[LeArc] Forecast Discussion : MLI@ 8/5/2003 3:30:08 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 050826
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
326 AM CDT TUE AUG 5 2003

SHORT TERM...TODAY THROUGH WED NIGHT...
FORECAST CHALLENGE IS PRECIP CHANCES AS PERSISTENT PATTERN AT UPPER 
LEVELS WITH GREAT LAKES TROUGH AND WESTERN CONUS RIDGE RESULTING IN 
NORTH TO NORTHWEST FLOW WITH AREA RETURNING UNDER MAIN STREAM OF 
UPPER LEVEL PERTURBATIONS WEDNESDAY. STRONG SHORTWAVE TOPPING RIDGE 
OVER NORTH DAKOTA ON 00Z ANALYSIS HAS CONTRIBUTED TO LINEAR MCS
MOVING ACROSS NORTHEAST NEB INTO WESTERN IA AT 07Z. THIS WAS 
OCCURRING AHEAD OF SURFACE LOW OVER CENTRAL SOUTH DAKOTA WITH TROUGH 
EXTENDING SOUTH TO ANOTHER LOW OVER OK. ALONG AND AHEAD OF THIS 
TROUGH...SURFACE TO H85 THETAE RIDGE WAS IN PLACE. ELEVATED 
CONVECTION OCCURRING ALONG EDGE OF H85 THETAE RIDGE/WARM FRONT AHEAD 
OF MAIN COMPLEX. ETA AND META SEEMED TO HAVE BEST HANDLE ON THIS 
SYSTEM...WITH 06Z META CAPTURING MCV MOVING INTO SW MN. GENERALLY 
FOLLOWED ETA SUITE TREND WITH COMPLEX FALLING APART AS IT MOVES AWAY 
FROM DEEPER MOISTURE AND INTO WEAK SURFACE RIDGING OVER IA AND MN 
THIS MORNING. CURRENT MOTION WOULD TAKE ANY DISSIPATING CONVECTION 
AT MOST ORGANIZED SOUTHERN END WELL TO SOUTH OF AREA BY LATE MORNING.

FOR NOW WILL COUNT ON SHOWERS TO DISSIPATE IN CENTRAL IA THIS 
MORNING AND KEEP ONLY SLIGHT CHANCE AFTERNOON POPS GOING FOR WESTERN 
ZONES AS MODEL TIME HEIGHT SECTIONS AND SOUNDINGS SHOW GRADUAL TOP 
DOWN INCREASING RH THROUGH AS SHORTWAVE APPROACHES. WEAK CAPPING 
AROUND H7 SHOWN BY ETA TO WEAKEN BY LATE AFTERNOON...BUT LAPSE RATES 
AND LOW LEVEL INSTABILITY INDICES UNIMPRESSIVE FOR MUCH CONVECTIVE 
POTENTIAL. MOST SIGNIFICANT IMPACT WILL BE ASSOCIATED CLOUDS. USING 
NOWCAST TOOLS...BACK EDGE OF CURRENT ENHANCED CLOUD COVER WILL EXIT 
SOUTHEAST PART OF CWA LATE AFTERNOON...BUT BY THAT TIME ONLY THIN CI 
ANTICIPATED. EFFECT OF THIS WILL BE TO LIMIT HIGHS TEMPERATURES 
CLOSE TO VALUES FROM YESTERDAY ESPECIALL CENTRAL AND NORTH...WHICH 
IS CLOSE TO COOLER MAV GUIDANCE. IN IMMEDIATE SHORT TERM...HAVE 
ADDED PATCHY FOG TO NORTHEAST ZONES THROUGH JUST AFTER SUNRISE...BUT 
OVERALL SITUATION NOT AS SUPPORTIVE AS MONDAY MORNING FOR WIDESPREAD 
FOG AND INCOMING HIGH CLOUDS WILL LIMIT FURTHER RADIATIONAL COOLING 
JUST BEFORE SUNRISE. 

TONIGHT...HIGH PLAINS SURFACE LOW WEAKENS TO JUST INVERTED TROUGH AS 
IT PUSHES INTO CENTRAL IA. CURRENT SHORTWAVE TOPPING WESTERN RIDGE 
SLIDES VORT MAX ACROSS CENTRAL IA. KEPT SCATTERED POPS IN WESTERN 
ZONES WHERE FORCING STRONGEST...AND SLIGHT CHANCE FURTHER EAST WHERE 
BETTER MID LEVEL INSTABILITY WILL LAY OUT DUE TO PROXIMITY TO UPPER 
TROUGH. ON WEDNESDAY...SOUNDINGS SHOW DEEP MOISTURE OVER AREA 
ALTHOUGH FORCING NOT VERY IMPRESSIVE AND CLOUD COVER MAY LIMIT 
INSTABILITY. HAVE THUS NOT BOUGHT INTO LIKELY POPS ADVERTISED BY ETA 
AND KEPT LOW CHANCES GOING. MODELS DEPICT ANOTHER SIGNIFICANT VORT 
MAX IN NORTHERLY FLOW WED NIGHT...BUT SIGNIFICANT DIFFERENCES IN 
TIMING AND LOCATION APPEAR. BLENDED CLOSEST TO GFS...PLACING BEST 
CHANCES IN EVENING AND ACROSS EAST FOR NOW.  ...SHEETS    

THURSDAY AND FRIDAY...
UPPER LEVEL PATTERN REMAINS NEARLY THE SAME...WITH STRONG RIDGE TO 
WEST AND STRONG TROUGH TO EAST...AND STRONG NORTHWEST FLOW ALOFT 
OVER THE CWA.  THOUGH SURFACE RIDGING REMAINS IN PLACE...IT IS 
WEAK...AND THE STRONGER SHORT WAVES HAVE BEEN KICKING OFF BANDS OF 
SHOWERS AND THUNDERSTORMS...AS HAS BEEN PROGGED FOR THE EARLIER 
PARTS OF THE FORECAST.  AVN AND ETA NOW RUNNING A SHORTWAVE 
SOUTHEAST ACROSS ILLINOIS ON THURSDAY...CREATING ONE OF THESE BANDS 
OF TSRA.  FOR NOW HAVE DECIDED NOT TO BUY INTO THIS AS IT IS A 
FAIRLY NEW FEATURE...AND MODELS COULD SEE-SAW ON IT AGAIN ON THE 
NEXT RUN.  FRIDAY STILL LOOKS DRY...

SATURDAY THROUGH MONDAY...UPPER LEVEL RIDGE FINALLY BUILDS INTO 
AREA...WITH SURFACE RIDGING IN PLACE FOR SATURDAY AND SUNDAY.  SOME 
QUESTION ABOUT LATE SUNDAY AND MONDAY...AS THE NEW MRF DEPICTING A 
SURFACE TROUGH TO DROP THROUGH THE AREA MONDAY MORNING.  HAVE 
DECIDED TO HOLD OFF ON THIS...AS IT LOOKS A LITTLE FISHY CONSIDERING 
THE FLOW...AND PREVIOUS MRF...UKMET AND ECMWF KEEP THE SURFACE LOW 
FEATURES TO THE WEST.  ...LE

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

$$