Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 260504
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1204 AM CDT TUE AUG 26 2014

.UPDATE...
ISSUED AT 955 PM CDT MON AUG 25 2014

MCS POTENTIAL IS STILL BEING MONITORED. HOWEVER...FOR NOW...THE
INITIALIZATION LOOKS TO BE OCCURRING VERY FAR WEST...AND IS SLOW
TO MOVE. I HAVE BUMPED POPS LOWER THE REST OF TONIGHT...BUT LEFT
THINGS IN THE CHANCE RANGE MORE OR LESS. THIS IS CERTAINLY
TRENDING TOWARD A CAN/T RULE IT OUT FORECAST VS A IT/S GOING TO
HAPPEN BUT WE DON/T KNOW WHERE SITUATION. THIS IS CERTAINLY A
TOUGH CALL.
ERVIN

&&

.SYNOPSIS...
ISSUED AT 336 PM CDT MON AUG 25 2014

STORMS WITH HISTORY OF DAMAGING WINDS CONTINUE ALONG STRONG THERMAL
AND INSTABILITY GRADIENT OVER NORTHWEST IL WITH WELL DEFINED
OUTFLOW BOUNDARY ARCING FROM NEAR TIPTON THROUGH THE QUAD CITIES
TO SOUTH OF PRINCETON IL. THIS ACTIVITY IS BEING AIDED BY AN
UPPER LEVEL SHORTWAVE OVER EASTERN IA APPROACHING MISSISSIPPI RVR.
RAIN COOLED AIRMASS AND CLOUDS HAVE LIMITED TEMPS INTO THE 70S
OVER PORTIONS OF NORTHEAST IA AND NORTHWEST IL. MEANWHILE...THE
SOUTHERN CWA IS SEEING DANGEROUS HEAT WITH TEMPS IN THE RANGE OF
90-95F AND HEAT INDEX VALUES AROUND 100-105. MSAS SURFACE PLOT AND
OBS DEPICT COLD FRONT AT 20Z EXTENDING FROM EASTERN MN THROUGH
CENTRAL IA THROUGH NORTHERN KS.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 336 PM CDT MON AUG 25 2014

LATE THIS AFTN SHOULD SEE STORMS CONTINUE TO MOVE OUT OF THE EASTERN
CWA WITH PASSAGE OF SHORTWAVE. MUCH OF THIS EVENING THEN APPEARS
WILL BE QUIET WITH SUBSIDENCE IN WAKE OF DEPARTING WAVE GOVERNING THE
CWA. LATER THIS EVE WILL BE WATCHING TO OUR WEST FOR LIKELIHOOD OF
SHOWERS AND STORMS DEVELOPING PORTIONS OF NE INTO WESTERN IA WITH
LOW LEVEL JET AND THETA-E ADVECTION. POTENTIAL FOR THIS ACTIVITY TO
DEVELOP INTO ORGANIZED COMPLEX AND MOVE EASTWARD NORTH OF FRONT AS
IT SAGS TO OUR SOUTH BY 12Z TUE... WITH GREATEST POTENTIAL MAINLY
NORTH OF HWY 34 AND ESPECIALLY NEAR/NORTH OF I-80. POPS AND QPF MAY
NEED TO BE ADJUSTED UPWARD LATE TONIGHT INTO TUE AM. LOWS SHOULD
RANGE FROM AROUND 60/LOWER 60S NORTHWEST SECTIONS TO LOWER TO POSSIBLY
MID 70S SOUTHEAST.

TUESDAY...HAVE LOWERED HIGHS ALL AREAS WITH FRONT TO THE SOUTH AND
NORTHERLY WINDS AND CLOUDS. COOLEST READINGS SHOULD BE NORTH HALF
WHERE LIKELY TO STAY IN THE 70S TO NEAR 80... WITH THE ANTICIPATION
OF CONVECTION AND DEBRIS CLOUDS LINGERING. WARMEST READINGS SOUTH
MID 80S WITH POSSIBLY UPPER 80S TO AROUND 90 DEPENDING ON AMOUNT OF
SUNSHINE. POPS HIGHEST NORTH HALF... BUT KEPT GENERAL CHANCE FOR NOW
AS AWAIT EVOLUTION OF CONVECTION TONIGHT.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 336 PM CDT MON AUG 25 2014

TUESDAY NIGHT THROUGH THURSDAY...LATEST 12Z RUN MEDIUM RANGE
SOLUTIONS CONTINUE TO GENERALLY SUGGEST ACTIVE AND POTENTIALLY WET
PATTERN TO CONTINUE THROUGH THE END OF THE WEEK. FLATTENED MEAN
STEERING FLOW WITH PARALLEL STALLED SFC/LLVL BOUNDARY UNDULATING
UNDER IT SOMEWHERE ALONG OR JUST SOUTH OF THE DVN CWA FROM THE
CENTRAL PLAINS TO NORTH OF THE OH RVR VALLEY. ISOLATED TO SCTRD
CONVECTION DURING THE DAY ESPECIALLY IN VCNTY OF THE MAIN FRONT OR
REMNANT OUTFLOW BOUNDARIES...THEN LLJ ADVECTING THTA-E RICH AIR FROM
THE SOUTH UP OVER THE BOUNDARIES FOR LARGER CLUSTERS OR MCS/S AT
NIGHT INTO THE EARLY MORNING PERIODS. MCS FORCING PARAMETERS SUGGEST
MAIN CONVECTIVE SPAWNING GROUNDS ACRS THE CENTRAL PLAINS INTO
WESTERN IA/SW MN BOTH TUE NIGHT AND WED NIGHT...WITH PORTIONS OF
THESE COMPLEXES EVENTUALLY FEEDING EASTWARD WITH SOME
COMPONENT...ENOUGH TO MAKE IT ACRS THE CWA. HOW FAR NORTH OR SOUTH
THEY DO STILL HAS SOME QUESTIONS...BUT THE SOUTHERN TWO THIRDS
CLOSER TO LLVL BAROCLINIC GRADIENT MAY BE MORE FAVORED. AGREE WITH
PREVIOUS FCST SHIFTS THAT ACCUMULATIVE HEAVY RAIN EVENTS WILL LEAD
TO BOTH SOME FLASH FLOODING...AS WELL AS SIGNIFICANT RISES ON
SEVERAL AREA RIVERS AND STREAMS. VERY CHALLENGING TEMP FCST CONTINUES
ESPECIALLY FOR HIGH TEMPS...WITH LARGE THERMAL GRADIENTS POSSIBLE
FROM NORTH TO SOUTH OR NE-TO-SW DEPENDING ON BOUNDARY PLACEMENT AND
LINGERING CONVECTIVE DEBRIS. ISOLATED SVR STORMS POSSIBLE CLOSE TO
THE BOUNDARY OR IF SOME SECONDARY INITIATION TAKES PLACE OVERHEAD
TUE AND WED NIGHT EAST OF MAIN FIRING ZONES OF KS/NEB/SD INTO
WESTERN IA AND SW MN.

FRIDAY THROUGH NEXT MONDAY...SEVERAL OF THE MEDIUM RANGE MODELS
CONTINUE TO DIVERGE ON HANDLING OF INCOMING SHORT WAVE TROF
EMBEDDED IN THE WESTERLIES RIPPLING EASTWARD ALONG THE FRONT...
MODELS WILL CONTINUE TO HAVE TROUBLE WITH LATENT HEAT RELEASE AND
CONVECTIVE FEEDBACK ISSUES IMPACTING THIS FEATURE. BUT WHEN IT
COMES THROUGH THERE MAY BE A MORE SIGNIFICANT AND WIDESPREAD
SHOWER/STORM EPISODE...THE 12Z GFS TARGETS LATE FRI THROUGH SAT...
WHILE THE 12Z ECMWF IS MORE IN THE WAY OF SAT INTO SUNDAY. GAIN SOME
TIME NEEDED FOR MODELS TO RESOLVE THIS PROCESS...BUT MORE RAIN TO
ADD TO POSSIBLE WATER ISSUES IF THIS ALL UNFOLDS THIS WEEK ACRS THE
FCST AREA/REPEATED ROUNDS OF SHOWERS-STORMS/. AFTER THIS TROF
PASSES...THERE FINALLY MAY BE REPRIEVE FROM THE RAIN FOR A DAY OR
TWO BEFORE LONGER RANGE INDICATIONS/UPPER JET TRENDS SUGGEST THE FLOW
TO FLATTEN BACK TO WEST-SOUTHWEST OVER THE MID CONUS NEXT WEEK AND
RELOAD.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1202 AM CDT TUE AUG 26 2014

THE NEXT 24 HOURS OFFER VERY POOR CONFIDENCE IN TAF
FORECASTING...WHILE A FRONT SLOWLY MOVES SOUTH OVER EASTERN IOWA
AND NORTHWEST ILLINOIS. NORTHEAST TO EAST WINDS HAVE ALREADY
ESTABLISHED THEMSELVES AT MLI AND DBQ...AND THIS SHOULD CONTINUE
AS THE FRONT MOVES SOUTH. BRL AND CID WILL SEE A WIND SWITCH
OVERNIGHT TO THIS EASTERLY FLOW. SHOWERS AND THUNDERSTORMS WILL BE
SCATTERED OVERNIGHT...AND POSSIBLY COULD ORGANIZE INTO AN AREA OR
MCS...BUT THIS TREND IS NOT FULLY CONFIDENT SO WE HAVE GONE WITH
SHORTER PERIODS OF TEMPO FOR BOTH LIGHT FOG AND SOME SHOWER/STORM
ACTIVITY AT SITS.

OTHERWISE...A PERIOD OF IFR TO MVFR FOG AND CIGS IS POSSIBLE IN
THE EARLY MORNING HOURS...MUCH LIKE THE PAST SEVERAL DAYS.
ERVIN

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

UPDATE...ERVIN
SYNOPSIS...05
SHORT TERM...05
LONG TERM...12
AVIATION...ERVIN






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