Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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974 FXUS63 KGRR 211732 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 132 PM EDT Fri Jun 21 2024 .KEY MESSAGES... - Chance of thunder today, better chance Saturday and Saturday night - Drying out Sunday; Pleasant Monday - Strong storms possible Tuesday/Tuesday night - Dry and cooler Wednesday through Friday && .UPDATE... Issued at 1116 AM EDT Fri Jun 21 2024 The clouds were decreasing around the CWA late this morning and the instability was building. ML CAPE values were up to 1000 J/kg. Effective bulk share values were elevated across the northern zones with a ribbon of 25+ knots. Cams were generating isolated storms by mid afternoon, which seems reasonable given the setup. Low level convergence remains weak/neutral through mid afternoon thus the low level lift may be a limiting factor. The values do increase inland, mainly east of the CWA by late afternoon so its possible stronger convection may develop then. We will also be monitor the convection currently in WI, along with renewed develop there this afternoon. If this batch of convection holds together, it may make a run at the Ludington region this evening. Projected heat index values still support values in the mid to upper 90s for the advisory area, away from the lakeshore. && .DISCUSSION... Issued at 338 AM EDT Fri Jun 21 2024 - Chance of thunder today, better chance Saturday and Saturday night The frontal boundary that triggered storms Thursday is now south of the cwa and pretty nondescript. In it`s wake, we`ll have a little less instability today, however, precipitable water values will remain north of 1.75 inches. We probably won`t see much precipitation this morning. However during the afternoon, the frontal boundary to the south will begin to move back north and there may be a 3-6 hr window beginning around 20z in which we see some convective development over the southeast cwa. There will likely be a decent lake shadow with any convective development due to persistent west winds. Gusty winds and torrential downpours are the main threat with any storms that develop today. Highs around 90 today and dewpoints in the lower 70s will send heat indices into the mid 90s again; no changes to the Heat Advisory. After a dry night tonight, chances for storms will increase Saturday from north to south. Showers/storms will likely be ongoing Saturday morning over northern Lower along the warm frontal boundary. Once the the attendant low moves east, the cold front will begin to drop south during the mid to late afternoon. Showers and thunderstorms will likely develop along the front and will mostly affect the northern cwa Saturday afternoon. SPC has placed the entire cwa in a Marginal Risk for severe storms Saturday/Saturday night. Heavy rain will also be a threat with PWATs closing in on 2.5 inches. Will maintain high probabilities (80-90 percent) for showers and thunderstorms on Saturday night as lead shortwave and sfc cold front pass through the region. Severe weather and heavy rain threat will linger in the evening then wane overnight with the passage of the cold front and departure of the 2"+ PWAT air. The frontal passage will also bring an end to the persistent heat and humidity. - Drying out Sunday; Pleasant Monday On Sunday the primary nrn stream H5 shortwave drops into the nrn GrtLks Rgn and a cooler/less humid air mass filters in on the heels of northwest winds. Morning clouds and lingering showers/drizzle giving way to decreasing clouds in the afternoon. Monday still looks like a pleasant day as the sfc ridge builds in. - Strong storms possible Tuesday/Tuesday night Tuesday could be an active weather day as the warm/humid air makes a quick return from the southwest and temps push toward 90 again. Fast northwesterly flow aloft could send an MCS or two our way from Wisconsin, thriving off cape values possibly in excess of 3000 J/KG. - Dry and cooler Wednesday through Friday The push of warmer air is short-lived as the passage of a cold front on Tuesday night/early Wednesday ushers in another installment cooler/drier air. Northerly winds on Thursday ahead of an advancing sfc high sends dew points down into the 40s/50s. Lows in the 50s and highs in the 70s expected later in the week as high pressure settles overhead by 12Z Friday. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 127 PM EDT Fri Jun 21 2024 Some showers/thunderstorms possible the next 6 hours before a quiet stretch should enter the forecast area. eastern areas most favored for shower/storms this afternoon so included some vcsh for GRR and LAN. could be a repeat of some fog tonight into early sunday but confidence too low to include at this time. showers and breezy conditions begin to work in toward the tail end of the taf period. && .MARINE... Issued at 338 AM EDT Fri Jun 21 2024 A weak pressure gradient today will result in low wind and waves. An approaching cold front Saturday will likely cause wind and waves to increase and a Small Craft Advisory/Beach Hazards Statement may be needed by Saturday afternoon. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 8 PM EDT Saturday for MIZ056-057-064>067- 071>074. MARINE...None. && $$ UPDATE...MJS DISCUSSION...Meade/04 AVIATION...Maczko MARINE...04