Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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690 FXUS63 KGRR 211756 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 156 PM EDT Tue May 21 2024 .KEY MESSAGES... - Severe Storms Possible Late Tonight - Dry for Wednesday and Thursday; Rain Chances Return Friday - Rain Chances Linger Through the Holiday Weekend && .DISCUSSION... Issued at 350 AM EDT Tue May 21 2024 - Severe Storms Possible Late Tonight A rapidly amplifying shortwave ejects out of the Central Plains into the Great Lakes this afternoon through late tonight. In response, a surface low deepens as it moves into northern Wisconsin and the UP while a trailing cold front becomes the focus for thunderstorm development. A cluster of storms currently working through Nebraska and western Iowa will be the focal point to monitor throughout the day today. Starting off semi-discrete, these storms will organize and transition into an organized line of storms by the time they reach central Iowa and western Wisconsin. Meanwhile across lower Michigan ahead of the storms, return flow moisture bumps dewpoints into the mid to upper 60s with afternoon highs peaking in the low to mid 80s. Diurnal cumulus may give way to a few showers or a stray thunderstorm ahead of the main line of storms late tonight. Hi-res cams are in good agreement on a midnight time of arrival of the main line of storms, and are also favoring a quick weakening trend into lower Michigan given the late hour and strong nocturnal limiting factors. The progression of SPC Enhanced in far western Michigan to Slight/Marginal Risk in central to eastern Michigan nicely depicts the weakening trend with eastward progression. Damaging wind will be the main hazard to monitor as the storm mode transitions into a well organized QLCS to our west and travels east towards lower Michigan. The eastward advancing cold front will be the focal point for any additional convection Wednesday, but as the boundary becomes parallel to the mean flow convection will be very limited and mainly shunted off to our far southeast. Therefore the risk of storms has shifted southeastwards. - Dry for Wednesday and Thursday; Rain Chances Return Friday Sfc frontal boundary will settle south of MI for Wednesday night through Thursday night with a sfc high and drier air mass sliding through, yielding dry conditions during this time. Current guidance indicates that the boundary lifts back north as a warm front on Friday afternoon and night as the next shortwave tracks across the nrn Plains into MN/WI. Pops returning as this occurs and this is faster than in previous model runs. - Rain Chances Linger Through the Holiday Weekend Depending on the timing of the Friday wave, its possible that Saturday ends up being a mostly dry (and cooler) day due to a period of subsidence behind it. Confidence is too low at this time though to advertise a dry start to the weekend and 20-40 pct pops will be maintained. It is possible that those rain chances end up being restricted top just the morning-time. A zonal flow aloft is progged throughout the holiday weekend with frontal zone/baroclinicity still nearby. This pattern will result in continued chances of showers and possible storms although the timing and coverage of convective events remains low confidence. Upshot is for a continuation of daily 20-40 pops but the weekend will certainly not be a washout and temperatures will average near to slightly above normal. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 156 PM EDT Tue May 21 2024 VFR conditions should predominate except for a brief period of MVFR/IFR conditions with the passage of thunderstorms tonight. We continue to expect a north-south oriented line of strong to severe storms coming onshore at MKG around midnight tonight and then moving east. The storms should weaken quite a bit as they move onshore followed by gradual additional weakening over Lower MI as the line moves east. Wind gusts in excess of 40 kts seem like a good bet at MKG and over 50 kt is not out of the question; farther inland, gusts may end up being considerably weaker. In any case, any given terminal can expect less than an hour of thunderstorms. The storms will be preceded and also followed by a period of LLWS that will peel off to the east and exit the area before 12Z. && .MARINE... Issued at 350 AM EDT Tue May 21 2024 Winds stay mainly offshore today, then will shift southwesterly this evening while building. Strong to severe thunderstorms will move through the region late tonight resulting in locally strong winds and choppy waves in the vicinity of storms. Apart from storms, conditons become hazardous to small craft late this evening as winds gust towards 20 to 30 knots through tomorrow morning. Meanwhile, waves will build late tonight through Wednesday morning, gradually subsiding from south to north Wednesday afternoon. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory from 10 PM this evening to 8 PM EDT Wednesday for LMZ844>849. && $$ DISCUSSION...Meade/Thielke AVIATION...TJT MARINE...Thielke