867  
FXUS63 KDVN 201734  
AFDDVN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE QUAD CITIES IA IL  
1234 PM CDT WED JUN 20 2018  
   
..AVIATION UPDATE
 
 
   
UPDATE
 
 
ISSUED AT 1032 AM CDT WED JUN 20 2018  
 
NEAR FULL SUN ACROSS THE SOUTHWEST HALF OF THE AREA IS ALLOWING  
TEMPERATURES TO CLIMB. AT THE SAME TIME, RADAR SHOWS THE PRECIP  
FROM EARLIER THIS MORNING DECAYING RAPIDLY.  
 
THUS THE FORECAST HAS BEEN UPDATED TO RAISE TEMPERATURES AND LOWER  
VERY SHORT TERM POPS. THE INCREASED DIURNAL HEATING SHOULD ALLOW A  
NEW ROUND OF SHOWERS/STORMS TO DEVELOP THIS AFTERNOON. THE  
APPROACHING UPPER LEVEL LOW WILL INCREASE LIFT FURTHER AND ALLOW  
LOCALLY HEAVY RAINFALL TO OCCUR.  
 
UPDATED FORECAST TO BE OUT SHORTLY.  
 

 
   
SYNOPSIS
 
 
ISSUED AT 330 AM CDT WED JUN 20 2018  
 
THE LATEST SFC ANALYSIS WAS INDICATING A WEAK LOW PRESSURE CENTER  
JUST WEST OF THE DSM AREA, WITH A QUASI-STATIONARY BOUNDARY  
UNDULATING EAST-SOUTHEASTWARD ALONG AND SOUTH OF THE I-80 CORRIDOR  
ACRS THE LOCAL AREA, AND INTO NORTHERN INDIANA. A LARGE MCS/MCC WAS  
ROLLING EAST-SOUTHEASTWARD ACRS THE CENTRAL INTO SOUTHERN PLAINS,  
WITH SECONDARY CONVERGENT ZONES PRODUCING WEST-EAST ORIENTED NARROW  
BANDS OF CONVECTION CURRENTLY ACRS WESTERN IA. ALOFT, THE LATEST  
UPPER AIR ANALYSIS AND WATER VAPOR IMAGERY WERE INDICATING CLOSED  
UPPER WAVE/LOW ACRS CENTRAL NE, WITH A LEE SIDE BUMP-UP RIDGE AXIS  
RIGHT ACRS THE MS RVR VALLEY, PROBABLY HELPING SUPPRESS OVERNIGHT  
CONVECTION LOCALLY. THIS AS WELL AS A RATHER WEAK WEST-SOUTHWEST LOW  
LEVEL JET. BEYOND TODAY, THE UPSTREAM UPPER LOW IS STILL ON TRACK TO  
BRING WAVES OF RAINY WEATHER TO PORTIONS OF THE MIDWEST AS IT SLOW-  
ROLLS EASTWARD THROUGH THE END OF THE WEEK.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 330 AM CDT WED JUN 20 2018  
 
LOW CLOUDS AND PATCHY FOG WILL CONTINUE INTO THE EARLY PORTIONS  
OF THE FIRST PERIOD, WITH SUCH A SATURATED BOUNDARY LAYER WITH  
LIGHT LLVL FLOW. AS A MORE SOUTHWEST ORIENTED LOW TO MID LEVEL  
FLOW STARTS TO EDGE EAST ACRS IA AND TOWARD THE LOCAL FCST AREA,  
SEE ISOLATED TO SCTRD SHOWERS AND THUNDERSTORMS DEVELOPING MORE  
THIS MORNING GENERALLY IN THE VICINITY OF THE FRONTAL BOUNDARY,  
GENERALLY WEST OF THE IOWA CITY AREA, SOUTHEASTWARD TO MONMOUTH IL  
AND MACOMB. THIS ACTIVITY WILL LOOK TO MOVE NORTH BUT DECREASE  
DIURNALLY THROUGH THE MID TO LATE MORNING.  
 
THEN AS THE UPPER LOW SYSTEM SLOW-ROLLS EAST-SOUTHEAST ACRS THE MO  
RVR VALLEY THROUGH THIS EVENING, CYCLONIC DIFFLUENT SOUTHWESTERLY  
FLOW WILL SPRAWL EASTWARD ACRS THE MID TO UPPER MS RVR VALLEY THIS  
AFTERNOON AND EVENING, AS WELL CONVERGENT LIFT. THEN DEPENDING ON  
EXTENT OF HEATING AND INSTABILITY BUILD UP THAT CAN OCCUR TODAY, THIS  
PROCESS WILL LOOK TO PRODUCE A NNW-TO-SSE ORIENTED BAND OF  
CONVECTION THAT WILL LOOK TO SPIRAL EASTWARD ACRS THE CWA BY LATE  
AFTERNOON AND INTO THE EVENING. WITH WARM FRONT CONTINUING TO WAVER  
ACRS THE LOCAL AREA FOR A TYPE OF TRIPLE-POINT, FCST SOUNDINGS SHOW  
A NICE SWATH OF LOW TO MID LEVEL DIRECTIONAL SHEAR, ALTHOUGH  
VELOCITIES MARGINAL TO MODERATE AT BEST. IF ENOUGH BUOYANCY OF AT  
LEAST 1000-2000 J/KG CAN BUILD UP(A BIG "IF", WITH EXPECTED MCS  
DEBRIS FROM OUT WEST SPILLING ACRS THE AREA FOR MUCH OF THE MORNING  
INTO MIDDAY), THE SHEAR PROFILE WOULD SUPPORT SOME STRONG TO SEVERE  
STORMS WITH ROTATING UPDRAFTS ESPECIALLY ALONG THE FRONT OR AND  
OTHER DIFFERENTIAL BOUNDARIES THAT CAN SET UP. THIS ALONG WITH  
SOUNDING INDICATED LOW LCL'S OF UNDER 2000 FT AGL, AGREE WITH SPC  
THAT THERE MAY BE SOME POTENTIAL FOR SUPERCELLS AND AT LEAST A WEAK  
TORNADO OR TWO DEVELOPING JUST TO THE LEE OF THE APPROACHING LLVL  
LOW. OTHER MODES OF SEVERE WOULD ALSO BE POSSIBLE ESPECIALLY  
DOWNBURST/DAMAGING WINDS.  
 
TIMING WILL BE KEY AS WELL, AND IT MAY BE MORE OPTIMUM FOR SUPERCELL  
SEVERE JUST TO THE WEST OF THE CWA, WITH BOWING SEGMENTS EVOLVING  
FROM THAT ACTIVITY INTO OUR AREA WITH MORE OF A WIND THREAT, BUT ALSO  
A MESO-VORTICE TORNADO POSSIBLE ON THE WARM FRONT TRIPLE POINT.  
ALONG WITH THE SEVERE WX, ANOTHER DAY OF HIGH PWAT FEED OF 1.8-2+  
INCHES TO FUEL TORRENTIAL RAINFALL AND AT HIGH RATES. THE STORMS  
SHOULD BE PROGRESSIVE HELPING LIMIT RESIDENCE TIME, BUT AREAS THAT  
GET HIT REPEATEDLY MAY STILL HAVE A LOCALIZED FLASH FLOOD THREAT  
INTO TONIGHT. SOME AREAS COULD GET 1-2+ INCHES EASILY BY THU  
MORNING. HIGHS TODAY A BIG CHALLENGE AGAIN WIHT LOCALIZED BUTS  
POTENTIAL, WITH CLOUD COVER AND A MOIST BL FIGHTING CLEARING  
BREAKS THAT WOULD ALLOW HEATING...AND KEEPING IN MIND CONVECTIVE  
DEBRIS FROM THE WEST. WILL GO WITH A RANGE OF MID 70S IN THE  
NORTH, TO THE MID 80S IN THE SOUTH.  
 
THE BAND OF CONVECTION WILL PIVOT ALONG AND NORTH OF I-80 LATER  
TONIGHT, WITH SOME SIGNS OF DECREASING IN INTENSITY AS IT DOES. BUT  
WILL HAVE TO WATCH FOR MORE SUBSTANTIAL RAINFALL BANDS TRYING TO MAKE  
IT ACRS THE RECENT HARD HIT BY HEAVY RAINFALL NW IL COUNTIES FOR  
RENEWED WATER TROUBLE. TODAY AND TONIGHTS RAIN AND RUN-OFF TO  
AGGRAVATE ONGOING RIVER FLOODING, AND POSSIBLY SET THE STAGE FOR  
OTHERS TO RISE INTO THE LATE WEEK. LOW TEMPS TONIGHT A SECONDARY  
CONCERN, BUT WILL BE DOWN IN THE 60S...ALONG WITH MORE PATCHY FOG  
POSSIBLE WHERE RAIN WANES AND CONVERGENT FLOW CONDENSES ON A  
BOUNDARY. ..12..  
   
LONG TERM
 
(THURSDAY THROUGH NEXT TUESDAY)  
ISSUED AT 330 AM CDT WED JUN 20 2018  
 
HIGHLIGHTS OF THE LONG TERM PERIOD ARE CONTINUED WET WEATHER AND  
MOSTLY BELOW NORMAL TEMPERATURES.  
 
THURSDAY AND FRIDAY: A SLOW MOVING H5 LOW WILL CONTINUE TO ROTATE  
THROUGH THE REGION WITH WIDESPREAD RAIN AND SOME SCATTERED STORMS.  
CONFIDENCE REMAINS HIGH IN WIDESPREAD SIGNIFICANT RAIN THIS PERIOD,  
WHILE SPECIFIC LOCATIONS AND BASINS IMPACTED THE MOST IS LESS  
CERTAIN. CANNOT RULE OUT SOME ISOLATED FLASH FLOODING WITH  
CUMULATIVE EFFECTS OF SEVERAL DAYS OF RAIN ON ALREADY SATURATED  
GROUND, BUT THE MAIN ISSUE WILL BE THE IMPACT ON RIVERS, WHICH IS  
DISCUSSED BELOW. RAIN WILL TAPER OFF FRIDAY NIGHT AS THE UPPER LOW  
EXITS TO THE EAST. THE SEVERE WEATHER RISK IS LOW. EXPECT HIGHS IN  
THE 70S, BELOW THE NORMAL HIGHS OF 80 TO 85.  
 
SATURDAY AND SUNDAY: A RATHER WEAK SHORTWAVE TROUGH MAY SUPPORT SOME  
SHOWERS AND STORMS LATE SATURDAY INTO SUNDAY MORNING, ESPECIALLY  
ACROSS THE SOUTH. AFTERNOON HIGHS WILL WARM SLIGHTLY INTO THE MID  
70S TO LOW 80S.  
 
MONDAY AND TUESDAY: ANOTHER POTENT H5 LOW WILL LIKELY IMPACT THE  
FORECAST AREA THIS PERIOD. SPECIFICS ARE STILL UNCERTAIN, BUT THE  
RISK OF HEAVY RAIN AND SEVERE WEATHER LOOK GREATER THAN THE WEEKEND  
SYSTEM. TEMPERATURES WILL WARM INTO THE 80S TO NEAR 90 DEGREES BY  
TUESDAY.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)  
ISSUED AT 1230 PM CDT WED JUN 20 2018  
 
MVFR/IFR CONDITIONS WILL SLOWLY IMPROVE TO VFR THROUGH 00Z/21  
ACROSS EASTERN IOWA AND NORTHERN ILLINOIS. AN APPROACHING UPPER  
LOW WILL HELP GENERATE SHRA/TSRA THROUGH AT LEAST 18Z/21. GIVEN  
THE HIGH MOISTURE LEVELS IN THE ATMOSPHERE, ANY TSRA/SHRA THAT  
AFFECTS A TAF SITE WILL HAVE THE POTENTIAL TO CREATE BRIEF MVFR  
IF NOT IFR CONDITIONS.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 330 AM CDT WED JUN 20 2018  
 
PERIODS OF HEAVY RAIN THROUGH FRIDAY WILL LIKELY HAVE A SIGNIFICANT  
IMPACT ON THE RIVER FLOODING SITUATION IN THE AREA. WIDESPREAD 1 TO  
3 INCH AMOUNTS STILL LOOK REASONABLE, ALTHOUGH CONFIDENCE IN FAVORED  
AREAS FOR HEAVIEST RAIN IS STILL LOW. NONETHELESS, WE CAN EXPECT  
DELAYED DROPS, RENEWED RISES, AND POTENTIALLY HIGHER CRESTS AT  
LOCATIONS IN OR NEAR FLOOD, AS WELL AS ADDITIONAL FLOODING POSSIBLE  
AT NEW LOCATIONS.  
 
WITH THE EXPECTED RAINFALL, FLOODING IS LOOKING MORE LIKELY ON THE  
ROCK BASIN THIS WEEK. A WARNING CONTINUE FOR JOSLIN WHILE MOLINE IS  
UNDER A FLOOD WATCH. DEWITT IS CURRENTLY FORECAST TO REMAIN IN  
MODERATE FLOOD FOR THE NEXT COUPLE OF DAYS BEFORE FALLING, ALTHOUGH  
THIS COULD CHANGE DEPENDING ON HOW THE WEATHER PLAYS OUT THROUGH  
FRIDAY. IN BANK RISES ARE ALSO FORECAST ALONG THE MAINSTEM  
MISSISSIPPI WITH INCREASED INPUT FROM THE TRIBS.  
 

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

 
 

 
 
UPDATE...08  
SYNOPSIS...12  
SHORT TERM...12  
LONG TERM...RP KINNEY  
AVIATION...08  
HYDROLOGY...RP KINNEY  
 
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