Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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578 FXUS63 KGRR 221932 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 332 PM EDT Sat Jun 22 2024 .KEY MESSAGES... - Strong/severe storms this evening into tonight - Round of storms possible for late Monday night into early Tuesday && .UPDATE... Issued at 1137 AM EDT Sat Jun 22 2024 Based on the latest wave model forecasts, we expanded the small craft advisory and beach hazards statement one county/zone further north. One area of heavy rain was tracking through the Pentwater to Ludington region. It appears that fairly widespread amounts of around an inch may accompany this initial batch. Additional heavy rain is likely this afternoon and evening with the storms in southern WI tracking east northeast. Off of SPC`s meso analysis page, PWAT values were around 2 inches in this region with really impressive 925-850 mb moisture transport going on. 12z soundings from GRB and APX support an efficient warm rain event along with warm topped convection with the MPL well under the trop. Rainfall rates could easily top an inch per hour. Thus we will maintain the flood watch. As for the severe potential, low level convergence was maximized closer to the warm front over the northern zones with divergence flow further south. Instability was building throughout the area with ML CAPE values up to 500 J/kg and bulk effective shear values over 30 knots. An area of stronger 0-1 km shear vectors was noted west of Pentwater and moving northeast. The flow remains relatively divergent for much of the CWA for a few more hours so we may struggle to develop widespread convection. However by mid afternoon and more so late afternoon we could start to see an increase in the low level convergence which would support newer storm development. We will also need to monitor the trends of the storms in southern WI as when the try to track into the CWA, they could generate enough low level lift to persist. Given the favorable instability and shear at that time, we could end up with an organized cluster of storms rolling through. Until then, it appears the northern parts of the region is the favored location for strongest storms given stronger 0-1 km bulk shear values through mid afternoon. && .DISCUSSION... Issued at 234 PM EDT Sat Jun 22 2024 - Strong/severe storms this evening into tonight The combination of decent ML CAPE values of 500 to 1000 J/kg, 100 to 125 J/kg of 0 to 3 km ML CAPE and increased surface convergence along a warm front has produced a favorable setup for some storms with rotating updrafts over northeast parts of the CWA. The low level convergence is progged to weaken over the next hour or two so that may limit the coverage of storms. By 23z, the storms in WI may be working into western parts of the CWA. Overall the low level convergence is still shown to be weak but high res models are showing another area of storms arriving in the 01z to 03z window. This is when the mid level jet is pushing in from the west. As a result these storms do have a potential for enhanced wind gusts if they do indeed form. Its not until 12z Sunday that the cold front moves in so another round of storms will be possible then. - Round of storms possible for late Monday night into early Tuesday Models are showing a mid level wave dropping down from the northwest during this time. MU CAPE values are over 1000 J/kg with favorable deep layer shear values. Thus a potential exists for a round of thunderstorms during this period. Given the combination of shear and instability the convection could become organized. Tuesday afternoon, MU CAPE values top 2000 J/kg and favorable deep layer shear is shown to exist but the models are also showing a cap. For now we will maintain a low risk for storms then. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 141 PM EDT Sat Jun 22 2024 Several rounds of showers and even a few thunderstorms look likely to impact the TAF sites into tonight. The first batch was moving onshore near KMKG and was tracking east. For now, it does not contain any lightning and recent radar trends have not shown an increase in the strength of the convection. Thus we will not feature thunderstorms over the next few hours, but will need to monitor that trend closely. A period of IFR/MVFR vsbys could accompany this first batch of showers due to the briefly heavy rainfall. Tonight a better chance for thunderstorms exist as there could be line that develops over Lake MI which then tracks east and into the TAF sites. I did not feature strong winds with those storms as there is some uncertainty with the timing and coverage but that wind gust risk is elevated. On the backside of the storms, IFR cloud cover will likely spread in as the winds shift around to the west northwest. Only gradual improvement to MVFR is expected Sunday. && .MARINE... Issued at 234 PM EDT Sat Jun 22 2024 Southwest winds out ahead of the main wave may gust over 20 knots at times this afternoon but stronger winds will be possible tonight into Sunday as the wave moves in. Thus we will maintain the marine an beach hazard headlines for tonight into Sunday morning. && .HYDROLOGY... Issued at 234 PM EDT Sat Jun 22 2024 The PWAT values are up around 2 inches and area soundings are showing low lcl`s along with thin deep CAPE, especially for northwest zones. Favorable 925 to 850 mb moisture transport exists through southern WI and into our northwest zones including the Pentwater to Ludington region. The deep wave moving in from the west will encounter an unstable air mass here in MI for this afternoon and into tonight leading to showers and storms with heavy rain. Already there has been 1.5 to 2.5 inches for parts of Mason, Oceana and Lake counties. High res models show swaths of heavier rain still to come with locally over another 1.5 inches looking likely. Given the risk for additional heavy rain in combination with the rainfall which has already fallen, there could be some flooding from these cells so we will keep the flood watch going. For the larger rives, they are relatively low. Projected rainfall amounts keep the forecast points under action stage at this time. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Flood Watch through late tonight for MIZ037>040-043>046-050>052. Beach Hazards Statement from 8 PM EDT this evening through Sunday morning for MIZ050-056-064-071. Heat Advisory until 8 PM EDT this evening for MIZ056-057-064>067- 071>074. MARINE...Small Craft Advisory from 8 PM this evening to noon EDT Sunday for LMZ844>847. && $$ UPDATE...MJS DISCUSSION...MJS AVIATION...MJS MARINE...MJS HYDROLOGY...MJS