Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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206 FXUS63 KGRR 240537 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 137 AM EDT Mon Jun 24 2024 .KEY MESSAGES... - Two Rounds of Strong to Severe Storms Possible Tuesday - Dry Mid Week With Rain Returning Friday && .UPDATE... Issued at 1024 PM EDT Sun Jun 23 2024 Have updated the forecast to include scattered showers along with isolated thunderstorms up in the northwest CWA towards Ludington. A strong upper shortwave trough is diving southeast through the Northern Great Lakes this evening. Cold mid levels associated with the trough and surface moisture via Lake Michigan are aiding in instability. Surface dew points around Lake Michigan remain in the 60s. HRRR soundings from out over the lake at 02Z show very small pockets of instability of 500-1000 j/kg. This is clearly enough instability to produce both showers and thunderstorms. At this point we have confined chances for showers and storms to the northwest forecast area to the north and west of GRR. If the activity holds together longer we will update the forecast as necessary. Otherwise expecting a clear / partly cloudy night with cool temperatures in the 50s. && .DISCUSSION... Issued at 257 PM EDT Sun Jun 23 2024 For tonight and Monday, no changes of note. Some model guidance brings some brief sprinkles to our northwest forecast area and adjacent waters, but this is low probability and non-impactful even if it occurs. Otherwise, we are seeing a gradual erosion in clouds and this should be hastened this evening by nocturnal stabilization of the boundary layer. - Two Rounds of Strong to Severe Storms Possible Tuesday An active long term period is expected across West Michigan. The first timeframe of concern will be early Tuesday morning as a typical "ridge rider" MCS pattern sets up. Thunderstorms across Minnesota and Wisconsin will grow upscale into an MCS. Consensus among a majority of the 12z CAMS is this arrives still intact with 500+ J/kg of MUCAPE advecting in ahead of it. Some uncertainty exists in two key areas that will determine whether damaging winds affect the CWA. First is the extent of low-level stability. Model soundings show a notable low-level stable layer which may limit to what extent winds can mix to the surface. Second is uncertainty as to how much instability advects in ahead of this feature determining how quickly the MCS dies. The best chance of any wind impacts if they occur will be along and northwest of a South Haven to Clare line. Given the progressive nature of the MCS flooding is not expected with this round. A second round of severe storms is possible Tuesday afternoon. However, certainty remains lower as afternoon convective evolution will depend on evolution of the morning MCS. Model consensus is that atmospheric recovery does occur behind the MCS with LREF 50th percentile CAPE values climbing to 1500 J/kg Tuesday evening. In addition, the morning MCS activity brings the potential of leaving a remnant outflow boundary which could serve as a convective trigger. By late Tuesday afternoon into the evening, a cold frontal boundary moves through the CWA bringing the potential for strong to severe storms mainly near and south of I96. The main question with this round is shear. While a low-level jet will be in place, the mid- level jet will be displaced to the Northwest limiting deep-layer shear. However, forecast soundings suggest 25-35 knots of effective shear which would be enough to support a severe weather risk combined with the ample CAPE. This will need to be monitored over the next 48 hours as mesoscale trends become more apparent. The other concern is excessive rainfall. Mean cloud-layer winds look to be front-parallel which brings a chance of training storms and locally heavy rain as a result. - Dry Mid Week With Rain Returning Friday Wednesday into Thursday will feature dry weather across West michigan as approaching surface and mid-level ridging cause dry conditions and at partly cloudy or better skies across West Michigan. By Friday into Saturday there is a decent signal across guidance for chances of showers and storms. Chances begin Friday associated with warm air advection and the lifting of a warm frontal boundary across the CWA. A cold frontal boundary causes shower and thunderstorm chances to continue into Saturday as a cold front passes through. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 137 AM EDT Mon Jun 24 2024 Small cluster of thunderstorms has bright very brief IFR conditions to MKG and GRR and these storms could affect AZO and BTL with brief IFR conditions as well between 06Z and 07Z. The storms are expected to weaken as they move south and genera;;y IFR conditions can be expected for the rest of tonight and on Monday. && .MARINE... Issued at 404 PM EDT Sun Jun 23 2024 Based on most recent trends and plenty of beach traffic per webcams, we decided to extend the Small Craft Advisory and Beach Hazards Statement from Grand Haven southward until 8 PM EDT. Previous discussion follows... We have seen a recent localized uptick in winds and waves at the Holland buoy and a similar wind bump at the Muskegon Coastal Marine station. This matches a small pocket of elevated winds advertised by the 17Z HRRR. This particular model run shows this pocket peeling quickly southward along the lakeshore as it becomes more diffuse, so we are therefore still comfortable with maintaining a 5 PM expiration for our Small Craft Advisory and accompanying Beach Hazards Statement. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ UPDATE...Duke DISCUSSION...TJT/Thomas AVIATION...Ostuno MARINE...TJT