Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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735 FXUS63 KGRB 061938 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 238 PM CDT Thu Jun 6 2024 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Isolated to scattered showers and gusty northwest winds will continue across the region through this evening. Winds will decrease slightly overnight but remain breezy. - Breezy conditions are expected Friday, with gusts to 25-30 mph. - Conditions hazardous to small craft are expected Friday. - Showers are possible at times this weekend, with a chance of thunderstorms Saturday afternoon. - Additional showers and thunderstorms are expected Tuesday afternoon into Tuesday night. - Below normal temperatures are forecast through early next week with warming temperatures by mid-week. && .DISCUSSION... Issued at 238 PM CDT Thu Jun 6 2024 Short Term...Tonight and Friday Mesoanalysis...Ongoing isolated to scatter this afternoon are being driven by cyclonic flow around a low pressure system centered just east of Lake Superior and steep low-level lapse rates around 8.5 to 9 C/km. Analysis soundings are showing mixing this afternoon to around 800-850 mb which is driving the stronger 35-40 mph gusts with these showers, especially in central WI. In addition to the gusts being produced by rain showers the pressure gradient is tightening which is driving up the gradient winds as well. With a lack of instability (SBCAPE < 200 J/kg) and weak 0- 3km shear(15-20 kts) none of these showers have been able to produce much in the way of thunder, but won`t rule out a few rumbles around peak heating this afternoon. Expect the showers and gusty winds to continue across the region through the remainder of the afternoon. Temperatures this afternoon will be held in check by the abundant cloud cover and showers with most locations reaming in the middle 50s to middle 60s. Tonight...Isolated to scattered shower activity should come to and end from south to north this evening with the lose of daytime heating and stabilization. While winds will back down from the peak gusts this afternoon, a tighter pressure gradient will continue to create breezy conditions with gusts of 15-25 mph overnight. Near normal temperatures overnight with lows dropping into the middle 40s to low 50s across the region. Friday...Dry and breezy conditions are expected Friday as the region resides on the backside of an upper trough with the surface low shifting off to the east. A strong 90-100kt upper jet is forecast to move directly overhead during the day which will bring plenty of energy into the region to drive stronger wind gusts. Forecast soundings look similar to today with mixing to around 1.5-2 kft which should be deep enough to bring some 25- 30 mph gusts down to the surface. In addition, the deeper mixing should aid in lowering surface dew points down into the middle to upper 40s. The lower dew points in combination with a surge of WAA bringing warmer temperatures into the middle 60s to low should make for a more fall like feel, rather than early summer. Long Term...Friday Night Through Thursday Main forecast focus remains on trying to time precipitation chances, especially next week as models continue to waffle on the direction/amplitude of the mean flow. A pair of closed upper lows, one over Quebec and the second over Alberta/Saskatchewan, will keep unsettled weather across the Great Lakes through the early part of next week. A west-northwest flow aloft will carry individual shortwaves across WI about every other day, but exact timing is a bit tricky. A more pronounced change has taken place for the middle of next week as models are not building a ridge over the east-central CONUS, instead keeping a flat, near-zonal flow across the CONUS. Temperatures to be below normal through Tuesday, then rise at or above normal mid-week. Friday night and Saturday... Clouds will be on the increase Friday night as the next mid-level shortwave trough dives southeast into the Upper MS Valley. Models indicate models levels of both Q-G and FGEN forcing with a weak frontal boundary to move into western WI after midnight. These factors should be enough to bring chance pops through at least central WI and perhaps reaching eastern WI toward daybreak. Min temperatures to be in the upper 40s to around 50 degrees north, lower to middle 50s south. This shortwave trough/frontal boundary push across WI on Saturday and bring a chance of showers across the entire forecast area. Instability looks weak at best with MUCAPES < 200 J/KG. However, shear is very strong (70-80 kts over central/east-central WI). Therefore, have kept thunder in the forecast for Saturday afternoon, but severe does not look likely as the mid-level shortwave trough to be exiting the area during peak heating. Max temperatures Saturday to be in the middle to upper 60s north, upper 60s to lower 70s south. Saturday night and Sunday... A few showers may linger into Saturday evening, but most location should be dry Saturday night as we lose daytime heating and there is no other trigger present. Sky cover will become mostly clear to partly cloudy with min temperatures in the upper 40s north, lower to middle 50s south. The combination of cyclonic flow, weak surface trough dropping south and cold air aloft to generate weak instability may be enough to spark a few afternoon showers across northeast WI on Sunday. Cool north-northwest winds will continue to keep temperatures in check with readings on Sunday in the lower to middle 60s north-central WI, upper 60s to around 70 degrees elsewhere. Sunday night and Monday... High pressure is forecast to build into the western Great Lakes to begin the new work week, thus mostly sunny skies and dry conditions are expected on Monday. Max temperatures will warm up a bit with middle to upper 60s near Lake MI, lower to middle 70s inland. Monday night and Tuesday... Dry conditions should hold through Monday night as the high pressure begins to shift east. By Tuesday, the next shortwave trough is progged to move into the Upper MS Valley with a cold front reaching the MN/WI border by 00Z Wednesday. Models differ a bit with the timing of this system as the GFS already has precipitation chances Tuesday morning, while the CMC is dry through the day. Have a minimal chance of showers/thunderstorms for the afternoon hours, but this may be tweaked in later forecasts. Max temperatures Tuesday to be around 70 degrees near Lake MI, lower to middle 70s north and middle 70s south. Tuesday night through Thursday... Best chance of seeing precipitation would be Tuesday night as the shortwave trough and cold front cross WI. Of course, the faster GFS ends the precipitation faster than other models, but this timing issue will be resolved with time. Model issues then persist for mid-week as they continue to waffle on whether an upper ridge will build over the east-central CONUS in response to an upper trough hitting the West Coast. Latest guidance does not show this ridge developing, instead keeping a near-zonal flow across the CONUS. This pattern could bring yet another shortwave trough into the Great Lakes Tuesday night into Wednesday. A northward moving warm front could also bring showers/storms to the area on Thursday, so the wet forecasts look to persist next week. Temperatures are forecast to go above normal for both Wednesday and Thursday. && .AVIATION...for 18Z TAF Issuance Issued at 1230 PM CDT Thu Jun 6 2024 Pop-up showers have developed north of an OSH to MTW this morning. The coverage of these showers is more widespread across northern WI with more isolated coverage further south. Expect these showers to continues across the region through the afternoon before waning this evening. Northwesterly winds have also increase this morning with gusts reaching 20-25 kts at most locations. Breezy conditions will remain through this afternoon and evening. A few strong gusts between 30-35 kts will also be possible this afternoon around any showers that move over a terminal. Low-end VFR cigs are forecast for this afternoon with periodic drops to MVFR north of a AUW to IMT line as showers move over terminals. Did include LLWS in the CWA, AUW, and RHI TAFs for a brief period around midnight as winds at the surface decrease slightly, but winds at 1.5-2 kft remain around 30-35 kts. Expect breezy conditions again Friday as a strong upper-level jet moves over the region. && .MARINE... Issued at 238 PM CDT Thu Jun 6 2024 With a similar syntopic set-up to today breezy conditions are expected near Lake Michigan Friday, strongest south of Sturgeon Bay. However, with no rain showers expected mixing may not be quite as efficient which would keep peak gusts more in a 25- 30 kts range. A Small Craft Advisory will likely be needed during the late morning and afternoon period before winds diminish Friday night. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....GK/Kallas AVIATION.......GK MARINE.........GK