[LeArc] Forecast Discussion : MLI@ 3/7/03 1:43:44 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 071953
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
150 PM CST FRI MAR 7 2003

.OVERVIEW...WHOA!!...VERY CHALLENGING FORECAST TO SAY THE LEAST...HAS
SOME FORCING/TRIGGER SIMILARITIES TO THE APRIL 1 "SURPRISE SNOW OF
LAST YEAR.  SNOW COVER HAVING MAJOR IMPACTS ON MODIFYING EVOLUTION OF
NEXT SYSTEM. WEAK REINFORCEMENT SHOT OF ARCTIC AIR HAS ARRIVED WITH
LOW CLOUDS KEEPING AREA IN 20S NW LOCATIONS AND 30S SE.  MODELS
(ESPECIALLY ETA) HAVING PROBLEMS HANDLING COLD AIR POOLING OVER AREA.
FAST ZONAL FLOW APPROACHING ALOFT FROM DEEP ARCTIC VORTEX OVER
ALBERTA WITH HIGH BAROCLINICITY. THIS IS PRODUCING WAVES AND AREAS OF
SNOW ON WESTERN (BACK) SIDE OF GREAT PLAINS COLD AIR DOME.  SATELLITE
AND SFC ANALYSIS SUPPORT LOW LEVELS TO REMAIN MOIST WITH VERY SLOW
DISSIPATION OF LOW CLOUDS BEHIND ARCTIC FRONT.

...SNOW IMPACTS ON TEMPS AND TONIGHT/S SYSTEM MAIN NEAR TERM FORECAST
ISSUE WITH MORE WINTER WEATHER EARLY NEXT WEEK...

.DIAGNOSIS AND DAYS 1-3...MODELS INITIALIZE POOR ON COLD AIR OVER
AREA WITH GFS-AVN THE LEAST WORST AT 18Z AND ETA ABNORMALLY BAD ON
LARGE SCALE FEATURES OF COLD AIR WHICH APPEARS TO BE A RADIATION
FEEDBACK PROBLEM WITH SNOW COVER AND COLD AIR.  THUS...WILL USE GFS
AND UKMET AND EVEN NGM LARGE SCALE FEATURES SUPPORTING LIKELY POPS
ALONG AND NORTH OF HIGHWAY 30 WITH THERMAL PROFILES SUGGESTING MAINLY
FREEZING RAIN AND SOME SLEET CHANGING TO SNOW AS SURFACE LOW SLIDES EAST
ALONG I-80.  PREFER UKMET SURFACE FORCING AND LOW TRACK WITH GFS-AVN AND
UKMET BLEND BASED ON 18Z VERIFICATION AND PERSISTENCE PAST FEW DAYS.
FOR RIGHT NOW...APPEARS AMOUNTS TO BE GENERALLY LESS THAN A TENTH OF AN
INCH...OR MINOR ICE AMOUNTS BUT STILL ENOUGH FOR TREACHEROUS GLAZE. YET
MODERATE RISK PRECIP AMOUNTS COULD BE SIGNIFICANT MORE WITH GOOD FORCING
AND IF COLD AIR DEEPENS ANOTHER 500 TO 1,000 FEET.  WILL PASS THIS TO
EVENING SHIFT AS A WINTER WEATHER ADVISORY MAY NEED TO BE ISSUED BY LATE
EVENING FOR NORTHERN AREAS LATE TONIGHT AND SATURDAY MORNING.  LOTS OF
LOW LEVEL MOISTURE AND LIGHT WINDS TONIGHT SUPPORT AREAS OF FOG...
LOCALLY DENSE PRIMARILY NORTH OF HIGHWAY 34 BEFORE SYSTEM ARRIVES. ALONG
I-80 CORRIDOR...WILL GO CHANCE POPS OF RAIN...POSSIBLY FREEZING AT TIMES
EARLY BUT WAA AND WEAKER FORCING LIMITS RISKS HERE A BIT. TEMPS...WILL
HAVE TO TRIM QUITE A BIT NORTHERN 2/3 TOMORROW BUT STILL SEE 40S UP TO
HIGHWAY 34 ALONG AND SOUTH OF SURFACE LOW TRACK. THEN STRONG ARCTIC PUSH
ON GUSTY NW WINDS OF 20 TO 30 MPH ARRIVES.  WILL TRIM TEMPS BACK A FEW
MORE DEGREES DUE TO STRENGTH OF COLD AND SINCE NORTHERN 2/3 AREA WILL
KEEP A SNOW COVER AND VERY COLD TEMPS MONDAY AM. MONDAY GFS-AVN AND
UKMET SHOW VIGOROUS CLIPPER WITH QPF AMOUNTS OF .1 TO .4 INCHES.
REASONABLE PRECIP TO OCCUR AND WILL MENTION SOME SNOW ACCUMULATIONS.

.EXTENDED (TUE-FRI)...CHANGEABLE CONDITIONS PERSIST BASED ON UKMET
AND GFS-AVN.  MAKE MINOR ADJUSTMENTS WITH VIGOROUS NW FLOW STILL
OVERHEAD AND ADD CHANCE POPS OF RAIN SOUTH AND RAIN/SNOW MIX NORTH
THURSDAY WITH NEXT CLIPPER SYSTEM.  TREND LOW SIDE OF MEX TIL SNOW
MELTS...OR ABOUT THURSDAY.  SLOW WARMUP TO A WELCOME NEAR NORMAL OR
POSSIBLY SLIGHTLY ABOVE NORMAL TEMPS REASONABLE BY LATE WEEK.

.DVN...
IA...NONE.
IL...NONE.
MO...NONE.

$$

NICHOLS