Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 190424
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1124 PM CDT MON MAY 18 2015

.UPDATE...
ISSUED AT 1003 PM CDT MON MAY 18 2015

SATELLITE IMAGERY SHOWS THE STRATUS FIELD THAT HAS BEEN ADVANCING
SLOWLY SOUTHWARD OUT OF MN TODAY HAVING NOW REACHED AS FAR SOUTH
AS THE I-80 CORRIDOR IN EASTERN IA AND NW IL. THIS...ALONG WITH
CONTINUED COLD AIR ADVECTION IN THE CYCLONIC FLOW AHEAD OF A
SURFACE THROUGH 850 MB TROUGH AXIS ADVANCING SE OUT OF THE UPPER
MS VALLEY...WAS KEEPING WINDS RATHER BRISK...STILL AT 15 TO 25 MPH
AT 9 PM.

BIG QUESTION TONIGHT IS HOW FAR SOUTH THE ADVANCING STRATUS DECK
WILL REACH AS MODELS KEEP THE DEEPER LOW LEVEL MOISTURE AND
TIGHTER 925 TO 850 MB CYCLONIC FLOW ONLY AS FAR SOUTH AS HIGHWAY
20 CORRIDOR TONIGHT. EVEN SHORT TERM HIGH RES MODELS HAVE BEEN
PLAYING CATCHUP WITH THE SOUTHWARD PROGRESSION. FOR NOW...HAVE
DROPPED CLOUDS AS FAR SOUTH AS THE HIGHWAY 34 CORRIDOR...BUT HAVE
NOT ALTERED MIN TEMPERATURES MUCH AS CONTINUED COLD AIR ADVECTION
ON MINIMAL 10 TO 15 MPH WINDS WILL DRAW DOWN THE 30S CURRENTLY IN
PLACE ACROSS MN INTO NORTHERN IA THIS EVENING. TUESDAY...CLOUDS
COULD POTENTIALLY LINGER OVER THE NORTH THROUGH AT LEAST LATE
MORNING BEFORE THE LOW LEVEL FLOW BECOMES MORE ANTICYCLONIC.

&&

.SYNOPSIS...
ISSUED AT 252 PM CDT MON MAY 18 2015

AS OF 230 PM CDT...COLD UPPER LOW POSITIONED OVER NORTHERN LAKE
SUPERIOR HAD AN EXPANSIVE STRATOCUMULUS CLOUD SHIELD ACROSS THE
UPPER MIDWEST. THE SOUTHERN EDGE OF THE CLOUDS HAVE ONLY MOVED
INTO THE FAR NORTHWEST PORTION OF THE DVN CWA...NORTHWEST OF A
CEDAR RAPIDS TO DUBUQUE LINE.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 252 PM CDT MON MAY 18 2015

THIS EVENING AND TONIGHT...GUSTY NORTHWEST WINDS BETWEEN 25-35 MPH
WILL DECREASE RAPIDLY AROUND SUNSET AS BOUNDARY LAYER MIXING WANES.
MOSTLY CLEAR SKIES AND DRY AIR WITH DEWPOINTS IN THE 30S WILL ALLOW
FOR EFFICIENT RADIATIONAL COOLING AND COOL OVERNIGHT LOWS. EXPECT
LOWS TO RANGE FROM THE LOWER 40S SOUTH TO THE UPPER 30S NORTH. THE
SFC HIGH WILL STAY WELL NORTHWEST OF E IOWA/W ILLINOIS...OVER THE
DAKOTAS...AND AS A RESULT THE SFC PRESSURE GRADIENT WILL BE STRONG
ENOUGH TO KEEP WINDS FROM COMPLETELY DECOUPLING AND TEMPS FROM
DROPPING FURTHER.

TUESDAY...AS LOW PRESSURE DEVELOPS OVER THE FOUR CORNERS REGION THE
SFC PRESSURE GRADIENT WILL SLACKEN ACROSS THE UPPER MIDWEST BUT
STRENGTHEN ACROSS THE CENTRAL PLAINS AND FOOTHILLS OF THE CENTRAL
ROCKIES. CONSEQUENTLY...MUCH LIGHTER WINDS ARE FORECAST FOR E IOWA
AND W ILLINOIS.

DRY ADIABATIC MIXING OF UNSEASONABLY COLD 850MB TEMPS...BETWEEN 0 TO
4C...TO THE SURFACE SHOULD YIELD SLIGHTLY LOWER MAX TEMPS COMPARED
TO MONDAY. CURRENT FORECAST IS FOR NEAR 60 F ON AVG IN THE DVN
FORECAST AREA ALONG WITH MAINLY CLEAR SKIES INTO THE AFTN.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 252 PM CDT MON MAY 18 2015

MAIN FORECAST CONCERN FOR THE LONG TERM ARE THE TWO SYSTEMS THAT
ARE FORECAST TO MOVE INTO THE AREA. THE SYSTEM FOR WEDNESDAY...NOW
SHOWS DIFFERENCES BETWEEN THE MODELS AND NOW LOWER CONFIDENCE IN
THE FORECAST. THE SYSTEM THIS WEEKEND WILL BRING RAIN AND THUNDER
TO THE AREA AS WELL. ISSUES OF TIMING BETWEEN SURGES OF MOISTURE
STILL REMAIN.

WEDNESDAY...A SYSTEM THAT HAD DECENT AGREEMENT THE PAST FEW DAYS
NOW LOOKS TO HAVE DIVERGED IN SOLUTIONS. AT THIS TIME THE GFS AND
CANADIAN SHOW LITTLE TO NO PRECIP ACROSS OUR AREA...WHERE THE
ECMWF AND NAM SHOWS THE ENTIRE AREA RECEIVING PRECIP. GFS 300K
ISENTROPIC SURFACE DEPICTS MINIMAL OVERRUNNING. THE ECMWF SHOWS
SLIGHTLY MORE. BY 00Z...ISENTROPICS SUGGEST THAT WE ARE IN
DOWNSLOPE AND THAT THE PRECIP SHOULD WANE QUICKLY. THE
NAM...DEPICTS H7 FRONTOGENESIS AT THIS TIME THROUGH 06Z ACROSS
NORTHERN ZONES. I HAVE LOW CONFIDENCE IN THIS OCCURRING SO WENT
WITH SCHC RAIN ACROSS THOSE AREAS. THIS EVENT LOOKS TO BE
STRATIFORM RAIN EVENT. I AM CONFIDENT THAT AREAS SOUTH OF I80 WILL
SEE SOME RAIN AND LESS CONFIDENT ON AREAS NORTH OF THERE. I DO NOT
THINK WE WILL SEE ANY THUNDER WITH THIS SYSTEM...CAPE DOES NOT
EXIST AND WE DONT SEE CONVECTIVE UPDRAFTS IN THE CHARGING REGION.

AFTER WEDNESDAY...WE WARM UP AND ARE RATHER PLEASANT BEFORE THE
FLOW TURNS TO THE SOUTHWEST. THIS WEEKEND THE FLOW RETURNS TO THE
SOUTHWEST. MOISTURE RETURNS TO THE AREA AND A DEEP TROUGH DIGS
INTO TO THE WESTERN US. A SERIOUS OF WAVES WILL MOVE ACROSS THE
AREA SATURDAY BEFORE THE MAIN WAVE MOVES IN SUNDAY. SUNDAY LOOKS
LIKE THE BEST DAY FOR THUNDER. SUPERBLEND HAS A CHANCE FOR THUNDER
AND RAIN THROUGHOUT THE REST OF THE EXTENDED.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1124 PM CDT MON MAY 18 2015

STRATUS DECK WITH CIGS HOVERING BETWEEN 2500 TO 3500 FT AGL
CONTINUES TO ADVANCE SOUTHWARD ACROSS EASTERN IOWA AND NORTHWEST
ILLINOIS LATE THIS EVENING. CIGS ARE NOW FORECAST TO REMAIN IN THE MVFR
RANGE THROUGH THE NIGHT AT CID AND DBQ...AND POSSIBLY DIP INTO
MVFR IN THE HOURS TOWARD SUNRISE AT MLI...WHILE BRL IS EXPECTED
TO REMAIN ON THE EDGE OF THE DECK AT VFR LEVELS. BRISK...GUSTY NW
WINDS SHOULD GRADUALLY DIMINISH THROUGH THE REST OF TONIGHT.
TUESDAY...THE LOW CLOUDS SHOULD DISSIPATE IN PLACE...WITH ALL
SITES LIKELY TO BE VFR BY LATE MORNING. VFR CONDITIONS ARE THEN
EXPECTED THROUGH THE REST OF THE DAY WITH NORTH WINDS BECOMING
LIGHT IN THE EVENING.

&&

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

$$

UPDATE...SHEETS
SYNOPSIS...UTTECH
SHORT TERM...UTTECH
LONG TERM...GIBBS
AVIATION...SHEETS


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