Severe Thunderstorm Warning 113, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
248 PM CDT WED AUG 18 1999

...GLOBALLY...
LONGWAVE PATTERN IS UNDERGOING A TRANSITION AND SOME AMPLIFICATION
ACROSS THE HEMISPHERE. GLOBAL MOSAIC OF WATER VAPOR FROM GMS-5...
GOES E/W...AND METEOSAT INDICATE ONE OF THE KEY FEATURES FOR THIS
CHANGE IS THE 100+ KNOT (BASED ON DARKNESS) JET RUNNING FROM THE
BERING SEA BACK ACROSS THE KAMCHATKA PENINSULA/SEA OF OKHOTSK AND
INTO SIBERIA. WATER VAPOR SHOWS HEIGHTS ARE BUILDING ACROSS WESTERN
NORTH AMERICA WHICH WILL ALLOW THE CURRENT SOUTHERN RIDGE TO
RETROGRESS TO THE ROCKIES. THE BUILDING HEIGHTS AND THE APPROACHING
SIBERIAN VORTEX WILL KICK THE GULF OF ALASKA LOW EASTWARD INTO THE
STRENGTHENING NORTHERN STREAM. THE EASTERN PACIFIC LONGWAVE TROF
SHOULD RETROGRESS ABOUT 20 DEGREES IN RESPONSE TO THE CURRENT UPPER
LOW OVER SIBERIA MOVING TO THE ALUETIAN PENINSULA.

GLOBAL MODELS ARE GIVING MIXED SIGNALS ON THE OVERALL OUTCOME OF THE
LONGWAVE PATTERN BUT THE JET SHOULD BE PUSHED NORTH INTO SOUTHERN
CANADA. WAVELENGTH WOULD THEN PLACE A NEW LONGWAVE TROF AROUND 55 TO
65W DURING THE COMING WEEK.

NET RESULT HERE IS AS FOLLOWS. AFTER A COOL LATTER HALF OF THIS WEEK
TEMPERATURES SHOULD REBOUND TO AROUND NORMAL THROUGH THE END OF
THE MONTH. WITH THE POLAR JET IN SOUTHERN CANADA PRECIPITATION
SHOULD BE BELOW NORMAL AS WELL.

...LOCALLY...
WATER VAPOR AND PROFILER DATA SHOWS A NICE MVC (NEDDY EDDIE) MOVING
EAST INTO NORTHEAST ILLINOIS AS A STRONGER SHORTWAVE ROTATES
SOUTHEAST THROUGH MINNESOTA. 18Z SURFACE ANALYSIS HAS A LOW NEAR
KMSP WITH THE COLD FRONT RUNNING FROM KAXA TO KTOP AND INTO THE
TEXAS PANHANDLE. A MESO LOW WAS STILL EVIDENT BETWEEN KIRK AND KOTM
WITH A OUTFLOW BOUNDARY FROM LAST NIGHTS MCS RUNNING FROM THE
MESOLOW INTO CENTRAL ILLINOIS. MOISTURE ANALYSIS HAS MID 60 DEW
POINTS ACROSS THE ENTIRE AREA WITH A POCKET OF 70 DEW POINTS AHEAD
OF THE COLD FRONT IN NORTHWEST MISSOURI AND SOUTHERN IOWA WHILE
VISIBLE IMAGERY SHOWS PLENTY OF LOW TO MID LEVEL CLOUDS ACROSS THE
AREA. DVN 88D INDICATES PRECIPITATION NOW MAINLY EAST OF THE
MISSISSIPPI WHILE REGIONAL LOOP SHOWS MORE TSRA HAS ORGANIZED INTO A
LINE ACROSS WESTERN WISCONSIN INTO SOUTHEAST MINNESOTA.

PROBLEMS THIS PACKAGE ARE MANY...PRECIP CHANCES EARLY ON AND THEN
OVERALL CLOUDS/TEMPERATURES.

12Z MODELS APPEAR TO HAVE INITIALIZED OK BUT ALL WERE HAVING SOME
PROBLEMS VERIFYING AT 18Z. MODELS ARE IN GENERAL AGREEMENT IN
PUSHING THE COLD FRONT THROUGH THE AREA TONIGHT AS CYCLONIC FLOW
SHARPENS ALOFT. PLENTY OF QG FORCING TO MOVE ACROSS THE AREA WHICH
COMBINED WITH LOWERING CONDENSATION PRESSURE DEFICITS SHOULD BE
ENOUGH TO BRING ANOTHER ROUND OF SHRA AND SOME TSRA TO THE AREA.
CURRENT ACTIVITY ACROSS MINNESOTA IN THE AREA OF STRONGER QG FORCING
ARGUES FOR HIGHER POPS DOWN HERE. TIMING INDICATES THAT MOST OF THE
PRECIP SHOULD BE OVER BEFORE MIDNIGHT WITH AREAS EAST OF THE
MISSISSIPPI AND DOWN SOUTH POSSIBLY LINGERING PAST MIDNIGHT.

AFTER THAT DEEP CLYCONIC FLOW ACROSS THE AREA ON THURSDAY WITH
PLENTY OF CLOUDS LIKELY. MODELS TRYING TO BREAK UP CLOUDS QUICKER OR
NOT INDICATING AS MUCH CLOUD COVER. HOWEVER CURRENT SATELLITE IMAGES
ARGUE AGAINST THE MODELS INDICATING FEWER CLOUDS. CLEARING SHOULD
OCCUR REASONABLY QUICKLY THURSDAY NIGHT WITH A GRADUAL WARMING TREND
AFTER THAT.

GIVEN CLOUD COVER TRENDS HAVE THROWN OUT FWC NUMBERS AND WILL START
WITH FAN NUMBERS AND MAKE ADJUSTMENTS. PERSISTANCE SUGGESTS
TEMPERATURES THURSDAY SIMILAR TODAY.

...EXTENDED...
CHANGES TO THE LONGWAVE PATTERN POINT TO A MODERATION OF
TEMPERATURES AND DRY CONDITIONS.

COORDINATED WITH DSM...LSE...CHI...SPI...AND STL.

.DVN...

NC