Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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011 FXUS63 KGRB 171132 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 632 AM CDT Tue Sep 17 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Summer-like temperatures continue through Thursday with highs in the 80s. Temperatures to stay in the 70s near Lake Michigan. Slightly cooler temperatures are expected this weekend, although should remain well above normal for this time of year. - The chances (40-60 percent) of showers and thunderstorms arrive Thursday night and linger into Friday as a weak cold front moves into and across the area. There is a continued chance for storms over the weekend, although there is a lot of uncertainty in the timing of the rain. && .DISCUSSION... Issued at 249 AM CDT Tue Sep 17 2024 Short Term...Today...Tonight...and Wednesday First off, seeing another early morning with locally dense fog closer to the warmer/moist waters of Lake Michigan. No real fog on the water, but the light southeast wind is adding moisture to low- levels and combining with nighttime cooling to form the fog. Have issued a special weather statement for the lakeshore counties. A few obs of fog farther inland, though this is probably more of a shallower type ground fog. For the short term looking at largely a persistence forecast through Wednesday. Little net change in upper-level pattern with higher heights holding to the north of the upper low over the southeast and also downstream of western CONUS troughing. Sfc pattern steady too with ridging continuing to persist out of northeast CONUS high pressure. Scattered thin high clouds and few-scattered fair weather cumulus should do little to impact temps. Highs last few days have shot past guidance and even what would be expected with full mixing to H85, perhaps due to recent dryness. Used that as guide to bump up high temps today and Wednesday to as warm as 87-89F. This is quite the contrast to the latest round of NAM MOS guidance which is much cooler for Wednesday (78 at GRB for example), but doesn`t seem reasonable given the pattern. Forecast will be much more in line, but still warmer than, the latest GFS MOS guidance (86 at GRB). Light southeast winds keep it cooler in the mid 70s at the Lake Michigan shoreline. Drying aloft as shown by higher H85 dewpoint depressions working in from the east resulted in lowering dewpoints/RH values both afternoons as well. Nighttime cooling will drop min temps tonight into the lower to mid 50s. Similar to the last few nights, have kept a mention of patchy fog near the bay and Lake Michigan. Long Term...Wednesday Night Through Monday The omega blocking pattern across the CONUS will gradually break down heading into the weekend. The ECMWF has a closed 500mb developing across Ontario on Sunday with a fairly zonal flow into early next week. Well above normal temperatures will continue into the weekend, then temperatures return closer to normal early next week. The best chance for rain will be Thursday night into Friday as an upper level disturbance and weak cold front move across the area. Model soundings would support the mention of thunder during this time frame, although the risk of severe weather is low. The latest model runs tonight are less bullish on the chances of rain late Friday night and Saturday. There is a lot of uncertainty in the rain chances late Saturday night into Sunday, but a better chance of rain may be on Sunday if the ECMWF and Canadian model are correct. The GFS kept this period dry at the moment. Based on model trends, raised high temperatures a few degrees on Thursday and trended a little higher for Friday and Saturday based on the latest numerical guidance. && .AVIATION...for 12Z TAF Issuance Issued at 630 AM CDT Tue Sep 17 2024 Local dense fog (VLIFR/LIFR) will impact near lakeshore areas such as MTW through 13z. Otherwise, expect VFR conditions with some mid and high clouds through tonight. Patchy fog (LIFR/IFR) possible again late tonight, mainly near the Lake Michigan shore (MTW). && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....JLA/Eckberg AVIATION.......JLA