Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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203 FXUS63 KGRR 040736 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 336 AM EDT Tue Jun 4 2024 .KEY MESSAGES... - Scattered thunderstorm chances today through Wednesday - Cooling down for the end of the week and possibly through the weekend && .DISCUSSION... Issued at 336 AM EDT Tue Jun 4 2024 - Scattered thunderstorm chances today through Wednesday Three main atmospheric features will provide chances for isolated storms today and tonight and a likelihood of at least scattered thunderstorms early morning to mid afternoon Wednesday. First, affecting west-central Lower Michigan today, is ongoing elevated convection in WI associated with narrow 850 mb moisture transport across IL/WI and a midlevel effective front extending west of a remnant mesolow near Muskegon county. Convection has not been making it into Michigan yet as 850 mb moisture transport is much weaker and instability is low. CAMs suggest the focus of isolated shower/thunderstorm development during the morning will shift northeast into west-central/northwest Lower Michigan, as a transition to diurnal surface-based mixing with southerly winds occurs, and broad upper-level ridging amplifies over the lower Great Lakes which will lead to warming midlevels and increasing convective inhibition with southeastward extent. Any storms that develop will exist in a weakly sheared environment. Today should be a very warm and somewhat humid day for many, easily the warmest day until at least mid June. Next, affecting west/southwest Lower Michigan late this evening through tonight, a compact 500 mb low over Missouri will move toward southern Lake Michigan tonight while weakening as it becomes incorporated into the flow ahead of the main feature, an advancing Upper Midwest trough. Southerly flow at 850-700 mb will increase during the night with some moisture transport, though our area will be in the divergent part of the developing speed max. HREF MUCAPE mean of 250-500 J/kg may support some convection, though not all member models develop storms before the early morning hours of Wednesday. The highest chance of scattered thunderstorms for the whole area will be Wednesday morning through mid afternoon, as a sharp upper- level trough over the Upper Midwest approaches and a surface cold front passes through. The timing of this, relatively early in the day, does mellow the threat, but growing surface- based CAPE to 500-1000 J/kg and 25 knots of 0-3 km shear by mid day could support a marginal severe wind threat for mid-southern to southeastern Michigan (including Lansing-Marshall areas and east). Briefly heavy rainfall rates may occur as deeper environmental moisture will be present through the potential convective layer. - Cooling down for the end of the week and possibly through the weekend Persistent cold air advection is advertised by the models through Friday as low pressure stalls out over northern Lake Huron/southeast Ontario. Ensemble temperature trends are lower in most models for Thursday and Friday and the mean max temp values support several degrees below normal for these two days. With several mid level vort maxes arriving Wednesday night and into Thursday, we could see at least scattered showers. As we go through the weekend, the models are showing some spread with the duration and strength of the stalled out low over the Great Lakes Region. The ECMWF has mid level heights rising as we go through the weekend, but the GFS actually deepens the low and sinks it southward into Lower MI. The Canadian is sort of in between the two. We will continue to feature below normal temperatures as that is supported by the latest ensemble forecasts. With an unseasonably deep low over the northern Great Lakes Region and a tight pressure gradient on the south side of this feature, gusty winds can be expected at times into the weekend. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1259 AM EDT Tue Jun 4 2024 Showers continue to weaken as the cross Lake MI west of KMKG. However, over the next couple of hours, there will likely be some in the vicinity of that airport. After that, patchy fog remains possible over the interior parts of Lower MI. Conditions will likely fall into the MVFR range, but very local IFR is a possibility that we will be monitoring through the night. Instability will be on the increase Tuesday, mainly over western parts of Lower MI. We will have to monitor any lake breeze that tries to develop. That feature could provide enough low level convergence to generate an isolated storm. Overall though that potential is too low at this time to add any thunder to the aviation forecast. && .MARINE... Issued at 336 AM EDT Tue Jun 4 2024 A south breeze today will build 1 to 3 ft waves, highest near the Sable Points. Prevailing winds and waves will provide a low swim risk today, then low to moderate Wed. Swim risk will be moderate or approaching high Thu-Fri 0amid west winds with cooler air. Today through Wed morning, other hazards to boaters and beachgoers would be from isolated to scattered thunderstorms. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...CAS/MJS AVIATION...MJS MARINE...CAS