Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000 FXUS63 KGRR 272300 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 700 PM EDT Sat May 27 2017 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 303 PM EDT Sat May 27 2017 Most of the night will be dry, but a few areas could pick up an isolated shower or storm. However Sunday will become wet for most areas by afternoon into the evening. Most areas will pick up a quarter to half inch of rain in this time period. The rains will end toward midnight Sunday night. Another round of showers and storms are expected for Monday afternoon, but these could begin across Central Lower during the morning hours. Then we will dry out Monday night. The rest of next week appears drier, but a few lingering widely scattered showers could occur Tuesday and Wednesday. After temperatures in the 70s through Memorial Day, we will cool into the 60s Tuesday and Wednesday. Then we should return to 70 to 75 for the latter portion of the week. && .SHORT TERM...(This evening through Monday night) Issued at 303 PM EDT Sat May 27 2017 We will see a couple of wet periods during the short term. These will be Sunday afternoon and evening, as well as Monday afternoon. A few hit and miss showers may occur outside of these periods as well. We will be transitioning into a wetter period. However the overnight period looks mainly dry, with an upper ridge sliding off to the east, and a cold front crossing WI. I did reduce the POPs tonight, but can`t rule out a shower or storm skimming across the Highway 10 region overnight, but this will be the exception. The cold front will arrive through the afternoon into the evening on Sunday, likely bring showers and storms. This is a bit slower than the previous forecast package. The best jet dynamics also arrives later in the day. Therefore I have adjusted the POPs to be focused on Western CWA in the afternoon, and over the Southeast CWA into the evening. Agree with the severe weather outlook that includes the marginal chance for severe storms over the SE CWA, where the instability maxes as the jet dynamics come overhead. Best chance for this appears to be late afternoon/early evening. Behind the front, an upper low develops over the Superior region and several spokes, or troughs come through during the late Sunday night through Monday night periods. Highest chance of additional showers and storms will come Monday afternoon, as we build instability, along with series of troughs. .LONG TERM...(Tuesday through Saturday) Issued at 303 PM EDT Sat May 27 2017 Some gradual improvement will occur in the extended period as an upper low slowly moves east. After some diurnally enhanced showers on Tuesday and to a lesser extent Wednesday, there should be a dry period as sfc high builds in and heights rise Wednesday night into Thursday. There is low confidence in the forecast by end of the week as ensemble spread increases. Canadian sfc high may hold on for Friday and Saturday or there could be an area of warm advection and isentropic ascent bringing scattered showers as a sfc low tracks across southern Canada. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 700 PM EDT Sat May 27 2017 Thunderstorms should develop Sunday around or shortly after 15z with strongest storms impacting lower Michigan from 18z through around 00z Monday. Greatest risk for storms appears to be from KGRR to KLAN and to the south and southeast. In and near any storms...periods of mvfr/ifr will be likely. && .MARINE... Issued at 303 PM EDT Sat May 27 2017 Thunderstorms will be the main threat for mariners on Sunday afternoon. WSW winds will increase by Memorial Day when rougher conditions can be expected. Waves should build to 2-3 feet, still below small advisory criteria, but a bit rough for the less seasoned boater. && .HYDROLOGY... Issued at 210 PM EDT Sat May 27 2017 River levels in the upper Grand and the Kalamazoo basins are running above normal for late May while elsewhere the levels are closer to normal. Rain totals around a half inch on Sunday will likely not be enough to produce flooding. Occasional showers over the upcoming week will be rather light. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ SYNOPSIS...JK SHORT TERM...JK LONG TERM...Ostuno AVIATION...Maczko HYDROLOGY...CAS MARINE...JK is the U.S. government's official web portal to all federal, state and local government web resources and services.