734  
FXUS63 KDVN 211201  
AFDDVN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE QUAD CITIES IA IL  
701 AM CDT MON AUG 21 2017  
   
..AVIATION UPDATE
 
 
   
SYNOPSIS
 
 
ISSUED AT 355 AM CDT MON AUG 21 2017  
 
A LINE OF ELEVATED, HEAVY RAIN PRODUCING STORMS HAS RECENTLY FORMED  
FROM FAIRFIELD UP TO SIGOURNEY. FURTHER WEST, THE MCS OVER CENTRAL  
IOWA PRODUCED LOCALIZED HEAVY RAINFALL AND FLASH FLOODING IN THE  
DENISON, IA AREA AND WIND GUSTS OVER 50 MPH NEAR ATLANTIC, IA.  
 
ACROSS THE REMAINDER OF E IOWA/NW ILLINOIS THERE HAS BEEN AREAS OF  
FOG THROUGH THE NIGHT, THE WORST OF WHICH OCCURRED IN THE COUNTIES  
ALONG I-80 AND HIGHWAY 30. A FEW SITES - MOLINE, IL AND SAVANNA,  
IL - HAVE BRIEFLY DROPPED TO 1/4 OF A MILE. HOWEVER, DENSE FOG  
HAS NOT BEEN PERSISTENT OR WIDESPREAD ENOUGH TO CONSIDER AN  
ADVISORY. CONDITIONS SHOULD GRADUALLY IMPROVE AS MID-LEVEL CLOUDS  
CONTINUE TO INCREASE DOWNSTREAM OF THE CONVECTION.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 355 AM CDT MON AUG 21 2017  
 
THROUGH MID MORNING  
 
HI-RES CONVECTIVE ALLOWING MODELS (HRRR/NMM/RAP) IN GOOD AGREEMENT  
ON BRINGING ELEVATED, WARM AIR ADVECTION DRIVEN SHOWERS AND  
THUNDERSTORMS INTO THE WEST-CENTRAL AND NW CWA EARLY THIS MORNING.  
THEY ARE ALSO SHOWING AN EXPANSION OF SCATTERED SHOWERS AND STORMS  
THROUGH OR SLIGHTLY SOUTH OF THE QUAD CITIES INTO CENTRAL ILLINOIS  
BETWEEN 7-10 AM. THESE STORMS ARE NOT EXPECTED TO BE SEVERE. HEAVY  
RAINFALL RATES OF 1-2"/HR AND LIGHTNING STRIKES ARE THE MAIN  
THREATS.  
 
THERE IS MORE FORECAST UNCERTAINTY TO THE SW. THIS REGION IS IN LINE  
FOR THE SFC-BASED PART OF THE MCS THAT IS MOVING SOUTHEASTWARD INTO  
A HIGH DCAPE ENVIRONMENT (>1000 J/KG). FURTHERMORE, LATEST SPC  
MESOANALYSIS SHOWS INCREASING 0-1 KM BULK SHEAR TO OVER 20 KTS,  
WHICH WOULD HELP TO BALANCE AND SUSTAIN THE CONVECTIVE COLD POOL.  
THE LIMITING FACTORS ARE MINIMAL SBCAPE AND LOW EFFECTIVE DEEP LAYER  
SHEAR.  
 
THE 06Z NAM IS AGGRESSIVE IN TRACKING THE SFC-BASED PORTION OF THE  
MCS THROUGH THE SW CWA. THIS SEEMS OVERDONE BECAUSE OF THE  
AFOREMENTIONED LIMITING FACTORS. IT IS MORE LIKELY TO EITHER FALL  
APART OR MOVE IN DURING A WEAKENING PHASE. UTTECH  
 
MID MORNING ONWARD: ANY CONVECTION SHOULD BE WANING BY LATE  
MORNING WITH THE DIURNALLY DISSIPATING LOW LEVEL JET AND  
INCREASING SUPPRESSION FROM A PERIOD OF SHORTWAVE RIDGING SHOWN BY  
00Z MODELS IN THIS TIMEFRAME. THIS IS ALSO ALONG THE LINES OF WHAT  
IS INDICATED BY MOST HIGH RES CONVECTIVE MODEL. FOR NOW, WILL HAVE  
SLIGHT TO LOW CHANCE POPS GOING FROM LATE MORNING THROUGH EARLY  
AFTERNOON DUE TO LOW CONFIDENCE IN THE TIMING. EXTENSIVE CLOUD  
COVER LINGERING FROM THE UPSTREAM NOCTURNAL COMPLEX WILL LIKELY BE  
DECREASING BY THIS TIME, BUT THERE IS LOW CONFIDENCE IN HOW  
TRENDS WITH LOW TO MID LEVEL CLOUDS DUE TO THE LOW LEVEL BOUNDARY  
THAT WILL GRADUALLY WEAKEN AND LIFT NORTH DURING THE DAY. THUS,  
FOR NOW, WILL CONTINUE TO GO WITH MOSTLY CLOUDY CONDITIONS, BUT  
THERE COULD BE SUFFICIENT BREAKS IN THE CLOUD COVER BY EARLY  
AFTERNOON TO PERMIT VIEWING OF THE PARTIAL SOLAR ECLIPSE AT  
MIDDAY IN SOME LOCATIONS.  
 
TEMPERATURES WILL BE LARGELY DEPENDENT ON CLOUD TRENDS AND FOR NOW  
HAVE LOWER 80S NORTH TO UPPER 80S SOUTH, COUNTING ON AT LEAST  
PARTIAL CLEARING BEFORE LATE DAY CONVECTION DEVELOPS.  
 
LATE THIS AFTERNOON AND TONIGHT: THUNDERSTORMS WILL LIKELY DEVELOP  
ALONG BOUNDARIES IN THE AFTERNOON, ESPECIALLY TO THE WEST AND  
NORTHWEST OF THE FORECAST AREA. TONIGHT, WITH MORE WIDESPREAD  
THUNDERSTORMS ARE EXPECTED WITH THE FRONT DROPPING SOUTHEAST ALONG  
WITH STRONG UPPER LEVEL SUPPORT. SPC HAS A SLIGHT RISK FOR SEVERE  
STORMS OVER THE ENTIRE FORECAST AREA. BASED ON FRONTAL TIMING AND  
CONVECTIVE ALLOWING MODELS, THE THREAT FOR SEVERE STORMS  
(INCLUDING WIND, HAIL AND TORNADOES) WILL LIKELY BE WELL WEST AND  
NORTHWEST OF THE FORECAST AREA IN THE AFTERNOON, BUT POSSIBLY  
REACH INTO EASTERN IA BY EARLY EVENING. LATER IN THE EVENING,  
MORE ORGANIZED STORMS ARE LIKELY AS THE FRONT APPROACHES AND A LOW  
LEVEL INFLOW SETS UP. THIS WILL LEAD TO A HEAVY RAINFALL THREAT  
OVER EAST CENTRAL IA INTO NORTHWEST IL AND POSSIBLE DAMAGING WINDS  
EARLY ON. OVERNIGHT, AS THE LOW LEVEL JET BECOMES MORE WEST TO  
NORTHWEST, THE HEAVY RAINFALL THREAT WILL DIMINISH WITH THE  
COMPLEX OF STORMS ADVANCING SOUTHEAST ACROSS THE FORECAST AREA.  
INSTABILITY WILL ALSO BE WANING BY THIS TIME, DIMINISHING THE  
THREAT OF DAMAGING WINDS AFTER MIDNIGHT. WIDESPREAD RAINFALL  
AMOUNTS WELL OVER 1 INCH WILL BE POSSIBLE, BUT THE PROGRESSIVE  
NATURE OF THE SYSTEM WILL NOT BE CONDUCIVE TO STORM TRAINING OR  
EXCESSIVE RAINFALL.  
   
LONG TERM
 
(TUESDAY THROUGH SUNDAY)  
ISSUED AT 355 AM CDT MON AUG 21 2017  
 
TUESDAY, CURRENT TIMING OF THE COLD FRONT INDICATES POST FRONTAL  
SHOWERS AND ISOLATED THUNDERSTORMS WILL BE ENDING ACROSS THE  
SOUTHEAST EARLY IN THE DAY. CLEARING SKIES AND NORTH WINDS THEN  
FOLLOW WITH AN INCOMING DRIER AIRMASS. MODEL BLEND HIGHS FROM THE  
MID 70S NORTH TO LOWER 80S SOUTH MAY BE TOO WARM.  
 
HIGH PRESSURE THEN PROVIDES SEASONABLY COOL AND DRY WEATHER  
THROUGH THE REST OF THE WEEK INTO THE WEEKEND. A WARMING TREND  
THEN DEVELOPS ON A RETURN FLOW OVER THE WEEKEND, RETURNING HIGHS  
TO THE 80S OVER AT LEAST THE SOUTH, WITH LOW CHANCES FOR SHOWERS  
OVER MAINLY THE NORTH BY LATE SUNDAY.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)  
ISSUED AT 647 AM CDT MON AUG 21 2017  
 
RAIN AND EMBEDDED THUNDERSTORMS WILL AFFECT THE TERMINALS THIS  
MORNING. ALTHOUGH KDBQ MAY STAY DRY OR ONLY RECEIVE A BRIEF PERIOD  
OF LIGHT RAIN. VISIBILITIES AND CEILINGS WILL OCCASIONALLY FALL  
TO MVFR IN MODERATE OR BRIEF HEAVY RAIN. IFR IS NOT EXPECTED.  
THERE WILL BE A QUICK WIND SWITCH FROM THE WNW TO THE E OR SE AS A  
MESOHIGH MOVES THROUGH E IOWA/NE ILLINOIS THIS MORNING INTO THE  
EARLY AFTERNOON.  
 
ANOTHER ROUND OF STORMS IS EXPECTED TONIGHT, WHICH MAY BE  
ACCOMPANIED BY STRONG WIND GUSTS AND BRIEF MVFR/IFR CONDITIONS.  
HOWEVER, CONFIDENCE IS LOW AT THIS LEAD TIME. UTTECH  
 

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

 
 

 
 
SYNOPSIS...UTTECH  
SHORT TERM...UTTECH/SHEETS  
LONG TERM...SHEETS  
AVIATION...UTTECH  
 
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