Forecast Discussions mentioning ACARS, received at FSL on 01/13/01

...SYNOPSIS... THE LAST WAVE OF THE CURRENT PACIFIC STORM WILL MOVE OUT TONIGHT. THIS WILL BRING AN END TO THE SHOWERS IN MOST AREAS BY LATE EVENING. LOCALLY HEAVY RAIN AND COASTAL WATERSPOUTS WILL STILL BE POSSIBLE UNTIL VERY EARLY THIS EVENING. LIGHT ACCUMULATIONS OF SNOW ARE EXPECTED ABOVE 3500 FEET IN SAN DIEGO COUNTY EARLY TONIGHT. THE HEAVY SURF WILL ABATE LATER TONIGHT. DRY WEATHER WILL OCCUR SATURDAY AS THE SYSTEM EXITS TO THE EAST...AND TEMPERATURES SHOULD START TO INCREASE...AND NEXT WEEK SHOULD GENERALLY BE PARTLY CLOUDY AS SYSTEMS MOVE BY TO THE NORTHEAST. THE PASSES AND CANYONS WILL HAVE SOME GUSTY WINDS MONDAY AND TUESDAY.

...DISCUSSION... THE VORT MAX IS A BIT LESS DEFINED RIGHT NOW...BUT IT APPEARS TO BE SE OF SAN CLEMENTE ISLAND AND MOVING ESE...SO IT SHOULD PASS NEAR OR JUST SOUTH OF SAN DIEGO AROUND 6 PM. ONCE THAT PASSES THROUGH...MOST OF THE PRECIP MECHANISMS SHOULD BE GONE AS THE LOW-LEVEL WINDS WILL BE MORE NORTHWESTERLY AND INSTABILITY DECREASES. ADDITIONAL ACCUMULATIONS SHOULD BE CONFINED TO SAN DIEGO COUNTY MTNS...AND BASED ON ACARS...RAWS AND SPOTTERS...THE SNOW LEVEL IS AROUND 3500 FEET.

THE MAIN CONCERN THIS AFTERNOON WILL BE THE WATERSPOUTS ASSOCIATED WITH THE TSTORMS OVER THE COASTAL WATERS DUE TO CLOSED CYCLONIC CIRCULATION OVER THE COASTAL WATERS FROM THE SURFACE ALMOST TO 700 MB COMBINED WITH LI VALUES BELOW ZERO. SEE LAXSMWSAN FOR MORE DETAILS.

IT LOOKS LIKE AFTER TONIGHT WE WILL BE PRECIP-FREE...THOUGH SOME RESIDUAL HIGH RH VALUES...ESPECIALLY OVER THE MTNS...WILL KEEP SOME CLOUDS AROUND. PATCHY FOG MAY DEVELOP TONIGHT JUST ABOUT ANYWHERE IN OUR FORECAST AREA DUE TO THE WET GROUND AND LIGHT WINDS.

ANOTHER LOW SLIDES BY TO THE NORTHEAST MON INTO TUE. WHAT SHOULD KEEP US PRECIP FREE IS THE OFFSHORE FLOW AT 850 MB AND JUST MODERATE RH VALUES AT 850/700. THE STORM TRACK GRADUALLY LIFTS FURTHER NORTH LATER IN THE WEEK...THOUGH OVERALL...WE SHOULD HAVE PARTLY CLOUDY SKIES...MAINLY DUE TO SOME RETURN FLOW AROUND THE INSIDE SLIDER. SOME SUPPORT ALOFT EXISTS FOR CANYON/PASS WINDS MAINLY TUE AM...THOUGH SURFACE PRESSURE GRADIENTS WILL BE QUITE MARGINAL.

SAN 600-

.SAN...SPECIAL MARINE WARNING...SEE LAXSMWSAN. HEAVY SURF ADVISORY...SEE LAXMWSSAN. MAXWELL



THERE ARE DEWPOINTS IN THE 30S AND WARM AIR ADVECTION OVER NORTHEAST ILLINOIS AND NORTHWEST INDIANA THIS AFTERNOON AND TONIGHT. THE CLOUDS ARE LOW AND ACARS SOUNDING AT 1855 UTC SHOWS AN INVERSION STARTING AT 1922 FT. WILL FORECAST FOG TONIGHT AND ISSUE AN ADVISORY FOR THE WHOLE FORECAST AREA. THE MESOETA SHOWS DEWPOINTS IN THE MIDDLE 20S. BUT THE SURFACE ANALYSIS AT 20 UTC SHOWS DEWPOINT IN THE LOW 30S. THERE IS ALSO A WEAK TROUGH AT 700 MB OVER NORTH ILLINOIS AS SEEN ON THE 700 MB PROFILER WINDS.

MOSTLY CLOUDY SATURDAY AS THE NEXT CYCLONE MOVES INTO NORTHWEST MISSOURI. THIS CYCLONE WILL CAUSE WARM AIR ADVECTION INTO NORTHEAST ILLINOIS AND NORTHWEST INDIANA SATURDAY AND SATURDAY NIGHT. 300 MB SUPPORT FOR PRECIPITATION AS SEEN IN THE DIVERGENCE FIELD AND DEFORMATION FIELD. FORECAST OMEGA FIELDS AT 700 MB SHOW THE PRECIPITATION BEGINNING BETWEEN 00 UTC AND 06 UTC SUNDAY. THERE IS ISENTROPIC LIFT SATURDAY NIGHT AND AGAIN SUNDAY EVENING. AS THE LOW IS EXPECTED TO MOVE OVER NORTHEAST ILLINOIS MONDAY. THICKNESS FORECASTS FROM THE ETA INDICATE RAIN THROUGH SATURDAY NIGHT AND SUNDAY WHILE THE AVN INDICATES RAIN CHANGING TO SNOW ESPECIALLY FOR THE ROCKFORD AREA.

WILL FORECAST SNOW AND RAIN MIXED WITH THE POSSIBILITY OF FREEZING RAIN FOR NORTHERN COUNTIES. RAIN WITH SNOW MIXED IN FOR SOUTHERN COUNTIES. FOR SATURDAY AND SUNDAY. WILL KEEP SOME PRECIPITATION IN FOR MONDAY.

.CHI...DENSE FOG ADVISORY FOR TONIGHT AND SATURDAY MORNING FOR ALL OF NORTHEAST ILLINOIS AND NORTHWEST INDIANA.

$$ WHW



UPPER SYSTEM IS CONTINUING ITS TRACK THROUGH THE SRN ROCKIES...AND AT 03Z THE WATER VAPOR LOOP INDICATED IT WAS APPROACHING THE 4 CORNERS. GRANADA PROFILER WINDS AROUND 200 MB HAVE BEEN SLOWLY INCREASING TO 120 KNOTS...AND AIRCRAFT OBS IN SRN NEW MEXICO SHOWED 140 KNOT JET MAX AT 00Z. THESE HIGHER WINDS ON THE FRONT SIDE APPEAR TO BE HELPING THE SYSTEM EJECT AT A GOOD PACE.

THERMAL FIELDS CONTINUE TO MAKE THIS A DIFFICULT FORECAST. IN ADDITION TO AFFECTING THE PRECIP TYPE FORECAST...THE NEW 00Z MODELS ARE SHOWING MORE OF A BAROTROPIC BOUNDARY LAYER...WHICH GIVEN THE LACK OF A DECENT THERMAL BOUNDARY ANYWHERE IN THE CONUS PLAINS SEEMS APPROPRIATE. THAT THERMAL REGIME ALLOWS FOR LITTLE FRONTOGENESIS TO TAKE PLACE WITH THIS SYSTEM OVER THE CWFA. MESOETA AT 21Z SATURDAY SHOWS 850 TEMPERATURES RANGING FROM +1 NEAR WICHITA KS TO -2 NEAR GRAND ISLAND. THUS ISENTROPIC LIFT IS NOT PROGGED TO BE MUCH OF A PLAYER WITH THIS SYSTEM...NOR IS FRONTOGENETICAL FORCING. HOWEVER THERE SHOULD STILL BE A VERY STRONG AREA OF UPPER DIVERGENCE ON THE TOP OF THIS SYSTEM...AND STRONG DPVA. EVENTUALLY THE UPPER SYSTEM IS PROGGED TO OUTRUN THE SURFACE LOW. SO THE LIFT LOOKS FAIR...BUT NOT GREAT...AS REFLECTED IN THE MODEL H7 OMEGA FIELDS. MOISTURE REMAINS PLENTIFUL...SO THE MODERATE LIFT SHOULD STILL SQUEEZE OUT THE 4-6 INCHES IN THE EXISTING WATCH AREA.

OTHER CONCERN IS THE NORTHERN EXTENT OF THE DRY SLOT...WHICH NOW LOOKS LIKE IT WILL GET INTO OUR KANSAS COUNTIES AT LEAST. THE MESO ETA SHOWS THE DRY SLOT PERHAPS AS FAR NORTH AS INTERSTATE 80 AT 21Z...BUT EVEN IF THIS IS THE CASE THE DEFORMATION ZONE SHOULD STILL SWEEP THROUGH AND PROVIDE 2-4 INCHES FOR SRN NEBRASKA COUNTIES. 1-2 LOOKS GOOD FOR NORTH CENTRAL KS.

THUS WILL NOT MAKE ANY SIGNIFICANT CHANGES TO THE EXISTING WATCH OR THE SNOW AMOUNTS. IF ANYTHING WILL POSSIBLY DEFINE THE ORD AREA WITH 6-8 INCHES...WHERE THE STRONGEST FORCING FROM THE DEFORMATION ZONE WILL BE TAKING PLACE AND THE COLD AIR WILL ARRIVE SOONER. THE TIMING ON THE PHASE CHANGE SEEMS OK AS WELL GIVEN FORECAST SOUNDINGS FROM NEW MODELS. 00Z 850 HAND ANALYSIS SHOWED NO COLD AIR IN THE AREA...BUT DYNAMICAL AND POSSIBLY SOME EVAPORATIVE COOLING SHOULD BE SUFFICIENT TO VERIFY THE MODELS THERMAL FIELD FORECASTS.

ALREADY MADE CHANGES TO MY EASTERN COUNTIES REGARDING THE STRATUS DECK AND COLDER SURFACE TEMPERATURES...AND WILL CONTINUE TO TWEAK THIS AREA AS NEEDED FOR FOG/STRATUS/DRIZZLE THREAT.

.GID...WINTER STORM WATCH NEZ039-040-041-046-047-048-060-061-072-073 -082 SATURDAY AFTERNOON AND SATURDAY NIGHT.

NIETFELD