Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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167 FXUS63 KGRR 020735 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 335 AM EDT Tue Jul 2 2024 .KEY MESSAGES... - Chance of Showers and Scattered Thunderstorms Through Wednesday - Risk for Stronger Storms Friday && .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 /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 140 AM EDT Tue Jul 2 2024 An area of showers and thunderstorms in southwest WI and southeast MN will continue to track towards the TAF sites through the remainder of the night and into Tuesday morning. As they approach MI, they are forecast to weaken. However it appears they will not completely dissipate before arriving so I featured VCSH at times in the TAF`s. Elevated instability is show to arrive later Tuesday and into Tuesday evening but confidence on thunderstorms at any particular TAF site was too low to include in the forecast at this time. && .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 from 10 AM EDT this morning through this evening for MIZ037-043. MARINE...Small Craft Advisory from 10 AM this morning to 8 PM EDT this evening for LMZ847>849. && $$ DISCUSSION...CAS/MJS AVIATION...MJS MARINE...CAS