AREA FORECAST DISCUSSION
NWS QUAD CITIES IA IL
AFDMLI 300 AM CST THU FEB 24 2000
...SHORT TERM...
WATER VAPOR AND PROFILER DATA SHOW A VERY MATURE SHORTWAVE MOVING
THORUGH WESTERN IOWA. A LLJ OF 40-50 KNOTS RUNS FROM ARKANSAS INTO
SOUTHERN LAKE MICHIGAN. ANOTHER SHORTWAVE WAS MOVING THROUGH
COLORADO WHILE THE NEXT BIG SYSTEM IS COMING ON SHORE IN CALIFORNIA.
PLENTY OF JET ENERGY IS ASSOCIATED WITH THE CALIFORNIA SYSTEM WITH
150-160 KNOTS AT 250 MB JUST OFF SHORE WITH AN AIRCRAFT REPORT OF
175 KNOTS. IR SHOWS CLOUD TOPS HAVE COOLED WITH THE AREA OF
SHRA/TSRA IN THE SOUTHERN PART OF THE FORECAST AREA. PER THE RUC
THIS AREA OF PRECIPITATION IS ASSOCIATED WITH A COMBINATION UPPER
TROF/850 MB WIND MAX. RADAR MOSAIC SHOWS A NARROW BAND OF SHRA/TSRA
OVER THE NORTH PART OF THE FORECAST AREA MOVING INTO WISCONSIN AHEAD
OF THE MAIN PRECIP AREA. 06Z SURFACE ANALYSIS HAS THE LOW BETWEEN
KCSQ AND KICL WITH AN OCCUDED FRONT RUNNING TO KIRK. A WARM FRONT
THEN RUNS INTO SOUTHERN ILLINOIS WITH THE COLD FRONT EXTENDING INTO
NORTHWEST ARKANSAS. MOISTURE ANALYSIS HAS 40 DEW POINTS OVER THE
IMMEDIATE AREA WITH 50 DEW POINTS JUST SOUTH OF THE FORECAST AREA.
DEW POINTS IN THE 60S ARE AS NEARBY AS KMEM.
PROBLEMS THIS PACKAGE ARE PRECIP TIMING...THEN CLOUDS/TEMPERATURES.
00Z MODELS APPEAR TO HAVE INITIALIZED OK BUT NONE OF THE MODELS WERE
CATCHING THE 60 DEW POINTS AS FAR NORTH AS KMEM AT 06Z. AVN/ETA HAD
BETTER POSITION OF THE MAIN FEATURES AT 06Z BUT WERE ON THE WEAK
SIDE (3-4 MB) FOR THE CENTRAL PRESSURE OF THE LOW IN IOWA. AVN/ETA
HAVE SLIGHTLY BETTER RUN TO RUN CONTINUITY THAN THE NGM AND THUS
WILL BE FOLLOWED. CURRENT TREND OF THE MODELS LATELY HAVE BEEN TO
UNDERESTIMATE THE STRENGTH OF THE SOUTHERN STREAM SYSTEMS AND ALSO
BE A TAD FAR NORTH AND WEST. AVN/ETA/RUC SHOW CURRENT PRECIP
SUPPORTED BY A SHORTWAVE TO EXIT MOST IF NOT ALL THE AREA BY 18Z.
CONDENSATION PRESSURE DEFICITS INDICATE PRECIP IS IN THE 30-40 MB OR
LESS AREA AND OTHER THAN PERHAPS FAR NORTHWEST ILLINOIS MOST OF THE
FORECAST ARE TO BE DRY AFTER 18Z. DRY CONDITIONS THIS AFTERNOON AND
MOST OF TONIGHT. LLJ SHIFTS INTO IOWA WITH QG FORCING AND
CONDENSATION PRESSURE DEFICITS LOWERING IN THE 850-700 MB LEVEL.
THIS SUGGESTS ELEVATED CONVECTION DEVELOPING TONIGHT. ETA HAS THIS
SWEEPING THROUGH MOST OF THE AREA BY 12Z FRIDAY WITH AVN HAVING IT
JUST REACHING THE AREA BY 12Z. THUS AN PERIOD OF PRECIP VERY LATE
TONIGHT AND INTO FRIDAY MORNING APPEARS LIKELY...MAINLY ALONG AND
WEST OF THE MISSISSIPPI.
MAIN EVENT THEN SETS UP FOR LATE FRIDAY AFTERNOON/NIGHT PERIOD.
STRONG DYNAMICS SETS UP WITH A LLJ OF AT LEAST 50 KNOTS OVER THE
AREA BY 00Z SATURDAY. ALL MODELS AGREE ON THIS WHICH IS SCARY...
SINCE THEY USUALLY DON/T DO THIS. STRONG QG FORCING AND LOWERED
CONDENSATION PRESSURE DEFICITS TO MOVE INTO THE AREA LATE FRIDAY
AFTERNOON AND MOVE THROUGH MOST OF THE FORECAST AREA BY 06Z
SATURDAY. SOUNDING PROFILES SHOW SSE QUICKLY TURNING TO SSW NOT FAR
OFF THE SURFACE AND THEN BEING UNIDIRECTIONAL THE REST OF THE WAY UP
WITH 40 KNOTS JUST OFF THE SURFACE. THUS A SQUALL LINE SHOULD
DEVELOP AHEAD OF THE FRONT AND THE SITUATION WOULD SUGGEST A LOW
TOPPED SQUALL LINE. POTENTIAL DOES INDEED EXIST FOR POTENTIAL
SEVERE...WITH THE MAIN THREAT BEING HAIL/WINDS.
FWC/FAN NUMBERS ARE REASONABLY CLOSE EARLY ON BUT THEN DIGRESS.
GIVEN CURRENT TEMPERATURES MAXES FOR TODAY LOOK LOW. FAN NUMBERS
PREFERRED ON FRIDAY FOR MAXES.
...EXTENDED...
DUE TO RUNNING LATE WON/T CHANGE THE EXTENDED BUT BASED ON NEW AVN
THERE MAY BE A CHANCE OF PRECIP SATURDAY IN THE COMMA HEAD OF THE
FRIDAY STORM SYSTEM.
COORDINATED WITH DSM...LSE...CHI...ILX...STL...AND SPC.
ZONES TO BE LATE BUT SHOULD BE OUT BY 400 AM.
.DVN...NONE.
NC