[LeArc] Forecast Discussion : MLI@ 1/27/03 2:40:23 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 270852
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
230 AM CST MON JAN 27 2003

DEAMPLIFICATION OF UPPER PATTERN WILL LEAD TO ZONAL/PROGRESSIVE PATTERN
WHICH WILL MEAN RETURN OF MILDER TEMPERATURES.
HOWEVER...THE TRANSITION WILL BRING UNSETTLED WX NEXT FEW DAYS WITH
CHALLENGES ON PCPN CHCS/TYPE. 

06Z SURFACE ANALYSIS SHOWS RIDGE AXIS EXTENDING FROM WESTERN WI THROUGH
WEST CENTRAL IL. IDEAL RADIATIONAL COOLING CONDITIONS WITH
CLEAR SKIES/FRESH LIGHT SNOW COVER/LIGHT WINDS HAS ALLOWED TEMPS TO PLUNGE
INTO THE DEEP FREEZE RANGING FROM -2 TO -8 F. TEMPS THOUGH STARTING
TO RISE IN WESTERN SECTIONS WITH LIGHT S WINDS DEVELOPING AND WARM ADVECTION
MID/HIGH CLOUDS INCREASING. REGIONAL RADAR LOOP SHOWS BAND OF SNOW
ASSOCIATED WITH STRONG WARM ADVECTION AND ISENTROPIC LIFT EXTENDING FROM
EASTERN DAKOTAS INTO WESTERN IA ATTIM. SURFACE OBSERVATIONS INDICATE
SNOW REACHING GROUND WEST OF DSM FROM STORM LAKE...TO CARROLL AND AUDUBORN.
VISIBILITIES QUICKLY DROP TO AROUND 2 MILES AT ONSET.

NO SHORTAGE OF CONCERNS. NEAR TERM...CONCERNS WITH CHC OF SNOW...TEMPS AND 
POTENTIAL FOR -FZDZ THIS AFTN/NGT. THEN...FOCUS SHIFTS TO NEXT SYSTEM
TUE AND CONCERNS WITH PCPN CHCS/TYPE/AMOUNTS AND IMPACT ON TEMPS.
COULD BE LOOKING AT FREEZING RAIN/SLEET WITH SLICK TRAVEL AND POSSIBLE
ADVISORIES TUE WITH OVERRUNING PATTERN.

NEAR TERM...MONITORING PROGRESSION OF SNOW BAND IN WESTERN IA. FORCING
LOOKS TO BE DRIVEN MAINLY BY ISENTROPIC LIFT AND IS DEPICTED
WELL IN 285K SFC OF META. IMPRESSIVE BAND OF ISENTROPIC LIFT TO SHIFT
EAST ACROSS CWA THIS MORNING AND EARLY AFTN. CONDENSATION PRESSURE
DEFICITS LOWER TO 10 MB OR LESS WITH 30-35 KTS OF WIND 
PERPENDICULAR TO TIGHT PRESSURE SURFACES...SHOULD BE SUFFICIENT TO BRING
BURST OF SNOW TO MANY LOCALES ESPECIALLY NORTHERN 2/3RDS OR SO.
CURRENT FORECAST HAS THIS HANDLED WELL WITH LIKELY POPS...AND SEE LITTLE
REASON TO CHANGE. QUICK MOVEMENT TO LIMIT ACCUMS TO LESS THAN 1 INCH.
STRONG LIFT DIMINISHES WEST OF RIVER BY LATE MORNING THROUGH MIDDAY AND
BY MID AFTERNOON IN THE FAR EAST. HOWEVER...WEAK ISENTROPIC LIFT
STILL PRESENT ONCE DEEPER MOISTURE AND LIFT DEPARTS...AND MODEL SOUNDINGS
INDICATE POTENTIAL FOR -FZDZ BUT SEE NO EVIDENCE IN ANY OBS TO OUR WEST.
TEMPS WILL BE TRICKY WITH CLOUDS AND PCPN. WILL SEE SLOW...BUT GRADUAL RISE 
WITH MAXES FOR THE DAY COMING AFTER DARK AS CONTINUED WARM ADVECTION 
NUDGES TEMPS UP GRADUALLY TONIGHT. 

NEXT SYSTEM FOLLOWS QUICKLY IN BEHIND FOR TUE. CYCLOGENESIS TO OCCUR IN THE
CENTRAL PLAINS BY 12Z TUE WITH AID OF RRQ OF 110 KT H3 JET.
OVERRUNNING PCPN EXPECTED TO BREAK OUT AND SURGE EASTWARD WITH MODELS
VARYING ON AMOUNTS AND PLACEMENT OF QPF. ETA OVERALL IS VERIFYING BEST WITH 
LLVL MOISTURE ALONG TX GULF COAST EARLY THIS MORNING. AVN/GFS BRING 
40+ DEG DEWPTS AS FAR NORTH AS NORTHERN MO DURING DAY ON TUE...WHICH LOOKS 
A BIT AGGRESSIVE GIVEN FLOW RELATIVELY WEAK AHEAD OF APPROACHING FRONTAL ZONE. 
IN FACT STRONGEST FLOW FURTHER SOUTH INTO SOUTHERN MO. THEREFORE...LIKE 
LIGHTER ETA QPF AMOUNTS OF ROUGHLY .10 TO .20. FORCING SUPPORTS 
LIKELY POPS ALREADY ADVERTISED. CONCERN THEN IS WITH PCPN TYPE AND POTENTIAL
FOR FREEZING RAIN EPISODE. FORECAST SOUNDINGS SHOW ELEVATED WARM NOSE
AROUND 4KFT BEFORE DEEPER SATURATION OCCURS...SUGGESTIVE OF POTENTIAL
FOR PCPN TO BEGIN AS FREEZING RAIN AND POSSIBLY SLEET. WILD CARDS - IMPACT
OF LIGHT FRESH SNOW COVER ON BLYR AND PCPN ONSET. GFS AND ETA SOUNDINGS 
INDICATE NEARLY ISOTHERMAL LOWER LAYER FOR MLI AND BRL...SO COULD BE BOUNCING 
AROUND ON PCPN TYPES. IN THE NORTH LOOKS COLD ENOUGH FOR MAINLY SNOW WITH
POSSIBLY SOME -FZRA. EXPECT THE WARM LAYER TO BE OVERCOME EVENTUALLY FROM 
DYNAMIC COOLING AND COLD ADVECTION IN AFTN/EVE TO CHANGE PCPN OVER TO ALL SNOW 
BEFORE ENDING. POTENTIAL EXISTS FOR SOME LIGHT ICE AND SNOW ACCUMS MAKING 
FOR HAZARDOUS TRAVEL AND WILL HIGHLIGHT IN MORNING HWO. HPC HAS AREA OUTLOOKED
IN LOW THREAT FOR .25 INCH. IF MODEL TRENDS CONTINUE THEN MAY HAVE TO 
CONSIDER WINTER WX ADVISORY AT SOME POINT NEXT COUPLE SHIFTS. 

NO MAJOR CHANGES TO EXTENDED DUE TO TIME CONSTRAINTS.

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

05