[LeArc] Forecast Discussion : MLI@ 10/14/02 2:46:31 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 141954
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
250 PM CDT MON OCT 14 2002

SHORT RANGE MODELS SIMILAR ON SWEEPING DRY FROPA UNDER CLEAR SKIES
THROUGH MOST OF THE CWA BY 12Z TUE. GUIDANCE ALMOST IDENTICAL ON
OVERNIGHT LOWS AND SEE NO REASON TO STRAY...ALSO MATCHES UP WELL WITH
ONGOING TEMPS. BEHIND FROPA...EXPECT STEEPENING LLVL LAPSE RATES WITH
COOLING MID LEVELS TO MAKE FOR GOOD MIXING AND THUS BREEZY
CONDITIONS ON TUE. MODELS SEEM TO BE UNDERDOING WIND POTENTIAL
SOME...AND WILL GO NORTH OR NORTHWEST 15 TO 25 MPH. THIS LLVL
INSTABILITY SET UP SHOULD ALSO TRANSLATE CU FIELD CURRENTLY OVER THE
DAKOTAS...TO MAKE IT DOWN ACRS MUCH OF THE CWA FOR PARTLY SUNNY
DAY...ALTHOUGH NORTH COULD FLIRT WITH MOSTLY CLOUDY PERIODS...WHILE
SOUTH MAY REMAIN MOSTLY SUNNY. LOOKING AT EXTENT OF INCOMING CAA AND
MIXING WITH SOME INSOLATION...WILL TAKE BLEND OF WARMER FWC AND
COOLER MAV HIGHS...EXCEPT ACRS NORTHWEST WHERE COOLER MAV VALUES WILL
BE FOLLOWED. COLD AND SUBSIDING RIDGE CENTER TO MAKE IT ACRS CENTRAL
IA TUE NIGHT. ALTHOUGH SKIES WILL BE MOSTLY CLEAR...THIS RIDGE
POSITION WOULD MAINTAIN AT LEAST A LIGHT NORTH BREEZE ACRS THE CWA
THROUGH WED MORNING. STILL...LOOKING AT UPSTREAM SFC CAA POTENTIAL...
ENTIRE CWA SHOULD EXPERIENCE SUB FREEZING TEMPS WITH ONE LAST FREEZE
HEADLINE PROBABLY NEEDED FOR SOUTHEAST THIRD OF CWA. THIS WILL NOT BE
HOISTED THOUGH UNTIL MID SHIFT TONIGHT OR DAY SHIFT TOMORROW.

FOCUS TURNS TO MAIN CHALLENGE OF WEEK WITH TIMING AND STRENGTH OF
CLIPPER-LIKE LOW DROPPING DOWN IN STEEP CYCLONIC FLOW TOWARD WEST IA
WED NIGHT INTO THU. AVN BIT SLOWER AND MORE VIGOROUS WITH VORT
STRENGTH...WHILE ETA QUICKER AND LESS VIGOROUS BUT STILL POTENT. WITH
EXTENT OF COOLING AND SATURATION WHICH WILL AFFECT PRECIP TIMING AND
TYPE STILL AT QUESTION...WILL ONLY INTRODUCE CHANCE ACRS THE WEST FOR
LATE WED NIGHT. 290-300 K ISENTROPIC ANALYSIS INDICATES FLOW
PARALLEL TO SFCS AT BEST WITH LITTLE UPGLIDE...BUT COND P-DEFS
SATURATE TO LEVELS ALLOWING ANY PRECIP TO REACH SFC. MANY SHORT RANGE
MODEL FORECAST SOUNDINGS...THERMAL AND CRITICAL THICKNESS PARAMETERS
POINT TO ALL SNOW OR SNOW/RAIN MIX WITH ONSET. BUT QUESTIONS OF
LINGERING WARMTH IN BOUNDARY LAYER TO MELT SNOW BEFORE SFC IMPACT...
AND EXTENT AND QUICKNESS OF SATURATION BY LATE WED NIGHT BY MODELS IN
A RATHER DRY(INITIALLY) ATMOSPHERIC COLUMN...MAKE FOR SOME
UNCERTAINTY. WITH SOME TIME LEFT TO GO BEFORE EVENT...WILL AGAIN JUST
GO WITH LOWER CHANCE FOR RAIN OR SNOW FOR NOW LATE WED NIGHT ACRS THE
WEST.

.LONGER RANGE(THU-MON)...MEDIUM RANGE MODELS PAINT SAME GENERAL
PICTURE OF POLAR VORTEX SETTING UP SHOP AND GYRATING OVER THE JAMES
BAY/NORTHERN GRT LKS REGION FOR EXTENDED PERIOD...WHILE REX BLOCK
OCCUPIES THE WEST COAST. THERE ARE HOWEVER...DEFINITE DIFFERENCES IN
TIMING AND STRENGTH OF DISTURBANCES AND EXTENT OF COLD AIR POOLS
ROTATING DOWN ACRS THE UPPER MIDWEST IN CYCLONIC FLOW OVER THE
WEEKEND. BIGGEST HEADACHE RIGHT OFF THE BAT FOR THU...WITH LATEST
MRF/EX AVN AGAIN MOST AGGRESSIVE IN EXTENT OF COLD AIR DUMP AND VIGOR
OF VORT DROPPING DOWN ACRS THE UPPER MS RVR VALLEY. LATEST MRF
ALGORITHM SUGGESTS 3 INCHES OF SNOW POSSIBLE BY THU EVENING...WHILE
UKMET AND LATEST EURO LLVL TEMPS AND THICKNESS TRENDS SUGGESTS
POTENTIAL OF RAIN MIXING WITH OR CHANGING OVER TO SNOW THU
AFTERNOON...MAINLY ACRS THE NORTHERN THIRD OR HALF OF CWA WHERE BEST
LLVL CONVERGENCE INTERMINGLES WITH DYNAMICALLY AND ADVECTIVE COOLING
PROCESSES. QUICK LOOK AT EXTENDED ETA SUGGESTS THE SAME...AND WILL
PLAY IT THAT WAY FOR NOW AND AWAIT FURTHER RUNS. REST OF EXTENDED
PERIOD OVER NEXT WEEKEND SHOULD SEE MAINLY DRY AND SEASONABLY COOL
CONDITIONS. THERE ARE SOME SLIGHT TO LOW CHANCE PERIODS OF PRECIP FRI
NIGHT INTO SAT...AND AGAIN SUN NIGHT BUT NOT WORTH MENTIONING AT THIS
POINT.

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

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