[LeArc] Forecast Discussion : MLI@ 8/20/02 1:36:18 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 201840
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
139 PM CDT TUE AUG 20 2002

SYNOPSIS...
RETURN FLOW ON BACK SIDE OF THE HIGH PRESSURE AREA WHICH IS CENTERED
JUST EAST OF THE CWA HAS HELPED SPAWN THE MCS OVER CENTRAL IOWA AND
NORTHERN MISSOURI OVERNIGHT.  UPPER LEVEL DIFFLUENCE AND MOISTURE
CONVERGENCE HAS CONTINUED IN THIS AREA...AND LINGERING CONVECTION
CONTINUES TO FIRE AT MID-DAY IN CENTRAL IOWA.  REMNANTS OF THE MCS ARE
NOW DECAYING RAPIDLY IN NORTHEAST MISSOURI.  THE STATIONARY FRONT TO
OUR SOUTH IS NOW RETURNING NORTHWARD THROUGH THE PLAINS...BUT REMAINS
STATIONARY FROM NORTHWEST MISSOURI...THROUGH CENTRAL ILLINOIS. 850 MB
FLOW IS NOW BACKING ACROSS THE PLAINS IN RESPONSE TO A SHORT WAVE
EJECTING OUT OF THE MONSOONAL FLOW.  NEW CONVECTION WILL LIKELY FIRE
ACROSS EASTERN SOUTH DAKOTA AT THE INTERSECTION OF THE 850MB FLOW AND
THE RETREATING WARM FRONT.


SHORT TERM...
MAIN CONCERN TONIGHT IS WHETHER CONVECTION FIRING TO OUR NORTHWEST WILL
SHIFT SOUTHEAST INTO CWA LATE.  NOT SURE WHETHER INTENSE CONVECTION
WILL HAVE THIS ABILITY...SINCE MAIN FORCING REMAINS NORTH OF THE AREA.
HOWEVER...850 MB CONVERGENCE AND WEAK FORCING WILL PROVIDE ENOUGH TO
WARRANT CHANCE POPS ACROSS THE NORTH...WITH A SLIGHT CHANCE IN THE
SOUTH.

OUTFLOW FROM TONIGHTS MCS IN THE UPPER MIDWEST WILL LIKELY BRING THE
STATIONARY FRONT BACK SOUTH INTO THE CWA WEDNESDAY.  A VERY MOIST
ATMOSPHERE WILL BE IN PLACE ALONG THIS BOUNDARY...AND AFTERNOON AND
OVERNIGHT CONVECTION IS LIKELY GIVEN PLACEMENT OF LLJ OVER THE CWA.

THURSDAY...THE STATIONARY FRONT CONTINUES TO LAG ACROSS THE AREA.
WITH SEVERAL SHORT WAVE TROUGHS EXPECTED TO RIPPLE THROUGH THE WESTERLY
500MB FLOW...WILL NOT GET OVERLY CUTE AND WILL MENTION SCATTERED TSRA
THROUGH THE DAY...WITH LIKELY WORDING THURSDAY NIGHT.

LATE THURSDAY NIGHT INTO FRIDAY...THE AVN CONTINUES TO ADVERTISE THE
DOOMSDAY MCS.  WHILE ACTIVE STORMS ARE NOT IN QUESTION...THE DIFFERENCES
IN THE MODELS ARE LARGE.  HEAVY RAIN APPEARS TO BE A THE ONLY THREAT
WITH ANY CONFIDENCE.  FUTURE SHIFTS WILL NEED TO LOOK AT WHETHER THE
SEVERE WEATHER THREAT IS LIKELY.

FRIDAY NIGHT...HIGH PRESSURE NOSES INTO THE MIDWEST...ADVANCING THE
COLD FRONT SOUTH THROUGH THE AREA.  I AM NOT CONVINCED THIS WILL TAKE
PLACE FRIDAY EVENING AS ADVERTISED BY THE 12Z AVN.  THIS APPEARS TO BE
DRIVEN BY CONVECTION RATHER THAN THE ACTUAL MOVEMENT OF THE CANADIAN
HIGH.

EXTENDED...
COLD FRONT FROPA EARLY SATURDAY MORNING APPEARS TO BE STILL ON TRACK...
THOUGH SLIGHTLY SLOWER ON 00Z MODELS THAN PREVIOUS RUNS.  SINCE
THIS IS A COMMON MODEL TREND FOR SUMMERTIME COLD FRONTS...I WILL GO
AHEAD AND BUMP UP HIGHS IN THE SOUTH...AS WELL AS LINGER THE CHANCE OF
MORNING PRECIP IN THE FAR SOUTH.  THE REST OF THE AREA SHOULD BE CLEAR
OF ALL PRECIP BY SUNRISE...WITH THE FRONT ARRIVING BEFORE MUCH DAYTIME
HEATING.  SUNDAY THROUGH TUESDAY CONTINUE TO LOOK DRY AND PLEASANT.
HIGH PRESSURE AT THE SURFACE AND ALOFT WILL KEEP WINDS LIGHT AND THE
HUMIDITY LOW.  WILL CONTINUE WITH PARTLY CLOUDY SKIES MONDAY AND
TUESDAY.



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

ERVIN