553
FXUS63 KDVN 120812
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
312 AM CDT SAT SEP 12 2026
KEY MESSAGES
- A COLD FRONT WILL BRING LOW CHANCES (10-20%) FOR SHOWERS AND
STORMS EARLY THIS MORNING WITH ISOLATED STORMS POSSIBLE
(20-30%) THIS AFTERNOON ALONG AND SOUTH OF HIGHWAY 34.
- AN ACTIVE PATTERN IS IN STORE NEXT WEEK WITH MULTIPLE ROUNDS
OF SHOWERS AND STORMS LIKELY THROUGH FRIDAY. CURRENTLY, THE
GREATEST SEVERE POTENTIAL IS MONDAY AFTERNOON AND EVENING
WHERE THERE IS A MARGINAL RISK, LEVEL 1 OUT OF 5, FOR EASTERN
IA AND NORTHWEST IL.
SHORT TERM /THROUGH SUNDAY NIGHT/
ISSUED AT 1222 AM CDT SAT SEP 12 2026
STORM CHANCES RETURN TODAY AS A COLD FRONT MOVES INTO THE AREA
FROM THE NORTHWEST. DURING THE MORNING HOURS, ISOLATED SHOWERS
AND STORMS (10-20% COVERAGE) WILL FORM ALONG THE FRONT ACROSS
EASTERN IOWA BEFORE FIZZLING OUT ONCE THEY REACH THE
MISSISSIPPI RIVER AS LOW-LEVEL WAA WEAKENS DURING THE AFTERNOON
AND THE WIND SHIFTS FROM SOUTHWESTERLY TO NORTHWESTERLY. THERE
IS SOME DISAGREEMENT AMONG CAMS ON A POSSIBLE SECOND ROUND OF
CONVECTION FORMING OVER SOUTHWESTERN IOWA AND MOVING EASTWARD
WITH A SUBTLE SHORTWAVE IN THE ZONAL FLOW, BUT CURRENT HREF
GUIDANCE ONLY HAS A 10-20% CHANCE OF THIS OCCURRING. IF ANY
STORMS DO REDEVELOP, FRONTAL PLACEMENT WILL ALSO BE KEY IN
DETERMINING THE SEVERE POTENTIAL ALONG AND SOUTH OF HIGHWAY 34
AS THERE IS GOING TO BE A SHORT WINDOW WHERE THE 250-500 J/KG OF
SBCAPE AND 25-30 KNOT 0-6-KM BULK SHEAR OVERLAP.
HEADING INTO TONIGHT, THE COLD FRONT PUSHES INTO NORTHERN MISSOURI
AND CENTRAL ILLINOIS BEFORE STALLING OUT, AND A WEAK HIGH PRESSURE
POSITIONS ITSELF OVER THE DAKOTAS AND MINNESOTA. WINDS WILL SHIFT TO
NORTHEASTERLY AS LOWS DROP INTO MID-50S TO LOW 60S. BY SUNDAY,
A LONGWAVE RIDGE BUILDS ACROSS THE NORTHERN ROCKIES AS ANOTHER
SHORTWAVE TROUGH SWINGS INTO THE GREAT LAKES REGION. A FRONT
RANGE LOW IS EXPECTED TO DEVELOP IN COLORADO IN RESPONSE,
ENABLING A MID-LEVEL F-GEN BAND TO DEVELOP OVER IOWA ON THE
NORTH SIDE OF THE STATIONARY FRONT AS A STRATIFORM RAIN SHIELD
FORMS WITH ISOLATED LIGHTNING. THERE WILL BE A BREAK IN THE
RAIN HEADING INTO SUNDAY NIGHT BEFORE STORMS REDEVELOP MONDAY
MORNING AS THE UPPER LEVEL FLOW BECOMES SOUTHWESTERLY,
CONVERTING THE STATIONARY FRONT INTO A WARM FRONT.
LONG TERM /MONDAY THROUGH FRIDAY/
ISSUED AT 1222 AM CDT SAT SEP 12 2026
MONDAY-TUESDAY...THE LONGWAVE RIDGE OVER THE NORTHERN ROCKIES SHIFTS
EASTWARD OVER THE MID-TO-UPPER MISSISSIPPI VALLEY AS A CLOSED
HEIGHTS CENTER REPLACES IT OVER THE NORTHERN ROCKIES. DIFFLUENT
FLOW ALOFT AND STRONG LOW-LEVEL WAA SHOULD SUPPORT STORMS
(50-80% COVERAGE) ALONG THE WARM FRONT IN EASTERN IOWA, BUT
LIMITED MOISTURE, ESPECIALLY NEAR THE SURFACE, WILL PUT A
HAMPER ON THE COVERAGE (20-40%) ACROSS WEST-CENTRAL AND
NORTHWEST ILLINOIS. REGARDLESS, THE SOUTHERLY RETURN FLOW BEHIND
THE WARM FRONT IS FORECASTED TO ALLOW DEW POINTS TO CLIMB BACK
INTO THE UPPER 60S AND LOW 70S ALONG THE COLD FRONT DIVING
SOUTHEASTWARD AS THE TROUGH OVER THE NORTHERN ROCKIES LIFTS
INTO SOUTH-CENTRAL CANADA. AFTER ANOTHER DRY PERIOD MONDAY
AFTERNOON, STORMS WILL ONCE AGAIN REDEVELOP MONDAY EVENING
ALONG THE APPROACHING COLD FRONT WHERE A 40-KNOT LLJ IS
EXPECTED TO ENHANCE THE LOW-LEVEL SHEAR. CURRENT LREF GUIDANCE
HAS THE SFC-TO-500 MB WIND SHEAR VECTOR ORIENTED AT A 45-DEGREE
ANGLE AND CLOSE TO 35 KNOTS WHICH WOULD SUGGEST A MIXED
CONVECTIVE MODE. HOWEVER, BY THE TIME ANY CONVECTION REACHES OUR
CWA, IT WILL LIKELY BE IN THE FORM OF LINEAR CLUSTERS,
PROMOTING A MORE DAMAGING WIND THREAT. THIS IS WHY THE SPC
HAS A MARGINAL RISK, LEVEL 1 OUT OF 5, FOR SEVERE STORMS MONDAY
NIGHT IN OUR NORTHWESTERN COUNTIES.
BY TUESDAY, THE STORMS ARE EXPECTED TO DECREASE IN INTENSITY
ALONG THE FRONT AS UPPER-LEVEL DYNAMICAL SUPPORT IS LOST. A
WEAK HIGH PRESSURE IS FORECASTED TO SLIDE INTO MINNESOTA
TUESDAY NIGHT, REINFORCING THE NORTHEASTERLY FLOW OVER THE CWA
AND PINNING THE STATIONARY FRONT IN OUR SOUTH. THIS STATIONARY
FRONT WILL ACT AS THE FOCAL POINT FOR SHOWERS AND STORMS THROUGH
THE MIDDLE OF NEXT WEEK.
WEDNESDAY-FRIDAY...THE ENTIRE AREA WILL BE SANDWICHED BETWEEN A
RIDGE OVER THE SOUTHEAST AND A POSITIVELY TILTED TROUGH OVER HUDSON
BAY THAT EXTENDS BACK TOWARDS THE PACIFIC NORTHWEST. THIS
PATTERN SHOULD SUPPORT DIFFLUENT FLOW ALOFT OVER THE RESIDUAL
STATIONARY FRONT AS ROUNDS OF STRATIFORM RAIN AND STORMS DEVELOP
ALONG IT ON WEDNESDAY AND THURSDAY. AS THE SOUTHEAST RIDGE
RETROGRADES WESTWARD, THE FLOW IS FORECASTED TO RETURN TO A MORE
STABLE ZONAL FLOW AS THE BOUNDARY BEGINS TO WASH OUT FRIDAY
WITHOUT ANY MAJOR AIR MASS CHANGES. BY THE END OF THE NEXT WEEK
THOUGH, THERE IS A GOOD CHANCE (50-80%) THAT AREAS ACROSS
EASTERN IOWA AND NORTHWEST ILLINOIS WILL SEE OVER 2 INCHES OF
RAINFALL WITH SWATHS OF 4+ INCHES POSSIBLE (20-30%).
AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
ISSUED AT 1209 AM CDT SAT SEP 12 2026
THE MAIN CONCERN OVER THE NEXT 24 HOURS IS A COLD FRONTAL
PASSAGE WITH A WIND SHIFT OUT OF THE SOUTH TO NORTHWEST. WITH
THIS FRONT, EXPECT SCT LOW AND UPPER-LEVEL CLOUDS, BUT GENERAL
VFR CONDITIONS ARE EXPECTED OUTSIDE A BRIEF PERIOD OF BKN MVFR
CEILINGS ALONG THE FRONT. THESE CLOUD WILL ALSO HELP SUPPRESS
WIDESPREAD FOG, BUT THERE IS A SMALL CHANCE (20-30%) THAT MVFR
VISIBILITIES COULD DEVELOP AT ANY SITE AROUND OR AFTER DAYBREAK.
IN TERMS OF PRECIPITATION CHANCES, POPS ARE 20% OR BELOW FOR
ALL TAF SITES WHICH LED TO THE EXCLUSION OF ANY PROB30S AT THIS
ISSUANCE. IF ANY SITE WOULD RECEIVE PRECIPITATION, IT WOULD BE
BRIEFLY THIS MORNING AT CID AND THIS AFTERNOON AT BRL.
DVN WATCHES/WARNINGS/ADVISORIES
IA...NONE.
IL...NONE.
MO...NONE.
SHORT TERM...DELAUNE
LONG TERM...DELAUNE
AVIATION...DELAUNE
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