Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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921 FXUS63 KGRR 202349 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 749 PM EDT Mon May 20 2024 .KEY MESSAGES... - Marginal Risk of Severe Weather This Evening - Slight Risk of Severe Weather Tuesday Night - Chance of Storms Wednesday && .DISCUSSION... Issued at 305 PM EDT Mon May 20 2024 - Marginal Risk of Severe Weather This Evening Multiple lines of convection from Lake Michigan to southern Wisconsin and northern Illinois this afternoon will be moving into Lower Michigan this evening. Latest radar trends are showing a weakening of the storms over Lake Michigan but these storms could strengthen again as they move back over land with 500 to 1000 J/kg of MUCAPE to work with. The main threat is isolated wind damage with the strongest convection. The severe threat will diminish with loss of sfc heating this evening. The showers will be exiting the eastern zones around midnight. - Slight Risk of Severe Weather Tuesday Night There should be a lull in the convection as the first shortwave trough minors out/moves east and is replaced by flat ridging before heights fall again late Tuesday afternoon and evening as the next shortwave trough axis swings through along with increasing shear profiles and deep lift. Scattered convection in the afternoon will give way to increasing POPs as organized convection along and ahead of the cold front pushes in from the west. Primary threat will again be scattered wind damage with stronger updrafts or bowing line segments, but model soundings from the GFS and NAM show possible QLCS tornado threat with favorable low level helicity as near sfc winds veer strongly with height. - Chance of Storms Wednesday The front bringing the chance for severe weather Tuesday night continues to drive south and east during the day on Wednesday. The GFS/NAM have trended towards the ECMWF suggesting the front clears our southeast CWA in the vicinity of 18z Wednesday. Given how early the front clears the area, the potential for convective redevelopment is uncertain. There are signals for the potential of showers and storms to develop south and east of Grand Rapids, mainly down towards Jackson, Wednesday afternoon and evening aided by a passing vorticity maximum.. If any development can happen on the warm side of the front, a strong to severe storm cannot be ruled out given 40-45 knots of deep layer shear hence the current marginal risk for severe storms. Rain chances end early Thursday. Dry weather is expected Thursday into Friday as surface ridging aided by zonal flow at 500mb ridging by Friday and little to no deep layer moisture. The lack of moisture also keeps plenty of sunshine in the forecast with highs well into the 70s Thursday and Friday. An lead shortwave ahead of a parent trough approaches early Saturday increasing clouds and rain chances, further increasing Saturday and into the day on Sunday as a weakening surface low sends a front through the area with renewed cyclogenesis over the central Great Lakes. Exact timing and placement of important features, as expected over 5 days out, is still uncertain but the broader signal across guidance is generally similar. So, while timing and extent of any precipitation is uncertain, the chance does exist for rain during the memorial day weekend. This means the NBM 30-40 percent PoPs are appropriate for the end of the week. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 743 PM EDT Mon May 20 2024 As expected, a line of thunderstorms is moving across Western Lower Michigan. Cig/Vis aren`t dropping too much as these storms go through, with conditions mostly staying low VFR, but winds do become briefly gusty and erratic. This line of storms moves east over the next several hours and is expected to be fully past Lansing and Jackson by 4-5z tonight. An area of low clouds and fog are still expected to develop for the 2nd half of the night and continue through sunrise. LIFR conditions still look likely, and recent model trends suggest AZO/BTL/LAN could get in on the cig/vis reductions now as well, though they should be on the edge of the worst conditions. Regardless, conditions improve rapidly after sunset tomorrow as strong mixing wipes out the clouds and sun takes back over. && .MARINE... Issued at 305 PM EDT Mon May 20 2024 Offshore winds and waves below 3 feet through Tuesday although there could be some locally strong winds and choppy waves in the vicinity of thunderstorms this evening and again Tuesday night. Winds will pick up Tuesday night and Wednesday with waves building to 6 to 8 feet Wednesday morning. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Ostuno/Thomas AVIATION...AMD MARINE...Ostuno