[LeArc] Forecast Discussion : MLI@ 8/31/02 1:26:54 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 310631
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
125 AM CDT SAT AUG 31 2002
 
00Z UPPER AIR ANALYSIS AND WATER VAPOR IMAGERY SHOWS TROFFING OVER THE
EAST/WEST COASTS. MID LEVEL LOW CENTERED SOUTHWEST OF LAKE WINNEPEG 
WITH NEG TILT TROUGH EXTENDING SOUTHWARD THROUGH THE NORTHERN/CENTRAL PLAINS. 
LATEST SURFACE ANALYSIS CONTINUES TO SHOW GREAT LAKES HIGH
WITH PERSISTENT/DOMINANT RIDGING THROUGH MID MISSISSIPPI VALLEY. 

NO MAJOR CONCERNS IN NEAR TERM. PATTERN UNDERGOING SLOW CHANGE WITH MID LEVEL
CIRCULATION AND ADDITIONAL ENERGY EJECTING FROM WESTERN TROUGH TO
FLATTEN UPPER RIDGE OVER GREAT LAKES THIS WEEKEND WITH POSITIVE HEIGHT 
ANOMALY SHIFTING BACK INTO THE DESERT SOUTHWEST. UPPER FLOW TRANSITIONS TO
FAST ZONAL ACROSS THE NORTHERN STATES AS MAIN WESTERLIES SHIFT SOUTH 
ALONG THE U.S./CANADIAN BORDER. 

EASTERLY BOUNDARY LAYER FLOW TO GIVE WAY TO MORE SOUTHERLY FLOW ESPECIALLY
ON SUNDAY RESULTING IN SOME WARMING AND INCREASE IN HUMIDITY. MODEL SOUNDINGS 
AND TSECTS INDICATE AMPLE LLVL MOISTURE AND GIVEN STEEP LLVL LAPSE RATES 
EXPECT SCT-BKN CU DEVELOPMENT NEXT COUPLE OF DAYS. AVN AND NGM 
SOUNDINGS SUGGEST CONVECTIVE TEMP TO BE NEARED OR REACHED IN FAR SOUTH LATE 
THIS AFTERNOON...AND BOTH DEPICT SOME UPPER LEVEL DIFFLUENCE...ALBEIT WEAK. 
INTERESTING THAT AVN ALSO INDICATES NARROW TONGUE OF HIGHER DEWPTS
(65-70F) THROUGH EASTERN MO AND WESTERN IL WITH AIM INTO FAR SOUTHERN ZONES.
AVN THOUGH NOT VERIFYING WELL ON CURRENT DEWPTS (TOO HIGH BY SOME 3 TO
6 DEGS)...AND GIVEN NO OTHER REAL FOCUS AND DEEP MOISTURE LACKING PCPN CHCS 
TOO LOW (10%) TO CONSIDER MENTION IN ZONES. SIMILAR PROBLEM 
ON SUNDAY WITH AVN SHOWING SPURIOUS WEAK VORT MAXES AND GENERATING LIGHT QPF 
JUST OUTSIDE OF CWA. NGM AND AVN SOUNDINGS REMAIN FAVORABLE FOR ISOLD 
CONVECTION WITH CONVECTIVE TEMPS IN MID 80S. NGM MEANWHILE PAINTING QUITE
A BIT OF LIGHT QPF ACROSS REGION BY 00Z MON...BUT SHOWS MORE
CONCENTRIC AND SLIGHTLY STRONGER VORT MAX APPROACHING WESTERN ZONES LATE.
DUE TO UNCERTAINTIES WITH REGARDS TO PLACEMENT AND STRENGTH OF VORT MAX WILL
CONTINUE WITH DRY FORECAST. PCPN CHCS WOULD APPEAR AGAIN TO BE TOO LOW 
TO MENTION IN ZONES BUT LATER SHIFTS WILL NEED TO MONITOR.

SOME DIFFERENCES WITH RESPECT TO QPF SUNDAY NIGHT...AS ETA AND UKMET GENERATE
QPF INTO NORTHWEST BY 12Z MON WITH LEAD SHORTWAVE. 
AVN FURTHER NORTH WITH THETA-E AXIS AND SLOWER WITH TIMING OF SHORTWAVE 
AND CONSEQUENTLY DELAYS QPF UNTIL MONDAY. MODELS ABOUT 12 HOURS SLOWER WITH
FRONTAL PASSAGE (WHICH HAS BEEN THE TREND THIS SUMMER)...AND NOW DEPICT
FRONT TO MEANDER THROUGH MONDAY NIGHT AND TUESDAY. WITH TIMING DIFFERENCES
ON LEAD SHORTWAVE AND GIVEN SLOWER TREND WITH FRONTAL PASSAGE...
MAY KEEP DRY FORECAST GOING SUNDAY NIGHT. WILL TAKE LOOK AT LATEST MRF BEFORE
DECIDING. 

MON POTENTIAL TO BE WARMEST OF THE NEXT FEW DAYS WITH WARM ADVECTION
AND PRE-FRONTAL COMPRESSION. UKMET MOST AGGRESSIVE DEPICTING H85 TEMPS OF 22-24C
WHILE AVN SHOWS 18-19C. LOW LEVEL THICKNESS WOULD SUPPORT
MID 80S NORTH TO AROUND 90 DEGS SOUTH. CLOUD COVER AND PCPN REMAIN WILD CARDS.
WITH SLOWER FRONTAL TIMING AM THINKING LESS CLOUD COVER AND THEREFORE 
BETTER SHOT AT OBTAINING POTENTIAL. CURRENT ZONES HAVE THIS IDEA WELL IN HAND
SO NO BIG CHANGES. 

SURFACE RIDGE BUILDS IN TUESDAY WITH HIGH SHIFTING ACROSS THE GREAT LAKES.
THIS WILL PRESENT CHALLENGES TO TEMP AND CLOUD FORECAST WITH
LAKE FETCH BY MIDWEEK. OVERALL...NOT PLANNING TO MAKE ANY SIGNIFICANT CHANGES 
ATTIM.


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



M^2