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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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478 FXUS63 KGRR 170156 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 956 PM EDT Fri Aug 16 2024 .KEY MESSAGES... - Potential for Thunderstorms into Saturday - Mostly dry and cool next week && .UPDATE... Issued at 956 PM EDT Fri Aug 16 2024 Solid line of showers with embedded thunder, associated with the next shortwave rotating around the upper low, continues to move slowly east across Lk MI. Other scattered cells have been developing ahead of the main line with MLCape around 1500 J/KG. Deep layer shear remains limited at only about 20-25 kts so not much organization to this line. Main impact should be locally heavy downpours and perhaps a few cloud to ground lighting strikes. && .DISCUSSION... Issued at 252 PM EDT Fri Aug 16 2024 - Potential for Thunderstorms into Saturday The mid level low in northern WI will slowly drop down into lower MI on Saturday. The deeper cyclonic flow associated with this feature along with the cooling aloft will support a continued environment favorable for shower formation. PWAT`s remain elevated with values up around 1.5 inches based off of the ensemble plots. Ensemble qpf plots suggest most locations will be seeing some rain during this period as most members are showing qpf. We also maintain some instability through the period so a risk for thunderstorms exists. The convection that has persisted this morning along the lakeshore was weakening. Overall the forcing remains weak this afternoon but decent surface based CAPE is expected with inland values up over 1000 J/kg. There will also be weak low level convergence inland. Based on this, any renewed convection this afternoon should be further inland with the coverage forecast to be isolated/scattered. Early this evening a stronger mid level vort max moves in and the lift associated with this feature is expected to lead to a an area of storms tracking eastward into the CWA. As for the severe thunderstorm risk, the core of stronger mid levels winds stays south and west of the CWA which will limit the deep layer shear and degree of storm organization. As for Saturday, much less instability is forecast. However with the cold temperatures aloft and deep cyclonic flow, any heating will generate showers and a few storms. We will maintain the risk for storms in the forecast into Saturday. - Mostly dry and cool next week A few lingering showers on Sunday will exit the area as the upper low in our neck of the woods finally moves off to the east. In it`s wake, Lower Michigan will spend the bulk of the upcoming week under the influence of northwest flow, thanks to an upper level ridge that reasserts itself over the plains. What this means for us is a cooler- than-normal airmass (highs pleasantly in the 70s), low humidity, plenty of sunshine, and relatively light winds. Overall, a very tranquil week appears to be on track for us. There are some indications that a shortwave comes over the ridge sometime in the 2nd half of the week and could produce a few showers for us, but this is far from certain, and regardless is not likely to "ruin" any days. Of note, overnight temperatures especially early in the week are likely to be fairly chilly and will be dropping down into the 40s - especially in rural/northern areas. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 803 PM EDT Fri Aug 16 2024 Thunderstorms approaching from the west at 00Z will impact the terminals between roughly 02Z and 06Z. Brief vsbys reductions to IFR in heavy rain and a local wind gust up to 30 kts are possible if any of the heavier cells pass over terminal. Even after those storms pass through later tonight, some lingering showers will persist overnight into Saturday. Cigs trending into the MVFR or possibly IFR category for late tonight/Saturday morning, then gradual improvement to cigs expected after 18Z Saturday. Cigs likely recovering to mostly VFR levels by 21Z, although scattered showers and a few tstms remaining possible, mainly inland from the Lk MI shoreline. && .MARINE... Issued at 252 PM EDT Fri Aug 16 2024 The winds and waves have decreased this afternoon as expected but they will increase again on Saturday, especially later in the day. Based on recent wave model forecasts, I decided to issue a small craft advisory and beach hazards statement for Saturday south of Grand Haven. It`s looking like the waves will reach 4 feet there tomorrow. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from 8 AM EDT Saturday through Saturday evening for MIZ056-064-071. MARINE...Small Craft Advisory from 8 AM to 10 PM EDT Saturday for LMZ844>846. && $$ UPDATE...Meade DISCUSSION...MJS/AMD AVIATION...Meade MARINE...MJS