Scientific Forecaster Discussion

000 fxus63 kgrb 201958 afdgrb Area forecast discussion National Weather Service Green Bay WI 258 PM CDT Sat Apr 20 2019 Forecast discussion for routine afternoon forecast issuance Short term...tonight and Sunday issued at 257 PM CDT Sat Apr 20 2019 Main forecast challenge to be trying to determine extent of precipitation on Sunday across the forecast area as a slow-moving cold front sags southward across the state. The 19z msas surface analysis showed a ridge of high pressure which extended from the Southern Plains northeast through east- central WI. A cold front was located from northern Ontario southwest through north-central Minnesota to central South Dakota where a weak low pressure area was situated. Visible satellite imagery indicated a large area of clouds (mainly of the mid-variety) along and behind the cold front. Radar mosaic had picked up on a few sprinkles from these clouds, however the air mass over WI is very dry initially so it would take some time to saturate. The weak surface ridge to slide to our east tonight, allowing for the cold front to sag toward northern WI by daybreak. Models all show any precipitation to be Post-frontal, thus do not anticipate any real chance of measurable rain, although a few sprinkles are possible across the far north after midnight. The rest of northeast WI to remain dry with a gradual increase in mid/high clouds. Inflow of warmer air aloft will prevent temperatures from falling too far tonight. Look for readings over most locations to settle into the 40-45 degree range. This cold front is forecast to continue slowly moving south into central/east-central WI on Sunday. Depending on the amount of cloud cover we see, the atmosphere may be able to destabilize enough such that a few thunderstorms could pop up in the afternoon (capes around 500 j/kg into central wi). Northern WI to be under a thicker cloud cover with a chance of rain showers. Quite a range in temperatures expected on Sunday with readings reaching the upper 50s near lake mi, around 60 degrees far north, to the middle to upper 70s over parts of central WI. Long term...Sunday night through Saturday issued at 257 PM CDT Sat Apr 20 2019 Precipitation trends and amounts from Sunday night through Tuesday morning, and associated flooding implications, are the main forecast concerns. A surface frontal boundary is expected to bisect the forecast area from central to northeast WI Sunday night, while an 850 mb front lingers near our far northwest counties. This frontal system will provide the focus for showers, which should be most numerous over the northwest part of the County Warning Area. The showers will become more widespread as a surface low lifts northeast along the boundary Monday afternoon and night. There will be a chance of storms across mainly central and east central WI Monday afternoon and evening, and these could locally boost rainfall totals. Lingering showers over the southeast part of the forecast area should taper off Tuesday morning. See the hydrology section below for information on potential flooding concerns. High pressure will bring some sunshine and a day of drying on Wednesday, with low relative humidity expected. A cold front will move through the region late Wednesday night into Thursday and bring a chance of showers and possibly a few thunderstorms. Dry conditions should return on Friday as high pressure returns. As the high shifts east on Saturday, return flow could bring showers back into the region. Temperatures should remain near or a bit above normal through most of the extended period. && Aviation...for 18z taf issuance issued at 1228 PM CDT Sat Apr 20 2019 Ridge of high pressure over eastern WI will shift to the east tonight and allow for a cold front to slowly sag toward Wisconsin. A band of mid and high clouds are expected to overspread most of northeast WI tonight with more clouds to the north near the approaching boundary. As the cold front continues to sag south on Sunday, this will bring a chance of showers to much of northern WI with only a slight chance farther to the south. While VFR conditions are expected, cannot rule out a few thunderstorms over parts of central Wisconsin where some instability to build during the afternoon. && Hydrology... issued at 257 PM CDT Sat Apr 20 2019 Minor to moderate flooding continues on several rivers across the area. Look for the the Wisconsin river to slowly fall through the weekend, while the Wolf and Menominee rivers remain steady or slowly rise. Much of the region should see a half inch to an inch of rain from Sunday night through early Tuesday, with locally higher amounts possible. The heaviest rainfall is expected over north central WI. Additional/new flooding concerns could arise, especially if we get totals approaching an inch or greater. && Grb watches/warnings/advisories... none. && $$

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