[LeArc] Forecast Discussion : MLI@ 9/23/02 3:01:38 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 232009
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
305 PM CDT MON SEP 23 2002

BROAD CYCLONIC FLOW TO REIGN OVER THE NORTHERN CONUS THROUGH WED...
AND AFTER VIGOROUS VORT NOW PUNCHING ACRS NORTHERN WI EXITS EAST ACRS
THE LAKES...NEXT VORT OF SIGNIFICANCE NOT SLATED TO DROP ACRS THE
AREA UNTIL LATE WED NIGHT/TOWARD 12Z THU. THIS FEATURE TO DIG AND
AMPLIFY SOUTHERN EXTENT OF POLAR VORTEX/TROUGH OVER THE NORTHERN
PLAINS IN THE PROCESS.

BEFORE THEN...MAIN NEAR TERM CONCERN IS NEED FOR FROST ADVISORY
HEADLINES TONIGHT OVER PORTIONS OF THE CWA. NORTHERN HALF CWA
INITIALLY LOOKS TO BE AT RISK...BUT OTHER FACTORS GOING AGAINST
WIDESPREAD EVENT. IN-BUILDING SFC RIDGE GRADIENT AND PRESSURE RISE
SURGE BEHIND COLD FRONT TO KEEP NORTHWEST WINDS GOING FOR AWHILE PAST
SUNSET...AT LEAST AROUND THE 10 KT RANGE THROUGH 11 PM. TIMING OF
RIDGE CENTER ACRS EAST IA AND THE LOCAL CWA SUPPORT THAT REAL WIND
DROP OFF TO LIGHT AND VARIABLE/CALM STATUS NOT TO OCCUR TIL CLOSE TO
11Z OR SO. BESIDES ADVECTIVE COOLING QUALITIES...THIS DOESN'T SUPPORT
GOOD RADIATIONAL SET-UP. WATCHING MN CU DECK ROTATING TOWARD
NORTHEAST IA...MAY LEAD TO SOME RADIATIONAL INHIBITING DEBRIS ACRS
THE NORTH AS WELL...ALTHOUGH THIS DECK WILL/IS HITTING A WALL OF DRY
SUBSIDING AIR STREAKING INTO SOUTHWEST FLANK OF NORTHERN WI CLIPPER.
AGREE WITH DMX THAT TEMPS ACRS EAST IA(UPPER 60S/LOWER 70S) WOULD
HAVE TO MAKE BIG DIURNAL DROP TO REACH LOW TO MID 30S FOR WIDESPREAD
FROST...EVEN TAKING ACCOUNT UPSTREAM SFC CAA OVERNIGHT. THUS...WILL
NOT GO WITH ADVISORY AND JUST KEEP FROST WORDING IN ZONES. MAY BE
CLOSE THOUGH IN SOME AREAS ACRS THE NORTHWEST...ESPECIALLY IN LOWER-
LYING COLD AIR DRAINAGE PRONE SITES. BULK OF CWA NOT TO DROP BELOW
THE UPPER 30S...AGAIN EXCEPT ACRS THE NORTHWEST WHERE MID 30S WILL
PREVAIL.

EVEN AFTER COOL START TO DAY...EXPECT ENOUGH THERMAL RECOVERY WITH
INSOLATION...AS SFC RIDGE SLIDES TO THE EAST...TO ALLOW SOUTHEAST SFC
FLOW TO DEVELOP AND BUMP TEMPS UP INTO MID 60S BY 3 PM TUE AFTERNOON.
EAST MAY BE COOLER THOUGH WITH THIS RETURN FLOW- "SLOSH BACK" EFFECT
FROM COOL RIDGE CENTER.

SHORT RANGE MODELS BREAK OUT LIGHT OVER-RIDING PRECIP JUT TO
THE NORTHWEST TUE NIGHT...BUT LOOKS OVERDONE/MODELS TOO QUICK TO
SATURATE/TAKING INTO ACCOUNT CONTINUING DEEP DRY AIRMASS. MAY JUST
HAVE SOME HIGHER CLOUDS BLEED INTO THE NORTHWEST. WITH MAIN FROPA
AHEAD OF NEXT COOL SURGE LATE WED NIGHT/THU MORNING...MODELS MAY BE
BIT QUICK AND FEEL EVENT TO TAKE PLACE MID THU MORNING. HIGH COND P-
DEFS TO OVERCOME AGAIN WED NIGHT FOR PRECIP CHANCE...BUT NORTHWEST
CORNER MAY SATURATE ENOUGH TOWARD MORNING FOR LIGHT RAIN TO REACH THE
SFC.

.LONGER RANGE(THU-MON)...WILL SIDE WITH LATEST UKMET AND MRF BLEND
WHICH SIMILARLY REINFORCE L/W TROUGH OVER MIDWEST NEXT WEEKEND...AS
POLAR VORTEX SWIRLS OVER THE HUDSON BAY REGION. AGAIN...MAIN FRONT
ASSOCIATED WITH THIS REINFORCEMENT STILL LOOKS SWEEP THROUGH THE AREA
ON THU MORNING WITH ACCOMPANYING RAIN THREAT....PRE AND POST. ANY
DELAY IN FROPA DUE TO ISIDORE INFLUENCE COULD ALLOW PRE-FRONTAL
WARMING TO PUSH THU HIGHS INTO THE UPPER 60S...BUT WILL BANK ON MID
MORNING TIMING AND CLOUDS/PRECIP KEEPING TEMPS IN LOW TO MID 60S.
THIS L/W TROUGH AND SFC FRONT SCENARIO WOULD EVENTUALLY SHUNT ISIDORE
ACRS LOUISIANA AND UP TN VALLEY THROUGH SAT MORNING...WITH PRECIP
SHIELD REMAINING TO THE SOUTHEAST OF LOCAL AREA OF CONCERN. TROPICAL
STORM /HURRICANE LANDFALL AND INLAND PATH STILL "IFFY" AT THIS
POINT...BUT AGAIN AT THIS POINT GOING WITH UKMET/MRF SOLUTION.
OTHERWISE...ANOTHER LARGE SFC ANTICYCLONE TO DUMP DOWN ACRS UPPER MS
VALLEY REGION FOR DRY AND SEASONABLY COOL START TO THE WEEKEND...WITH
FRI/SAT HIGHS GENERALLY IN MID TO UPPER 50S AND LOWS IN THE 30S.
UPPER RIDGE STARTS TO EDGE ACRS THE REGION FROM THE WEST...BRINGING
THERMAL MODERATION SUNDAY AND ESPECIALLY MON. RIDGE SHOULD DE-AMPLIFY
NEXT WEEK AS IT GETS PUMMELED BY PACIFIC AND GULF OF AK ENERGY.

COORDINATED WITH ARX...DMX...THANX!



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

JDH