[LeArc] Forecast Discussion : MLI@ 1/31/03 1:35:11 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 311944
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
140 PM CST FRI JAN 31 2003

.OVERVIEW...FIRST...A FEW WORDS ABOUT YESTERDAY/S DEBACLE.  IT IS
THIS FORECASTERS VIEW IT IS NO SOLACE THAT ALL MODELS GENERATED OVER
A THIRD OF AN INCH OF PRECIPITATION...AND MOST NEAR TO JUST ABOVE
.5".  IT IS OUR JOB TO CORRECTLY DIAGNOSE THESE MODEL ERRORS. DESPITE
TRIMMING DOWN BY 25-35% ON MODEL SNOW AND QPF AMOUNTS AND ADJUSTING
FOR SPURIOUS AND BOGUS QPF TYPES...THIS STILL LEFT AMOUNTS THAT WERE
20 TO 80 PERCENT TOO HIGH (AREAS ALONG HIGHWAY 20 GOT 2-3+ INCHES)
DEPENDING ON LOCATION! THE REASON FOR THIS WAS OBVIOUS...CONCEPTUALLY
A DIVING MAIN VORT MAX UPSTREAM GENERATED PRECIPITATION IN MISSOURI
(WHICH IT SHOULD HAVE...DESPITE THE MODELS MISSING THIS) AND CUT OFF
THE MOISTURE FEED. THIS FORECASTER SHOULD HAVE BETTER DIAGNOSED
THIS...BUT IS EASIER SAID THAN DONE...FOR A VARIETY OF REASONS.

NOW FOR THE FORECAST...DESPITE RIDGING UPSTREAM...LOTS OF LOW CLOUDS
NOTED BACK TO MISSOURI RIVER BASIN...AND STRONG PACIFIC JET SUPPORTS
BAROCLINICITY AND FRONTOGENETICAL FORCING.  THUS ANY CLEARING
APPEARS TO SHORT LIVED.  WEAK MIXED PRECIPITATION SHOWERS WITH
SURFACE LOW NOW DEPARTING SOUTHEAST.  LARGE PRESSURE FALLS OVER HIGH
PLAINS IN LINE WITH MORE PACIFIC ENERGY TO LIMIT CLEARING AND THUS
SUPPORTING MORE CLOUDINESS.  NEXT PACIFIC SYSTEM STILL WELL OFFSHORE
BUT LARGE SCALE FEATURES HANDLED OK.

.DIAGNOSIS AND DAYS 1-3...LOW CLOUDS ARE HANDLED REASONABLY WELL MOST
AREAS EXCEPT WHERE ARE SHALLOW.  WILL USE BLEND OF ETA AND GFS-AVN
WITH SOME INPUTS FROM UKMET AND NGM.   THIS SUPPORTS CLOUDY MOST
AREAS TONIGHT WITH SOME PARTIAL CLEARING SOUTHWEST LATE.  THEN...
DESPITE A PERIOD OF SOME SUNSHINE POSSIBLE MANY AREAS.  LOW LEVEL
CONVERGENCE SHOULD KEEP OR BRING BACK IN LOW CLOUDS.  THUS WILL RAISE
MIN TEMPS TONIGHT WITH ETA 2M RIDICULOUSLY TOO COLD...TO A CATEGORY
ABOVE FWC/MAV BLEND.  USING MODEL JET ENERGETICS...SATURDAY TO SEE
LOTS OF LOW CLOUDS WITH SE TO E WIND AND WILL KEEP TEMPS IN MID 30S
TO LOWER 40S WITH FAR SOUTH POSSIBLY HIGHER NEAR SURFACE WARM FRONT.
MAY SEE AREAS OF FOG IF CLEAR OUT BUT RIGHT NOW DON'T SEE IT TONIGHT.
ALSO SOME CONCERN FOR FOG LATER SATURDAY EVENING BUT WILL JUST ADD
PATCHY FOG FOR NOW AND PASS TO LATER SHIFTS.  SUNDAY APPEARS WARM
FRONT TO STRADDLE AREA ALONG I-80 FOR 20-25 DEGREE GRADIENT OR MORE
FOR HIGH TEMPS.  ALSO KEEP AREAS OF FOG NORTH OF HIGHWAY 30 WITH
CHANCE OF RAIN.  NEXT PACIFIC SYSTEM MODELS STILL DIVERGE WITH LARGE
UNCERTAINTY ON PHASING.  BEST ESTIMATE OF MODEL CONSENSUS AND JET
ENERGETICS SUPPORT SURFACE LOW(S) PASSING FAR SE SECTIONS MONDAY.
LIKELY TAKE ANOTHER 24 PLUS HOURS TO SEE IF COMES OUT IN ONE PIECE OR
FRAGMENTED...WITH REGIME THIS WINTER WILL TAKE MORE CONSERVATIVE
LEANING ON QPF.  THUS FOR MONDAY...RAIN TO SNOW SOUTHEAST WITH
MODERATE ACCUMULATIONS.  CENTRAL AREAS WILL GO LIKELY POPS WITH RAIN
CHANGING TO SNOW EARLY AND LIGHT ACCUMULATIONS.  WILL SCALE BACK TO
CHANCE NW BUT PHASING PROBLEMS AND LACK OF RESOLUTION OF NW UPPER
TROUGH SUGGEST THIS A TAD TOO DRY MANY MODELS. THUS...OUR SOLUTION
IS MIDWAY BETWEEN GFS-AVN AND UKMET WITH MINOR INPUTS FROM ETA.
TEMPS TO SLOWLY FALL MOST DAY MONDAY. WILL UPDATE HWO TO REFLECT
LATEST STORM THINKING.

.EXTENDED (TUE-FRI)...ALL MODEL SUPPORT GOING BACK INTO ARCTIC AIR.
KEY QUESTION IS HOW MUCH (IF ANY) SNOW WE GET AND IMPACTS ON TEMPS.
LARGE SCALE FORCING SUPPORTS AT LEAST SOME MOST AREAS SO WILL USE
THIS TO OFFSET NORMAL MEX/FMR COLD BIAS.  CHANCE OF SNOW WITH NEXT
UPPER TROUGH LATE NEXT WEEK.

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

NICHOLS