Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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520 FXUS63 KGRR 201734 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 134 PM EDT Thu Jun 20 2024 .KEY MESSAGES... - Continued hot/humid with scattered storms - Very warm and windy Saturday; Heat Advisory extended - Showers and Thunderstorms Saturday night - Dry and somewhat more comfortable Sunday through Tuesday && .DISCUSSION... Issued at 340 AM EDT Thu Jun 20 2024 - Continued hot/humid with scattered storms Radar shows scattered storms moving east of US-131 and north of I-96. These formed southwest of GRR earlier in an area where low level lapse rates were maxed around 5.5 c/kg and LI`s were around -5c. These storms will move out of the cwa by 12z. Surface obs indicate a weak cold front is located near M-46 and moving south. Convergence near this boundary coupled with various weak outflow boundaries will continue to produce convection today. Additionally, northeast winds behind the frontal boundary will converge with lake breeze boundaries that develop behind the wave of low pressure that the GFS/ECMWF have for a couple of days showed that moves ENE along the frontal boundary and that will likely result in more showers/storms today. PWATs are progd close to 2 inches again this afternoon, so a heavy rain threat exists. Indeed, local probability matched mean from the 00z HREF shows the potential for 1-2 inch rainfalls in the heavier cells that develop. The rain loading could also result in some stronger wind gusts. South of the frontal boundary, heat and humidity will remain with heat indices 95-97 degrees. Temperatures will fall to around 60 tonight over the northern cwa that will be influenced by the northeast winds from Lake Huron. Elsewhere lows will fall into the upper 60s. Generally dry conditions are expected tonight. Friday will see highs 85 to 90 with heat indices 94-96 degrees. The weak frontal boundary from today will move north Friday generating more scattered convection. Given PWATs aoa 2 inches, a heavy rain threat will exist. - Very warm and windy Saturday; Heat Advisory extended Breezy warm sector will overspread Southwest Michigan on Saturday as a warm front lifts into nrn Lwr MI with a cold front situated to our west from near MSP to DSM. Southwest wind gusts of 30-35 mph possible in the afternoon once deeper mixing gets going within tightening, cyclonic sfc pressure gradient. Much of the day should be dry, at least near and south of I-96, with highs in the lower 90s away from Lk MI. The heat advisory over srn sections has been extended into Saturday to account for this final surge of hot air. Highest pops will be up near U.S. 10, closer to the sfc warm front. - Showers and thunderstorms Saturday night A shortwave preceding the primary H5 trough approaching from the northwest comes through on Saturday night along with the sfc cold front. While deep layer shear values around 35 kts would support the possibility of strong to severe storms, it`s questionable how much instability will be available given the late-night frontal passage. Either way will have high pops (60-90 percent) during this time. - Dry and somewhat more comfortable Sunday through Tuesday We eventually dry out on Sunday behind the cold front with temps and dew points falling to more comfortable levels. A surface high moves in for Monday and that may keep things dry into Tuesday as well. However pops ramp up again by midweek as the next cold front and H5 trough drop in from the northwest. An even cooler air mass looks to follow that front by around Thursday of next week with dew pts dropping into the 40s. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 126 PM EDT Thu Jun 20 2024 Showers and storms are expected this afternoon, especially between 19Z to 23Z. All terminals except MKG could see TSRA. Some storms have already started to develop in and around KGRR, AZO and BTL. Between 18Z and 00Z is the timing of most concern. Potential for fog overnight between 06Z and 18Z, especially southern TAF sites. && .MARINE... Issued at 340 AM EDT Thu Jun 20 2024 High pressure over Lake Superior will produce a very weak pressure gradient during the next couple of days resulting in low wave heights. Southwest winds will increase Saturday ahead of the next cold front and may pose a threat to boaters and beachgoers. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 8 PM EDT Saturday for MIZ056-057-064>067- 071>074. MARINE...None. && $$ DISCUSSION...Meade/04 AVIATION...Meade/Ceru MARINE...04