616  
FXUS63 KDVN 262104  
AFDDVN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE QUAD CITIES IA IL  
404 PM CDT WED APR 26 2017  
   
..HYDROLOGY UPDATE
 
 
   
SYNOPSIS
 
 
ISSUED AT 245 PM CDT WED APR 26 2017  
 
SURFACE ANALYSIS AT 2 PM CDT SHOWED AN AREA OF LOW PRESSURE NEAR  
KISW IN WISCONSIN ,WITH A COLD FRONT EXTENDING SOUTH INTO  
ILLINOIS JUST EAST OF THE MISSISSIPPI TO NEAR KUIN. TEMPERATURES  
AHEAD OF THE FRONT, WERE IN THE 60S WITH DEWPOINTS IN THE 50S.  
BEHIND THE FRONT, TEMPERATURES STRUGGLED TO RISE MUCH WITH  
READINGS WEST OF A MONTICELLO TO MOUNT PLEASANT LINE, ONLY IN THE  
UPPER 40S AND LOWER 50S. NEXT WAVE OF ENERGY TO IMPACT THE AREA  
THIS EVENING WAS TRACKING OVER OKLAHOMA.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH THURSDAY)  
ISSUED AT 200 PM CDT WED APR 26 2017  
 
FORECAST FOCUS IN THE SHORT TERM IS ON PRECIPITATION CHANCES THIS  
EVENING AND OVERNIGHT.  
 
SURFACE LOW CURRENTLY IN NORTHWEST ARKANSAS WILL LIFT NORTHEAST  
ALONG THE FRONTAL BOUNDARY INTO EAST CENTRAL ILLINOIS BY 03Z THIS  
EVENING. LATEST 12Z MODEL SOLUTIONS SHOW STRONG LOW LEVEL  
CONVERGENCE AND UPPER AIR SUPPORT WITH THIS WAVE TO BRING  
SCATTERED SHOWERS TO THE AREA LATE THIS EVENING AND OVERNIGHT.  
AS FAR AS THUNDER POTENTIAL, 700-500 MB THETA-E LAPSE RATES OFF  
THE 18Z RAP, GO NEGATIVE JUST TO THE SOUTHEAST OF THE CWA AFTER  
00Z. CAN'T RULE OUT AN ISOLATED THUNDERSTORM OVER THE FAR SE  
PORTIONS OF THE CWA, BUT MOST OF RAIN SHOULD BE MORE STRATIFORM  
TONIGHT. THERE IS ALSO A POSSIBILITY THAT AREAS NORTH AND WEST OF  
A OSKALOOSA TO MANCHESTER LINE, MAY SEE LITTLE TO NO RAIN  
OVERNIGHT TONIGHT.  
 
THIS SYSTEM WILL ALSO HAVE PLENTY OF MOISTURE TO WORK WITH AS IT  
LIFTS INTO ILLINOIS. 12Z OBSERVED DVN SOUNDING SHOWED 1.31" PW  
THIS MORNING, WHICH IS ALMOST 200% OF NORMAL. THIS FACT, COMBINED  
WITH MODEL PROGS OF MOISTURE TRANSPORT SUGGEST THAT RAINFALL MAY  
BE HEAVY AT TIMES OVERNIGHT, ESPECIALLY EAST OF THE MISSISSIPPI.  
RAIN AMOUNTS EAST OF THE MISSISSIPPI, ARE EXPECTED TO BE BETWEEN A  
QUARTER AND THREE QUARTERS OF AN INCH BY 12Z THURSDAY. PRECIPITATION  
TO END ACROSS THE ENTIRE AREA BY 15Z, WITH THE REST OF THE DAY  
REMAINING DRY.  
 
COOLER AIR FILTERS INTO THE AREA ON THURSDAY, AS 850 MB  
TEMPERATURES DROP BELOW 0C. THIS WILL KEEP AFTERNOON HIGHS IN THE  
LOWER 50S NORTH OF HIGHWAY 30, TO THE UPPER 50S SOUTH.  
   
LONG TERM
 
(THURSDAY NIGHT THROUGH WEDNESDAY)  
ISSUED AT 200 PM CDT WED APR 26 2017  
 
THURSDAY NIGHT AND FRIDAY:  
 
LIGHT WINDS AND INITIALLY CLEAR SKIES LATE THURSDAY NIGHT COULD  
RESULT IN PATCHY FROST BEFORE MID-LEVEL CLOUDS INCREASE INTO  
FRIDAY MORNING IN THE COUNTIES ALONG HIGHWAY 20. FORECAST LOWS  
ARE IN THE MID 30S IN THIS AREA. FOR FRIDAY, MODELS DEVELOP A  
CLOSED 850MB CIRCULATION OVER EASTERN NEBRASKA AND SW IOWA WHICH  
WILL FORCE AN ELEVATED WARM FRONT AND ZONE OF THETA-E ADVECTION TO  
THE NORTH AND EAST. SCATTERED SHOWERS ARE EXPECTED TO MOVE FROM  
SOUTH TO NORTH THROUGH THE CWA FROM THE MORNING THROUGH THE  
EVENING. FORECAST PWATS UNDER 1" AND MODEST FORCING FOR ASCENT  
ARE SUPPORTIVE OF MAINLY LIGHT RAIN. MAX TEMPS WILL BE COOL IN THE  
50S, ALTHOUGH A LITTLE WARMER OVER THE SE THIRD OF THE CWA IN THE  
LOWER TO MID 60S.  
 
SATURDAY AND SUNDAY:  
 
MODELS CONTINUE TO ADVERTISE A RAPIDLY DEEPENING SFC LOW TRACKING FROM  
KANSAS INTO IOWA AND WISCONSIN WITH A CENTRAL PRESSURE POSSIBLY  
BELOW 990MB. A 125 KT JET STREAK IS FORECAST TO ROUND THE BASE OF  
A DEEP TROUGH OVER THE SOUTHERN PLAINS BEFORE APPROACHING THE  
UPPER MISSISSIPPI VALLEY. THE END RESULT IS STRONG AND EXPANSIVE  
UPPER DIVERGENCE BENEATH A COUPLED JET STRUCTURE. FURTHERMORE, THIS  
SYSTEM IS FORECAST TO INTENSIFY A LOW- LEVEL BAROCLINIC ZONE AS IT  
TRACKS INTO THE MIDWEST. THUS, EXPECT A DYNAMIC SYSTEM WITH  
SEVERE WEATHER IN THE WARM SECTOR AND SNOW POSSIBLE TO THE NW OF  
THE LOW TRACK. FOR E IOWA/NW ILLINOIS, WIDESPREAD MODERATE RAIN IS  
LIKELY FROM SATURDAY MIDDAY THROUGH SUNDAY. THERE IS ALSO THE  
POTENTIAL FOR THUNDERSTORMS ON SUNDAY. HOWEVER, IT IS TOO EARLY TO  
ASSESS THE RISK FOR SEVERE STORMS.  
 
AT THIS TIME, THE SIGNAL FOR HEAVY, POSSIBLY FLOODING RAIN, IS TO  
THE SE OF THE LOCAL AREA (ACROSS CENTRAL MISSOURI INTO CENTRAL  
ILLINOIS) WHERE DETERMINISTIC MODELS AND THE NAEFS ARE PLACING  
THE BEST DEEP LAYER MOISTURE TRANSPORT. INTEGRATED WATER TRANSPORT  
VALUES FROM THE NAEFS ARE ALREADY OVER 2 STANDARD DEVIATIONS  
ABOVE THE AVG FOR LATE APRIL IN THE AFOREMENTIONED AREA. WE'LL  
HAVE TO SEE IF THE MODELS TREND NW WITH THIS FEATURE WHICH WOULD  
PLACE HEAVIER RAIN INTO AT LEAST THE SE PORTION OF THE CWA.  
 
MONDAY THROUGH WEDNESDAY:  
 
LINGERING SHOWERS AND BREEZY BEHIND THE STRONG LOW ON MONDAY.  
FINALLY DRYING OUT AND QUIET FOR TUESDAY THROUGH MOST OF  
WEDNESDAY. UTTECH  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)  
ISSUED AT 200 PM CDT WED APR 26 2017  
 
MVFR CONDITIONS WILL CONTINUE THROUGH MUCH OF THE TAF CYCLE. AN  
UPPER LEVEL DISTURBANCE WILL BRING A SURFACE LOW UP ACROSS  
ILLINOIS THIS EVENING AND OVERNIGHT. PRECIPITATION WILL LIFT  
ACROSS THE AREA CAUSING IFR CONDITIONS AT SEVERAL OF THE TERMINALS  
FOR A FEW HOURS. THERE IS VERY LOW CONFIDENCE IN ANY MENTION OF  
THUNDER FOR TONIGHT AND HAVE OPTED TO LEAVE OUT OF THE TAF FOR  
NOW. PRECIPITATION WILL END AT ALL SITES BY 15Z WITH CONDITIONS  
IMPROVING TO MVFR.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 356 PM CDT WED APR 26 2017  
 
WIDESPREAD RAINFALL EXPECTED SATURDAY THROUGH SUNDAY LEADING TO  
RISES ON AREA RIVERS INTO NEXT WEEK.  
 
A STRONG AREA OF LOW PRESSURE IS FORECAST TO TRACK THROUGH THE  
MIDWEST. HEAVY RAIN ON THE ORDER OF 1-3 INCHES IS POSSIBLE OVER  
PORTIONS OF IOWA, MISSOURI, AND ILLINOIS. HOWEVER, SINCE THIS  
SYSTEM IS STILL SEVERAL DAYS AWAY, CONFIDENCE ON THE EXACT  
PLACEMENT OF THE HEAVIEST PRECIPITATION IS LOW. AT THIS TIME, THE  
FAVORED LOCATION FOR AMOUNTS CLOSER TO 3 INCHES IS TO THE  
SOUTHEAST OF E IOWA/NW ILLINOIS - THROUGH CENTRAL MISSOURI AND  
CENTRAL ILLINOIS.  
 
PLEASE CHECK BACK FOR FORECAST UPDATES THROUGH THIS WEEK AS WE  
TRY TO ZERO IN ON THE REGION OF HEAVIEST RAINFALL.  
 

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

 
 

 
 
SYNOPSIS...GROSS  
SHORT TERM...GROSS  
LONG TERM...UTTECH  
AVIATION...GROSS  
HYDROLOGY...UTTECH  
 
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