Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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278 FXUS63 KGRR 041148 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 748 AM EDT Thu Jul 4 2024 .KEY MESSAGES... - Warm Independence Day With Slight Chance of a Shower - Scattered Thunderstorms Friday, Low Confidence of Severe Potential - Showers Possible Saturday, Unsettled Pattern Continues Next Week && .DISCUSSION... Issued at 350 AM EDT Thu Jul 4 2024 - Warm Independence Day With Slight Chance of a Shower Temperatures are expected warm up into the mid 80s today with light winds. The cloud cover forecast for late morning through afternoon has become a little more pessimistic, as there may be several hours when it is mostly cloudy. Also feel compelled to broad brush a slight chance of showers everywhere south of Whitehall to Mount Pleasant for the afternoon and evening. A midlevel shortwave trough, augmented by overnight storms in Kansas, is likely to spread cirrus and altostratus over Lower Michigan during the late morning and afternoon. This cloud deck will likely contain ice and may precipitate as virga or sprinkles, but would also serve as ice nuclei feeders to the diurnal cumulus that might develop underneath. Whether the models are overdeveloping cumulus underneath the midlevel clouds remains to be seen, but zones of surface convergence may be a focus for some development, and also reasonably steep lapse rates suggested in the models above the LCL up to the altostratus cloud deck would allow cumulus to attain decent depth. The number of convection-allowing models among the 00Z suite producing scattered light rain showers between afternoon and dusk, perhaps even an isolated downpour, seemed too great to ignore. On the plus side, the chance of lightning does appear to be rather small given the CAPE and better updraft strength would be in the lower/warmer part of the cloud. You shouldn`t be rained out of your holiday outdoor activities unless you are really unlucky. - Scattered Thunderstorms Friday, Low Confidence of Severe Potential A round or two of scattered showers/storms is likely between Friday morning and afternoon, but uncertainty in the evolution of the responsible low-pressure system makes it difficult to ascertain if there is much threat of severe weather. A broad synoptic-scale trough over the northern Plains today should deepen a little as it progresses east, closing into a 500 mb low over Minnesota tonight. By 8 AM Friday, a surface to 850 mb low should be located somewhere over Wisconsin with a quasi-stationary or warm front extending east across Lower Michigan. Models differ greatly in the position and strength of the surface low Friday morning, and the strength of the pressure field near the frontal triple point over Lower Michigan by mid day. The surface to 850 mb wind fields around this low also vary greatly among each model, resulting in substantial differences in vertical shear profiles/hodographs, some of which would support severe weather, including a tornado, and some of which would not. This will have to be monitored closely, though, given the reasonable magnitude of 0-6 km bulk shear, 0-3 km CAPE, and total MLCAPE advertised by most models. - Showers Possible Saturday, Unsettled Pattern Continues Next Week As we enter this holiday weekend there remains quite a bit of uncertainty headed in the mid to long range pattern. The upper level jet stream should remain over the region Saturday through Sunday. This should provide enough dynamics that, coupled with mid to low level moisture and with the instability brought by a positively tilted trough, should allow for a chance of showers Saturday. Any showers should be scattered and light QPF associated given lack of deep moisture. The operational models and ensembles diverge on a signal into early next week, however there remains chances for showers and storms especially Monday into Tuesday. There remains a low confidence in timing. Max Temperatures look to remain below normal through the upcoming week. This should make the week quite comfortable, depending on humidity this week. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 747 AM EDT Thu Jul 4 2024 VFR will persist through the forecast period. There is low confidence in a slight chance for showers this afternoon. Have continued with VCSH into the TAF but any showers are a low probability and shouldn`t reduce cigs/vsbys. Showers and storms will move into the region overnight into Friday with periods of showers moving into MKG after 11Z. Not expecting reductions at this time. && .MARINE... Issued at 350 AM EDT Thu Jul 4 2024 Light winds and waves 1 foot or less for Independence Day. On Friday, scattered thunderstorms could cross Lake Michigan between morning and afternoon. Somewhat stronger winds could build up waves and perhaps make the swim risk moderate, though there is more variability than typical among the models regarding the exact wind speeds and direction through the day. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...CAS/Ceru AVIATION...Ceru MARINE...CAS