Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000 FXUS63 KDVN 050432 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 1032 PM CST Thu Mar 4 2021 ...AVIATION UPDATE... .SYNOPSIS... Issued at 305 PM CST Thu Mar 4 2021 Sunshine prevailed over the region this afternoon with 2 pm temperatures ranging from the mid 30s in northwest Illinois to the mid 50s in far northeast Missouri. Clear skies were courtesy of high pressure centered over the western Great Lakes and subsidence in the northwest flow aloft. Low clouds that swept through the area this morning along a backdoor cold front from Lake Michigan have since dissipated. Low level east to northeast winds were advecting a dry airmass into the area with dewpoints only in the upper teens to mid 20s over southern WI and northern IL. && .SHORT TERM...(This Evening through Friday) ISSUED AT 305 PM CST Thu Mar 4 2021 Dry and seasonably cool weather will continue as high pressure remains anchored over the western Great Lakes region through Friday. Tonight, the light east to northeast low level flow will continue to advect a cool, dry airmass into the area. Models have the surface high center shifting southwest into eastern Iowa overnight into midday Friday, allowing winds to become light and variable. This weaker flow will be less favorable for any lake additional lake enhanced stratus to advance into the region. Also, like last night, low level moisture will likely remain shallow enough to deposit as frost versus the fog that is indicated by the WRF/NAM. Low temperatures will be cooler than last night, especially over the remaining snowfields of northwest Illinois and eastern Iowa, where lows in the upper teens look likely. Elsewhere, lows are advertised in the lower to mid 20s. Friday looks mostly sunny with perhaps some patchy mid level clouds. Light winds and shallow mixing, in the same airmass as today, will lead to somewhat similar results with highs in the 40s over the snowfields in the north, and lower 50s in the south. .LONG TERM...(Friday Night through next Thursday) ISSUED AT 305 PM CST Thu Mar 4 2021 Saturday and Sunday...With sfc ridge axis still implanted acrs the western GRT LKS and easterly flow, Sat may not be the mildest of days especially looking at the weak mixing profiles on FCST soundings. But if sfc winds go light and variable and more March insolation than clouds, we may over achieve especially over eroded snowpack areas. Will go with 50 percentile low to mid 40s in the northeast, to the mid 50s in the far southwest as a compromise, but again some worry that those values may still be too mild in spots. Low chance for patchy fog worth mention later Sat night. Increasing south to southeast sfc winds possibly to 15 to 25 mph on Sunday, and much deeper mixing profiles support higher percentile high temps in the upper 50s to low 60s acrs much of the area, with the north and northeast held down in the low to mid 50s. Agree with previous shift that here may be a marginal enhanced fire danger of cured grasses in the southern CWA(if somehow they were managed to get ignited) where they have been clear of snowpack for longer duration. This enhanced grassland fire danger may spread further north in the breezy warming days early next week. Monday and Tuesday...Broad omega upper ridge complex settles acrs the mid and upper CONUS this period, with increasing southwesterly warming LLVLS/flow undercutting it acrs the region. Currently projected thermal profiles/thicknesses support much of the DVN CWA warming into the low to mid 60s Monday as long as we have adequate insolation, with lingering snowpack areas of the north held down in the upper 50s to around 60. Digging longer wave troffiness west of the Rockies and large LLVL ridge complex along the Atlantic coast sets up the warming and increasing moisture fetch/conveyor up off the western Gulf starting on Tuesday. Could be a windy south- southwest wind 20 to near 30 MPH, with increasing sfc DPTs and humidity hopefully limiting what would be a more enhanced fire danger day. High temps may be a few degrees milder than Monday. Tuesday night may be the first round of WAA-type of showers as an embedded short wave in organizing southwesterlies aloft moves in from the west-central plains. Temps will look to be held up in the 50s in warm sector Tue night. Wednesday and next Thursday...A potentially active and wet period depending on where LLVL boundaries lay out parallel under southwesterly steering flow where gulf moisture can converge, fueling rounds of moderate to heavy rain showers and even some thunderstorms. Models and ensemble output continue with variable placement and marginal at best agreement with the potential action swaths for heavy rain in or near the local fcst area. Of course, with recent snow melt and lingering wet ground, seasonably significant rainfall would be a big factor on local rivers as well as possible inland nuisance flooding. The latest CPC 6-10 day outlooks maintain a high likelihood of above normal precipitation and above normal temperatures for next Wednesday through next Sunday. ..12.. && .AVIATION...(For the 06Z TAFS through 06Z Friday Night) ISSUED AT 1009 PM CST Thu Mar 4 2021 VFR conditions are expected to last through most of the period. As earlier noted, some MVFR vsbys are possible tonight and thru daybreak. Otherwise, no sig weather impacts expected. && .HYDROLOGY... Issued at 305 PM CST Thu Mar 4 2021 Some Creek flooding is continuing in a few locations due to the on- going snowmelt. While not widespread, this is likely impacting ditches and fields, primarily in rural areas. Most area rivers remain well below flood stage with minor within bank daily fluctuations at some sites following diurnal snowmelt trends in eastern Iowa and northwest Illinois basins. A few basins still in the lingering snowpack areas along and north of I80, such as the lower Wapsipinicon, portions of the Iowa, and Rock are(or will be soon) experiencing moderate within bank rises. The NCRFC continues to update forecasts for the North Skunk River near Sigourney Iowa, expecting a rise to around action stage by Saturday morning, due to snowmelt. But there is some uncertainty in the extent of additional snow melt that will occur to push the river to this level. Back to the Wapsi, longer range snow melt-driven river forecasts/ensembles suggest that the Wapsi near De Witt may be susceptible to minor flooding just from snow melt by March 9th or 10th of next week. Will continue to monitor the potential for breakup ice jams, as temperatures continue to average above normal and rise to well above normal through this weekend and going into next week. This threat appears to be greatest for a few rivers north of I-80 such as the Rock River in Illinois. But some recent remote sensing NOHRSC aerial survey along the Rock suggests much of the main channels are open water, with some stretches of side channel ice or ice flows. Portions of the Wapsi and Maquoketa will also have to be watched for ice action. Otherwise, no rain is forecast until Tuesday night at the earliest. The transition to a wetter weather pattern still looks to be on track for mid week and into the following weekend, but after the rest of or nearly all the existing snow has melted. However, with area soils likely to be still moist and possibly saturated through this time, the threat of moderate to heavy rainfall and potential river flooding will need to be monitored. Also, longer range ensemble forecasts model a few rivers embedded in the current deeper snow pack areas(Iowa, Cedar, Wapsi, Rock) to be experiencing the peak snow melt crests or rise bumps during mid to late next week. This is when we may get a few rounds of moderate to heavy rainfall on top of those higher levels and depending on extent of run-off, may be able to push some rivers closer to action or flood stages. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && $$ SYNOPSIS...Sheets SHORT TERM...Sheets LONG TERM...12 AVIATION...Gibbs HYDROLOGY...12

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