FXUS66 KSTO 250358
AFDSAC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
855 PM PDT THU JUL 24 2003

GOES SATELLITE STILL DEPICTS ABUNDANT PRECIPITABLE WATER OVER NORCAL 
THIS EVENING RANGING FROM .80 OVER THE HIGH SIERRA NEVADA TO 1.50 
INCHES OVER THE VALLEY. KREV SOUNDING PW IS DOWN FROM AN IMPRESSIVE 
1.30 INCHES AND NOW AT 0.86 INCHES. SO DRYING IS THERE BUT ITS ALL 
RELATIVE. STORMS FIRED TODAY ALONG THE SIERRA NEVADA CREST THANKS TO 
ANOTHER DAY OF LOW LEVEL CONVERGENCE OVER THE REGION BUT THE SHIFT 
TO A MORE SOUTHWESTERLY STEERING FLOW (190 AT 500 MB BUT 220 NEAR 
600 MB AND 240 AT 700MB) WAS EVIDENT AS THE CONVERGENCE SHIFTED EAST OF 
THE CREST. LAPS ANALYSIS SHOWED THAT INSTABILITY WAS PLENTIFUL OVER 
THE WEST SLOPES...COASTAL RANGE AND SACRAMENTO VALLEY (400 TO 1000 
J/KG) THIS AFTERNOON BUT LACK OF DYNAMICS TO REACH THE STILL VERY 
HIGH LFC LEFT THESE PLACES DRY. WATER VAPOR CLEARLY DEPICTS ANOTHER 
SHORT WAVE NOW LIFTING OUT OF FAR NORCAL (ANALYZED AS A 15 UNIT VORT 
OVER ALDER SPRINGS). THIS SYSTEM BROUGHT ELEVATED SHOWERS TO THE FAR 
NORTHERN VALLEY THIS AFTERNOON...AND AIDED STRONG SURFACE BASED 
CONVECTION OVER THE TRINITY ALPS (NORTH OF OUR CWA). OFFSHORE THERE 
IS A SERIES OF VORT MAXS THAT HAVE BEEN DEPOSITED IN A WEAK WIND 
FIELD AND THESE CIRCULATIONS TRIGGERED SEVERAL ELEVATED 
THUNDERSTORMS THIS AFTERNOON OVER THE OCEAN. INLAND THIS HOUR A BAND 
OF ALTOCUMULUS CASTELLANUS HAS FORMED JUST EAST OF SACRAMENTO WITH 
AT LEAST ONE SHOWER DEPICTED OUT THE WINDOW AND SHOWED UP TO 30DBZ 
ON THE COMPOSITE RADAR. THIS LATER ACTIVITY CLEARLY SHOWS THE 
CONDITIONAL UNSTABLE MID AND UPPER LEVELS THAT HAVE BEEN PRESENT AND 
REMAIN OVER NORCAL AND THE EAST PACIFIC THANKS TO THE RECENT 
SUBTROPICAL MOISTURE PUSH AROUND THE DOMINATE LARGE UPPER RIDGE IN 
THE WESTERN UNITED STATES. TEMPS TODAY REBOUNDED TO THE H85 
POTENTIAL (24-25C OBSERVED) WITH 102F IN DOWNTOWN SAC AS THE DELTA 
BREEZE WAS MINIMAL DESPITE THE MARINE LAYER UP TO 1500 FEET...MUCH 
OF THE STRATUS WAS MIXED OUT AND THE UPVALLEY FLOW WAS WEAK...LITTLE 
INCREASE TO THE ONSHORE FLOW...AND THE NORTHERLY ACV-SFO FLOW 
INCREASING TO 4 MB. CLOUD COVER KEPT THE NORTHERN ZONES COOLER 
TODAY...SIMILAR TO WHAT WE SAW OVER THE SAC AREA ON WEDNESDAY. SHORT 
TERM ISSUES WILL BE THE TREND OF THE SEA BREEZE (12KT KSUU THIS 
HOUR) AND POTENTIAL FOR ADDITIONAL ELEVATED SHOWERS AND 
THUNDERSTORMS.

TONIGHT THE STRONGER UPPER RIDGE WILL LOSE ITS GRID SOMEWHAT AND 
SHORT WAVE ENERGY WILL MOVE ALONG THE NORTH COAST AND TO THE OREGON 
BORDER FRIDAY MORNING. THUS BEST LIFT FOR DESTABILIZATION AND 
ELEVATED CONVECTION WILL BE JUST NORTHWEST AND NORTH OF OUR CWA BUT 
CURRENT FORECAST OF JUST SLIGHT CHANCE FOR THE FAR NORTHERN ZONES 
LOOKS GOOD OVERNIGHT...AS A FEW SHOWERS AND THUNDERSTORMS MAY 
DEVELOP ON THE SOUTHERN EDGE AND MOVE OVER THE REGION IN THE 
SOUTHWEST STEERING FLOW. RADAR ALREADY DETECTS ELEVATED BASED 
SHOWERS MOVING ALONG THE NORTH COAST AND INTO THE SHASTA TRINITY 
ALPS. OVERSHOOTING TOPS ARE EVIDENT AND SOME OF THIS RAIN IS 
REACHING THE GROUND...AND A COUPLE LIGHTNING STRIKES ARE POSSIBLE.
MIN TEMPS WILL STILL BE MILD TONIGHT IN THE VALLEY BUT SHOULD BE 
COOLER WITH LESS CLOUD COVER AND SOME COOLING FROM THE DELTA. WE MAY 
NEED TO RAISE TEMPS IN THE NORTHERN VALLEY. SURFACE BASED CONVECTION 
LOOKS VERY MINIMAL OVER THE SIERNEV ON FRIDAY AS SOUTH-SOUTHWEST 
DOES NOT MAKE IT STABLE OR DRY IN THIS CASE BUT SHUNTS LOW LEVEL 
CONVERGENCE TO THE CREST EASTWARD. SOUNDINGS STILL REMAIN VERY MOIST 
AND UNSTABLE OVER THE MOUNTAINS. CONVECTION SHOULD BE SIMILAR AS 
TODAY WITH ACTIVITY OVER THE SHASTA TRINITY REGION AND EAST SLOPE OF 
THE SIERNEV. H85 TEMPS ARE 23-24C ON FRIDAY SO OUTSIDE THE DELTA 
AREAS IT WILL STILL BE QUITE WARM...ABOUT 100F.

THE UPPER RIDGE RETROGRADES ON SATURDAY SUSTAINING SOUTHERLY FLOW 
(190 DEGREES H5) BUT SHIFTING 700MB TO THE SOUTH AS WELL AND SENDING A 
WEAK VORT MAX UP FROM SOUTHERN CA. PLENTY OF MOISTURE (PW 0.90 
INCHES AT BLUE CANYON) LINGERS BUT AGAIN THE NEEDED LOW LEVEL 
CONVERGENCE TO REACH THE LEVEL OF FREE CONVECTION OF ABOUT 600 MB OR 
15,000 FEET WILL BE LIMITED TO THE CREST AND EASTWARD. H85 TEMPS 
REMAIN AT 23-25C SO LITTLE CHANGE IN TEMPS MOST LOCALES. IF THE 
BUFKIT ETA TIME SECTION IS ON TARGET...AND SEE NO REASON WHY 
NOT...THEN THE MARINE DEPTH AT OAKLAND WILL REMAIN NEAR 1500 FEET 
FRIDAY AND SATURDAY. THIS IS ENOUGH FOR SOME COOLING IN THE DELTA 
AND EVEN SAC AREA...ESPECIALLY EVENINGS.

BY SUNDAY MODELS DEPICT THE UPPER RIDGE TAKING CONTROL OF OUR WEATHER 
AGAIN AND THE MARINE LAYER LOWERS TO 1000 FEET. H5 HEIGHTS BUILD TO 
594-DM OVER NORCAL PER UKMET AND GFS RUNS. THE WARMING CONTINUES 
INTO MONDAY (H85 TEMPS 28C FOR TEMPS WELL OVER 100F) AS THE UPPER RIDGE 
IS PROGGED TO LIFT INTO NEVADA CREATING ANTICYCLONIC FLOW INTO 
CENTRAL CA...AND INCREASING MOIST CONVECTION OVER THE SIERNEV. AT 
THE SAME TIME A WEAK UPPER LOW SITS OVER 135W AND 35N ENHANCING 
SOUTHERLY FLOW. IN THIS PATTERN WE WILL BE SUSCEPTIBLE TO INVERTED 
EASTERLY MID LEVEL WAVES FROM THE SOUTHEAST AND THEN EVENTUALLY 
DYNAMICS FROM THE UPPER LOW IF IT DRIFTS INLAND AND ACTS ON THE 
PLENTIFUL SUBTROPICAL MOISTURE (1.50 INCHES) AND INSTABILITY. THIS 
PATTERN IS ALL TOO COMMON IN THE SUMMER AND WHAT WE JUST RECENTLY 
EXPERIENCED.

.STO...NONE.

$$

TARDY