Forecast Discussions mentioning ACARS, received at FSL on 02/06/01

...ONCE AGAIN TEMPERATURES WILL BE THE NEAR TERM QUESTION...

IN THE 12Z ANALYSIS PACKAGE THE H3 JET STREAK NOW OVER THE NORTHERN PLAINS CONTINUES TO DIG INTO THE WEST SIDE OF THE EASTERN US UPPER TROUGH WHILE AT H5 A WELL ESTABLISHED BAROCLINIC ZONE APPEARS FROM THE PACIFIC NORTHWEST STATES SOUTHEAST ACROSS THE CONUS TO GEORGIA. A SERIES OF FAST MOVING AND DAMPENED WAVES ARE IN THIS PATTERN WITH THE MOST OBVIOUS ONE CURRENTLY MOVING INTO WYOMING. THIS FEATURE APPEARS ON TRACK TO PUSH A COOL FRONT SOUTH ACROSS THE CENTRAL PLAINS TONIGHT. THIS WILL REPLACE THE WARM LEE TROUGH IN PLACE OVER THE CENTRAL HIGH PLAINS TODAY. LOWER LEVEL ANALYSIS INDICATES LITTLE IN THE WAY OF MOISTURE AVAILABLE FOR THIS FRONT. THE H8 ANTICYCLONE OVER EXTREME SOUTH TEXAS INTO NORTHERN MEXICO CONTINUES TO PREVENT THE RETURN OF GULF MOISTURE FOR THE NEAR TERM.

THE MODELS INITIALIZED WELL OVER THE DATA RICH CONUS AGAIN TODAY BUT PROBLEMS WERE FOUND OVER THE GULF OF ALASKA. WATER VAPOR IMAGERY AND HAND ANALYSIS OF THE H3 AIREP DATA INDICATE A SPLIT IN THE JET LEVEL FLOW JUST SOUTH OF THE ALEUTIANS WITH A NORTHERN BRANCH ANTICYCLONIC STREAK ACROSS ALASKA WHICH DIVES SOUTH INTO THE WEST SIDE OF THE UPPER LEVEL LOW NOW WEST OF JUNEAU. THIS FEATURE APPEARS POORLY IDENTIFIED IN THE MODEL INITIALIZATIONS AND MAY HAVE SIGNIFICANT IMPACT ON THE LATE PERIODS OF THIS FORECAST. COORDINATION WITH THE NCEP SDM INDICATES THAT A RECONNAISSANCE AIRCRAFT IS DISPATCHED NEAR THIS AREA FOR LATER TODAY SO HOPEFULLY TONIGHTS MODELS WILL HAVE BENEFIT OF SOME DROPSONDE DATA IN THIS AREA.

FOR THE NEAR TERM THEN THE BALANCE BETWEEN DOWNSLOPING, REMAINING SNOW PACK, AND COLD AIR ADVECTION WITH THE FRONT WILL DETERMINE OVERNIGHT LOWS TONIGHT AND THE MOS GUIDANCE LOOKS QUITE GOOD. HIGHS ON TUESDAY WILL BE A BALANCE BETWEEN THE COLDER AIR AND THE AMOUNT OF MID AND UPPER LEVEL CLOUD. MOS LOOKS AWFULLY COOL AND WILL GO ABOVE IT.

TUESDAY NIGHT AND WEDNESDAY SHOULD SEE CONSIDERABLE CLOUD ALONG WITH SOME RATHER BRISK WARM AIR ADVECTION AS THE UPSTREAM SYSTEM DIGS INTO THE SOUTHERN ROCKIES. GREAT UNCERTAINTY CONTINUES OVER THE TIMING, LOCATION AND STRENGTH OF THIS SYSTEM FOR REASONS MENTIONED ABOVE, BUT EVEN AT THAT MOS LOOKS TOO COLD FOR TUESDAY NIGHT AND WEDNESDAY AND WILL ALTER TEMPERATURES IN THIS TIME FRAME TOWARD WARMER READINGS.

IF THIS NEXT SYSTEM MATURES SIMILAR TO THE MODELS, THE ENTIRE COLUMN SHOULD BE TOO WARM FOR SNOW OVER SOUTHWEST KANSAS. AVAILABLE LOW LEVEL MOISTURE REMAINS SOMEWHAT OF A QUESTION MARK AT THIS TIME BUT THE SYSTEM SHOULD WRING OUT AT LEAST ENOUGH MID AND UPPER LEVEL MOISTURE TO COUPLE WITH UPSLOPE FLOW SATURATING THE LOWER LEVELS SO WILL NEED AT LEAST SOME POPS FOR WEDNESDAY FOR RAIN. WILL STAY CLOSER TO THE AVN FOR NUMBERS IN THIS PERIOD.

EXTENDED DISCUSSION... MODELS IN SURPRISINGLY GOOD AGREEMENT WITH SYSTEM THAT WILL AFFECT THE CENTRAL PLAINS FOR THE MID TO LATTER PART OF THIS WEEK. TIMING WILL BE CRITICAL IN TERMS OF THE JUXTAPOSITION OF UVVS, MOISTURE, AND COLD AIR TO PRODUCE SNOW. WITH LOW-LEVEL WAA BECOMING LESSER IN MAGNITUDE LATE WEDNESDAY NIGHT, WILL GO AHEAD AND MENTION RAIN OR SNOW. WITH UPPER SYSTEM TO OUR SOUTHWEST ON THURSDAY, AND CAA TAKING PLACE, WILL JUST MENTION SNOW.

SURFACE HIGH WILL MOVE OVERHEAD FRIDAY INTO SATURDAY, SO WILL PLAN TO MENTION COLDER TEMPS FOR FRIDAY. UPPER SYSTEM WILL BE OFF TO OUR SOUTHEAST BY FRIDAY, SO WILL NOT MENTION POPS FOR FRIDAY OR SATURDAY.

LEESIDE TROFFING WILL INCREASE DURING NEXT WEEKEND, THEREFORE WILL PLAN TO WARM TEMPS UP AS A RESULT. NEXT UPPER SYSTEM LOOKS TO AFFECT OUR WX BY LATE SUNDAY INTO MONDAY, SO WILL INTRODUCE POPS THESE DAYS. AT THIS TIME, WILL NOT TRY TO NAIL DOWN PCPN TYPE AND JUST MENTION RAIN OR SNOW.

PRELIMINARY GUIDANCE FOR COORDINATION ONLY. OFFICIAL FORECASTS ARE CONTAINED WITHIN THE DODGE CITY ZONE FORECAST.

DDC 028/039 030/043 030 002 GCK 026/038 030/042 030 002 EHA 029/041 029/045 030 002 LBL 030/042 030/045 031 002 HYS 026/037 027/038 027 002 P28 033/041 034/049 038 002

.DDC...NONE

JOHNSON/MCCAMMON



DRAMATIC CHANGES ARE IN STORE FOR THE DISTRICT THROUGH THE NEXT FEW DAYS. IN THE SHORT TERM...MARINE LAYER CLOUDINESS IS DEVELOPING QUITE WELL ALONG THE CENTRAL COAST ATTM...WITH A LARGE AREA OF CLOUDS FORMING OFFSHORE OF LA AND ORANGE COUNTIES AS WELL. WITH ALL GRADIENTS TRENDING STRONGLY ONSHORE...BELIEVE AREAS OF LOW CLOUDS ALONG WITH LOCALLY DENSE FOG WILL MOVE INTO MOST OF THE COASTAL SXNS THIS MORNING. WEAK EDDY IS ALSO PRESENT...APPARENT FROM THE OFFSHORE OBS... BUT NOT REFLECTED AS MUCH ALONG THE COAST. WITH THE EDDY RELATIVELY FAR OFFSHORE...AND THE INVERSION STILL SURFACE BASED ON RECENT ACARS SOUNDINGS...BELIEVE IT WILL BE DIFFICULT FOR LOW CLOUDS TO MOVE INTO THE VALLEYS THIS MORNING. CONCERNED THAT LOW CLOUDS WILL HAVE DIFFICULTY CLEARING OUT OF THE AREAS THEY DO MOVE INTO THIS MORNING... BUT WILL STAY OPTIMISTIC FOR NOW AND INDICATE BECOMING PARTLY CLOUDY THIS AFTERNOON.

WEATHER FOR THE NEXT COUPLE OF DAYS WILL BE CONTROLLED BY A VERY STRONG UPPER TROF...CURRENTLY MOVING INTO THE PACIFIC NW...WHICH WILL DIVE SOUTHWARD INTO CALIFORNIA THRU WED. THIS WILL CAUSE HEIGHTS TO CRASH ACROSS THE REGION...WITH 500 MB HGT FALLS OF 200-250M BY WED AM. MODELS HAVE BEEN GRADUALLY TRENDING WESTWARD WITH THE 500 MB CENTER OF THIS SYSTEM...AND THE 06Z MESO-ETA CONTINUED THIS TREND...SHOWING THE MOVEMENT OF THE SYSTEM SLOWER AND MORE TO THE WEST THAN 00Z AVN/ETA RUNS. LATEST MESO-ETA ACTUALLY CLOSES OFF THE 500 MB CENTER OVER THE MOJAVE DESERT BY MIDDAY WED. ALL MODELS DO SHOW A TREMENDOUS AMOUNT OF COLD AIR POURING INTO THE DISTRICT ON TUE NIGHT AND WED...WITH 850 MB TEMPS DROPPING BELOW ZERO ACROSS THE ENTIRE AREA ON WED AM.

THE MAIN WEATHER EFFECTS ACROSS THE FORECAST AREA FROM THIS SYSTEM WILL BE WIND...MUCH COLDER TEMPERATURES...AND THE THREAT OF SHOWERS ALONG WITH POTENTIALLY VERY LOW SNOW LEVELS. WIND...EXPECT STRONG NW WINDS ALONG THE CENTRAL COAST THIS AFTERNOON...SPREADING INTO THE SBA MTNS AND S COAST THIS EVENING...THEN INTO THE LA/VTU MTNS OVERNIGHT AND INTO THE LA/VTU COASTS AND VALLEYS ON WED. WIND ADVISORIES WILL PROBABLY BE NEEDED FOR SOME AREAS TONIGHT AND WED. TEMPS...READINGS TODAY WILL FEEL COOL COMPARED TO THE RECENT HEAT WAVE...WITH HIGHS IN THE 60S FOR MOST LOCATIONS. THEN THE BOTTOM FALLS OUT ON WED...WITH HIGHS EXPECTED TO REACH ONLY INTO THE 50S FOR MOST COAST/VALLEY AREAS...30S IN THE MTNS AND 40S IN THE DESERT. STRONG AND GUSTY WINDS WILL MAKE IT FEEL EVEN COLDER...AND WIND CHILLS NEAR OR BELOW ZERO ARE LIKELY IN THE MTNS. AS FOR THE SHOWER CHANCES...MOISTURE IS QUITE LIMITED WITH THIS SYSTEM... BUT WITH SUCH STRONG DYNAMIC FORCING...AND BOTH RUNS OF THE ETA SPITTING OUT SOME PRECIP ACROSS THE EASTERN PORTION OF THE FCST AREA...WILL MAINTAIN THE SLIGHT CHC OF SHOWERS FOR MOST OF LA/VTU COUNTIES LATE TNGT AND WED...AND CHANCE POPS FOR THE LA/VTU MTNS... AS GOOD UPSLOPE FLOW SHOULD PILE MOISTURE AND LIFT ALONG THE NORTHERN SLOPES. SNOW LEVELS WILL BE VERY LOW...AROUND 2500 FEET TUE NIGHT AND WED MORNING...RISING ONLY TO NEAR 3000 FEET IN THE AFTERNOON. THIS HAS THE POTENTIAL TO CAUSE PROBLEMS ON MUCH OF I-5 THRU THE GRAPEVINE...AS WELL AS ON HIGHWAY 14 AND INTO THE ANTELOPE VALLEY. HOWEVER...WITH THE LIMITED MOISTURE IT IS VERY UNCERTAIN HOW MUCH SNOW..IF ANY...WILL FALL IN THESE AREAS.

EXTENDED...WEDNESDAY NIGHT SHOULD BE VERY COLD IN AREAS SHELTERED FROM THE WIND. COULD SEE FREEZING TEMPERATURES AT MANY LOCATIONS FROM VTU COUNTY NORTHWARD. BELIEVE THERE WILL BE TOO MUCH NORTHERLY FLOW INTO LA COUNTY TO ALLOW WIDESPREAD FREEZING TEMPS THERE...ALTHOUGH LOCATIONS SHELTERED FROM THE WINDS COULD DROP TO THE FREEZING MARK. COOL...BREEZY AND DRY THU...THEN THE NEXT UPPER TROF DROPS DOWN THE COAST...BRINGING A CHANCE OF SHOWERS TO THE CENTRAL COAST FRI...SPREADING TO SOUTHERN AREAS BY LATE FRI NIGHT INTO SAT. MODELS DIVERGE SOMEWHAT BY THE WEEKEND...WITH MRF MORE PROGRESSIVE WITH THE MAIN TROF AXIS THAN THE OTHER GLOBAL MODELS. UKMET/CANADIAN HOLD BACK MUCH OF THE ENERGY OFFSHORE ON SAT...THEN THE UKMET BRINGS A DEEP TROF THRU THE AREA ON SUN. ACCORDING TO THE MRF...BRISK NORTHERLY FLOW ALOFT CONTINUES WELL INTO NEXT WEEK...WITH THE TROF JUST CLOSE ENOUGH TO THREATEN SHOWERS. WILL CONTINUE WITH THE BROADBRUSH CHANCE OF RAIN FORECAST FOR ALL ZONES DURING THE SUN THRU MON PERIOD. COOL WEATHER APPEARS LIKELY TO CONTINUE INTO NEXT WEEK.

LAX 022. JACOBSON

.LAX...GALE WARNING/SMALL CRAFT ADVISORY (SEE LAXCWFLAX).