[LeArc] Forecast Discussion : MLI@ 9/26/02 3:10:10 PM

[learc@mailman.qth.net]

The following weather message is provided by McDonough County E.S.D.A.


FXUS63 KDVN 262017
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
ISSUED BY NWS LA CROSSE WI
317 PM CDT THU SEP 26 2002

DATA ANALYSIS SHOWING TWO MAIN SYSTEMS OF INFLUENCE THAT ARE
AFFECTING THE SENSIBLE WEATHER ACROSS THE FORECAST AREA.  THE FIRST
IS THE DEEP MID/UPPER LEVEL SYSTEM OVER CENTRAL CANADA.  THE SECOND
IS THE SOON TO BE REMNANTS OF ISIDORE...NOW CENTERED OVER THE
GULF COASTAL STATES.  THE EVOLUTION OF THESE AND THEIR AFFECT ON THE
FORECAST AREA WILL BE THE MAIN FORECAST PROBLEMS OVER THE NEXT FEW
DAYS.

UPSTREAM...A VIGOROUS UPPER LEVEL DISTURBANCE /NOTED ON WATER VAPOR/
IS DROPPING SOUTH THROUGH BRITISH COLUMBIA THROUGH THE UPPER LEVEL
FLOW.  THIS SYSTEM HAS BEEN RESOLVED BY THE MODELS VERY WELL DURING
THE PAST SEVERAL RUNS.  THIS HAS RESULTED IN LARGE VARIANCES WITH
REGARDS TO THE PRECIPITATION EXPECTED OVER THE FORECAST AREA THIS
WEEKEND.  THIS ALSO HAS IMPLICATIONS WITH THE TIMING OF THE FRONTAL
PASSAGE EARLY NEXT WEEK.

SURFACE ANALYSIS SHOWS A SLOW MOVING COLD FRONT EXTENDING ROUGHLY
FROM KGRB-KDBQ-KDSM.  REGIONAL RADAR DATA SHOWING THE PRECIPITATION
NORTH OF THE FRONT.  FORCING ANALYSIS DEPICTS THIS WELL /MOST NOTABLE
IN THE 850-700MB LAYER/.  WATER VAPOR SHOWING STRONG SUBSIDENCE
OCCURRING IN THE AREA BETWEEN THE FRONT AND THE TROPICAL SYSTEM OVER
THE GULF COASTAL STATES.  THIS HAS RESULTED IN CLEAR SKIES AND WARM
TEMPERATURES ACROSS THE FORECAST AREA.

TONIGHT...THE COLD FRONT SHOULD EDGE SOUTHWARD...FAR ENOUGH TO
WARRANT SMALL CHANCE OF PRECIPITATION ACROSS THE NORTHERN ZONES.
ACROSS THE REMAINDER OF THE FORECAST AREA...SUBSIDENCE REMAINS IN
PLACE...PRECLUDING CLOUDS/PRECIPITATION.  ON FRIDAY...THE
FRONT WEAKENS AS THE FORCING WEAKENS DRAMATICALLY /850-700 MB
LAYER/.  THIS OCCURS AS THE FRONT MOVES SOUTHEAST THROUGH THE
FORECAST AREA.  THUS...PRECIPITATION CHANCES SHOULD REMAIN LOW FOR
FRIDAY.

AVN/ETA CONTINUE TO SHOW POOR RUN TO RUN CONSISTENCY...AND
AGREEMENT...WITH THE HANDLING OF THE DISTURBANCE CURRENTLY MOVING
THROUGH BRITISH COLUMBIA.  THERE HAS BEEN A TREND TOWARD A STRONGER
SYSTEM...WHICH IS CERTAINLY SUGGESTED BY THE WATER VAPOR IMAGERY.
THIS WOULD RESULT IN A UPPER LEVEL SYSTEM BEING MORE
CLOSED/CONCENTRIC OVER THE WESTERN STATES THIS WEEKEND...CAUSING THE
NORTHERN STREAM TO REMAIN FURTHER NORTH.  THIS WOULD KEEP THE BULK OF
THE FORCING FROM THE NEXT SYSTEM THAT IS A NORTHERN STREAM SYSTEM...
NORTH OF THE FORECAST AREA LATE SATURDAY INTO SUNDAY.  THIS AGREES
WITH DPROG/DT.  AS A RESULT...WILL TAILOR PRECIPITATION CHANCES
TOWARD THIS THINKING.

GRADUAL HEIGHT RISES AND SOUTHERLY FLOW BUILD INTO THE REGION DURING
THE NEXT FEW DAYS AHEAD OF THE NEXT SYSTEM EARLY NEXT WEEK.  THIS
SYSTEM...WHICH IS THE AFOREMENTIONED DISTURBANCE OVER THE WEST...
WILL BE FORCED EAST AS THE DISTURBANCE OVER THE ALEUTIANS PUSHES IT
EAST.  THIS WILL BE THE MAIN INFLUENCE OF PRECIPITATION/TIMING OF
NEXT FRONTAL PASSAGE.

THINK THERE IS CONSENSUS AMONG THE MEDIUM RANGE ENSEMBLES THAT A
WARMING TREND IS IN STORE...SHOWING A GRADUAL INCREASE IN
HEIGHTS/850 MB TEMPERATURES/SOUTHERLY FLOW AHEAD OF THE NEXT
SYSTEM /SUNDAY-MONDAY TIMEFRAME/.  GIVEN THE STRONGER DISTURBANCE OUT
WEST...KEPT THE FRONTAL PASSAGE BACK TO TUESDAY...WITH WARM
TEMPERATURES AHEAD OF THE FRONT.  COOL CONDITIONS RETURN ON WEDNESDAY
AND THURSDAY.

COORDINATED WITH ARX.

.DVN...NONE.

KRC