[LeArc] Forecast Discussion : MLI@ 7/20/2003 4:09:13 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 202058
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
358 PM CDT SUN JUL 20 2003

SYNOPTIC PICTURE LATE THIS AFTERNOON SHOWS A COMPLEX COLD FRONT
EXTENDING FROM NORTHEAST KANSAS THRU EASTERN NEBRASKA TO A LOW NEAR
FSD...THEN NORTHEAST TO ANOTHER LOW IN SOUTHWEST ONTARIO.  AT 500MB
A SHORT WAVE EXTENDS FROM NORTHWEST MINNESOTA INTO EASTERN KANSAS.

THE PRIMARY FORECAST CONCERN FOR THE NEXT 7 DAYS IS IN THE SHORT-
TERM...WITH THE COLD FRONT PASSING THRU THE FORECAST AREA TONIGHT.
THE NEXT CHANCE FOR PRECIPITATION WILL BE AHEAD OF THE NEXT COLD
FRONT NEXT SATURDAY...AND WITH THE FRONT ON SUNDAY.

THE SHORT-TERM MODELS HAVE BEEN HAVING A HARD TIME RESOLVING THE
FEATURES ASSOCIATED WITH THE INCOMING FRONT.  FRONT WILL PROBABLY
PASS THRU DVN IN THE 03Z-06Z TIME FRAME...WITH A FEW ILL-DEFINED LOWS
ALONG THE FRONT.  AS THE FRONT MOVES EAST OF THE AREA INTO THE LATE
NIGHT HOURS...IT WILL STRENGTHEN...WITH ONE LOW PREDOMINATING...
PERHAPS OVER SOUTHERN OR CENTRAL MICHIGAN.

SCATTERED SHOWERS AND THUNDERSTORMS ACROSS NORTH CENTRAL IOWA...
ASSOCIATED WITH A VORT MAX...ARE MOVING SOUTHEAST ALONG A SURFACE
OUTFLOW BOUNDARY INTO THE DVN FORECAST AREA BY LATE AFTERNOON...WHERE
THEY ARE RUNNING INTO A RIDGE OF HIGH PRESSURE EXTENDING FROM SOUTH
CENTRAL ILLINOIS INTO SOUTHEAST IOWA.  WHETHER THEY CONTINUE INTO
LATE AFTERNOON IS QUESTIONABLE...DESPITE HIGH CAPES.  A SECOND AREA
OF CONVECTION BEGINNING OUT IN THE FSD AREA...ALONG THE FRONT AND
JUST AHEAD OF ANOTHER VORT MAX...MAY TURN OUT TO BE THE PRIMARY
CONVECTION WITH THIS EVENT...ARRIVING IN THE DVN AREA MID EVENING.
CAPES AND LI'S WILL STILL BE HIGH THIS EVENING...WITH A LOT OF LOW-
LEVEL MOISTURE...STRONG 700MB VV'S...AND MODERATE VEERING OF WINDS
WITH HEIGHT. A WET-BULB ZERO AROUND 12K FT WILL ALLOW HAIL UP TO
AROUND AN INCH IN DIAMETER. 500MB WINDS WILL BE 45 TO 50KT...WHICH
WHEN MIXED DOWN TO THE SURFACE...COULD PRODUCE STRAIGHT LINE WINDS OF
60 TO 80 MPH. HELICITIES WILL BE BETWEEN 100 AND 200...BUT A
RELATIVELY LIGHT SURFACE WIND AND HIGH LCL WILL LIMIT TORNADIC
POTENTIAL TO THE BOW OF ANY MCS...OR THE TRIPLE POINT...IF IT IS WELL
DEFINED...WHICH IS QUESTIONABLE. THE OUTCOME...BASED ON CURRENT
TRENDS...IS STILL HIGHLY UNCERTAIN. ONE THING THAT CAN BE SAID WITH
SOME CONFIDENCE IS THAT WHATEVER FORMS WILL GAIN STRENGTH TONIGHT
MOVING EAST OF THE MISSISSIPPI RIVER INTO NORTHEAST ILLINOIS...AND
THEN NORTHERN INDIANA OR SOUTHERN MICHIGAN...WHERE THE UPPER JET
WILL BE MORE FAVORABLE.

LOOKING FURTHER AHEAD...THE MEDIUM-RANGE MODELS AGREE ON ANOTHER
COLD FRONT THE NEXT SUNDAY TIME FRAME.

WILL CONTINUE WITH ONGOING FORECAST WILL LITTLE CHANGE.


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

$$

REA