Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 280007
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
707 PM CDT MON JUL 27 2015

.UPDATE...
ISSUED AT 706 PM CDT MON JUL 27 2015

MCS CONTINUES TO DIVE SOUTHEAST WITH THE NORTHERN EDGE OF THE
LINEAR THUNDERSTORM COMPLEX OF STRONGEST STORMS WITH HEAVY
RAINFALL ALONG THE SOUTHERN HANCOCK BORDER ABOUT TO EXIT
SOUTHEAST WITHIN THE NEXT HOUR. A LARGER...MAINLY STRATIFORM...
AREA OF LIGHT RAIN EXTENDED NORTH TO JUST SOUTH OF A WASHINGTON
TO MUSCATINE LINE PROGRESSING EASTWARD AS WELL.

THE ONLY SIGNIFICANT CHANCE FOR THUNDERSTORMS IN THE NEAR TERM
WILL BE ALONG THE FAR SOUTH...WHILE WIDESPREAD...MAINLY LIGHT
RAIN GRADUALLY WANES OVER SE IA INTO W CENTRAL IL THIS EVENING
WITH ONLY LIGHT AMOUNTS EXPECTED. HAVE UPDATED THE FORECAST FOR
THESE TRENDS. THE REST OF THE NIGHT LOOKS QUIET BUT MUGGY WITH
THUNDERSTORM CHANCES CREEPING BACK INTO THE NW TOWARD SUNRISE.

&&

.SYNOPSIS...
ISSUED AT 330 PM CDT MON JUL 27 2015

FOR DETAILS REGARDING ONGOING CONVECTION ENTERING INTO THE
SOUTHWESTERN PORTION OF THE DVN CWA PLEASE SEE THE SHORT TERM
SECTION OF THE DISCUSSION.

OVERVIEW...STRONG HEIGHT FALL/RISE COUPLET WILL PROPAGATE THROUGH
THE NORTHERN ROCKIES INTO TUESDAY MORNING. FOR E IOWA/W
ILLINOIS...WE WILL JUST SEE MINOR HEIGHT RISES DURING THIS TIME
WITH THE 500MB RIDGE AXIS BECOMING ALIGNED FROM OKLAHOMA
NORTHEASTWARD TROUGH THE WESTERN GREAT LAKES REGION INTO ONTARIO.
THIS SYNOPTIC PATTERN WILL SET THE STAGE FOR POTENTIALLY DANGEROUS
HEAT INDICES ON TUESDAY...ALTHOUGH EXTENT OF CONVECTIVE CLOUD
DEBRIS WILL PLAY A ROLE ON FINAL MAX TEMPS.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 330 PM CDT MON JUL 27 2015

THIS EVENING AND TONIGHT...THE MODELS DID A POOR JOB INITIALIZING THE
THUNDERSTORM COMPLEX ACROSS WESTERN IOWA THIS MORNING WHICH IS NOW
ONLY A TIER OF COUNTIES WEST OF MY CWA. THE 12Z/MONDAY NAM12 AND
HRRR/HRRRX ARE MOST AGGRESSIVE IN BRINGING AT LEAST REMNANTS OF
THE MCS INTO THE SOUTHWEST THIRD OR SO OF THE DVN CWA...THE
SREF/GFS/ECMWF ARE ALL DRY FOR THE OVERNIGHT.

THE CURRENT SBCAPE GRADIENT...STORM MOTION VECTORS...AND RECENT
PROJECTS BY THE CONVECTIVE ALLOWING MODELS...ALL FAVOR A
SOUTHEASTWARD TRACK OF THE COMPLEX TOWARD MY SOUTHWEST CWA LATE
THIS AFTN INTO THIS EVENING. HAVE INCREASED POPS INTO THE 40-60
PERCENT RANGE. IF ANY STRONG WINDS WERE TO OCCUR WITH THE
MCS...THEY WOULD BE LOCALIZED AND WOULD BE MOST PROBABLE OVER THE
FAR SOUTHWEST FORECAST AREA WHERE MUCAPE VALUES ARE 3000 J/KG OR
HIGHER.

SINCE PWATS ARE QUITE HIGH ACROSS THE WESTERN FORECAST AREA AT
1.75 INCHES AND STORM MOTION VECTORS ARE ONLY NEAR 10-15
MPH...PRIMARY THREAT WITH ANY STORMS THAT FORM IS HEAVY RAINFALL
LOCALIZED FLASH FLOODING.

TUESDAY...UNSEASONABLY STRONG UPPER LOW DEVELOPING ACROSS
SASKATCHEWAN/MANITOBA/ONTARIO IS FORECAST TO ADVECT VERY WARM AIR
ALOFT OVER THE MIDWEST...SETTING UP ANOTHER DAY OF HIGH HEAT INDICES
NEAR OR OVER 100 F.

850MB WARM AIR ADVECTION RAMPS UP DURING THE MORNING AND LASTS INTO
THE AFTN. GFS/ECMWF HAVE 850MB TEMPS IN THE LOWER 20S CELSIUS AND
1000-500MB THICKNESSES NEAR 582 DAM. FORECAST SOUNDINGS INDICATE
DEEP BOUNDARY LAYER MIXING POTENTIALLY UP TO 850-875MB...CREATING
SOUTHERLY GUSTS AROUND 20 MPH. ALSO...MODELS IN GOOD AGREEMENT ON
DEWPOINTS IN THE MID TO UPPER 70S. WILL LET MIDNIGHT SHIFT MAKE
DECISIONS ON HEAT LINES BECAUSE OF THE CHANCE FOR CONVECTIVE
CLOUD DEBRIS HOLDING TEMPS DOWN INTO THE MID/UPPER 80S AND BECAUSE
AREAS THAT DO CLEAR OUT SOUTH OF I-80 MAY REACH HEAT WARNING
CRITERIA WITH VALUES OVER 105 F.

CONVECTIVE FORECAST...SPC OUTLOOK HAS A SLIGHT RISK FOR SEVERE
STORMS ROUGHLY ALONG AND WEST OF THE MISSISSIPPI RIVER. MODEL
CONSENSUS IS TO BRING A SQUALL LINE ACROSS THE CWA FROM WEST TO EAST
TUESDAY NIGHT. PRIOR TO THIS A ROUND OF SHOWERS AND STORMS IS
POSSIBLE TUESDAY MORNING INTO THE EARLY AFTN BEFORE A BREAK THROUGH
THE AFTN AND INTO THE EVENING. WIDESPREAD SEVERE WEATHER IS NOT
ANTICIPATED DUE TO WEAK ENVIRONMENTAL SHEAR.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 330 PM CDT MON JUL 27 2015

MAIN FORECAST CONCERN FOR THE LONG TERM IS THE COLD FRONT FORECAST
TO MOVE THROUGH THE AREA TOMORROW NIGHT INTO EARLY WEDNESDAY
MORNING.  MAIN THREAT ASSOCIATED WITH THESE THUNDERSTORMS WILL BE
HEAVY RAIN. THERE IS ALSO A SLIGHT RISK FOR SEVERE WEATHER OVERNIGHT
WITH THE COLD FRONT.  ONCE THE COLD FRONT PASSES...WE SHOULD HAVE A
QUIET REST OF THE WORK WEEK UNTIL THE CHANCE FOR SHOWERS AND
THUNDERSTORMS RETURN.

HIRES MODELS SUGGEST THAT A LINE OR BROKEN LINE OF CONVECTION WILL
BE ONGOING AT THE BEGINNING OF THE PERIOD.  THESE SHOWERS AND
THUNDERSTORMS WILL MOVE ACROSS THE CWA THROUGH THE EVENING AND
OVERNIGHT HOURS.  MODELS ARE IN GOOD AGREEMENT WITH THE TIMING OF
THE FRONT.  IT  APPEARS THE FRONT WILL BE SOUTH OF THE QCA BY 10Z TO
12Z ON WEDNESDAY.  AS FAR AS SEVERE WEATHER GOES...DEEP LAYER SHEAR
IS WEAK AND THEREFORE SUGGESTS THAT MULTICELL STORMS WILL BE THE
DOMINANT MODE. SFC WINDS ARE PROGGED TO BE EAST OF SOUTH...THIS IS
CONCERNING FROM A TORNADO THREAT...HOWEVER WINDS WILL BE WEAK AND
SPEED SHEAR IS NONEXISTENT.  MY THOUGHTS ARE THAT THESE BACKED WINDS
AND INCREASED HELICITY COULD SERVE AS DRIVERS FOR A SEVERE WIND
THREAT IN THE STRONGEST OF STORMS.  CAPE SHOULD BE WEAKENING AND
STORMS WILL LIKELY BE TRANSITIONING TO ELEVATED INFLOWS.  THIS MEANS
THAT AS THE EVENING GOES ON THE SEVERE THREAT SHOULD DIMINISH.  OF
GREATER THREAT WILL BE THE HEAVY RAIN THREAT.  WARM CLOUD PROCESSES
SHOULD DOMINATE CONVECTION.  WITH PWAT VALUES AROUND OR EXCEEDING 2
INCHES THERE IS A GOOD POSSIBILITY FOR HEAVY RAIN.  I DO THINK THAT
THE FAST MOVING FRONT WILL MOVE STORMS THROUGH THE AREA QUICKLY AND
THEREFORE LIMIT THE OVERALL FLASH FLOODING THREAT.  REGARDLESS THIS
WILL NEED TO BE WATCHED TOMORROW.

AFTER THE FRONT...THE FLOW IS STILL FORECAST TO TURN NW.  THIS MEANS
THAT DRIER AIR...COOLER TEMPS AND NO POP CHANCES ARE FORECAST
THROUGH THE WORK WEEK.  THIS WEEKEND THERE ARE STILL DISCREPANCIES
IN THE MODELS AS FAR AS SYSTEMS MOVING THROUGH OUR AREA.  WITH THE
NW FLOW...WE ARE SET UP FOR ANY RIPPLES IN THE FLOW TO LEAD TO
POSSIBLE RAIN AND THUNDERSTORMS.  SUPERBLEND HAS CHC POPS THIS
WEEKEND.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 706 PM CDT MON JUL 27 2015

A COMPLEX OF SHOWERS AND THUNDERSTORMS WILL EXIT INTO W CENTRAL IL
EARLY THIS EVENING...AFFECTING THE BRL TERMINAL WITH LIGHT RAIN
AND PERHAPS RAIN THE VCNTY OF MLI. OTHERWISE...VFR CONDITIONS WITH
VERY LIGHT E-SE WINDS WILL CONTINUE THROUGH THE NIGHT WITH LIGHT
FOG POSSIBLY RESULTING IN MVFR CONDITIONS LATE. ANOTHER ROUND OF
THUNDERSTORMS MAY MOVE INTO EASTERN IA EARLY TUESDAY MORNING...BUT
CHANCES ARE GREATER IN THE AFTERNOON. FOR NOW...CONFIDENCE REMAINS
LOW WITH THE TIMING AND COVERAGE OF THESE EVENTS AND PROB30
WORDING HAS BEEN USED.

&&

.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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