[LeArc] Forecast Discussion : MLI@ 7/20/2003 4:58:53 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 200956
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
415 AM CDT SUN JUL 20 2003

SEVERE CONVECTION IN A COUPLE OF MODES (SUPERCELL AND BOW ECHO) HAS
BEEN RAPIDLY DEVELOPING WITHIN THE LAST FEW HOURS OVER THE
DAKOTAS. CONVECTION BEING FUELED BY VORT MAX AND INCREASING 
UPPER DIFFLUENCE AHEAD OF VIGOROUS SHORTWAVE DIVING E/SE THROUGH 
MANITOBA CANADA...AND IS GENERALLY OCCURRING ON THE 
COOL SIDE OF H85-H7 THERMAL GRADIENT. MAIN CONCERN IN SHORT TERM 
THEN...IS EVOLUTION AND INTENSITY OF ND/SD CONVECTION WITH IMPACTS 
ON POPS AND SEVERE POTENTIAL. CONVECTIVE TRENDS AND SEVERE THREAT REMAIN
PRIMARY CONCERN TONIGHT.

SURFACE FRONT PROGGED TO MOVE ACROSS THE CWA BETWEEN 00Z AND 12Z MON.
UPPER DYNAMICS AND INCREASING MOISTURE MAKE THUNDERSTORMS GOOD
BET NEXT 18-24 HRS...ESPECIALLY THE NORTHERN 1/2 TO 2/3RDS 
IN CLOSE PROXIMITY TO BEST UPPER LEVEL DIVERGENCE. MONITORING CONVECTION
OVER THE DAKOTAS WHICH IS SHIFTING INTO WEST AND SOUTHWEST MN ATTIM 
AND MOVING QUICKLY SOUTHEAST. CLUSTER IN SOUTHWEST MN 
TAKING ON MORE OF BOW ECHO CONFIGURATION. GIVEN LOCATION OF H85-H7 THERMAL
GRADIENT AND CWA ON COOL SIDE OF THIS...BELIEVE THIS COULD
ENTER NORTH/WEST PORTIONS OF CWA BY MID MORNING. THIS COUPLED WITH 
POTENTIAL OUTFLOW SUGGESTS PCPN THREAT ANYTIME FROM MID MORNING
ON ESPECIALLY ACROSS THE NORTHERN HALF OR SO. MID TO LATE AFTERNOON 
COULD SEE SECOND ROUND OF CONVECTION DEVELOPING OVER PORTIONS OF 
NORTHWEST AND CENTRAL IA WITH INTERSECTION OF OUTFLOW AND COLD 
FRONT. CORFIDI FORWARD PROPAGATING VECTORS FAVORABLE FOR THIS TO MOVE
ACROSS CWA THIS EVENING...WITH ADDITIONAL DEVELOPMENT ALONG THE
FRONT ITSELF. SO IN A NUTSHELL...WOULD NOT BE SUPRISED TO SEE SEVERAL
WAVES OF CONVECTION THE NEXT 18-24 HRS WITH THE POTENTIAL FOR HEAVY 
RAIN AND LOCALIZED FLOODING. SEVERAL COMPLICATING
FACTORS THOUGH WITH REGARDS TO SEVERE POTENTIAL. FIRST IS CLOUD 
COVER. 11-3.9 MICRON SATELLITE SHOWS STRATUS EXPANDING ACROSS THE 
CWA NORTH OF I-80...THOUGH RECENT SCANS SHOW SOME E/SE
MOVEMENT. EXPECT THE LOW CLOUDS TO HANG AROUND UNTIL MID MORNING 
AT WHICH TIME LLVL WINDS WILL INCREASE FROM THE SOUTHWEST 
WHICH SHOULD HELP TO BREAK IT UP. HOWEVER...CIRRUS SHIELD FROM ND/SD
CONVECTION RAPIDLY APPROACHING. SO BETWEEN THE STRATUS AND THE
CIRRUS...IT WOULD APPEAR THAT SOLAR INSOLATION WILL BE SOMEWHAT 
LIMITED TODAY...THEREBY REDUCING THE AMOUNT OF INSTABILITY. 
ANOTHER POTENTIAL COMPLICATING FACTOR IS OUTFLOW...WHICH THE ETA AND
GFS CONTINUE TO SHOW MOVING INTO THE NORTHERN ZONES LATER THIS
MORNING. SHOULD THIS OCCUR THEN THIS WOULD STABILIZE THE LOW LEVELS
THUS LIMITING SEVERE POTENTIAL. STILL...LOTS OF FORCING 
WITH JET AND DIFFLUENCE AND WITH WINDS INCREASING IN THE MID LEVELS 
TO BETWEEN 40 AND 50 KTS...FEEL THREAT EXISTS FOR DAMAGING WINDS. 
SFC TO H7 SHEAR ALSO CLIMBS TO AROUND 30 KTS THIS 
AFTERNOON/EVENING...SUPPORTIVE OF BOW ECHOES...THOUGH CONCERNS STILL 
WITH BL INSTABILITY GIVEN CLOUDS. SOUTHERN CWA LIKELY TO SEE THE 
MOST SUNSHINE AND BELIEVE THIS AREA WILL BE PRIMED FOR BEST 
POTENTIAL OF INTENSE BOW ECHO...BUT WILL ALSO BE ON THE EDGE OF 
BETTER DYNAMICS. ATTIM...WON/T DISCRIMINATE ON SEVERE POTENTIAL AND 
HAVE PLACED DAMAGING WIND THREAT IN ALL ZONES. 
DAY CREW CAN RE-EVALUATE AS SYNOPTIC AND MESOSCALE FEATURES PLAY 
OUT. TEMPS WILL BE QUITE CHALLENGING TODAY. TOOK A BLEND THOUGH LEANED
TOWARD THE COOLER MAV GUIDANCE CENTRAL AND NORTH WITH THE
ANTICIPATION OF PLENTY OF CLOUDS AROUND INTO THE AFTERNOON. WHERE
MORE SUNSHINE WILL BE FOUND IN THE SOUTH...LEANED TOWARD THE
WARMER MET GUIDANCE.  

ON MONDAY...THE FRONT WILL BE SOUTH OF CWA WITH NORTHWEST FLOW 
SURFACE AND ALOFT GRADUALLY USHERING IN SOMEWHAT DRIER AND 
COOLER AIR. GIVEN THE AMOUNT OF COLD ADVECTION AND CYCLONIC LLVL 
FLOW SIDED TOWARD PESSIMISTIC CLOUD TRENDS...THUS FAVORED COOL END 
OF GUIDANCE.  

GFS INDICATES WEAK SHORTWAVE MONDAY NIGHT AND WITH CYCLONIC FLOW AND
COLD AIR ALOFT NOT OUT OF THE QUESTION TO SEE SOME LIGHT PCPN.
INHERITED DRY FORECAST...AND HAVE KEPT OUT POPS FOR NOW...BUT DAY 
CREW WILL WANT TO RE-EVALUATE.  ...MM


TUESDAY THROUGH SATURDAY...DID NOT REALLY CHANGE GRIDS AS QUIET WX 
EXPECTED PER MODELS. TUESDAY IS A QUESTION. CYCLONIC FLOW ALOFT/COLD 
POOL MIGHT BE ENOUGH TO GENERATE SHRA/TSRA. EXTRAPOLATION OF 120 HR 
AVN SUGGESTS MORE HUMID WX ARRIVING FOR FRI AND MAYBE SAT TIME 
PERIOD.   ...BP

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

$$