AREA FORECAST DISCUSSION

 
 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.
 
 &&
 
 $$