Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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177 FXUS63 KGRR 230055 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 855 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 855 PM EDT Sat Jun 22 2024 A marginal threat for severe weather, chiefly in the form of damaging wind gusts, will continue for southwest Lower MI until shortly after midnight. Severe convection moving east across southern WI at this time appears to be congealing into a line and we would expect a continued linear storm mode as this activity crosses Lake MI into Lower MI. The downstream thermodynamic and kinematic environment over Lower MI is not overly favorable for sustaining intense thunderstorms. Typically we would want to see substantial DCAPE and steep low level lapse rates over Lower MI. Neither of these features is present at this time. Moreover, the upper jet as depicted on WV imagery suggests the best PV forcing will pass north of the area and there is no downstream upper jet to provide any sort of coupled forcing for ascent. We still have to monitor the threat for localized flooding however, especially if the boundary associated with the congealing line of convection becomes oriented more west to east overnight. && .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 /00Z TAFS THROUGH 00Z MONDAY/... Issued at 741 PM EDT Sat Jun 22 2024 Thunderstorms crossing Lake Michigan should affect MKG shortly after the starting valid time of 23/00Z for this latest TAF package. Farther south, we could be looking at much more of a delay at the other terminals, where I did try to refine timing with a brief period of -TSRA for each site. As noted before, wind intensity associated with convection remains uncertain and have therefore downplayed this for now, but may have to add gusts in the 30-40kt range depending on initial observations on this side of the lake. Expect LLWS to manifest at MKG especially after thunderstorms that are currently over Lake MI pass east of the terminal. 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 until 6 AM EDT Sunday for MIZ037>040-043>046-050>052. Beach Hazards Statement through Sunday morning for MIZ050-056- 064-071. MARINE...Small Craft Advisory until noon EDT Sunday for LMZ844>847. && $$ UPDATE...TJT DISCUSSION...MJS AVIATION...TJT MARINE...MJS HYDROLOGY...MJS