EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 900 AM PST SAT JAN 27 2001
...SYNOPSIS...
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL OCCUR TODAY AS
VERY COLD LOW PRESSURE ALOFT CONTINUES TO DRIFT EAST THROUGH
SOUTHERN CALIFORNIA. SNOW WILL FALL BELOW 3000 FEET IN A FEW
AREAS...INCLUDING THE APPLE VALLEY...WHERE A SNOW ADVISORY CONTINUES
UNTIL NOON. THE SHOWERS WILL DECREASE TONIGHT AS MOISTURE ALOFT AND
LOW PRESSURE GRADUALLY MOVES EAST OUT OF THE AREA. WEST FLOW WITH
WEAK LOW PRESSURE TO THE NORTH WILL KEEP SOME CLOUDS THROUGH
TUESDAY...THEN CLEARING AND WARMING WILL OCCUR.
...DISCUSSION...
THE BIG EVENT THIS MORNING WAS THE SNOW OVER THE APPLE VALLEY...WITH
6 INCHES REPORTED AT 4000 FEET IN PINON HILLS AND 2 INCHES ALONG
I-15 JUST NORTH OF THE CAJON PASS. RADAR AND SPOTTER REPORTS INDICATE
THIS SNOW IS DECREASING...BUT I WILL KEEP THE SNOW ADVISORY GOING A
WHILE LONGER EVEN IF ONLY LIGHT SNOW OCCURS SINCE CHAINS ARE STILL
REQUIRED IN SOME AREAS AND HIGHWAY 138 IS CLOSED. THE SNOW WAS
TRIGGED BY A VORT MAX...WHICH IS NOW MOVING THROUGH THAT AREA...SO
DVV WILL OCCUR LATER THIS MORNING.
THE ATMOSPHERE IS QUITE UNSTABLE WITH A 500 MB TEMP OF -32 DEG C! LI
VALUES ARE AROUND ZERO...AND ACARS SOUNDINGS SHOW INSTABILITY
RELATIVE TO THE MOIST ADIABAT UP TO 450 MB. WITH RH VALUES STILL AT
OR ABOVE 70 PERCENT AT 700/850 MB...MORE SHOWERS WILL DEVELOP...WITH
ISOLATED TSTORMS POSSIBLE. MOST OF THE TSTORMS IN THE PAST 24 HOURS
HAVE BEEN OVER THE COASTAL WATERS. THE ISLAND CONVERGENCE BANDS ARE
SE OF THE ISLANDS AND NOT EAST DUE TO THE NW FLOW...SO MOST OF THE
COASTAL WATER TSTORMS SHOULD STAY ALONG AND SOUTH OF THE MEXICAN
BORDER. SINCE DYNAMICS WILL NOT BE TOO GOOD AFTER THE VORT MAX
DRIFTS SOUTH...MOST OF THE SHOWERS SHOULD BE LIGHTNING-FREE. HAIL
WILL CERTAINLY BE A POSSIBILITY IN THE STRONGER CELLS AS THE SNOW
LEVEL WILL BE AROUND 3000 FEET THIS AFTERNOON.
SOME RESIDUAL MOISTURE LINGERS SUNDAY FOR SOME CLOUDINESS AND
POSSIBLY A MTN SHOWER. LOOKING AHEAD TO MON NIGHT/TUE...THE MODELS
ARE TRENDING FURTHER NORTH WITH THE WAVE...INCLUDING THE PREVIOUSLY
VERY BULLISH NOGAPS. SO...PRECIP IS LOOKING LESS LIKELY FOR
THEN...AND I SEE NO NEED TO ADD IT OR UPGRADE IT (MTNS) INTO THE
EXTENDED. IT STILL LOOKS LIKE WE WILL HAVE RIDGING AND SOME OFFSHORE
FLOW LATER IN THE WEEK.
AN UPDATE WILL NOT BE ISSUED NOW...BUT BASED ON WHAT HAPPENS WITH
ANY LINGERING SNOW IN THE HIGH DESERTS AND OUTLOOKS ON CONVECTION
ELSEWHERE...ONE MAY BE ISSUED LATER THIS MORNING.
SAN 42-
.SAN...SNOW ADVISORY...SEE LAXWSWSAN.
...MARINE WEATHER STATEMENT...SEE LAXMWSSAN.
MAXWELL