Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 242046
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
346 PM CDT SUN MAY 24 2015

.SYNOPSIS...
ISSUED AT 325 PM CDT SUN MAY 24 2015

AS OF 230 PM...GOES WATER VAPOR LOOP OVER PAST SEVERAL HOURS SHOWED
A CONTINUAL TRANSPORT OF MOISTURE FROM THE WESTERN GULF OF MEXICO
NORTHWARD THROUGH THE CENTRAL PORTION OF THE U.S. AND INTO THE UPPER
MIDWEST. INSTABILITY HAS BEEN RATHER LIMITED ACROSS THE MIDWEST
THROUGH THIS AFTERNOON WITH ANY POCKETS OF LIGHTNING LOCATED TO THE
SOUTH OF EVEN FAR SOUTHEASTERN IOWA.

LAST GOES IR SATELLITE AND KDVN DOPPLER RADAR TRENDS HAVE SHOWN AN
INCREASE IN CONVECTIVE SHOWER DEVELOPMENT AND COVERAGE ACROSS
NORTHEASTERN MISSOURI/EASTERN IOWA/WEST-CENTRAL ILLINOIS.

SPC MESOANALYSIS PLACED A MUCAPE GRADIENT JUST TO THE SOUTH OF I-80
WITH VALUES GOING FROM NEAR 100 J/KG ON ITS NORTHERN EDGE TO
SLIGHTLY OVER 500 J/KG SOUTH OF HIGHWAY 34...WHERE TEMPS WERE
WARMEST IN THE MIDDLE TO UPPER 70S SOUTH OF A SFC WARM FRONT.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 325 PM CDT SUN MAY 24 2015

REST OF THIS AFTERNOON AND THIS EVENING...

CONVECTIVE SHOWERS WILL CONTINUE TO INCREASE IN COVERAGE AS
NORTHWARD LOW-LEVEL MOISTURE TRANSPORT CAUSES MUCAPE VALUES TO
SLOWLY INCREASE AND 850-700MB WAA PROVIDES SUBTLE BUT SUFFICIENT
LIFT. A FEW STRONG OR SEVERE STORMS ARE POSSIBLE MAINLY SOUTH OF I-
80 THROUGH THIS EVENING WHERE SFC WINDS ARE BACKED TO THE
SOUTHWEST...EFFECTIVE BULK SHEAR IS NEAR 35-40 KTS...MUCAPE IS
APPROACHING 1000 J/KG...AND LCLS ARE LOW NEAR 750 METERS. FOR
THESE REASONS THERE IS A LOW CHANCE FOR STRONG THUNDERSTORM WINDS
OR AN ISOLATED TORNADO.

AS LOW PRESSURE MOVES FROM WESTERN IOWA TO SOUTH-CENTRAL
MINNESOTA...SOUTHERLY SFC WINDS WILL KEEP THE FORECAST AREA
RELATIVELY MILD AND HUMID THROUGH THE NIGHT. FORECAST PWAT VALUES
NEAR 1.75 INCHES ARE APPROXIMATELY 2.5-3 STANDARD DEVIATIONS ABOVE
THE MEAN OR THE 99TH PERCENTILE FOR THE END OF MAY. THEREFORE...THE
ENVIRONMENTAL CONDITIONS ARE PRIMED FOR LOCALIZED HEAVY DOWNPOURS
WHICH COULD EXCEED 0.75-1.00 INCH/HR AT TIMES. 850MB MOISTURE
TRANSPORT AND MOISTURE FLUX CONVERGENCE WILL MOSTLY LIKELY BE
FOCUSED THROUGH THE HEART OF THE DVN CWA IN THE COUNTIES ALONG
BOTH SIDES OF THE MISSISSIPPI RIVER.

A SECOND ROUND OF PRECIP IS FORECAST AFTER MIDNIGHT AS PVA ATTENDANT
TO THE MAIN SHORTWAVE ROTATES THROUGH NORTHERN MISSOURI/E IOWA/W
ILLINOIS. THE GOOD NEWS WITH THIS SECOND ROUND IS THAT INSTABILITY
WILL BE LOWER AS 700-500MB LAPSE RATES DECREASE TO NEAR 5.5 C/KM.
SO MAINLY JUST RAIN SHOWERS AND ONLY ISOLATED THUNDERSTORMS. THE
HEAVIEST RAIN IN THIS PERIOD SHOULD OCCUR FROM LATE THIS
AFTERNOON THROUGH MIDNIGHT TONIGHT.

MONDAY...BREEZY SOUTHWEST WINDS WILL DEVELOP AND GUST OVER 20-25 MPH
AT TIMES. HIGHS WILL BE IN THE LOWER 80S WHICH WILL YIELD MODERATE
LEVELS OF CONDITIONAL INSTABILITY AS MUCAPE VALUES INCREASE TO 1500-
2000 J/KG OR GREATER BY THE EVENING. HOWEVER..E IOWA/W ILLINOIS WILL
BE BETWEEN TWO SHORTWAVE FEATURES....SO EXPECT MAINLY DRY WEATHER
THROUGH THE DAY. THEN...ONE OF THE MID-LEVEL SHORTWAVES WILL SLIDE
UP FROM THE SOUTHWEST AND CROSS THE DVN CWA DURING THE LATE EVENING
AND EARLY NIGHTTIME BRINGING A SLIGHTLY BETTER CHANCE FOR SCATTERED
SHOWERS AND STORMS.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 325 PM CDT SUN MAY 24 2015

TUESDAY AND TUESDAY NIGHT...SHOWERS AND THUNDERSTORMS...SOME WITH
HEAVY RAIN...ARE EXPECTED AS AN NEGATIVELY TILTED SHORTWAVE ALOFT
MOVES ACROSS THE UPPER MISSISSIPPI RIVER VALLEY. ISOLATED SEVERE
WEATHER IS POSSIBLE DEPENDING ON HOW UNSTABLE THE ATMOSPHERE GETS
DURING THE AFTERNOON. INSUFFICIENT HEATING IS POSSIBLE DUE TO
CONVECTIVE CLOUD DEBRIS ACROSS THE REGION.

WEDNESDAY AND THURSDAY...ECMWF/GFS/NAM PROG THIS PERIOD TO BE MAINLY
DRY AS A WEAK COOL FRONT MOVES SOUTH OF THE FORECAST AREA AND
SURFACE HIGH PRESSURE BUILDS IN UNDER A WEAK 500 MILLIBAR RIDGE
ALOFT. HIGH TEMPERATURES WILL BE IN THE UPPER 70S TO AROUND 80.

THURSDAY NIGHT THROUGH SATURDAY... ACTIVE PATTERN RETURNS FOR LATE
IN THE WEEK AS A SOUTHWEST FLOW ALOFT AND SOUTHERLY FLOW AT THE
SURFACE ADVECTS GULF MOISTURE INTO THE UPPER MISSISSIPPI RIVER
VALLEY. WITH AMPLE MOISTURE IN PLACE AND A SERIES OF UPPER LEVEL
DISTURBANCES MOVING ACROSS THE REGION...THERE WILL BE SEVERAL
PERIODS OF SHOWERS AND THUNDERSTORMS...SOME WITH HEAVY RAIN...BUT IT
IS TOO EARLY TO PIN DOWN THE TIMING OF THESE STORMS.

SUNDAY AND MONDAY...CONFIDENCE IS LOW DURING THIS TIME. THE ECMWF
PROG A SURFACE BOUNDARY TO BE LYING ACROSS THE REGION WHICH WOULD
PROVIDE A FOCUSING MECHANISM FOR SHOWERS WHILE THE GFS SHOWS THIS
BOUNDARY SOUTH OF THE AREA WITH DRY HIGH PRESSURE BUILDING IN. IF
THE ECMWF IS RIGHT WE CAN EXPECT SHOWERS NEXT SUNDAY AND MONDAY. IF
THE GFS IS CORRECT SKIES SHOULD BE MAINLY DRY.  WITH LARGE MODEL
DISCREPANCIES THIS FAR OUT IN THE FUTURE ONLY TIME WILL TELL WHICH
SOLUTION IS CORRECT.

WITH AN ACTIVE WEATHER PATTERN EXPECTED AND THE POTENTIAL FOR
SEVERAL PERIODS OF HEAVY RAIN...RIVER LEVELS WILL NEED TO BE
MONITORED DURING THE WEEK AHEAD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 111 PM CDT SUN MAY 24 2015

MAINLY VFR CONDITIONS ARE FORECAST INTO THE LATE AFTN WITH
BRIEF PERIODS OF MVFR UNDER SHORT-LIVED CONVECTIVE RAIN
SHOWERS.

LATE THIS AFTN AND THIS EVENING INSTABILITY WILL INCREASE
SLIGHTLY AND SCT SHOWERS AND THUNDERSTORMS WILL DEVELOP. INCLUDED
THUNDER AT KMLI AND KBRL WHERE CONFIDENCE IS MUCH HIGHER THAN AT
KCID AND KDBQ. CONDITIONS WILL DETERIORATE LATE THIS EVENING AND
OVERNIGHT AS CIGS GRADUALLY LOWER TO AROUND 1 KFT AGL AND VSBYS TO
2 MILES OR LOWER AT TIMES.

FAIRLY HIGH CONFIDENCE IN A PROLONGED PERIOD OF CONDITIONS AT THE
MVFR/IFR THRESHOLD BETWEEN 05Z-13Z/MONDAY. SW WINDS WILL INCREASE
AFTER 12Z/MONDAY AND CONDITIONS WILL IMPROVE TO MVFR BY MID
MORNING.


&&

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

$$

SYNOPSIS...UTTECH
SHORT TERM...UTTECH
LONG TERM...UTTECH
AVIATION...UTTECH


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