Heavy Rain in California, May 2, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
915 PM PDT TUE MAY 1 2007

.DISCUSSION...
COLD FRONT CONTINUES TO MOVE QUICKLY INLAND THIS EVENING WITH
PRECIPITATION NOW GENERALLY AS FAR SOUTH AS ABOUT I-80. SO FAR THE
MOST SIGNIFICANT PRECIPITATION HAS BEEN LIMITED TO THE NORTHERN
MOUNTAINS WHERE 1/4 TO 1/2 INCH HAS FALLEN. A FEW SPOTS EAST OF
CHICO HAVE REPORTED AROUND 2 TENTHS OF AN INCH THIS EVENING.

 SATELLITE IMAGERY SHOWS THE STRONG SHORTWAVE OFFSHORE MOVING
RAPIDLY TOWARD THE COAST. THIS FEATURE WILL PUSH THE FRONT WELL
INLAND LATER TONIGHT AND EARLY WEDNESDAY FOCUSING THE HEAVIEST QPF
ACROSS THE HIGHER ELEVATIONS OF THE NORTHERN SIERRA FROM NORTH OF
BLUE CANYON SOUTHWARD TO TUOLUMNE COUNTY.

WEDNESDAY STILL APPEARS QUITE CONVECTIVE WITH THE UPPER TROF
OVERHEAD AND CYCLONIC JET TO THE SOUTH...THOUGH LATEST MODELS APPEAR
THEY MAY BE TOO SLOW IN MOVING THE UPPER TROF AXIS INLAND ON
WEDNESDAY.

&&

.PREVIOUS DISCUSSION...
MODELS HAVE BEEN HANDLING THIS BIG PATTERN CHANGE PRETTY WELL SO
FAR...AND CONTINUE DECENT RUN TO RUN CONTINUITY TODAY. THEREFORE...
NO BIG CHANGES PLANNED FOR THE AFTERNOON PACKAGE.

LIGHT RAIN HAS ALREADY OVERSPREAD THE NORTHWEST HALF OF OUR FORECAST
AREA THIS AFTERNOON. PRECIP AMOUNTS HAVE BEEN UNIMPRESSIVE WITH
MESONET TURNING UP LESS THAN 0.10 INCHES AT ALL LOCALES SO FAR.
INITIAL SHORTWAVE WEAKENED AS IT ENCOUNTERED DOWNSTREAM RIDGING.
ASSOCIATED LOW LEVEL BOUNDARY HAS SUBSEQUENTLY UNDERGONE FRONTOLYSIS
WITH ONLY WEAK CONVERGENCE REMAINING OVER OUR AREA. LOOKS LIKE A BIT
OF A LULL IN THE ACTION THIS EVENING BEFORE NEXT WAVE OF DYNAMIC
ENHANCEMENT DEVELOPS AHEAD OF NEXT SHORT WAVE BETWEEN 06Z AND 12Z.

WEDNESDAY LOOKS LIKE A VERY ACTIVE WEATHER DAY WITH EXIT REGION OF
CYCLONICALLY CURVED UPPER JET PROGGED TO DIVE JUST SOUTH OF OUR
AREA.  WE WIND UP ON THE COLD SIDE OF THE JET DURING THE DAY WITH
CONTINUED CYCLONIC CURVATURE ALOFT. MODELS ARE A LITTLE MORE ROBUST
IN GENERATING INSTABILITY OVER OUR AREA THANKS TO STEEPENING MID
LEVEL LAPSE RATES UNDER DEEPER COLD POOL. MAY BE DEALING WITH A
DECENT CONVECTIVE SITUATION...ALTHOUGH RELATIVELY WEAK SHEAR
PARAMETERS SUGGEST AN OVERALL LACK OF ORGANIZATION TO ANY STORMS
THAT DO FORM.  WILL NEED TO PAY ATTENTION TO ANY FORCINGS THAT CAUSE
THE SURFACE WINDS TO BACK WHICH WOULD RESULT IN MORE FAVORABLE SHEAR
PARAMETERS.  AS NOTED...VERY FEW CHANGES TO GOING FORECAST.

JUSKIE

&&

.AVIATION...
SHOWERS HAVE SPREAD INLAND ALONG AND AHEAD OF A COLD FRONT INTO THE
INTERIOR OF NORTHERN CALIFORNIA NORTH OF I-80 THIS EVENING. MORE
WIDESPREAD PRECIPITATION IS EXPECTED ACROSS THE REGION TONIGHT WITH
MVFR AND IFR CONDITIONS POSSIBLE IN LOCATIONS. SNOW SHOWERS ARE
POSSIBLE ABOVE 6000-7000 FEET. SHOWERS AND ISOLATED THUNDERSTORMS
WILL AFFECT THE CENTRAL VALLEY DURING THE DAY WEDNESDAY...WITH SNOW
LEVELS DROPPING TO AROUND 5000-6000 FEET.

&&

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

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SACRAMENTO CA
600 AM PDT TUE MAY 1 2007

CAZ013>019-063-064-066>069-021400-
SHASTA LAKE AREA/NORTHERN SHASTA COUNTY-
BURNEY BASIN/EASTERN SHASTA COUNTY-NORTHERN SACRAMENTO VALLEY-
CENTRAL SACRAMENTO VALLEY-SOUTHERN SACRAMENTO VALLEY-
CARQUINEZ STRAIT AND DELTA-NORTHERN SAN JOAQUIN VALLEY-
MOUNTAINS SOUTHWESTERN SHASTA TO NORTHERN LAKE COUNTIES-
CLEAR LAKE/SOUTHERN LAKE COUNTY-MOTHERLODE-
EAST FOOTHILLS/NORTH SACRAMENTO VALLEY-
WESTERN PLUMAS COUNTY/LASSEN PARK-WEST SLOPE NORTHERN SIERRA NEVADA-
600 AM PDT TUE MAY 1 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR INTERIOR NORTHERN CALIFORNIA.

.DAY ONE...TODAY

A PACIFIC FRONT WILL BRING A CHANCE OF SNOW AND GUSTY WIND OVER
INTERIOR NORTHERN CALIFORNIA MOUNTAINS AND SIERRA NEVADA TONIGHT.
SNOW LEVELS EXPECTED TO LOWER TO AROUND 6000 FEET OVERNIGHT.

.DAYS TWO THROUGH SEVEN... WEDNESDAY THROUGH MONDAY

PERIODS OF MOUNTAIN SNOW AND GUSTY WIND ABOVE 4000 FEET ARE POSSIBLE
WEDNESDAY THROUGH FRIDAY AS THE COLD LOW PRESSURE SYSTEM MOVES
THROUGH. ISOLATED THUNDERSTORMS ARE POSSIBLE IN THE INTERIOR VALLEY
AND SIERRA NEVADA FOOTHILLS WEDNESDAY. HIGH PRESSURE BUILDS INLAND
OVER THE WEEKEND WITH LOCALLY STRONG NORTH WIND POSSIBLE SATURDAY
AND SUNDAY.

THE LATEST WEATHER INFORMATION IS AVAILABLE ON THE INTERNET AT
(LOWER CASE): HTTP://WWW.WRH.NOAA.GOV/STO