[LeArc] Forecast Discussion : MLI@ 10/12/02 2:22:04 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 120729
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
229 AM CDT SAT OCT 12 2002

FORECAST CHALLENGE CENTERS ON TEMPERATURES TODAY WITH STRONG COLD 
FRONTAL PASSAGE...THEN FROST/FREEZE POTENTIAL TONIGHT AND SUNDAY 
NIGHT. FRONT AT 06Z RIGHT ON SCHEDULE FROM MN ARROWHEAD THROUGH NW 
CORNER OF IA TO LOW OVER OK PANHANDLE. AREA 88DS SHOW TWO MAIN BANDS 
OF SHOWERS AND FEW TSRA WITH MOST ORGANIZED CONVECTION ALONG FRONT 
IN MN WHERE MID LEVEL DYNAMICS AND 40 KT H85 JET INTERACT. SECONDARY 
MORE POST FRONTAL BAND FROM SW NEB TO W CENTRAL MN OCCURING AHEAD OF 
VORT MAX ROUNDING BASE OF LONGWAVE TROUGH WITH HELP FROM ENTRANCE 
REGION OF 110KT 250 JET. 

MODELS REMAIN IN GOOD AGREEMENT WITH TIMING OF FRONT AND UPPER 
TROUGH THROUGH FORECAST AREA TODAY. STILL LOOKING AT FRONT KNOCKING 
ON DOOR TO FAR NW EASTERN IA ZONES AT 12Z AND EXITING IL ZONES 
SHORTLY AFTER 18Z. WITH MUCH AGREEMENT...WILL MAINLY FOLLOW META IN 
SHORT TERM DUE TO HIGHER TEMPORAL RESOLUTION. HIGHS WILL BE IN 
MORNING FOR EASTERN IA AND WITH PREFRONTAL MID CLOUDS STREAMING IN 
FROM CENTRAL IA...DO NOT EXPECT MUCH WARMING BEYOND SUNRISE 
READINGS. AREAS OF LOW CLOUDS STARTING TO FORM IN EASTERN IA AND 
SATELLITE SHOWS BANK OF LOW CLOUDS SURGING N ACROSS IL AND EASTERN 
MO WITH LOW LEVEL MOISTURE ADVECTION. CURRENT TRENDS AND LATEST RUC 
INDICATE CONSIDERABLE LOW CLOUDS AND PATCHY FOG WILL BE IN PLACE AT 
SUNRISE OVER CENTRAL ZONES WITH INCOMING MID CLOUDS TO PREVENT MUCH 
BREAKUP WILL THUS BACK OFF MORNING HIGHS CLOSER TO 00Z GUIDANCE WITH 
LOWER TO MID 60S. IL ZONES WILL BE WARMEST WITH LATEST FROPA AND 
BEST CHANCE FOR BREAKS IN CLOUDS AND WILL GO NEAR OR ABOVE WARMEST 
MET GUIDANCE. 

STILL EXPECT SEVERAL HOUR PERIOD OF POST FRONTAL LIGHT RAIN OVER 
ENTIRE AREA AND WILL KEEP LIKELY POPS GOING. BEST CHANCE MEASURABLE 
WILL BE OVER CENTRAL AND NORTH WHERE BEST H5-H7 Q-VECTOR CONVERGENCE 
OCCURS AND SOUTHERN EXTENT OF JET DIVERGENCE OVERLAP. BACK EDGE OF 
POST FRONTAL CLOUDS OVER CENTRAL SD SHOULD ALLOW SOME LATE AFTERNOON 
SUNSHINE INTO WESTERN ZONES...BUT NOT ENOUGH TO RAISE TEMPS ABOVE 
MORNING HIGHS. TIGHT PRESSURE GRADIENT BEHIND FRONT AND DOWNWARD 
VERTICAL MOTION TO WARRANT WINDY WORDING DURING DAY AND BREEZY INTO 
EVENING. OVERNIGHT...WILL GO WITH ETA/GFS SOLUTION AND CLEAR ENTIRE 
AREA OUT. MAIN QUESTION IS AMOUNT OF DECOUPLING AND IMPACT ON 
FALLING TEMPERATURES AS SURFACE PRESSURE GRADIENT RELAXES WITH HIGH 
SETTLING INTO OK PANHANDLE BY MORNING. WITH CONTINUED COLD ADVECTION 
THROUGH NIGHT WITH H85 TEMPERATURES IN RANGE OF -4 TO -8 C BY 12Z...
LOWER 30S LOOK REASONABLE OVER FORECAST AREA NORTH OF HIGHWAY 34 AND 
WILL GO AHEAD AND ISSUE FROST ADVISORY FOR THIS AREA. EXCEPTION WILL 
BE NW ZONES WHERE KILLING FREEZE ALREADY OCCURRED. 

SURFACE HIGH MOVES EAST SUNDAY WITH RETURN FLOW BRINGING H85 WARM 
ADVECTION SUNDAY NIGHT. WITH INITIALLY CLEAR SKIES AND DRY AIRMASS 
DEEP INVERSION SHOULD DEVELOP WITH FREEZING TEMPERATURES AGAIN A 
THREAT AND MAY NEED A FROST/FREEZE HIGHLITE FOR REMAINING SOUTH 
ZONES.

IN EXTENDED...NEXT COLD FRONT PUSHES THROUGH LATE MONDAY NIGHT WITH 
STRENGTHENING UPPER TROUGH MID WEEK. GFS ODD MODEL OUT WITH 
DEEPENING LOW OVER UPPER GREAT LAKES WHILE CANADIAN AND UK KEEP LOW 
WELL TO NORTH. WILL FOLLOW BLEND WITH WEAKER MID LEVEL WAVE TUESDAY 
AND WITH DRY AIR REMOVE PRECIP CHANCES. OTHERWISE DO NOT ANTICIPATE 
MAJOR CHANGES TO EXTENDED. 

.DVN...
IA...FROST ADVISORY TONIGHT SOUTH OF A NORTH ENGLISH...CEDAR RAPIDS 
TO DUBUQUE LINE AND NORTH OF HIGHWAY 34.
IL...FROST ADVISORY TONIGHT NORTH OF HIGHWAY 34.
MO...NONE.

DLS