Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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982 FXUS63 KGRR 021743 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 143 PM EDT Tue Jul 2 2024 .KEY MESSAGES... - Chance of Showers and Scattered Thunderstorms Through Wednesday - Risk for Stronger Storms Friday && .UPDATE... Issued at 1100 AM EDT Tue Jul 2 2024 No major changes to the forecast. Showers continue to move into the region from the west with them moving over a dry air mass which should limit most rain to north of the I 96 corridor. Latest CAMS do have some increase POPS possible along and just to the south of the I 96 corridor this afternoon. Waves along the lake are currently low along and south of Muskegon. Winds and waves are expected to increase north of Muskegon this afternoon into the evening hours. && .DISCUSSION... Issued at 335 AM EDT Tue Jul 2 2024 - Chance of Showers and Scattered Thunderstorms Through Wednesday Warm advective pattern over Lower Michigan resumes on the west side of the departing high pressure area, while a weak surface low associated with an upper-level shortwave trough will organize over Iowa and move toward Northern Michigan tonight. As midlevel moisture streams in today, altostratus clouds will thicken and occasionally produce precip amid isentropic lift and perhaps some weak and shallow instability layers. The lower atmosphere is still fairly dry so will tend to reduce the precip to sprinkles south of I-96. North of Muskegon to Mt Pleasant has the better chance of measurable rainfall during the day. Continued 850-700 mb moisture advection tonight and slightly cooler air above may yield instability deep enough for scattered thunderstorms, especially NW of Grand Rapids. HREF member models overall are not producing much convection given the limited instability and lifting mechanisms. If storms do occur, forecast soundings are still fairly dry below 5,000 feet, and with low- level winds just above the stable surface layer increasing to 40+ knots, there is potential for locally gusty conditions early Wed. On Wednesday, the surface trough / weakening cold front will progress east of most of the CWA, leaving the chance of afternoon convection development constrained to near and south/east of Jackson. - Risk for Stronger Storms Friday The ECMWF continues to advertise a stronger southwesterly upper level jet streak arriving here in MI during the day on Friday. A digging 500 mb trough forms into a closed low as is tracks northeastward through the state. The surface pattern shows a weak warm front extending eastward through the CWA midday Friday before lifting northeast of the CWA later in the afternoon. Deep layer shear and surface based instability both show favorable setup for at least a period of organized storms as the instability axis shifts northeast through the region during the early to mid afternoon hours on Friday. The GFS is similar to the ECMWF with the setup, although it is several hours slower with the warm front and instability axis shifting through the region and the Canadian is even slower than the GFS. Thus, uncertainty exists with the timing, which will be important when determining how much if any impact the region see`s from the storms. The various model ensemble qpf output shows considerable spread in the values amongst the members so that adds the the uncertainty. For now, we will continue to feature higher POPs for Friday throughout the CWA as most ensemble members are showing measurable values. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 143 PM EDT Tue Jul 2 2024 Our focus of this forecast period will be on trends of shower activity, and any associated low clouds/fog that will be associated with them. The first main batch of rain is affecting mainly KMKG at press time, with lots of rain not reaching the sfc elsewhere further south and east. Dry air below 8-12k ft agl is holding on at all of the other sites where the rain is not as heavy. We expect a few light showers/sprinkles at the other sites, and will account for this with some VCSH/p6sm -shra wording. There will be a lull in the widespread activity then this evening and early overnight. A core of winds from the SW around 40 knots at 2k ft at the northern terminals and lighter winds at the sfc will produce enough low level wind shear to mention. The southern terminals will not see as much wind aloft. Additional rain showers will move in later tonight from west to east ahead of a front. The lower levels are expected to moisten a bit, and allow more rain to reach the ground everywhere. We do anticipate that all sites should see MVFR conditions late tonight and Wednesday morning. Clouds will lift toward and just after the end of this forecast period Wed afternoon. && .MARINE... Issued at 335 AM EDT Tue Jul 2 2024 The small craft / beach hazards threat today and Wednesday will come in two parts. Will issue advisory/statement for the first part today and adjust them later on if needed for Wednesday. South-southeast winds over Lake Michigan strengthen late this morning to mid afternoon as a pressure gradient briefly tightens between relatively higher pressure ridging over southern Michigan and lower pressure troughing over the UP. Frequent gusts 25 to 30 knots are most favored north of Whitehall, according to the varied solutions of the short-term models. There may be a few hours when winds become hazardous to small craft between Whitehall and Grand Haven but this is less certain. Given the southeast component of winds and thus limited fetch, the high risk of hazardous waves and currents for swimmers may stay focused around Whitehall to Little Sable Point and also Ludington State Park and Big Sable Point, while a moderate risk extends south from Whitehall to Grand Haven. The risk may coincide with the arrival of rain showers. Winds veer southwest early Wednesday morning in the vicinity of a cold front with scattered showers and thunderstorms that may sporadically increase the gust potential. Hazardous conditions for swimmers and small craft may develop along much of the West Michigan shoreline pre-dawn Wednesday into mid day. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement until 8 PM EDT this evening for MIZ037- 043. MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ847>849. && $$ UPDATE...Ceru DISCUSSION...MJS/CAS AVIATION...NJJ MARINE...CAS