Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 172323
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
623 PM CDT FRI APR 17 2015

.SYNOPSIS...
ISSUED AT 321 PM CDT FRI APR 17 2015

12Z UA ANALYSIS HAS WEAK 850MB LOWS IN SOUTHEAST COLORADO AND ALONG
THE ARKANSAS/LOUISIANA BORDER. A SUBTLE 850MB HIGH APPEARED TO BE
OVER WESTERN IOWA. SATELLITE TRENDS THROUGH MID AFTERNOON SHOW
DIURNAL CLOUDS ACROSS THE WESTERN GREAT LAKES WITH MORE SUBSTANTIAL
CLOUDS FROM THE APPROACHING SYSTEM ACROSS THE PLAINS.

18Z SFC ANALYSIS HAS A BOUNDARY/FRONT RUNNING FROM WESTERN LAKE
SUPERIOR INTO NORTHERN NEBRASKA WHILE HIGH PRESSURE WAS OVER THE
OHIO VALLEY. DEW POINTS RANGED FROM THE TEENS TO 30S BEHIND THE
BOUNDARY/FRONT IN THE NORTHERN PLAINS WITH 40S AND 50S ACROSS MUCH
THE MIDWEST AND PLAINS

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 321 PM CDT FRI APR 17 2015

QUIET AND DRY CONDITIONS WILL BE SEEN FROM LATE AFTERNOON THROUGH
MIDNIGHT ACROSS THE AREA. DIURNAL CLOUDS WILL DISSIPATE WITH SUNSET
FOLLOWED BY A GRADUAL INCREASE IN CLOUDS STARTING LATE THIS EVENING.

AFTER MIDNIGHT...CLOUDS WILL SLOWLY INCREASE ACROSS THE AREA AS
MOISTURE/FORCING BEGIN TO INCREASE AHEAD OF THE APPROACHING STORM
SYSTEM. NOCTURNAL CONVECTION WILL DEVELOP FROM WESTERN MISSOURI INTO
WESTERN IOWA THAT SLOWLY MOVES EAST. HOWEVER...THE BETTER
MOISTURE/FORCING REMAINS WEST OF THE AREA SO DRY CONDITIONS ARE
EXPECTED THROUGH SUNRISE SATURDAY.

ON SATURDAY...THE WEAK BOUNDARY/FRONT APPEARS TO DROP INTO THE AREA
DURING THE DAY AND INCREASES THE EASTERLY FLOW OFF LAKE MICHIGAN.
THIS SITUATION BRINGS INTO QUESTION HOW FAR EAST SHOWERS WILL MAKE
IT INTO THE AREA DURING THE DAY.

BASED ON WHAT IS BEING SUGGESTED BY THE MODELS...SPRINKLES/LIGHT
SHOWERS SHOULD SLOWLY MOVE EAST TOWARD THE I-380/US 218 CORRIDOR
SATURDAY MORNING. DURING THE AFTERNOON HOURS...THIS PRECIPITATION
SHOULD SLOWLY SPREAD EASTWARD AND COVER THE WESTERN HALF OF THE AREA
BY LATE AFTERNOON. ALTHOUGH NOT CERTAIN...A FEW RUMBLES OF THUNDER
MAY BE POSSIBLE ALONG/WEST OF THE I-380/US 218 CORRIDOR.

THE DEPTH/STRENGTH OF THE DRY EASTERLY FLOW WILL BE KEY AS TO HOW
FAR EAST THE PRECIPITATION GETS ON SATURDAY. IT IS POSSIBLE...AND
SUGGESTED BY A COUPLE OF MODELS...THAT THE PRECIPITATION MAY FALL
APART AS IT MOVES EAST INTO THE AREA ON SATURDAY. IF SUCH A SCENARIO
OCCURS...THEN PRECIPITATION CHANCES FOR SATURDAY WOULD HAVE TO BE
REDUCED IN LATER FORECASTS.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 321 PM CDT FRI APR 17 2015

INITIAL FOCUS IS ON THE UPPER WAVE LIFTING NORTHEAST THAT WILL BRING
A GOOD CHANCE OF RAIN AND ISOLATED THUNDERSTORMS SATURDAY NIGHT
THROUGH SUNDAY NIGHT. DEVELOPING NW FLOW THAT FOLLOWS WILL PROVIDE A
STRETCH OF BELOW NORMAL TEMPERATURES AND MAINLY DRY WEATHER THROUGH
NEXT WEEK.

CONSENSUS OF 12Z MODELS HAS THE 4 CORNERS UPPER LOW PHASING WITH
NORTHERN STREAM ENERGY OVER THE NORTH CENTRAL U.S. LATE SATURDAY AND
SUNDAY...WITH SLIGHTLY SLOWER EVOLUTION THAN PREVIOUS RUNS. A VORT
MAX AHEAD OF THE FILLING SOUTHERN STREAM UPPER LOW...COMBINED WITH
MOISTURE ADVECTION AND A MODEST 850 MB WARM ADVECTION REGIME...WILL
SPREAD A GOOD CHANCE FOR SHOWERS OVER THE AREA SATURDAY NIGHT.
POSITIVE MID LEVEL THETAE LAPSE RATES...ALONG WITH UNFAVORABLE MID
LEVEL THERMAL LAPSE RATES AND LIMITED MUCAPE ARE UNSUPPORTIVE OF
ANYTHING OTHER THAN ISOLATED THUNDERSTORMS...ESPECIALLY GIVEN THE
WEAK FORCING. RAIN CHANCES LOOK BETTER FOR LATE SUNDAY MORNING INTO
AFTERNOON AS THE FILLING UPPER WAVE ROTATES THROUGH MO INTO
IL...WHERE MODELS DEVELOP A SURFACE LOW THAT IS SHOWN LIFTING NEARLY
DUE NORTHWARD ACROSS EASTERN IL OR INDIANA INTO LAKE MI OR SOUTHERN
LOWER MI SUNDAY NIGHT. CONVECTION CLOSER TO THIS LOW MAY LIMIT QPF
TO LIGHT AMOUNTS AND PREVENT INSTABILITY SUFFICIENT ENOUGH TO
SUPPORT THUNDERSTORMS OVER THE FORECAST AREA. BASED ON THE
LIKELIHOOD OF A RESULTING LOW LEVEL EASTERLY FLOW OF DRY AIR INTO
ESPECIALLY NW IL INTO EAST CENTRAL IA AND CONTINUED MODEL EVOLUTION
OF THIS SYSTEM...WILL CAP POPS AT THE LIKELY LEVEL FOR NOW. POPS WERE
INCREASED FOR SUNDAY NIGHT INTO EARLY MONDAY AS IT NOW APPEARS TO BE
THE PERIOD OF STRONGEST UPPER FORCING AHEAD OF THE UPPER TROUGH THAT
PASSES THROUGH DURING THE DAY MONDAY. TOTAL QPF FOR THIS SYSTEM
LOOKS LIKELY TO BE A WIDESPREAD QUARTER TO HALF INCH...WITH THE
POTENTIAL FOR SOME LOCATIONS TO END UP WITH ONLY A FEW HUNDREDTHS
DEPENDING ON COVERAGE OF SHOWERS.

MONDAY WILL BE BREEZY AND COOL AS SURFACE LOW LIFTS AWAY OVER THE
GREAT LAKES WITH POSSIBLE SHOWERS OVER THE NORTH AND EAST IN THE
MORNING. THE REST OF THE WEEK WILL BE UNDER A NW FLOW ALOFT...WHICH
WILL KEEP TEMPERATURES BELOW NORMAL AND PRIMARILY STEER SYNOPTIC
SYSTEMS AND THEIR RAIN CHANCES WELL TO THE NORTH AND SOUTH. THE
EXCEPTION IS THU AND THU NIGHT...WHEN THE GFS SENDS A WAVE OF LOW
PRESSURE TO THE SOUTH...POSSIBLY SPREADING RAIN INTO THE SOUTHERN
THIRD OF THE FORECAST AREA CONTRIBUTING TO THE MODEL CONSENSUS
CHANCE POPS FOR THESE PERIODS. HIGH PRESSURE AND SUB ZERO 850 MB
TEMPERATURES OVER THE REGION WED NIGHT INTO THU MORNING MAY LEAD TO
MORNING FROST...WHICH MAY NEED TO BE ADDED IN LATER FORECASTS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 620 PM CDT FRI APR 17 2015

VERY SLOW MOVING LOW PRESSURE ALOFT WILL CONTINUE TO DRIFT TOWARDS
THE UPPER MIDWEST THROUGH SATURDAY. DRY AIR IN PLACE OVER EASTERN
IOWA AND NORTHWEST ILLINOIS...WILL KEEP CONDITIONS DRY...VFR...AND
MAINLY SCATTERED TO BROKEN MID AND HIGH CLOUDS...AT LEAST THROUGH
LATE AFTERNOON SATURDAY. BY SATURDAY NIGHT...RAIN SHOWERS MAY
BEGIN MOVING INTO EASTERN IOWA...WITH SOME POSSIBLE MVFR CIGS
ACCOMPANYING THEM. THIS IS AT THE END OF THE PERIOD TIMING...AND
NOT YET INCLUDED DUE TO LOW CONFIDENCE. WINDS WILL BE LIGHT EAST
TO SOUTHEAST THROUGH THE PERIOD.
ERVIN

&&

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

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...SHEETS
AVIATION...ERVIN





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