Drought in California, August 1 to 31, 2004

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JOAQUIN VALLEY - HANFORD CA
905 PM PDT SAT JUL 31 2004

.UPDATE...FOR THE CENTRAL CALIFORNIA INTERIOR...THE FEW CUMULUS THAT
DEVELOPED OVER THE CREST OF THE SOUTHERN SIERRA NEVADA THIS
AFTERNOON HAVE DISSIPATED...LEAVING THE CENTRAL CALIFORNIA INTERIOR
UNDER CLEAR SKIES. THE GOES WATER-VAPOR LOOP SHOWS THE UPPER-LEVEL
LOW NEAR 38N/126W...WEST OF SANTA ROSA...AS IT CONTINUES TO DROP
SOUTHWARD. THE ASSOCIATED TROUGH IS ALONG THE CALIFORNIA COAST...AND
ALLOWED THE MARINE LAYER TO DEEPEN TO AROUND 3000 FEET THIS MORNING
BEFORE LOWERING TO 2300 FEET THIS AFTERNOON. THE MARINE LAYER HAS
BEGUN DEEPENING AGAIN...AND SOUTHWEST GUSTS TO 34 KTS AT TRAVIS AFB
AT 03Z WILL BRING MORE MARINE AIR THROUGH THE SACRAMENTO DELTA INTO
THE SAN JOAQUIN VALLEY...AS WELL AS THE DEEPENING MARINE LAYER
SPILLING THROUGH THE PASSES OF THE COASTAL RANGE.

THE 00Z ETA/NGM ARE IN GOOD AGREEMENT WITH LITTLE CHANGE IN 500-MB
HEIGHTS OVER THE CENTRAL CALIFORNIA THROUGH 24 HOURS...THEN A 10-20-
METER HEIGHT RISE FOR DAY 2. THERE ALSO IS LITTLE CHANGE IN 1000-500-
MB THICKNESSES THROUGH 00Z MONDAY...AND ONLY MINOR FLUCTUATIONS IN
THICKNESSES FOR MONDAY.

THE NGM FORECASTS LITTLE CHANGE IN 850-MB TEMPERATURES THROUGH
SUNDAY AFTERNOON...THEN A 2 C COOLING FOR MONDAY. THE ETA HAS 1 C
WARMING THROUGH 00Z MONDAY...THEN LITTLE CHANGE IN 850-MB
TEMPERATURES THROUGH 00Z TUESDAY.

WILL GO WITH PERSISTENCE TEMPERATURES AT THE HIGHER ELEVATIONS THE
NEXT COUPLE OF DAYS...BUT COOL THE SAN JOAQUIN VALLEY A COUPLE OF
DEGREES MORE SUNDAY WITH THE INFLUX OF MORE MARINE AIR. WILL MAKE
MINOR ADJUSTMENTS TO TEMPERATURES BASED ON TODAY/S HIGHS.

CONCERNING POSSIBLE CONVECTION OVER THE SOUTHERN SIERRA NEVADA
SUNDAY AFTERNOON...THE WS-ETA FORECASTS CAPES OF ONLY 120-160
JOULES/KG OVER THE CREST AT 00Z MONDAY...WITH 850-700-MB LAYER
RELATIVE HUMIDITIES BETWEEN 40-50 PERCENT. LIFTED INDEXES ARE
FORECAST TO REMAIN POSITIVE. THE MESO-ETA FORECASTS SLIGHTLY HIGHER
CAPES...PEAKING AT 210 JOULES/KG...BUT SIMILAR 850-700-MB RELATIVE
HUMIDITIES TO THE WS-ETA. THE BIGGEST DIFFERENCE IS THAT THE
MESO-ETA FORECASTS NEGATIVE LIFTED INDEXES...WITH -3.5 ALONG THE
CREST.

SATELLITE LOOPS DO SHOW SOME MID- AND HIGH-LEVEL MOISTURE OVER
MEXICO AND ARIZONA...WRAPPING AROUND THE UPPER-LEVEL RIDGE OVER THE
SOUTHWESTERN UNITED STATES. BOTH THE WS-ETA AND MESO-ETA FORECAST A
STRONG PUSH OF 700-500-MB MOISTURE INTO SOUTHERN CALIFORNIA
SUNDAY...BUT THIS MOISTURE ONLY BRUSHES THE HANFORD WARNING/FORECAST
AREA AND INCREASES THE 700-500-MB LAYER RELATIVE HUMIDITY OVER THE
SOUTHERN SIERRA NEVADA TO 50-60 PERCENT. THE CURRENT POPS OVER THE
HIGHER ELEVATIONS OF THE SOUTHERN SIERRA NEVADA FOR SUNDAY ARE ONLY
10 PERCENT OR LESS...AND THERE IS ENOUGH UNCERTAINTY...ESPECIALLY
WITH THE MESO-ETA LIFTED INDEX FIELDS...TO KEEP THE POPS IN THE
FORECAST FOR NOW.

.FROM PREVIOUS DISCUSSION...

.SHORT TERM...FOR THE CENTRAL CALIFORNIA INTERIOR...WATER VAPOR
IMAGERY SHOWS THE UPPER LOW STILL SPINNING AND SLOWLY TRANSLATING
SOUTHEAST OFF THE NORTHERN CALIFORNIA COAST. DRY SOUTHWEST FLOW IN
RESPONSE TO THIS LOW CONTINUES TO DOMINATE OVER CENTRAL
CALIFORNIA...HOWEVER A SMALL FETCH OF SUBTROPICAL MOISTURE IS NOTED
OVER NORTHERN BAJA...HEADING TO THE NORTHWEST. THE MAIN QUESTION IN
THE SHORT RANGE FORECAST IS THE THREAT OR LACK OF A THREAT OF
CONVECTION OVER THE SIERRA ON SUNDAY AFTERNOON. IT DOESN/T APPEAR
THAT THE THREAT WILL BE TOO LARGE, AS THE VERY DRY AIRMASS WILL TAKE
A LITTLE TIME TO MOISTEN UP. IT APPEARS THAT IF ANY CONVECTION DOES
OCCUR...IT WILL HAVE TO BE ON SUNDAY AFTERNOON AS THE MESO-ETA
MODEL...AND THE GFS TO A LESSER DEGREE...BRING THE NORTHERN BAJA
MOISTURE INTO SOUTHERN CALIFORNIA AND THEN NORTHEASTWARD EITHER
ALONG THE SIERRA CREST PER THE MESOETA SOLUTION...OR JUST EAST OF
THE CREST AS SUGGESTED BY THE GFS. WITH THIS SCENARIO AND THE FACT
THAT WE JUST HAVE AROUND 10% POPS OVER THE SIERRA CREST...WILL LEAVE
THE FORECAST INTACT FOR SUNDAY AFTERNOON. BY MONDAY AND TUESDAY...
THE MODELS AGREE NICELY THAT THE FLOW WILL TURN BACK TO A VERY DRY
SOUTHWEST DIRECTION...THUS ENDING ANY CHANCES OF SIERRA CONVECTION.

AS FOR TEMPERATURES...THE MARINE LAYER DEPTH AT FORT ORD CONTINUES
TO INCREASE, WITH CURRENT LEVELS ABOVE 2500 FEET. WITH THE UPPER LOW
OFFSHORE...THIS MAY INCREASE SOME MORE AND BASED ON HOW MUCH OF THIS
COOLER AIR SPILLS INTO THE SJV...TEMPERATURES IN THE MARINE
INFLUENCED AREAS OF MERCED COUNTY MAY BE HAVE TO BE ADJUSTED
DOWNWARD. THE AFFECT IS MOST NOTED AT SAN LUIS DAM...WHERE READINGS
ARE RUNNING DOWN AROUND 5 DEGREES. WITH THE FORECAST MODELS ONLY
VERY SLOWLY MOVING THE OFFSHORE UPPER LOW NORTHEAST OVER THE NEXT 2
DAYS...THE MARINE LAYER SHOULD STAY DEEP...THUS ADDITIONAL COOLING
IS LIKELY IN PARTS OF THE SJV. OVER THE REMAINDER OF THE FORECAST
AREA...LITTLE DAY TO DAY CHANGE IN HEIGHTS IS PROGGED...THUS
TEMPERATURE TRENDS SHOULD SHOW LITTLE CHANGE. WILL HAVE TO MAKE SOME
ADJUSTMENTS IN THE HIGH TEMPERATURES AT THE ABOVE MENTIONED MARINE
INFLUENCE AREAS...BASED ON WHAT HAS OCCURRED THIS AFTERNOON.

.LONG TERM...FOR TUESDAY NIGHT THROUGH SATURDAY...THE MEDIUM RANGE
MODELS ARE IN GOOD AGREEMENT AND FORECAST AN UPPER LEVEL TROUGH TO
LINGER OFF THE WEST COAST THRU THE PERIOD. WITH SW FLOW PREVAILING
ALOFT...THE WEATHER PATTERN WILL REMAIN DRY THRU DAY 7. WEAK ONSHORE
GRADIENTS IN THE LOW LEVELS WILL BRING SHALLOW INTRUSIONS OF MARINE
AIR INTO THE SJ VLY AND KEEP TEMPS CLOSE TO NORMAL THRU THE PERIOD.

&&

.HNX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

SANGER/DUDLEY/DURFEE