Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000 FXUS63 KGRR 250003 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 803 PM EDT WED AUG 24 2016 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 330 PM EDT Wed Aug 24 2016 A low pressure system moving slowly through the Great Lakes region will bring scattered showers and a few thunderstorms through Thursday afternoon. High pressure will build in and bring fair weather Thursday night through Friday night. The next chance for showers and thunderstorms will come late Saturday through Sunday. && .SHORT TERM...
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(This evening through Friday night) Issued at 330 PM EDT Wed Aug 24 2016 Primary short term fcst concerns involve determining potential for convection late this afternoon through Thursday afternoon. 18Z mesoscale analysis indicates weak instability over our fcst area with ml cape values aob 500 j/kg. This is the main reason convection has not developed and ir sat trends and sfc obs continue to show rather extensive cloud cover across most of our area. A few thunderstorms could develop late this afternoon and evening if more breaks in cloud cover develop allowing instability to increase a bit. However a consensus of latest short range guidance suggests much stronger instability will stay well sw to south of our fcst area. The vast majority of convection and severe weather will stay south of our fcst area across portions of IL/IN/OH late this afternoon and evening. However the chance for showers and a few storms remains in our fcst overnight though due to forcing from the cold front that will move into our nw fcst area very late tonight. The cold front will only very slowly move se across the remainder of our fcst area Thursday and will bring scattered showers and a few thunderstorms. The relatively best chc for convection Thursday will be over our se fcst area given the cold frontal timing. Sb/ml cape values could potentially reach around 1000 j/kg over toward KJXN tomorrow aftn prior to fropa. Deep layer shear values are also favorable at around 40-45 kts. So a strong to potentially severe storm seems possible over our se fcst area tomorrow aftn depending largely on the degree of destabilization prior to fropa. However short range guidance consensus suggests that greater instability and the primary threat for severe wx will stay se of our fcst area. High pressure will build in to produce fair weather Thursday night through Friday night. .LONG TERM...(Saturday through Wednesday) Issued at 330 PM EDT Wed Aug 24 2016 Sfc high retreats to the northeast on Saturday with return flow moistening and some warm advection showers encroaching on the western zones in the morning, spreading east in the afternoon. A weak shortwave trough is damping out as it tops the upper high centered over the Mid-Atlantic states. Showers and thunderstorms will be tapering off on Monday, as weak sfc ridging builds in. Generally zonal flow or flat ridging for Tuesday and Wednesday with weak impulses moving through and bringing some isolated showers at times.
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&& .AVIATION...
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(For the 00Z TAFS through 00Z Thursday evening) Issued at 800 PM EDT Wed Aug 24 2016 Generally VFR conditions are expected this evening although some ocnl MVFR cigs are possible for the next couple hours in the vicinity of the scattered rain showers south and east of GRR. The soupy air mass now in place with sfc dew points in the lower 70s and subsidence in between short waves should lead to the development of some stratus and fog overnight. Medium confidence exists that IFR or lower conditions will impact much of the area between roughly 09z and 13z Thursday. Widespread rain showers are expected to arrive from the southwest around 12z Thursday morning, which should mix out the low stratus and fog by 14z, but will result in numerous MVFR cigs and vsbys lingering through at least 18z. The rain should be moving out/dissipating after 18z Thursday but tstms could redevelop around JXN 18z-22z.
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&& .MARINE... Issued at 330 PM EDT Wed Aug 24 2016 A small craft advisory remains in effect from South Haven north to Manistee through very late tonight. South to southwest winds of 15 to 25 kts will result in wave heights of 3 to 6 feet. The highest wave heights within that range will be found north of Holland. && .HYDROLOGY... Issued at 121 PM EDT Wed Aug 24 2016 A Flood Warning remains in effect for the Portage River near Vicksburg into the weekend. More rain is expected for this area and river levels will be slow to fall. River levels are above normal across the area but falling. Additional rainfall may bring levels near bankfull, but new river flooding is not expected through the weekend. && .GRR Watches/Warnings/Advisories... MI...Beach Hazards Statement until 2 AM EDT Thursday for MIZ037-043- 050-056-064. LM...Small Craft Advisory until 2 AM EDT Thursday for LMZ845>849. && $$ SYNOPSIS...Laurens SHORT TERM...Laurens LONG TERM...Ostuno AVIATION...Meade HYDROLOGY...63 MARINE...Laurens

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