Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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177 FXUS63 KGRR 210751 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 351 AM EDT Tue May 21 2024 .KEY MESSAGES... - Severe Storms Possible Late Tonight - Dry for 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 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 /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 152 AM EDT Tue May 21 2024 Stratus and fog will produce IFR/LIFR conditions through 14Z or so before mixing out, mainly north of a AZO to LAN line. Otherwise VFR conditions prevailing from mid morning into the evening before a possible squall line races across Lk MI toward Midnight. Southerly winds will increase substantially after 02-03Z tonight in front of that approaching line, with LLWS becoming likely. The timing of the line of strong to severe storms tonight is toward the very end of the TAF period, but if the line holds together there could be gusts as high as 50 kts associated with it shortly after Midnight. && .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...Meade MARINE...Thielke