Scientific Forecaster Discussion

000 fxus63 kgrb 180346 afdgrb Area forecast discussion National Weather Service Green Bay WI 1046 PM CDT Mon Jun 17 2019 Updated aviation portion for 06z taf issuance Synopsis... issued at 230 PM CDT Mon Jun 17 2019 Seasonably cool weather is expected this week, along with some showers at times (mainly early in the week). More humid conditions and an increased chance for rain are likely for the weekend. The current diffuse low-amplitude upper pattern across the northern Continental U.S. And southern Canada will persist for a bit longer. But the westerlies will strengthen and amplify during the middle to latter portion of the work week as jet energy begins to work inland from the Pacific. That will initially lead to the development of a strong upper trough over the intermountain west, and later downstream ridging over the middle and upper Mississippi Valley. The ridge axis will begin to shift east by the weekend, leaving the forecast area in a favorable location for heavy rainfall at the downstream end of a long fetch of southwest upper flow. Daytime temperatures will remain near to modestly below normal into the weekend, then trend upward. More humid conditions are also likely by the weekend. Scattered showers early in the period will result in light to moderate amounts. But the bulk of the rain in the period is likely to occur during the second half of the period as shortwaves ejecting out of the western trough begin to affect the area. && Short term...tonight and Tuesday issued at 230 PM CDT Mon Jun 17 2019 The main forecast challenge remains timing/extent of precipitation from later tonight through Tuesday. Temperatures appear to be near seasonal normal for this time of year. The 19z msas surface analysis showed a weak area of high pressure near Lake Huron, a cold front that arced from northwest Minnesota through southeast Minnesota, then turned southwest through western Iowa. Another area of high pressure was located over north-central ND. Radar mosaic had picked up on showers/thunderstorms over southern Minnesota and northwest Iowa. The modest cold front is forecast to push southeast into northwest WI this evening and reach central WI by daybreak. There will also be a weak mid-level shortwave approaching WI tonight that may provide enough forcing to accompany the lift from the front, to set off a chance of showers over most of the area (primarily after midnight east). Instability looks weak enough to limit any thunderstorms to widely scattered at best. Thickening clouds will provide for a mild night temperature-wise with readings around 50 degrees north, middle 50s south. The cold front is expected to slowly move through the rest of WI on Tuesday and with additional weak shortwaves traversing the region, anticipate more showers/thunderstorms to develop. Instability remains marginal at best, so no strong storms to worry about. Nevertheless, have raised pops up to high chance or likely for eastern WI. Rainfall amounts overall will be modest with most locations receiving 0.10-0.25" of rain with locally higher amounts of up to 0.50" under any thunderstorms. Max temperatures to range from the middle to upper 60s near lake mi, to the middle 70s south. Long term...Tuesday night through Monday issued at 230 PM CDT Mon Jun 17 2019 The likelihood of having a dry period during the middle to latter part of the week looks better than yesterday. An area of low pwats is forecast to circulate back into the are from the east. That combined with rising upper heights and increasingly anticyclonic flow aloft favor dry weather. Considerable uncertainty still exists concerning how quickly rain chances will return late in the week, so pops late Thursday night into Friday may require substantial adjustment in later forecasts. Beyond that, showers and thunderstorms are likely at times during the upcoming weekend. A heavy rainfall and/or severe weather threat may evolve during the weekend, depending on exactly where the primary frontal zone sets up. The Standard forecast initialization grids looked good for the most part. The most significant change was to further reduce some low-end pops in the mid-week time frame. && Aviation...for 06z taf issuance issued at 1046 PM CDT Mon Jun 17 2019 Clouds will increase and lower tonight in advance of a modest cold front dropping southeast from the northern plains. Although activity is very isolated tonight, coverage should pick up during the day on Tuesday as the heating of the day provides a boost as was the case during the day on Monday. Cigs are expected to drop into the MVFR range with any showers/storms. The activity should end across the north and west later Tuesday afternoon, but continue across the far east into the evening hours. && Grb watches/warnings/advisories... none. && $$

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