071 FXUS63 KGRR 172022 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 422 PM EDT Sat Aug 17 2019 LATEST UPDATE... Marine .SYNOPSIS... Issued at 322 PM EDT Sat Aug 17 2019 - Multiple chances for thunderstorms exist through mid week. Strong storms are possible. - Dangerous swimming conditions are expected Sunday. - Cooler temperatures prevailing into next weekend. && .DISCUSSION...(This evening through next Saturday) Issued at 322 PM EDT Sat Aug 17 2019 The main forecast concern is the potential for thunderstorms into mid week, as zonal flow brings multiple weak waves over the area. Ridging will then form in the west by Wednesday and move toward Lower Michigan forcing the waves to the north of the region. Therefore, the second half of the week into the weekend should be more tranquil. Due to the uncertainty in timing of the waves and the location of the convection as they react with meandering fronts, confidence remains low for the first half of the forecast. The wave moving by the area today will move away late this evening, only to be followed by a stronger wave Sunday and a weaker pulse Sunday night. Looking like strong thunderstorms are possible Sunday with hail and gusty winds as the main hazards. The additional waves, Tuesday through Wednesday, appear to again be weaker and should result in non severe weather with some thunderstorms. Besides the thunder threat, patchy fog is expected late tonight with locally dense fog possible. Fog could also be a problem into mid week, as the forecast rainfall and atmospheric moisture could lead to fog any night as temperatures cool off. Temperatures will be above normal into mid week, then fall to below normal into the weekend. Normal highs this time of year are around 80 degrees and normal lows are around 60 degrees. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) Issued at 114 PM EDT Sat Aug 17 2019 Two chances for storms during the period. The first is later this afternoon and will mainly affect the southern TAF sites. An area o showers/storms is moving east from Chicago and will move along I-94 mid to late afternoon. The second chance arrives closer to 12z. Confidence is moderate that we`ll see some storms after 12z and these should affect all of the TAF sites. MVFR cigs expected overnight, especially along I-94 where moisture from recent rain will enhance fog/low cig chances. && .MARINE... Issued at 420 PM EDT Sat Aug 17 2019 Winds and waves Sunday on Lake Michigan should reach Small Craft Advisory levels (SSW winds of 15 to 25 knots and 3-5 foot waves), so an Advisory was issued from 8 AM to 8 PM. Winds and waves will increase in the morning resulting in longshore currents and waves topping piers given the high water levels. A Beach Hazard Statement will also be issued for Sunday. Calmer conditions are expected to start the workweek. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from Sunday morning through Sunday evening for MIZ037-043-050-056. LM...Small Craft Advisory from 8 AM to 8 PM EDT Sunday for LMZ846>849. && $$ SYNOPSIS...63 DISCUSSION...63 AVIATION...04 MARINE...63

NWS GRR Office Area Forecast Discussion

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