Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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966 FXUS63 KGRR 220614 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 214 AM EDT Sun Sep 22 2024 .KEY MESSAGES... - Rain moves in Sunday with Thunderstorms in the afternoon - Chance of Showers and Storms Tuesday, More Uncertain Late Week && .DISCUSSION... Issued at 347 PM EDT Sat Sep 21 2024 - Rain moves in Sunday with Thunderstorms in the afternoon Some much needed rain is expected on Sunday as a negatively- tilted upper trough axis across southern Canada moves east and a trailing cold front pushes through Lower Michigan. We expect showers and thunderstorms to form ahead of the cold front and reach western zones later tonight then expand east across the forecast area on Sunday. Model sounding suggest enough instability for convection during the late morning through afternoon and wind profiles show about 25 to 30 knots of deep layer shear. So some of the convection could be persistent and organized. The storms move east as the front pushes through Sunday night with fair and cooler weather moving in. - Chance of Showers and Storms Tuesday, More Uncertain Late Week As the wave from Sunday pulls away, Monday will be dry as surface high pressure and upper-level shortwave ridging sit over the Great Lakes. These exit Tuesday as a mid-level southern stream wave ejects from the Plains into the central Great Lakes driving an associated surface low with it. This will provide our best chance of rain for the week, however many ensemble members are unenthusiastic about rain chances given questions in evolution of the mid-level pattern. Most solutions keep any rain, if it occurs, under 0.5 inches but there are a few that make a run at 24 hour totals of 1-1.5 inches. Uncertainty only increases mid to late next week as ensembles show a cutoff low developing between the northern and southern stream jets. However where this low forms and how it interacts with northern stream ridging remains highly uncertain at this range. Latest cluster analysis shows the most likely outcome is a dry Thursday However, there`s still about 40 percent of members that keeps more persistent troughing and associated shower chances. Outgoing forecast leans to the more likely outcome. While the where of the cutoff low is uncertain, better cluster agreement exists in this low moving closer to the Great Lakes shower chances so have introduced low PoPs, albeit with still plenty of support for a dry Friday in the ensembles. This flavor of uncertainty is quite common with medium range upper-low setups. Temperature wise, there`s still a 4-8 degree spread in the 25th-75th percentile of high temps given the uncertainty in the upper level pattern. The median solution at present favors a near normal temperature pattern with highs in the low to mid 70s. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 214 AM EDT Sun Sep 22 2024 A cold front is located upstream tonight stretching from portions of Central Wisconsin into Eastern Iowa. VFR weather is occurring well east of the front here in Southwest Lower Michigan with scattered areas of MVFR near the front off to our west. Showers and thunderstorms are occurring at 06z especially over southern Wisconsin. The front will make steady progress to the east today and move through Southwest Lower Michigan in the afternoon and evening hours. MVFR conditions will show up this afternoon as lower ceilings fill in, which will trend to IFR in the late afternoon and evening. Ceilings will dip below 1,000 feet between 21z and 02z near and just behind the front. At this point have showers in the forecast, but we may need to add some thunder with time as the threat gets closer. The thunder threat is not significant or high, but will come between 18z and 23z. Isolated to scattered storms are possible. && .MARINE... Issued at 347 PM EDT Sat Sep 21 2024 Winds and waves will be relatively light through Sunday then increase behind a cold front on Sunday night. A small craft advisory may be needed Sunday night and Monday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Ostuno/Thomas AVIATION...Duke MARINE...Ostuno