000 FXUS63 KGRR 281734 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 134 PM EDT Thu May 28 2020 LATEST UPDATE... Aviation .SYNOPSIS... Issued at 330 AM EDT Thu May 28 2020 - Showers and thunderstorms into tonight - Lingering showers Friday and cooler - Much cooler this weekend - Next system mid next week brings convection back && .DISCUSSION...(Today through next Wednesday) Issued at 330 AM EDT Thu May 28 2020 -- Showers and thunderstorms into tonight -- Today will not be a lot different than yesterday in terms of afternoon and evening convection. However I do not think the convection that is there today will be as vigorous as the past 2 days have been. Precipitable water values are up near 1.5 inches. Model sounding are rather moist all the way up today into tonight. So it does look like locally heavy rainfall once again. The HREF 6hr PMM (probability matched mean) shows similar rainfall for this afternoon, as it did yesterday for yesterday afternoon, and mostly the similar places. However the severe threat is less today than the past 2 days. The model sounding as mentioned above do look rather saturated so downdraft capes are significantly lower than the past 2 days. Also due to the incoming upper wave, heights lower and so do thickness values which means the air will not be as warm , plus with all of that mid level moisture it should be more of a mostly cloudy sky too. Which means less instability. Less instability is shown by numerous models and model sounding today as well as the SPC SREF. The SREF 3 hour calibrated probability of severe storms never gets to more than 2 percent and that is only over our extreme southwest CWA during the late afternoon. Since the soundings are so moist, the only risk would be for gusty winds since there is not enough cape in the mid levels for hail. Downdraft capes are less than 500 j/kg so that threat is rather low today actually. The convection associated with the shortwave ahead of the cold front comes through this evening but instability falls considerably after midnight. I wounder if there will even be enough instability for thunderstorms. The greatest threat for thunderstorms today is mid afternoon into mid evening. That is also the time with the greatest threat for heavy rainfall. -- Lingering showers Friday and cooler -- There is a threat of showers into Friday morning but once the upper trough moves into the area by midday, skies should clear and will not be nearly as warm. -- Much cooler this weekend -- A deep upper trough digs into the Great Lakes this weekend and the southern stream jet core will be south of Michigan. We will be rather chilly with frost not out of the question near route 10 Saturday and Sunday morning. Highs should only get into the 60s both days. -- Next system mid next week brings convection back -- A Pacific shortwave moves through the pattern in the Tuesday to Wednesday time frame. This brings back warmer air and convection. Hard to say this far out how this will play out but it could be another wet pattern. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 130 PM EDT Thu May 28 2020 Occasional reductions in cigs and visibility are possible as showers and a few thunderstorms develop this afternoon and evening. These reductions can go into IFR fairly quickly but may not last more than 30 minutes or an hour at any one point. The more likely timeframe for IFR looks to be late tonight and early Friday morning as a cold front approaches. Ceilings may be IFR at any point from 04z-12z Friday especially. && .MARINE... Issued at 330 AM EDT Thu May 28 2020 Not to much in the way of Marine hazards at this point expect for thunderstorms this afternoon and evening and possibly some patchy fog. && .HYDROLOGY... Issued at 330 AM EDT Thu May 28 2020 The Grand River at Comstock Park and Robinson Township continues to fall and should fall below flood stage today. However, any substantial rainfall from today and tomorrows storms could slow the descent and the fall below flood stage may be delayed. Heavy rainfall today will be localized however there could be brief rises in creeks, streams and urban areas may see localized flooding today as there was yesterday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ SYNOPSIS...WDM DISCUSSION...WDM AVIATION...Hoving HYDROLOGY...WDM MARINE...WDM

NWS GRR Office Area Forecast Discussion

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