[LeArc] Forecast Discussion : MLI@ 8/26/02 2:29:55 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 261934
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
230 PM CDT MON AUG 26 2002

NOT MUCH CHANGE EXPECTED THROUGH WEDNESDAY WITH BLOCKING PATTERN FIRMLY
IN PLACE OVER CENTRAL U.S. MORNING UA ANALYSIS SHOWED WEAK H5 LOW
CUTOFF OVER KY WITH DEVELOPING TROF FROM NRN ROCKIES INTO CENTRAL CA.
IN BETWEEN RIDGE EXTENDS FROM SOUTHWEST U.S. INTO NORTH CENTRAL U.S.
SURFACE FLOW RELATIVELY WEAK BUT CYCLONIC FLOW NOTED JUST SE OF CWA...
ASSOCIATED WITH UPPER LOW.  INTERESTING VISIBLE SAT IMAGE THIS MORNING
WITH LOW LEVEL CIRCULATION EVIDENT IN CU FIELD OVER WEST CENTRAL IL
AFTER FOG LIFTED.  JUST BEFORE NOON MODERATE SHRA DEVELOPED IN THIS
AREA. SHRA WAS ALSO ENHANCED COOL POOL ASSOCIATED WITH UPPER LOW.

MAIN CONCERN THIS FORECAST WILL BE FOG POTENTIAL AGAIN TONIGHT AND
THEN PRECIPITATION CHANCES BY THURSDAY AS BLOCKING PATTERN BREAKS DOWN.
MODELS WERE IN GENERAL AGREEMENT THROUGH WEDNESDAY BUT DIFFER ON ENERGY
COMING OUT OF SW U.S. TROF LATE IN THE WEEK WITH AVN BEING THE MOST
AGGRESSIVE.  NO MAJOR INITIALIZATION ERRORS NOTED...WITH THE EXCEPTION
OF THE HIGH OVER EASTERN CANADA...WHICH MODELS HAVE INITIALIZED TO
WEAK.

WITH MODELS UNDERESTIMATING PRESSURE GRADIENT ASSOCIATED WITH CANADIAN
HIGH PRESSURE FEEL EASTERLY FLOW TONIGHT WILL BE A LITTLE STRONGER
THAN PROGGED.  STRONGER FLOW SHOULD LIMIT FOG POTENTIAL...ESPECIALLY IN
THE NORTHEAST...BY ADVECTING IN SLIGHTLY LOWER DEWPOINTS AND PROVIDING
SOME MIXING NEAR THE SURFACE.  WILL CONTINUE TO INCLUDE FOG WORDING...
BUT FOG SHOULD BE SHALLOW AND PATCHY.  WILL ALSO STAY ON THE LOW SIDE
OF GUIDANCE FOR TEMPS WITH DEWPOINTS LOWERING MORE THAN PROGGED.  NOT
MUCH CHANGE IN CONDITIONS INTO WEDNESDAY AND WILL RELY ON PERSISTENCE.
THURSDAY MODELS BRING S/W ENERGY OUT OF THE SOUTHWEST BUT IT APPEARS
THAT BEST MOISTURE AND FORCING WILL BE TO OUR WEST.  NORTHWEST CWA
COULD SEE SOME CONVECTIVE DEBRIS FROM PLAINS CONVECTION THURSDAY AND
WILL CONTINUE CHANCE POPS THERE...BUT WILL DROP MENTION FOR REST OF
CWA.

.EXTENDED (FRI THRU MON)...LONG RANGE MODELS IN GENERAL AGREEMENT THAT
WEAK BLOCKING PATTERN IN PLACE OVER SOUTHERN U.S. AT THE BEGINNING
OR THE PERIOD WILL GRADUALLY DETERIORATE.  MODELS...ESPECIALLY THE
AVN/MRF...BRING A DECENT S/W ACROSS REGION SATURDAY AND STALL IT
JUST EAST OF CWA SUNDAY. HOWEVER...SURFACE SYSTEM STAYS WELL TO THE
WEST AS STRONG TROUGH DEVELOPS OVER WESTERN U.S.  APPEARS S/W WILL HAVE
LITTLE LOW LEVEL MOISTURE AVAILABLE WITH SURFACE RIDGE ACROSS GULF
COAST BLOCKING MOISTURE RETURN.  WILL ADD POPS TO SATURDAY AND
CONTINUE MENTION FOR SUNDAY.  MONDAYS FORECAST WILL BE DRY FOR NOW WITH
QUESTIONABLE MOISTURE RETURN AND BEST FORCING STILL OVER THE PLAINS.
TEMPS THROUGH SATURDAY SHOULD BE SIMILAR AS THOSE EARLIER IN THE WEEK
WITH SOME WARMING EXPECTED SUNDAY/MONDAY WITH INCREASING SLY FLOW.


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

DLF