Forecast Discussions mentioning ACARS, received at FSL on 03/03/00

LARGE SCALE...RATHER BROAD BUT PERSISTENT UPPER TROUGH AROUND THE DATELINE IF FORECAST TO CHANGE CHARACTER DURING THE NEXT WEEK OR SO. RATHER THAN SERIES OF IMPULSES EMANATING FROM THIS REGION AND SWINGING SEWD THROUGH SRN CALIF THEN INLAND ACROSS CENTRAL US IT APPEARS THAT IT WILL SUPPORT MORE RIDGGING ALONG THE WEST COAST. THIS MEANS A BLOCKING SITUATION IS SHAPING UP WITH THE GT LAKES ON THE FRONT CONFLUENT END...AND PERHAPS A BIT MORE OPEN TO COOLER AIR INTRUSIONS. IN THE SHORTER TERM THOUGH ACTIVE SYSTEMS WILL BYPASS NRN ILLINOIS TO THE SOUTH (TODAY) OR FOLLOW RECENT HISTORY AND APPROACH FROM THE SW.

REGIONAL AND FORECAST...UPPER VORTEX OVER CENTRAL KANSAS THIS MORNING FORECAST TO DRIFT EAST OR A LITTLE SOUTH OF EAST AS IT WEAKENS AND IS CAUGHT UP BY LARGER SYSTEM OFF EAST COAST. CLOUD SHIELD WILL TICKLE SOUTHERN SUBURBS OF CHI FOR A WHILE TODAY. WEAK SURFACE ANTICYCLONE OVER WESTERN LAKES SHOULD KEEP WINDS LIGHT/VARIABLE EXCEPT ONSHORE WITH A WEAK LAKE BREEZE NEAR LM.

SECOND WEAK TROUGH MOVING ALONG CANADIAN BORDER ALSO FORECAST TO SLIDE SE THROUGH WESTERN LAKES LATE TONIGHT OR EARLY SAT. DEFORMATION PROCESSES AT MID LEVELS AND LACK OF ANY WATER TO START WITH SUGGESTS ONLY PATCHY CLOUDS ARE LIKELY WITH THIS SYSTEM. IT WILL HOWEVER USHER IN A WARMING TREND AS AIRMASS SOURCE IS DOWNSLOPED AND WINDS REVERT QUICKLY AROUND TO SW AGAIN SAT NIGHT AND SUNDAY.

IT APPEARS NEXT SIGNIFICANT THREAT OF PRECIP WILL BE AROUND MIDWEEK AS PATTERN CHANGE BEGINS TO KICK IN. UNTIL THEN ACTIVE WEATHER SHOULD HOLD WELL TO THE WEST AND SOUTH OF NRN ILLNOIS.

ACARS PROFILE THIS MORNING VIRTUALLY ISOTHERMAL SO WARMING WILL BE A STRUGGLE ESPECIALLY SINCE LIGHT WINDS WILL NOT AID MIXING MUCH. STILL..SUN IS GETTING STRONGER SO HEATING WILL NOT BE TRIVIAL. COOLER NGM MOS MAY BE A BETTER FORECAST TODAY BUT WILL GO ALONG WITH LOWER FAN NUMBERS FOR MAX TEMPS ON SATURDAY...STILL ALMOST 10 DEG ABOVE TODAY. MINS TONIGHT APPEAR REASONABLE. KML

.CHI...NONE

...SYNOPSIS...

A STORM MOVING SOUTH ALONG THE CALIFORNIA COAST WILL STALL OVER SOUTHERN CALIFORNIA OR NORTHWEST MEXICO FRIDAY NIGHT. THIS SYSTEM WILL BRING A CHANCE FOR SHOWERS OR THUNDERSTORMS THROUGH SUNDAY. TEMPERATURES WILL BE NOTICEABLY COOLER THIS WEEKEND.

...DISCUSSION...

MID AND HIGH CLOUDS ASSOCIATED WITH A SURFACE COLD FRONT OVER THE COASTAL WATERS WILL MOVE ACROSS SOCAL TONIGHT. THE COLD FRONT MARKS THE LEADING EDGE OF A COLDER AIR WHICH WILL REMAIN OVER THE REGION THROUGH THE WEEKEND. THE MODELS HAVE HANDLED THE TIMING AND POSITION OF STORMS ERRATICALLY THIS WEEK. FORECASTERS MAY HAVE TO RELY ON REAL TIME DATA (SATELLITE LOOPS...ACARS DATA...MESOSCALE ANALYSIS) AND PERSONAL EXPERIENCE.

SUBSIDENCE ASSOCIATED WITH DIGGING SYSTEM HAS RENDERED DETECTION OF CIRCULATION CENTERS ON THE WATER VAPOR IMAGES DIFFICULT THIS EVENING...BUT THE LAST FEW FRAMES DETECTED A CYCLONIC SWIRL NEAR THE BAY AREA...AND A SECOND CIRCULATION NEAR PT CONCEPTION. AVN AND RUC MODELS HAVE PICKED UP ON THESE FEATURES. WILL TREND TOWARD THESE SOLUTIONS...AT LEAST IN THE SHORT TERM.

IR IMAGERY SHOWS COLD AIR STRATOCUMULUS OVER THE OCEAN STREAMING SOUTHWARD TOWARD OUR COASTAL WATERS...AN INDICATION THAT LOW LEVEL MOISTURE WILL BE INCREASING OVER THE NEXT 24 HOURS. THE 00Z ANALYSIS SHOWED STRONG JET STREAM WINDS IN EXCESS OF 100 KTS WEST OF THE VORTICITY CENTER NEAR SFO...SO THIS VORTEX WILL MOVE RAPIDLY SOUTHWARD AND BE WEST OF SAN DIEGO BY 12Z FRIDAY.

MODEL SOLUTIONS DIFFER DRAMATICALLY FRIDAY NIGHT AND SATURDAY. THE ACTUAL STORM TRACK WILL HEAVILY INFLUENCE WHAT KIND OF WEATHER WE GET. ETA BRINGS THE STORM INTO NORTHERN BAJA WITH A COLD CORE ALOFT (-24C AT 500 MB) AND STRONGEST UPPER LEVEL DYNAMICS SOUTH OF THE BORDER. IN CONTRAST...THE AVN STALLS THE UPPER CLOSED UPPER LOW FARTHER NORTH (WEST OF SAN DIEGO) AND KEEPS THE COLD CORE ALOFT (-26C AT 50 MB) FARTHER NORTH AS WELL. THIS SOLUTION WOULD GIVE US A BETTER CHANCE FOR SIGNIFICANT RAINFALL FROM SHOWERS AND THUNDERSTORMS THAN THE ETA SOLUTION.

ETA HAS HISTORICALLY BEEN A LITTLE TO AGGRESSIVE WITH DIGGING SHORTWAVES TOO FAR SOUTH. BUT THE AVN VORTICITY FIELDS BEYOND 00Z SATURDAY LOOK UNREALISTIC. SO I AM INCLINED TO GO WITH A COMPROMISE SOLUTION OF THE ETA AND AVN. THIS WILL BRING MOST OF THE RAIN SOUTH OF THE BORDER...BUT STILL PRODUCE SCATTERED SHOWERS AND POSSIBLE THUNDERSTORMS TO SOCAL AS WE WILL STILL BE CLOSE ENOUGH TO THE UNSTABLE COLD AIR ALOFT AND THE LOW LEVEL MOISTURE.

ONE OTHER ITEM WORTH NOTING. WITH THE SURFACE LOW SOUTHWEST OF SAN DIEGO...LOW AND MID LEVEL FLOW WILL REMAIN EAST-SOUTHEASTERLY...AND OROGRAPHICS WILL NOT BE MUCH OF A FACTOR IN ENHANCING MOUNTAIN PRECIPITATION.

SURF WILL INCREASE OVER NIGHT AND HEAVY SURF ADVISORIES MAY BE NEEDED THIS WEEKEND.

SAN 3654

.SAN...NONE.

MOEDE