Expires:No;;121366 FXUS63 KGRR 130707 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 307 AM EDT Mon May 13 2024 .KEY MESSAGES... - Shower and Thunderstorm Chances Today into Tuesday - Drying Out Midweek - Periodic Risk for Rain Thursday Night into the Weekend && .DISCUSSION... Issued at 244 AM EDT Mon May 13 2024 - Shower and Thunderstorm Chances Today into Tuesday A few lingering light showers this morning to exit to the east prior to daybreak with a dry start expected this morning. Stalled out front near I-96 to provide the focus mechanism for increasing shower and thunderstorm potential mid to late this afternoon. Severe weather is not expected. Coverage of showers/storms should be near I-96 and south with northern areas remaining mostly dry. Initial shower/storm development will be more scattered in coverage before a transition toward a more widespread steady rain occurs late tonight into early Tuesday. Some locations could see over an inch of rain over the next 24 hours or so. High pressure slowly building in will begin to dry things out Tuesday afternoon. Prior to onset of showers later today, temperatures will warm up nicely with mid to upper 70s for most with a non zero chance of a few locations topping out at or above 80 degrees. - Drying Out Midweek Modest mid level height rises and dry surface to 850 mb northeasterly flow is expected for the midweek period beginning Tuesday night and lasting through Wednesday. Low and mid level flow veers southwest by Thursday out ahead of the next system slated to impact the region by week's end. But the majority of Thursday is likely to remain dry as well at this point. - Periodic Risk for Rain Thursday Night into the Weekend Currently, the most likely period for rain is Thursday night into Friday. Uncertainty exists regarding the synoptic pattern for the weekend. For Late Thursday into Friday, an upper trough is forecast to move through. Upper jet divergence is favored for our region. A weak LLJ is shown to nose into the southern portion of Michigan, especially by the 00z GFS and GEM. ECE and GEFS ensemble guidance suggests PWATs rising into the 1.00"-1.25" range. With synoptic scale lift, increasing moisture, and marginal elevated (and potentially some surface based) instability present, showers and thunderstorms remain in the forecast mainly from Thursday evening/night into Friday. POPs are around 50% but likely trending up as we get closer, once medium range guidance pins down the timing. Following this system, much depends on how strong the upper ridging gets over the upper Midwest and Great Lakes, and whether a renewed LLJ develops an orientation that brings in low level moisture and forcing to the region. Various model solutions exist over the weekend, leading to low confidence in the synoptic pattern evolution. Ensemble guidance 50th percentile 24hr QPF currently favors little in the way of rainfall, but several individual ensemble members have some significant rain amounts over an inch. With convectively driven precipitation, that is to be expected this far out. NBM POPs of around 30% for the weekend look good. Highs in the 70s are favored at this time. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 120 AM EDT Mon May 13 2024 Showers and a few thunderstorms have occurred across the region during the early morning hours. The expectation is for any thunderstorms to be moving out of the region by 07z or so. But some showers may remain. Low level wind shear is likely to continue through mid morning before diminishing. A wider coverage of showers will likely move in toward late afternoon or evening, and some thunderstorms will also be possible. No VCTS mention yet, but possible inclusion may be featured with time. && .MARINE... Issued at 244 AM EDT Mon May 13 2024 Lighter winds expected today and much of tonight before an increase in winds occurs closer to Tuesday morning. Small Craft Advisory still looking likely beginning early Tuesday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Maczko/Hoving AVIATION...Hoving MARINE...Maczko