Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 280443
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1143 PM CDT MON JUL 27 2015

.UPDATE...
ISSUED AT 924 PM CDT MON JUL 27 2015

HAVE UPDATED THE FORECAST TO GO OUT WITH A HEAT ADVISORY FOR
ROUGHLY ALONG AND SOUTH OF THE HIGHWAY 34 CORRIDOR FOR TUESDAY
AFTERNOON AND EARLY EVENING. CONFIDENCE IS SUFFICIENTLY HIGH THAT
TEMPERATURES WILL REACH AT LEAST THE LOWER 90S IN THE SOUTH DURING
THE AFTERNOON WITH DEWPOINTS CONSERVATIVELY REACHING THE MID TO
UPPER 70S. THIS RESULTS IN HEAT INDEX VALUES FROM 100 TO NEAR
110...WELL ABOVE OUR ADVISORY THRESHOLD OF 100.

THE SETUP LOOKS LESS FAVORABLE FOR A STRAY MCS TO SPILL INTO
THE SOUTH AS OCCURRED TODAY...AND THE NEW AFTERNOON CONVECTION
SHOULD DEVELOP ACROSS THE NW AND NORTH. THIS SHOULD ALLOW THE
SOUTH TO REACH THE 90S...WHICH WERE WIDESPREAD JUST TO THE W AND SW
OF WHERE TODAY/S MCS ROLLED THROUGH.

&&

.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 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1143 PM CDT MON JUL 27 2015

LINGERING LOW LEVEL MOISTURE WILL AGAIN LEAD TO A GOOD POTENTIAL
FOR MVFR FOG AT ALL SITES LATE TONIGHT THROUGH SUNRISE TUESDAY.
OTHERWISE...SKIES WILL BE MOSTLY CLEAR WITH LIGHT E-SE WINDS.
TUESDAY...AN APPROACHING COOL FRONT WILL BRING INCREASING CHANCES
FOR THUNDERSTORMS FROM AROUND MID AFTERNOON ONWARD. THIS IS
MENTIONED WITH PRO30 GROUPS INITIALLY...WHERE THE TIMING OF THE
ONSET OF STORMS IS UNCERTAIN. THUNDERSTORMS WILL BE MORE LIKELY IN
THE EVENING AS THE FRONT NEARS...WHERE TEMPO GROUPS ARE UTILIZED.
WHILE THE MENTION OF THUNDER ENDS AT 04Z...THERE IS A HIGH
LIKELIHOOD THAT THUNDERSTORMS WILL STILL BE AFFECTING THE AREA
THROUGH MIDNIGHT TUESDAY NIGHT.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...HEAT ADVISORY FROM NOON TO 7 PM CDT TUESDAY FOR DES MOINES-HENRY
     IA-LEE-VAN BUREN.

IL...HEAT ADVISORY FROM NOON TO 7 PM CDT TUESDAY FOR HANCOCK-
     HENDERSON-MCDONOUGH-WARREN.

MO...HEAT ADVISORY FROM NOON TO 7 PM CDT TUESDAY FOR CLARK-SCOTLAND.

&&

$$

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



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