Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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641 FXUS63 KGRR 190549 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 149 AM EDT Wed Jun 19 2024 .KEY MESSAGES... - Small Risk for Stronger Storms into Late This Afternoon - Backdoor Cold Front may drop down from the north Thursday - Heat/Humidity Persists into Saturday - Cooler Weather Behind a Cold Front Sunday && .UPDATE... Issued at 1047 PM EDT Tue Jun 18 2024 While there was some instability aloft as indicated by some altocumulus, overall the divergent pattern kept any convection from forming. Still keeping an eye as long line of showers and storms moves into Wisconsin. Latest CAMS continues the trend of showing this line weakening as the night continues. Have left slight chance POPS in the far northwest in case the remnants clip the region overnight. && .DISCUSSION... Issued at 240 PM EDT Tue Jun 18 2024 - Small Risk for Stronger Storms into Late This Afternoon Low level convergence has been relatively weak so for and the instability has been building steadily. Surface based instability ranged from around 1000 J/kg south to 2000 J/kg north with ML values about half those values. A mid level vort max was tracking through western parts of the CWA and that feature will push northeast over the next few hours. Based on the instability values and lift, a few storms could get going, primarily over eastern parts of the CWA in the next couple of hours. They could have the potential to produce locally stronger wind gusts, but even that risk looks low given the lack of DCAPE. On the backside of this mid level wave, NVA will generate some subsidence which would limit the storm risk for western parts of the region. - Backdoor Cold Front may drop down from the north Thursday This feature could keep temperatures down a few degrees Thursday, lessening the risk for heat related impacts. Ensemble output from the Canadian and GFS suggest the Grand Rapids area will likely fall short of 90 degrees for high temperatures Thursday but the 12z ECMWF still has central parts of the CWA reaching into the low 90`s. We will not change the headline for Thursday just yet, but confidence on reaching criteria has trended lower. - Heat/Humidity Persists into Saturday No changes to headlines planned. As noted previously, Saturday looks quite hot, perhaps even more so than the preceding days. This will be at the end of a prolonged and deleterious stretch of heat and humidity. Moreover, being the weekend, there will be even more exposure to the risk. All of this supports the notion of extending the heat advisory into Saturday - but as it currently is only Tuesday, we still more time to assess trends. - Cooler Weather Behind a Cold Front Sunday As noted previously, guidance is starting to converge on a solution that brings showers and thunderstorms through the forecast area Saturday night. As is often the case, the best upper PV forcing will be shifted a bit poleward of the best instability, so it`s unclear how strong convection will get. But, as I noted previously, the odds favor at least some strong/severe convection during this time given the pronounced airmass change. Predictability really falls off the shelf after Monday, although generally speaking, we can expect another round of above normal temperatures and precipitation chances right around climatology starting Tuesday. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 149 AM EDT Wed Jun 19 2024 VFR continues with cloud bases at or above 12,000 ft. Widely scattered tstms developing this afternoon and continuing into early evening. Local/brief IFR conditions possible should a storm with heavy rainfall pass over a terminal, with the main risk of storms being south and east of GRR between roughly 20Z and 02Z. Southwest winds 10 to 20 kts (higher at MKG), diminishing later in the day and especially this evening. && .MARINE... Issued at 1059 PM EDT Tue Jun 18 2024 While there have been periods of SCA criteria the winds have slackened However LDM and Big Sable Point remains gusty up to 25kts so will keep SCA going overnight. Latest models keep marginally hazardous conditions through tomorrow morning. Previous Discussion: The southwest winds at 925/850 mb are progged to increase this evening as the pressure gradient at those levels tightens. This will likely result in increasing southerly surface winds especially north of Grand Haven. Based on this we will maintain the headlines for small craft and swimmers in those locations. We will need monitor locations further south as conditions are likely to be become marginally hazardous. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement through this afternoon for MIZ037-043- 050. Heat Advisory until 8 PM EDT Friday for MIZ043>046-050>052- 056>059-064>067-071>074. Air Quality Alert until midnight EDT tonight for MIZ050-056-057- 064-071. MARINE...Small Craft Advisory until 4 PM EDT this afternoon for LMZ847>849. && $$ UPDATE...Ceru DISCUSSION...MJS/NJJ AVIATION...Meade MARINE...MJS/Ceru