Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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857 FXUS63 KGRR 161905 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 305 PM EDT Sun Jun 16 2024 .KEY MESSAGES... - Thunderstorms Tonight - Hot, humid with occasional thunder this week && .DISCUSSION... Issued at 305 PM EDT Sun Jun 16 2024 - Thunderstorms Tonight The showers and storms across the central and northern zones will move east this afternoon and should be moving east and out of the forecast area this evening. Then we watch an MCV moving through northern Illinois and southern Lake Michigan into our southwest zones with the potential to bring locally heavy rain, hail and high winds overnight across the southern half of the forecast area. SPC marginal risk covers this threat area. - Hot, humid with occasional thunder this week The MCV propagates east and out of the forecast area by Monday morning but is expected to leave behind an outflow boundary across the southern forecast area that could focus some convection Monday afternoon. The HREF has apparently picked up on this idea and now has 70 to 80 percent probabilities of 0.1 QPF in this area on Monday afternoon. We painted an area of higher POPs there but kept them in the 25 to 35 percent range given lack of confidence in the specifics. The Heat Watch was not changed and it still appears that this could be a long duration event where the cumulative effect of high daytime and night time temperatures could necessitate a warning being issued even without warning criteria being met on any one day. There remains uncertainty on extent of convection on Tuesday afternoon, but the the biggest uncertainty remains on Thursday and Friday as a cold front or convective outflow could modify temperatures across the northern half of the forecast area. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1210 PM EDT Sun Jun 16 2024 Clusters of thunderstorms and moderate to heavy rain continue to develop between Muskegon and Milwaukee. Models suggest less instability available with eastward extent into Michigan, which would support a slow weakening trend, so not confident enough yet to include GRR in a TS around 18-19 Z but will do so for MKG. There has been an increase in the number of short-term models which capture the mesoscale convective vortex over northern Missouri to southeast Iowa and thus produce thunderstorms over some of our aerodromes tonight. If this MCV indeed tracks through northern Illinois later today and into southwest Lower Michigan with thunderstorms, storms in our area would be capable of the usual hazards including IFR visibility with heavy rain, lightning, LLWS or 30-45 knot surface wind gusts and wind shifts. Most likely affected would be AZO, BTL, and GRR, and MKG. Will go with VCSH for now but later forecasts may need to narrow down a time frame to add TS at some point between 02 and 12 Z. && .MARINE... Issued at 305 PM EDT Sun Jun 16 2024 No changes to the SCA or CFW. Current forecast on track with southerly winds driving some higher waves from Grand Haven north with structural and longwave currents making swimming dangerous. Winds and waves could be locally higher in thunderstorms this evening south of Muskegon. Winds and waves will decrease slightly on Monday as the sfc pressure gradient slackens a little, but the night shift can evaluate this and determine if small craft and swim conditions will improve enough for the SCA and CFW to expire at 2 am or have to be extended. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement until 2 AM EDT Monday for MIZ037-043-050- 056. Air Quality Alert from midnight tonight to midnight EDT Monday night for MIZ037-043-050-056-064-071. Excessive Heat Watch from Monday afternoon through Friday evening for MIZ043>046-050>052-056>059-064>067-071>074. MARINE...Small Craft Advisory until 2 AM EDT Monday for LMZ847>849. && $$ DISCUSSION...Ostuno AVIATION...CAS MARINE...Ostuno