NZUS93 KDVN 210747 LLLDVN IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-009-015>018- 024>026-034-035-MOZ009-010-211947- Public Information Statement National Weather Service Quad Cities IA IL 247 AM CDT Wed May 21 2025 Key Messages Cloudy and showery/drizzly today into this evening with many areas seeing another 0.25-0.40” before drier air moves in for Thursday. Cooler than normal temperatures will continue through the next week with 40s/50 today and then the 60s for high temperatures. Depending on cloud cover, light winds could promote some frost Friday morning in central Wisconsin. The holiday weekend looks mainly dry with northeast IA and southern WI possibly seeing some shower chances on the northern side of central/southern U.S weather systems. Confidence is leaning toward a drier forecast, but some small chances are in the forecast for light rain showers for that area. More Rain Expected Today Into Tonight, Then Some Drying GOES water vapor imagery at 06Z showing the broad large scale trough over the upper Mississippi river valley with numerous shortwave troughs pinwheeling around the low. A strong eastward push is seen to the southern side of the trough in the zonal jet flow across the Ohio Valley. A sharp surface trough is located from Aberdeen SD to around the I-80 corridor of Illinois with the local area under continued easterly flow. Precipitable water values regionally are still around an inch, with GRB and MPX showing abundant saturation through much of the troposphere. Radar is showing abundant shower activity and rainfall amounts of up to 0.30” in the last few hours. East/southeasterly flow in the low-levels is continuing a moist flow with troughing overhead today and cyclonic flow, all promoting saturation, clouds, drizzle and showers until this air mass can shift out of the area. That air mass change comes later tonight and early Thursday as a well agreed upon large scale trough shifts in from the Hudson Bay region to provide some drying and an air mass change from the north/northeast, ejecting the trough over the area downstream into the eastern U.S. Some lingering troughiness at the surface across the forecast area and the influence of cooler air aloft from the large scale trough over eastern Lake Superior could still spawn a few showers Thursday afternoon with stratocumulus development assured. So maybe some peaks of sun in the morning, then clouding up. The Cooler Pattern Continues, Frost is Possible Friday Morning The area remains under the influence of northwest flow and at times is brushed by shortwaves moving through the Great Lakes. Normal highs this time of year are now in at least the upper 60s into the 70s, but the forecast continues to show temperatures will be below that by 6-10 degrees into next week. With weak high pressure building in at the surface for Friday, depending on the extent of cloud cover, some frost could be observed in central WI in the morning. The latest tNBM would put a 20-30% chance there for 35F or less. However, the probabilities are likely higher with the warm bias shown by all the models on these radiative nights in the sand country / bogs of central WI. Will have to see the cloud extent details as we approach Friday morning for the frost potential. After that, temperatures should moderate slightly to avoid frost/freeze but northerly flow persists at the low-levels. Holiday Weekend Forecast By Saturday night and Sunday, troughing moving into the Central/Southern Plains will battle the Great Lakes ridging and drier easterly flow, trying to push moisture and precipitation chances in across areas south and west of La Crosse. It remains to be seen if the activity across the Central/Southern Plains can overcome the dry air in place for showers this far north. The latest 20.12Z Grand Ensemble available suggests this probability is low with the GEFS solutions providing a more aggressive forecast for rain. Some low chances for rain are out there for the weekend forecast, but those may be removed in future forecasts based on trends on the northern extent of the systems moving through to the south. On Monday, yet another shortwave trough influences the area from the northwest and has moderate confidence and agreement in the models for some shower chances.