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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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442 FXUS63 KGRR 160121 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 921 PM EDT Thu Aug 15 2024 .KEY MESSAGES... - Chances of showers and thunderstorms through the weekend - Cooler than normal much of next week && .UPDATE... Issued at 921 PM EDT Thu Aug 15 2024 Widespread coverage of showers associated with lead shortwave, elevated warm front, and incoming axis of higher PWATs continues to slowly march across the area. There has been no thunder at all with this activity as the leading edge of any respectable MUCape values is still well to our west. The risk for a tstm does increase late tonight as RAP MUCapes of 500-1000 J/KG arrive and the next shortwave currently over Iowa/srn MN approaches. Only change to the fcst was to drop the mention of thunder in the grids until after 06Z and that was done earlier this evening. && .DISCUSSION... Issued at 245 PM EDT Thu Aug 15 2024 - Chances of showers and thunderstorms through the weekend As the low pressure system tracks into the region from the west through Friday, it will bring with it moisture, lift and instability. SPC HREF 4 hr thunder probabilities don`t really increase significantly until after 08z tonight. They remain high until mid morning when they then decrease steadily. So it looks like a break in the storm activity is expected late morning into part of the afternoon. We do destabilize in the afternoon with surface based CAPE values likely to reach 1000 J/kg away from Lake MI. Forcing is shown to be weak then. So if storms do develop then, then should remain isolated/scattered during the mid to late afternoon hours. The main mid level wave/vort max arrives from west in the 00z-04z Sat period. There`s a signal in the models for a cluster of storms to accompany this feature. The SPC HREF 4h thunder probabilities increase once again. LPMM 24 hr qpf values show small swaths of values over 2 inches 00z Fri to 00z Sat so locally excessive rain may occur. We will feature relatively high POPs trough the period as a result. Vertically stacked and slow-moving area of low pressure will be centered over Lower Michigan on Saturday and southwest Ontario on Sunday. Scattered showers or thunderstorm cells will tend to be reinvigorated with daytime heating, with greater precip chances inland and away from Lake Michigan. CAPE will be more modest than Friday, and shear will still be limited, but 20-25 knot winds in the lower atmosphere not far off the surface may allow for localized gusts over 30 mph to mix down with some showers. Though high temperatures will be cooler than normal, dew points will still be on the muggier side. - Cooler than normal much of next week A tendency for synoptic-scale ridging over the Rocky Mtn front range and troughing over the eastern Great Lakes early-mid next week will provide a flow of drier and cooler-than-normal air as high pressure builds in the Midwest. Good confidence among the ECMWF and GFS ensembles for highs mostly in the mid 70s. A small minority of members give rain chances Tuesday night or Wednesday depending on strength and location of shortwave troughs moving over the ridge. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 723 PM EDT Thu Aug 15 2024 No significant changes to the going forecast. A band of showers crosses through West Michigan through the evening with more scattered showers behind it. Instability builds in early Friday morning bringing thunder chances with a cluster of showers moving through in the 08z-12z range. Have VCTS in the TAFs given the more scattered nature of thunderstorms. Isolated thunder is possible earlier but confidence is too low for TAF inclusion. MVFR and lower visibilities are possible in any thunderstorms. A few hours of MVFR cigs are likely Friday morning, longest at MKG. Uncertainty exists in how long MVFR cigs continue into the morning as it will depend in part on how much rainfall occurs. Even worst case scenario, any MVFR cigs lift to VFR by the afternoon. An isolated shower or storm is possible in the afternoon but coverage is to low to warrant TAF inclusion at this time. The next organized complex of storms holds off until after 00z Friday. && .MARINE... Issued at 245 PM EDT Thu Aug 15 2024 The winds and waves will remain elevated through much of tonight as the pressure gradient tightens up as a result of the approaching low pressure system We did slightly expand the hazardous beach/boat risk this afternoon based on the latest model and observational trends. On and off hazardous conditions are predicted into the weekend so we will adjust headlines as we get closer to those periods. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement until 2 AM EDT Friday for MIZ037-043-050- 056. MARINE...Small Craft Advisory until 2 AM EDT Friday for LMZ846>849. && $$ UPDATE...Meade DISCUSSION...MJS/CAS AVIATION...Thomas MARINE...MJS