMPERATURES TO PEAK THIS AFTERNOON IN THE 50S THIS AFTERNOON
IN THE VALLEY AND FOOTHILLS WITH 40S FOR THE HIGHER ELEVATIONS. MORE
FOG MAY BE IN STORE LATE TONIGHT INTO THURSDAY MORNING.
A SECOND WAVE WILL QUICKLY FOLLOW ON THE HEELS OF THE FIRST...IN THE
THURSDAY NIGHT TO FRIDAY TIMEFRAME. THIS SECOND WAVE WILL TAKE A
SLIGHTLY MORE SOUTHERLY TRACK THAN THE FIRST...LIKELY BRINGING
PRECIPITATION SOUTHWARD TO THE INTERSTATE 80 CORRIDOR. UPPER SUPPORT
IS FAIRLY WEAK WITH THIS FRIDAY SYSTEM AND PRECIPITATION TOTALS
SHOULD REMAIN ON THE LIGHT SIDE. SNOW LEVELS LOOK TO DIP TO THE
3500-4500 FT RANGE.
A CLEARING AND WARMING TREND IS LOOKING TO START SATURDAY AS AN
UPPER RIDGE AMPLIFIES ALONG THE WEST COAST...SENDING THE STORM TRACK
NORTHWARD. WHILE WE MAY CONTEND WITH SOME MORNING VALLEY
FOG...TEMPERATURES LOOK TO WARM BACK UP TO NEAR OR SLIGHTLY WARMER
THAN NORMAL LEVELS. DANG
.EXTENDED DISCUSSION (SUNDAY THROUGH WEDNESDAY)...
DAMPENING UPPER TROF/WEAKENING COLD FRONT ARE FORECAST TO BRUSH
ACROSS INTERIOR NORCAL ON SUN...POSSIBLY BRINGING A LOW CHANCE OF
LIGHT PCPN TO THE NRN MTNS OF INTERIOR NORCAL. OTHERWISE A HIGHLY
AMPLIFIED RIDGE IS FORECAST TO BECOME RE-ESTABLISHED ALONG THE W
COAST ON MON WHICH SUBSTANTIALLY WEAKENS THE NEXT UPPER TROF/COLD
FRONT AS IT MOVES INTO THE HIGHLY AMPLIFIED RIDGE ON TUE. AND...IT
LOOKS AS IF THE RIDGE WILL STRENGTHEN DURING THE MID WEEK PERIOD AS
THE ECMWF/GEM/GFS ENSEMBLES DIG/DEEPEN THE ERN PAC TROF AND AMPLIFY
THE DOWNSTREAM RIDGE ALONG THE W COAST. THIS WILL MEAN A PERIOD OF
DRY AND SEASONABLY VERY MILD WX FOR INTERIOR NORCAL WITH TEMPS NEAR
OR A LITTLE ABOVE NORMAL...OUR "FEBRUARY THAW" IF YOU WILL. WE
USUALLY EXPERIENCE A MILD SPELL LIKE THIS IN FEB WHERE WE ENJOY SOME
EARLY "SPRING-LIKE" WX. IN 2009...WE HAD A JAN AND EARLY FEB
THAW...BEFORE A MUCH STORMIER PATTERN DEVELOPED BY THE MIDDLE OF FEB
AND PARTIALLY SAVED THE WATER YEAR.
THE INCREASING LARGE SCALE SUBSIDENCE DURING THIS PERIOD WILL ALSO
MEAN STRATUS/FOG ARE LIKELY DURING THE MORNINGS IN THE INTERIOR AND
MTN VALLEYS. THIS WILL NOT BE THE "CLEANEST" RIDGE AS CLOUD COVER IS
LIKELY TO SPREAD ACROSS INTERIOR NORCAL AS THE WEATHER SYSTEMS PASS
BY TO THE N. LESS CLOUD COVER IS EXPECTED AS THE RIDGE STRENGTHENS
BY THE MIDDLE OF THE WEEK. JHM
&&
.AVIATION...
STRATUS/STRATOCUMULUS SPREADING NWD AND NWWD ALONG THE FOOTHILLS AND
E SIDE OF THE SRN SAC/NRN SAN JQN VALLEY THIS MORNING AS DEPICTED
VERY WELL BY THE NAM12 BOUNDARY LAYER RH PROG. THIS AREA OF
CLOUDINESS DEVELOPED IN THE CONVERGENCE ZONE OF THE DOWN VALLEY NLY
FLOW AND DOWNSLOPE ELY FLOW FROM THE SIERNEV. BASES ARE GENERALLY
AROUND 030 IN THE VALLEY...AND PROBABLY 1000-1500 FEET LOWER IN THE
FOOTHILLS. SOME PATCHY IFR STRATUS/FOG IS ALSO LIKELY THIS MORNING
MAINLY ON THE E SIDE OF THE CENTRAL/SRN SAC VLY WHERE WINDS ARE
L/V...WHILE DOWN VALLEY NLY FLOW WILL PRECLUDE FOG OVER MUCH OF THE
W SIDE OF THE VALLEY. THE LOW CLOUDS ARE EXPECTED TO SPREAD NWD TO
ABOUT THE MYV AREA...ALSO WHERE SOME STRATUS/FOG MAY FORM. THE CLOUD
COVER IS EXPECTED TO MIX OUT IN THE VALLEY AFTER 18Z-20Z...BUT MAY
LINGER OVER THE SRN MOTHERLODE AS UPSLOPE FLOW DEVELOPS.
CLOUDS EXPECTED TO INCREASE TONIGHT AS COLD FRONT MOVES INTO THE PAC
NW THIS EVENING. RAIN IS EXPECTED TO BEGIN OVER THE NRN MTNS AND NRN
TAF SITES AFT 06Z THU WITH CIGS LOWERING TO MVFR. HOWEVER...VFR
CONDITIONS EXPECTED FARTHER S WITH CIGS REMAINING ABOVE 050.
&&
.STO WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
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