Scientific Forecaster Discussion

000 fxus63 kgrb 251754 afdgrb Area forecast discussion National Weather Service Green Bay WI 1254 PM CDT Thu Apr 25 2019 Updated aviation portion for 18z taf issuance Short term...today...tonight...and Friday issued at 318 am CDT Thu Apr 25 2019 A weak cold front continues to slowly makes its way through the western Great Lakes early this morning. The front was currently located across northwest Wisconsin and will sweep through the area later this morning and into the early afternoon hours. The front will bring thickening clouds and isolated showers given the weak forcing and lift associated with the system this morning. Showers may become scattered this afternoon across Central, Northeast and east-central Wisconsin as a mid level shortwave tracks through the western Great Lakes area. Some lingering showers are possible across east-central Wisconsin and the Lakeshore this evening as this shortwave continues to track through and a secondary cold front sweeps through the region. Behind this cold front a ridge of high pressure will build in across the upper Mississippi Valley on Friday, keeping the weather dry. Highs today will mainly be in the 60s with lows tonight in the middle 30s to lower 40s. Highs Friday will range from the lower 50s across the north, with highs around 60 across east-central and northeast Wisconsin. Long term...Friday night through Wednesday issued at 318 am CDT Thu Apr 25 2019 Forecast concerns generally revolve around the details with a storm system that is projected to impact the region early this weekend. In general, models are more tightly clustered with the track and intensity of the surface low, which is forecast to move across Iowa and central Illinois on Saturday afternoon and Saturday evening. Will use a blend of the GFS and ECMWF given their better agreement. However, the model spread remains quite large with the details for early next week, so will have to stick with a general model blend for later periods. Friday night through Saturday night...an area of low pressure will be moving across the Central Plains on Friday night. Clouds will be on the increase ahead of the system from late evening into the overnight from west to east. But with the surface high stretching across northeast WI and a very dry airmass ahead of the storm system, will stick with a dry forecast. This dry air will play a role in regards to how far north the precip reaches on Saturday. But the latest indications suggest precip will start to overwhelm the dry air over central WI from mid to late morning before spreading across east-central and possibly northeast WI in the afternoon. The strongest forcing via mid-level fgen on the nose of a 45 kt low level jet is expected to just clip areas from wood to Manitowoc counties. Max wet bulb temps aloft are forecast to be within a degree or two of freezing within the heaviest precip from late morning through early evening, so ptype will be strongly influenced by boundary layer temps. Given surface temps ranging from the mid to upper 30s, a rain snow mix looks likely, with some accumulations (perhaps an inch or two?) Possible on grassy surfaces. Accumulations on roads will be rather difficult given the time of day of the heaviest precip and the very high sun angle. The precip will be exiting in the evening, with dry air reasserting itself through the night, leading to clearing skies overnight. Highs on Saturday will be the coolest over the period, and range from the mid 30s to low 40s. Rest of the forecast...high pressure will provide dry and cool conditions on Sunday. Then shortwave energy will push an inverted surface trough towards the area on Monday and Monday night, which possibly could linger into Tuesday. Precip chances will remain on the lower side given the model spread. How far south the front stalls thereafter will help determine how quickly the threat of precip returns during the middle to end of next week. && Aviation...for 18z taf issuance issued at 1254 PM CDT Thu Apr 25 2019 A narrow band of rain showers has spread across the region from central Wisconsin to far northeast Wisconsin this afternoon. The rain showers have brought scattered MVFR visibilities to the taf sites across central Wisconsin with VFR ceilings between 3500 to 7000 feet. These rain showers will track southeast through late this evening bringing the MVFR visibilities and VFR ceilings to the east-central Wisconsin taf sites. As the rain showers exit the region, skies will clear from northwest to southeast. It is possible for some low level wind shear to impact the central and north- central Wisconsin taf sites mainly between 06z to 12z Friday. && Hydrology... issued at 318 am CDT Thu Apr 25 2019 Rivers and streams across northeast WI remain at high levels. This includes high flows in and around area dams as excess water is being released from earlier rainfall and snowmelt. While light rain is expected today and this evening, amounts should not impact Current River levels. Please monitor the latest river forecasts for further information on flooding in your local area. && Grb watches/warnings/advisories... none. && $$

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