613 FXUS63 KGRR 212353 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 753 PM EDT Sat Aug 21 2021 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 328 PM EDT Sat Aug 21 2021 -Widely scattered showers and tstms through Sunday -Continued quite warm next week with low storm threat && .DISCUSSION...(This evening through next Saturday) Issued at 328 PM EDT Sat Aug 21 2021 --Widely scattered showers and tstms through Sunday-- Weakening, slow moving sfc cold front drifts in from the west tonight, triggering a few showers and tstms. Coverage is expected to be limited though due to lack of upper support/shear. Heights are actually shown to rise overnight and the associated subsidence should suppress the convective threat. That said, wouldn't rule out a few very localized heavier downpours since the axis of 2 inch PWATs along and just ahead of the front will move in later tonight. Decent area of sfc convergence related to the sfc front is shown for Sunday near/east of Hwy 131 and near/south of I-96. Expect diurnal flare up of widely scattered convection in this area Sunday afternoon as ml capes reach or exceed 1000 J/kg, but no severe weather expected due to continued lack of shear. Highest pops, although still <40 pct, will be around LAN and JXN. --Continued quite warm next week with low storm threat-- High confidence for dry conditions Monday due to sfc ridging in the wake of the departing front, but a somewhat challenging fcst for the rest of next week. We'll be pinned in between the belt of stronger westerlies to our north and the subtropical high to our south. Overall guidance trends the last few days has been for a farther north position of these features, implying that the best coverage and highest frequency of convection next week will be generally to our north (and remaining very warm and humid). Other complicating factor is low confidence in the daily position/orientation of a wavy sfc frontal boundary during the week which could be a focus for scattered convection. Currently our best chance of showers and storms looks to be on Tues night/early wed, otherwise just frequent 20-30 pops in the fcst through the week. Confidence is high though that highs temps will continue to be to the mid to upper 80s through next weekend with dew pts mostly at or above 65. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 753 PM EDT Sat Aug 21 2021 First order of business are the showers and thunderstorms moving out over Lake Michigan from Wisconsin. Instability is much greater over Wisconsin as compared to over Lake Michigan and Lower Michigan. We expect the showers and storms to largely dissipate over the Lake. A stray shower or storm may impact KMKG, otherwise the TAF sites should stay dry tonight. Cannot rule out an isolated shower or storm this evening over Lower Michigan, but the chance is so small left out of the other TAFs. Next concern is the threat of low ceiling developing near and behind a cold front tonight. These MVFR ceilings will likely impact KMKG, KGRR and KAZO late tonight into Sunday morning, between 09z and 16z. Light fog (MVFR) will likely impact much of the TAF sites tonight with visibilities in the 3-5SM range between 09z and 14z. Scattered showers and thunderstorms are expected to develop in the 18z to 23z time frame on Sunday for areas to the south and east of KGRR. So, KBTL, KLAN and KJXN will likely be impacted Sunday afternoon. && .MARINE... Issued at 328 PM EDT Sat Aug 21 2021 Have expanded the Small Craft Advisory and Beach Hazard Statement issued earlier (north of Whitehall) farther south but with a later start time. Adverse conditions develop first late tonight near Big and Little Sable Points as a NNE wind to 30 kts develops behind the cold front. It really takes until Sunday afternoon though for conditions to worsen south of Whitehall, once the winds bend around more northwesterly. The marine headlines in the southern zones begin at 11 AM Sunday and the highest waves will be south of Holland. The lowest waves heights at the shoreline will be around Muskegon and Grand Haven as is typical in a northerly flow regime. Winds and waves subsiding after sunset Sunday with tranquil conditions following for Monday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from Sunday morning through Sunday evening for MIZ050-056-064-071. Beach Hazards Statement from 2 AM EDT Sunday through Sunday evening for MIZ037-043. LM...Small Craft Advisory from 2 AM to 8 PM EDT Sunday for LMZ848-849. Small Craft Advisory from 11 AM to 8 PM EDT Sunday for LMZ844>847. && $$ SYNOPSIS...Meade DISCUSSION...Meade AVIATION...Duke MARINE...Meade