Scientific Forecaster Discussion

000 fxus63 kgrb 222322 afdgrb Area forecast discussion National Weather Service Green Bay WI 622 PM CDT Mon Apr 22 2019 Updated aviation portion for 00z taf issuance Short term...tonight and Tuesday issued at 221 PM CDT Mon Apr 22 2019 Main forecast concern remains on amount of rainfall from late this afternoon through tonight, especially as area rivers are still running high. The 19z msas surface analysis indicated an area of low pressure centered over central Iowa. A quasi-stationary front stretched northeast from the surface low across southern WI and a cold front extended southwest from the low pressure into the Southern Plains. The radar mosaic showed several bands of rain showers with a few embedded thunderstorms from the upper Midwest into the Great Lakes. The surface low is forecast to track into southwest WI this evening before moving toward northern sections of Lake Huron by 12z Tuesday. Just enough instability to exist into the evening to justify carrying a chance of thunderstorms over central/east- central WI. While the vast majority of these storms will be of the garden-variety, cannot rule out a couple of stronger storms over the southern sections of the forecast area with marginal hail being the main threat. The larger threat for tonight will be the locally heavy rainfall with precipitable water values at 1.0" or greater over most of northeast WI. Sufficient lift to be provided by the surface low and the favorable right entrance region of the upper jet situated over Ontario. Furthermore, a mid-level shortwave trough to accompany the surface low across WI to add decent q-g forcing. Expect to see rain amounts of 0.50 to 1.00" with locally higher amounts possible under any thunderstorms. The highest totals appear to be focused across parts of central and most of east- central WI and occur mainly during the evening hours. Prefer to keep the Flood Watch going even across the north since that part of the state has already had rain earlier. Min temperatures to range from the middle 30s north-central, to the lower to middle 40s east-central WI. Back edge of light rain showers should be pulling away from far eastern WI early Tuesday morning, so will need to carry a minimal pop for a few hours after sunrise. Otherwise, a ridge of high pressure is forecast to build across WI on Tuesday, bringing decreasing clouds, a drier air mass and slowly subsiding winds. Look for Max temperatures to range from the lower to middle 50s near lake mi, to the lower to middle 60s over parts of central WI. Long term...Tuesday night through Monday issued at 221 PM CDT Mon Apr 22 2019 Generally dry weather is anticipated Tuesday night into Wednesday. The GFS/Gem models brings some showers to the WI/Upper Michigan border area on Wednesday, but with the warm front north of the border, this seems unlikely. A dry, breezy and mild day looks like a good bet, along with elevated fire weather conditions. A cold front and rrq of an upper level jet will move through the region late Wednesday night into Thursday, but precipitation amounts are uncertain at this time. The GFS is much more aggressive with quantitative precipitation forecast than the ECMWF, and seems overdone. There may be just enough instability to generate a few thunderstorms along and ahead of the front Thursday afternoon. Dry conditions return on Thursday night and Friday as high pressure arrives. Wet weather may return late Friday night into Saturday, as strong warm air advection/isentropic lift develops on the nose of a 40+ knot low level jet. Medium range models both indicate low pressure moving through the region on Saturday, but the GFS is much deeper and farther north than the 00z European model (ecmwf). The 12z European model (ecmwf) has trended much farther south and weaker. For now, will continue with the model blend and likely pops for Saturday, but this may need to be changed with subsequent forecasts. The eventual track will have big implications on precipitation trends, temperatures and possibly precipitation type. Forecast confidence is low for the rest of the weekend and early next week, so will stick exclusively with the model blend during that period. Temperatures will remain mild through the rest of the work week, then likely cool off for the weekend and early next week. && Aviation...for 00z taf issuance issued at 621 PM CDT Mon Apr 22 2019 Flying conditions will continue to deteriorate this evening as an area of low pressure rides northeast along a quasi-stationary front into southwest WI this evening, then across east-central WI around midnight. Showers will accompany this system with moderate to locally heavy rainfall expected, especially across central and east- central WI. Some thunderstorms are possible, mainly for the eastern taf sites early this evening. Cigs/vsbys are forecast to settle into IFR conditions for the bulk of tonight. Winds are expected to become north- northwest once the low departs and become gusty at times. A ridge of high pressure will move into the region Tuesday morning, bringing decreasing clouds and a return to VFR conditions over central WI by around 12z and eastern WI by 15z. Good flying conditions can then be expected late Tuesday morning through the rest of the taf period. && Hydrology... issued at 221 PM CDT Mon Apr 22 2019 A Flood Watch will remain in effect for the most the area, except the Lakeshore counties through tonight. We are still expecting rainfall amounts of one-half to one inch with locally higher amounts possible under any thunderstorms. The heavy rain will cause additional rises in river levels and may cause additional flooding. Urban street flooding and ponding of water on area roadways may also occur. && Grb watches/warnings/advisories... Flood Watch through Tuesday morning for wiz005-010>013-018>021- 030-031-035>039-045-048-049-073-074. && $$

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