Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000 FXUS63 KGRR 202303 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 603 PM EST Mon Nov 20 2017 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 325 PM EST Mon Nov 20 2017 A predominately dry and benign weather pattern will prevail this week, including the Thanksgiving travel period. A cold front will pass through on Tuesday but will have little precipitation associated with it. Another cold front over the weekend will bring some rain and snow showers, although minimal travel impacts are expected at this time. && .SHORT TERM...(This evening through Wednesday night) Issued at 325 PM EST Mon Nov 20 2017 Strong southwest flow off lake MI will lead to a temperature contrast across the area tonight, with overnight min temps ranging form the mid 30s inland where boundary decoupling occurs to the mid 40s along the lakeshore. The pesky area of stratocumulus clouds which was north and west of a Holland to Harrison early today has mixed out, but may return again late tonight due to Lk MI effects. The cold front on Tuesday is moisture starved as it comes through Michigan but models do suggest a band of rain showers developing along the front about the time it`s exiting the state late in the day. Best pops tomorrow therefore, although still just chance, will be around JXN in the afternoon. The air behind the cold front late Tuesday and Tuesday night is plenty cold enough for lake effect, but as with the last few pushes of cold air the moisture is quite shallow. So while we will have some lake effect snow showers on Tuesday evening, they will be mostly light with little or no accumulation expected. Surface ridging returns on Wednesday, although with the center of the high being south of Michigan and our low level flow remaining westerly, some lake effect cloudiness may linger. .LONG TERM...(Thursday through Monday) Issued at 325 PM EST Mon Nov 20 2017 The only weather in the extended period is a clipper moving across southern Canada which brings a trailing cold front through Michigan Friday night. Warm advection ahead of the front should bring max temps to near 50 on Friday then strong cold advection kicks in for Saturday with a reinforcing cold shot behind an arctic front coming through Saturday night. Lowered model blend temperatures for Saturday through Sunday as 850 mb temps tumble to about minus 15C Sunday afternoon. Maxes should remain below freezing Sunday afternoon. Also bumped up POPs as light lake effect snow showers in northwest flow will continue into Sunday evening before sfc ridging builds in and inversion heights lower. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 603 PM EST Mon Nov 20 2017 I expect VFR conditions to prevail at all of our TAF sites overnight. There is a chance that MKG, more so than any other of our TAF sites, may see MVFR cigs develop by midnight partly due to the lake wind speed convergence and shallow moist layer seen in the model soundings. Otherwise all taf sites will be impacted by a very strong low level jet, between 03z and 06z there is 50 to 60 knots down as low as 1500 agl. Given winds at the surface will be only 10 to 20 knots, that would be significant low level wind shear. I included that in all of our tafs. On Tuesday a cold front quickly moves west to east across the TAF sites between 12z at MKG and 16z at JXN. Once the cold front comes through I expect MVFR cigs to follow quickly. The low clouds will last past 00z. I do not at this point believe there will be any precipitation through. Bottom line is low level wind shear tonight and mvfr cigs Tuesday with no significant precipitation. && .MARINE... Issued at 325 PM EST Mon Nov 20 2017 Wind speeds have not reached gale force yet, but the winds are forecast to further increase late this afternoon and evening. Will not be making any changes to the ongoing Gale Warning. Winds and waves will subside below gales on Tuesday afternoon but will remain strong enough to warrant Small Craft Advisories after the Gale Warning expires. && .HYDROLOGY... Issued at 1145 AM EST Mon Nov 20 2017 Few rivers continue to rise, but rises have slowed, while others are showing signs of stabilizing. There are small chances for precipitation Tuesday afternoon and Wednesday. Amounts, if measurable, should not have any impact on rivers. Beyond Wednesday, weather looks relatively quiet. Despite elevated river levels, additional river flooding is of low concern. Rivers are likely to recede through the course of the upcoming week. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...Gale Warning until 10 AM EST Tuesday for LMZ844>849. && $$ SYNOPSIS...Meade SHORT TERM...Meade LONG TERM...Ostuno AVIATION...WDM HYDROLOGY...JAM MARINE...Meade

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