Heavy Snow and Cold in California, September 19 to 22, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
950 PM PDT TUE SEP 18 2007

.DISCUSSION...
.ANOTHER RELATIVELY QUIET NIGHT TONIGHT BEFORE WHAT COULD BECOME THE
FIRST STORM OF AN EARLY FALL SEASON. CURRENT SATELLITE INDICATES THE
LOW IS DIGGING SOUTH TOWARD NORTHERN CALIFORNIA HOWEVER AT THIS TIME
THERE DOES NOT APPEAR TO BE AS MUCH MOISTURE ASSOCIATED WITH IT THAT
THE MODELS HAVE PROGGED.  EXPECT IT WILL ENTRAIN MORE IN AS IT DIVES
INTO OUR AREA.  THE TEMPERATURES HAVE ALREADY STARTED DECREASING AND
THE SOUTHERLY WINDS ARE ALREADY PICKING UP ACROSS THE VALLEY. DO NOT
SEE ANY PROBLEMS WITH CURRENT FORECAST PACKAGE, SO NO UPDATES NEEDED
AT THIS TIME. RANDY HARTLEY

.PREVIOUS DISCUSSION...
SHORT WAVE TROUGH HAS MOVED EAST OF THE REGION. SKIES ARE FAIRLY CLEAR
WITH ONLY SCATTERED CUMULUS FORMING OVER THE NORTHERN MOUNTAINS. THE
CURRENT TEMPERATURES ARE ABOUT THE SAME ACROSS THE REGION EXCEPT 2 TO 5
DEGREES COOLER IN THE NORTHERN SACRAMENTO VALLEY...DUE TO THIS
MORNINGS CLOUD COVER.  THE UPPER LEVEL LOW THAT WILL BE THE WEATHER
MAKER FOR THE NEXT SEVERAL DAYS REMAINS CLOSE TO THE CANADIAN-US
COASTLINE. LOW CENTER IS FORECAST BY GFS TO DROP SOUTHWEST TO ROUGHLY
NORTHWEST CALIFORNIA BY WEDNESDAY AFTERNOON...THEN CONTINUE SOUTHWARD
TO A POSITION ALONG THE CENTRAL COAST BY THURSDAY MORNING. THIS
SOLUTION IS NOW FAIRLY CONSISTENT WITH OTHER MODELS AND CONFIDENCE HAS
INCREASED. SHORTWAVE TROUGHS ROTATING AROUND THIS LOW WILL LIKELY
TRIGGER SHOWERS OVER THE CWA BUT MODEL RESOLUTION LIKELY NOT GOOD
ENOUGH TO PINPOINT EXACT TIMING OR POSITIONS. THEREFORE...HAVE LEFT
GENERAL CHANCES OF SHOWERS DROPPING SOUTHWARD ON WEDNESDAY THEN ACROSS
ENTIRE CWA WEDNESDAY NIGHT AS LOW CONTINUES SOUTH. AIRMASS COOLS
SIGNIFICANTLY WITH GFS SHOWING 1000 TO 500MB THICKNESS DROPS OF 18
DECAMETERS OR MORE BY WEDNESDAY AFTERNOON. THIS WILL PUT DAYTIME HIGHS
ON WEDNESDAY 15 OR MORE DEGREES BELOW NORMAL FOR THIS TIME OF YEAR. LOW
FORECAST TO CONTINUE SOUTHWARD WITH A CENTER POSITION JUST OFF THE
CENTRAL COAST BY THURSDAY AFTERNOON. NAM AND GFS DO BOTH INDICATE THAT
A SHORTWAVE WILL BE ROTATING AROUND THE NORTH SIDE OF THE LOW AND
WESTWARD THROUGH THE SIERRA CASCADE RANGE THURSDAY AFTERNOON AND NIGHT.
HAVE KEPT CHANCE POPS THERE FOR THURSDAY. UPPER LOW BEGINS TREK INLAND
INTO SOCAL ON FRIDAY. GFS STILL SHOWS SOME UPWARD MOTION IN THE OMEGA
FIELD FOR THE SIERRA SO LEFT SOME CHANCE POPS IN FOR FRIDAY. THE 18Z
GFS RUN IS IN GOOD AGREEMENT WITH THE PREVIOUS RUN EXCEPT THIS LATEST
RUN SHIFTS THE LOW EASTWARD MORE QUICKLY ON SATURDAY AFTERNOON WHICH IS
ALSO IN LINE WITH THE ECMWF MODEL. A WEAKLY TROFFY PATTERN WILL REMAIN
OVER NORTHERN CALIFORNIA AND NEVADA THROUGH THE REMAINDER OF THE
WEEKEND IN RESPONSE TO DEEPENING LOW OVER EASTERN CANADA/ATLANTIC OCEAN
AND MIDWEST RIDGING. OCCASIONAL WEAK WAVES MOVING THROUGH THE FLOW
EARLY NEXT WEEK BUT OVERALL LOOK FOR WARMING AND DRYING.  MODELS IN
GOOD AGREEMENT ON FEATURES THROUGH NEXT TUESDAY BUT ECMWF AND GFS GET
OUT OF PHASE BY LATE NEXT WEEK.

&&

.AVIATION...
MVFR CEILINGS AFTER 10Z NEAR THE COAST...OTHERWISE VFR CONDITIONS
OVERNIGHT BUT CLOUDS DEVELOPING AND INCREASING FROM THE NORTHWEST
AFTER 06UTC DUE TO A DEEPENING TROUGH OF LOW PRESSURE.  SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS IN THE NORTH WEDNESDAY MORNING
AND SPREADING SOUTH DURING THE AFTERNOON.

&&

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

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SACRAMENTO CA
530 AM PDT TUE SEP 18 2007

CAZ013>019-063-064-066>069-191400-
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-
530 AM PDT TUE SEP 18 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR INTERIOR NORTHERN CALIFORNIA.

.DAY ONE...TODAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN... WEDNESDAY THROUGH MONDAY

A STRONG UPPER LOW WILL TRAVERSE SOUTHWARD ACROSS THE REGION ON
WEDNESDAY AND THURSDAY BRINGING A CHANCE OF SHOWERS AND
THUNDERSTORMS ALONG WITH COOLER TEMPERATURES AND BREEZY CONDITIONS.
THE LOW WILL MOVE TO ALONG THE CENTRAL CALIFORNIA COAST BY LATER
THURSDAY...BUT COULD STILL GENERATE A FEW SHOWERS ACROSS THE REGION
INTO THE EARLY PART OF THE UPCOMING WEEKEND. OTHERWISE...NO
HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

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

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SACRAMENTO CA
1008 PM PDT TUE SEP 18 2007

CAZ013>019-063-064-066>069-190715-
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 COUNTY TO NORTHERN LAKE COUNTY-
CLEAR LAKE/SOUTHERN LAKE COUNTY-
NORTHEAST FOOTHILLS/SACRAMENTO VALLEY-MOTHERLODE-
WESTERN PLUMAS COUNTY/LASSEN PARK-
WEST SLOPE NORTHERN SIERRA NEVADA-
1008 PM PDT TUE SEP 18 2007

...AN EARLY FALL-LIKE WEATHER SYSTEM WILL BRING UNSETTLED WEATHER
TO THE REGION DURING THE SECOND HALF OF THE WEEK...

THE FIRST SIGNIFICANT WEATHER SYSTEM TO AFFECT NORTHERN CALIFORNIA
IN SEVERAL MONTHS COULD BRING A DRAMATIC CHANGE IN THE WEATHER TO
THE REGION BEGINNING ON WEDNESDAY. A STRONG LOW PRESSURE SYSTEM
ORIGINATING ALONG THE WEST COAST OF CANADA IS MOVING SOUTHWARD INTO
NORTHERN CALIFORNIA WEDNESDAY...BRINGING INCREASING CLOUDS...SHOWERS
AND THUNDERSTORMS...AS WELL AS COOLER TEMPERATURES AND BREEZY
CONDITIONS. THE LOW PRESSURE SYSTEM WILL MOVE SOUTHWARD TO ALONG
THE CENTRAL CALIFORNIA COAST BY LATE THURSDAY...BUT PARTS OF THE
REGION WILL CONTINUE TO SEE CHANCES OF SHOWERS INTO SATURDAY.

PEOPLE SHOULD BE PREPARED FOR A SIGNIFICANT WEATHER CHANGE
STARTING WEDNESDAY. EVEN LIGHT AMOUNTS OF RAIN WILL RESULT IN
SLIPPERY CONDITIONS ON ROADWAYS DUE TO MONTHS OF DRY WEATHER
ALLOWING OIL RESIDUES TO BUILD UP. IF YOU ARE PLANNING OUTDOOR
ACTIVITIES BE PREPARED FOR COOL AND BLUSTERY WEATHER WITH
SCATTERED SHOWERS AND POSSIBLE THUNDERSTORMS...AND EVEN THE
POSSIBILITY OF A DUSTING OF SNOW ACROSS THE HIGHEST ELEVATIONS
OF THE NORTHERN SIERRA NEVADA...THE SOUTHERN CASCADES...AND THE
INTERIOR COASTAL RANGE.

RCH/DR

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SACRAMENTO CA
1010 PM PDT TUE SEP 18 2007

CAZ013>019-063-064-066>069-191715-
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 COUNTY TO NORTHERN LAKE COUNTY-
CLEAR LAKE/SOUTHERN LAKE COUNTY-
NORTHEAST FOOTHILLS/SACRAMENTO VALLEY-MOTHERLODE-
WESTERN PLUMAS COUNTY/LASSEN PARK-
WEST SLOPE NORTHERN SIERRA NEVADA-
1010 PM PDT TUE SEP 18 2007

...AN EARLY FALL-LIKE WEATHER SYSTEM WILL BRING UNSETTLED WEATHER
TO THE REGION DURING THE SECOND HALF OF THE WEEK...

THE FIRST SIGNIFICANT WEATHER SYSTEM TO AFFECT NORTHERN CALIFORNIA
IN SEVERAL MONTHS COULD BRING A DRAMATIC CHANGE IN THE WEATHER TO
THE REGION BEGINNING ON WEDNESDAY. A STRONG LOW PRESSURE SYSTEM
ORIGINATING ALONG THE WEST COAST OF CANADA IS MOVING SOUTHWARD INTO
NORTHERN CALIFORNIA WEDNESDAY...BRINGING INCREASING CLOUDS...SHOWERS
AND THUNDERSTORMS...AS WELL AS COOLER TEMPERATURES AND BREEZY
CONDITIONS. THE LOW PRESSURE SYSTEM WILL MOVE SOUTHWARD TO ALONG
THE CENTRAL CALIFORNIA COAST BY LATE THURSDAY...BUT PARTS OF THE
REGION WILL CONTINUE TO SEE CHANCES OF SHOWERS INTO SATURDAY.

PEOPLE SHOULD BE PREPARED FOR A SIGNIFICANT WEATHER CHANGE
STARTING WEDNESDAY. EVEN LIGHT AMOUNTS OF RAIN WILL RESULT IN
SLIPPERY CONDITIONS ON ROADWAYS DUE TO MONTHS OF DRY WEATHER
ALLOWING OIL RESIDUES TO BUILD UP. IF YOU ARE PLANNING OUTDOOR
ACTIVITIES BE PREPARED FOR COOL AND BLUSTERY WEATHER WITH
SCATTERED SHOWERS AND POSSIBLE THUNDERSTORMS...AND EVEN THE
POSSIBILITY OF A DUSTING OF SNOW ACROSS THE HIGHEST ELEVATIONS
OF THE NORTHERN SIERRA NEVADA...THE SOUTHERN CASCADES...AND THE
INTERIOR COASTAL RANGE.

RCH/DR