Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000 FXUS63 KDVN 191134 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 634 AM CDT Mon Apr 19 2021 ...AVIATION UPDATE... ...CLIMATE UPDATE... .SYNOPSIS... Issued at 325 AM CDT Mon Apr 19 2021 At 2 AM, a cold front stretched from a surface low near KMQT southward into central Wisconsin then southwestward into northeast Iowa to KVTI to CTNU to KBIE in northeast Kansas. Ahead of the front, temperatures were in the mid to upper 40s and immediately behind the front temperatures were in upper 30s and lower 40s. Scattered rain showers stretched from northeast Iowa into central Nebraska. && .SHORT TERM...(Today and Tonight) ISSUED AT 325 AM CDT Mon Apr 19 2021 The main forecast concerns were chances of precipitation and the precipitation type. Models are in good overall agreement and all models have continued the southeastward trend in forcing and precipitation. The NAM is the most aggressive with precipitation and the Canadian the least. The cold front is forecast by guidance to be exiting into northern Missouri and central Illinois by 12 UTC. The better moisture and forcing will slowly sink southward through the day behind the front. This will result in clouds spreading southward through the day. The best chances of precipitation will be along the Highway 20 corridor by 15 UTC and then south of the Highway 34 corridor or a Fairfield to Galesburg line in the 21 to 00 UTC timeframe. By 00 UTC, precipitation will have come to an end north of the Highway 30 corridor. Thermal profiles keep precipitation as rain showers through the day. After 3 UTC, thermal profiles support a rain/snow mix slowly spreading southward with the exception of west central Illinois by 06 UTC. Rainfall amounts through the day will be up to two tenths of an inch between the Highway 30 and Highway 34 corridors with much less on either side of that line. After midnight, a secondary shortwave and jet streak will begin to overspread the region with lift in conjunction with increasing frontogenetical forcing overspreading the region. This will result in precipitation overspreading the entire area as a rain and snow mix. Precipitation is forecast to slowly change over to all snow from north to south by 12 UTC. The best forcing will be south of Fairfield to Sterling Rock Falls line through this period. The snow will be falling on warm ground and pavement so accumulations will be limited with only a few tenths of an inch of snow expected by 12 UTC Tuesday. High temperatures on Monday will range from the lower 40s northwest of a Iowa City to Dubuque line to the lower 50s in far southeast Iowa, northeast Missouri and west central Illinois. Low temperatures on Tuesday morning will be in the lower 30s with temperatures at or slightly above freezing south of a Cedar rapids to Clinton to Sterling Rock Falls line. .LONG TERM...(Tuesday through Sunday) ISSUED AT 325 AM CDT Mon Apr 19 2021 Key Points: *Light snow expected Monday night into Tuesday morning, steadiest south of I-80. Little if any accumulation is anticipated on pavement. *Freeze Watch in effect for Tuesday Night into Wednesday morning. Freezing temperatures are also forecast Wednesday night into Thursday morning. Tuesday A positively tilted shortwave trough will swing across the Upper Mississippi Valley with the 500mb vorticity max tracking from northern Kansas to southeast Iowa to northern Indiana. The attendant surface low will track well to our south across the Ohio Valley. Widespread precipitation, mainly in the form of snow, is expected north of the low along a zone of sloped frontogenesis. With the low tracking so far to the south, the strongest ascent and highest QPF is forecast to be across central Missouri into central Illinois, slightly south our southern and east-central counties. Model consensus has continued to trend southward with the snow band and now the best chance for 1" or more of accumulation is along/south of highway 34 (per WPC`s ensemble distribution). The NAM and HREF mean are further north and heavier, but have little weight in our latest forecast. There are several factors that will limit snow accumulation: warm ground, generally light snowfall rates, and ambient temps at or above freezing (32-35 F) for most of the snowfall duration. Thus, lowered SLRs to under 10:1 which limits accumulations to 1-2" south of highway 34. If any heavier banding of snow were to develop, amounts up to 3 inches would be possible across the southern tier of counties, especially west of the Mississippi River. Thinking accumulation will be restricted to the grass and elevated surfaces with pavement likely staying wet. Heading into the afternoon, the stratiform precip is expected to quickly shift to the east. Then there could be scattered rain and snow showers that develop as surface temps warm and the air mass aloft remains very cold. Tuesday Night and Wednesday Issued a Freeze Watch for Tuesday night into Wednesday morning. Coordination with local agricultural partners informed us that vegetation is susceptible along/south of highway 30 with more of a mixed susceptibility to the north. Decided to issue a Freeze Watch for the entire forecast area due to the rapid green-up that has taken place through the middle of the month. Forecast lows are in the upper 20s on average across the forecast area, which is close to record territory for some locations (see climate section for details). The current forecast is right near the 50th percentile of the NBM. If temps trend colder toward the 25th percentile, we`ll have widespread lows in the mid to upper 20s. A widespread freeze is again forecast for Wednesday night. Thursday through Sunday The NBM has slightly below normal temps for the end of the week and upcoming weekend, generally 50s to low 60s. There are occasional chances for light precipitation as disturbances move through in NW flow aloft. Uttech && .AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning) ISSUED AT 626 AM CDT Mon Apr 19 2021 MVFR ceilings will impact the terminals this morning as a low cloud deck moves in behind a cold front. Patchy light rain is possible this morning. Then a steadier band of rain is forecast to set up over MLI and BRL this afternoon, which could lead to brief IFR ceilings. A few snowflakes could even mix in at BRL this evening before the precip ends. VFR is expected tonight ahead of the next system that will spread low ceilings and a band of snow into parts of eastern Iowa and northwest Illinois Tuesday morning. && .CLIMATE... ISSUED AT 620 AM CDT Mon Apr 19 2021 Record Lows for April 20... Moline.........24 in 2018 Cedar Rapids...25 in 2018 Dubuque........26 in 1956 Burlington.....28 in 1956 Record Lows for April 21... Moline.........27 in 1953 Cedar Rapids...23 in 1934 Dubuque........26 in 1982 Burlington.....27 in 1904 Week 2...April 26 - May 2 Continued below normal temperatures with near normal rainfall. This due to the Arctic Oscillation/North Atlantic Oscillation remaining negative anomaly which favors a northwest flow. Haase && .DVN WATCHES/WARNINGS/ADVISORIES... IA...Freeze Watch from Tuesday evening through Wednesday morning for Benton-Buchanan-Cedar-Clinton-Delaware-Des Moines-Dubuque- Henry IA-Iowa-Jackson-Jefferson-Johnson-Jones-Keokuk-Lee- Linn-Louisa-Muscatine-Scott-Van Buren-Washington. IL...Freeze Watch from Tuesday evening through Wednesday morning for Bureau-Carroll-Hancock-Henderson-Henry IL-Jo Daviess- McDonough-Mercer-Putnam-Rock Island-Stephenson-Warren- Whiteside. MO...Freeze Watch from Tuesday evening through Wednesday morning for Clark-Scotland. && $$ SYNOPSIS...Cousins SHORT TERM...Cousins LONG TERM...Uttech AVIATION...Uttech CLIMATE...Uttech/Haase

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