[LeArc] Forecast Discussion : MLI@ 6/25/2003 4:59:43 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 250957
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
445 AM CDT WED JUN 25 2003

CONVECTIVE DEBRIS OFF NORTHWEST/WESTERN IA MCS AND ANY INCOMING
OUTFLOW BOUNDARY TO BE WILD CARD IN TODAY'S FORECAST...OTHERWISE A
DAY SIMILAR TO YESTERDAY WOULD BE ON TAP FOR MOST OF THE CWA.

WELL ADVERTISED FRONTAL BOUNDARY ALIGNED IN A NORTHEAST-TO-
SOUTHWEST FASHION FROM NORTHEAST MN...INTO SOUTHWEST KS...IS
CURRENTLY HUNG UP IN SOUTHWEST LOW TO MID LEVEL FLOW. BUT SFC
PRESSURE RISES BUILDING ACRS THE NORTHERN PLAINS...ALONG WITH UPPER
WAVE OVER THE NORTHERN ROCKIES STARTING TO SHOW SOME PUSH EASTWARD...
SIGNALING SFC BOUNDARY TO EVENTUALLY MAKE HEADWAY AND SWEEP EAST.
GENERAL SHORT RANGE MODEL ENSEMBLE SUGGESTS FROPA ACRS MS RVR
AROUND 10Z OR SO THU MORNING...WITH A NIGHT FULL OF CONVECTION
BEFORE THEN OUT AHEAD OF IT.

SOME SHORT RANGE MODELS KEEP CWA DRY TODAY UNTIL CONVECTION BLEEDS
OUT OF CENTRAL IA INTO THE FAR NORTHWESTERN CWA BY LATE AFTERNOON...
WHILE A FEW OTHERS LIGHT UP THE WESTERN HALF BY MIDDAY/EARLY
AFTERNOON. AM CONCERNED WITH POTENTIAL OF OUTFLOW BOUNDARY
PROPAGATING FROM NORTHWEST IA ACTIVITY AND INTO THE NORTHWEST CWA BY
MID MORNING...SETTING UP POTENTIAL FOCAL POINT FOR 25-30 KT
SOUTHWESTERLY LLVL FLOW TO PLOW INTO AND POSSIBLE PUNCH THOUGH
WEAKENING CAP. THUS HAVE OPTED TO GO WITH CHANCE POPS FOR WEST HALF
OF THE CWA FOR TODAY TAKING INTO ACCOUNT POSSIBLE MID MORNING
CONVECTION IN VCNTY OF OUTFLOW...AND THEN BETTER ORGANIZED POTENTIAL
OF STORMS ERUPTING IN CENTRAL IA AND MAKING HEADWAY INTO THE WEST BY
LATE AFTERNOON/EVENING AS A LINEAR MCS. FCST SOUNDINGS SUGGEST
SIMILAR THERMAL AND INSTABILITY PARAMETERS SETTING UP THIS AFTERNOON
AS YESTERDAY...AS LONG AS DEBRIS FROM THE NORTHWEST AND NOCTURNAL AC
DECK CURRENTLY IN PLACE ERODE AS DAY PROGRESSES FOR MAXIMUM HEATING.
BETTER PROGGED DEEP CONVECTIVE INDICES SET UP RIGHT OVER THE CWA
THIS AFTERNOON...AFTER DWELLING WELL TO THE WEST THE PAST 36-48
HRS...BUT NOT QUITE AS IMPRESSIVE AS IT WAS OVER THE CENTRAL AND
NORTHERN PLAINS AND MN LAST NIGHT AND TUESDAY. 1000-H85 MB THTA-E
ADVECTION AND CONVERGENCE WAS XTREME OVER NE INTO SOUTHEAST SD
OVERNIGHT...BUT WON'T BE NEAR THAT OVER THE LOCAL AREA THIS
AFTERNOON OR TONIGHT. BUT STILL ENOUGH TO FEED EXPECTED CONVECTION.

THUS...WITH EXPECTED HEATING OVER AT LEAST THE EASTERN 2/3'S
SUGGESTS CAPES OVER 4K AND A LOADED ATMOSPHERIC COLUMN READY TO FUEL
CONVECTION WILL AGAIN BE PRODUCED AS FRONT PUSHES TOWARD THE
CWA FROM THE WEST TONIGHT. NORTHWEST CWA MAY BE HELD DOWN TO UPPER
80S TO LOWER 90S FOR HIGHS WITH MORE IMPACT OF DEBRIS AND ANY
POTENTIAL LATE MORNING CONVECTION FIRING/OUTFLOW BOUNDARY. EAST HALF
OF THE CWA TO REMAIN IN THE HOT BOX AND SHOULD BE SIMILAR...OR EVEN A
TOUCH WARMER THAN YESTERDAY LOOKING AT PROJECTED THERMAL PROFILES AND
MIXING...MAINLY LOW TO MID 90S. SFC DPTS IN THE LOWER 70S TO AGAIN
BRING HEAT INDICES INTO THE ZONE MENTIONABLE RANGE OF 100 TO 105.
INTERESTING MOST MODELS SUGGEST BEST FORCING TO SCRAPE THE FAR
NORTHERN CWA FROM 00-06Z THU...AND SOUTHERN INTO CENTRAL MO AS WELL.
HEAVIEST CONVECTION TO THEN PASS JUST TO THE NORTH(STILL IMPACTING
THE DBQ AREA THOUGH)...AND SECOND AREA OFF TO THE SOUTH TONIGHT? NICE
UPPER DIFFLUENCE OFF LEE SIDE OF 85-100 KT H25 MB JET STREAK AHEAD OF
IMPINGING FRONT INTO LOADED AIRMASS STILL SUGGESTS ENTIRE CWA WORTHY
OF AT LEAST LIKELY POPS.
..12..

LONGER RANGE...SUNDAY THROUGH THURSDAY...
THE MEDIUM RANGE MODELS AGREE ON A COLD FRONT DRAGGING THRU THE
FORECAST AREA EITHER SATURDAY AFTERNOON OR SATURDAY NIGHT...AND THEN
MOVING SLOWLY SOUTH OF THE AREA SUNDAY.  NO SIGNIFICANT COLD PUNCH
BEHIND.  500MB SHORT WAVE MOVES NORTH OF THE AREA AT THE SAME TIME.
ONLY MINIMAL GULF CONNECTION BUT DEW POINTS MAY POOL INTO THE MID
60S WITH THE FRONT.  FRONT MAY MOVE SLOWLY ENOUGH THAT POPS MAY BE
NEEDED SUNDAY SOUTH...BUT WILL HOLD OFF FOR NOW.  NEXT CHANCE OF
PRECIP WILL BE AHEAD OF THE NEXT COLD FRONT...WHICH WILL BE
APPROACHING THE AREA IN THE TUESDAY NIGHT/WEDNESDAY TIME FRAME.
..REA..


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

$$

12/REA