Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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929 FXUS63 KGRR 191852 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 252 PM EDT Thu Sep 19 2024 .KEY MESSAGES... - Chance for Storms Tomorrow - Several Chances of Showers and Storms into Next Week && .DISCUSSION... Issued at 252 PM EDT Thu Sep 19 2024 - Chance for Storms Tomorrow Clouds begin to increase late tonight as an upper low tracking from the Northern Plains into Manitoba sends a trailing front towards lower MI, arriving in our area Friday afternoon and evening. Spotty showers will begin to move through the area around late morning to mid- day, then storms will be possible during the afternoon. Diurnal instability up to 1000 to 1400 J/kg (highest over southern lower MI) and bulk shear to 35 to 40 knots will support a few strong storms, with the highest chance in far southwest lower Michigan. Damaging wind gusts will be the primary concern with any strong storms. - Several Chances of Showers and Storms into Next Week The weekend starts off dry as a period of brief ridging and high pressure advects dry air across the area. Precipitation chances then increase later Sunday and especially Sunday Night into Monday. This is driven by a closed low over the southwest US ejecting into the main flow pattern and bringing ample moisture with it. Can`t even rule out a bit. Ensemble CAPE forecasts suggest the chance of isolated thunderstorms also exists. Grand Ensemble precipitation probabilities show the chance for a needed soaking rain is definitely there. Chances of over 0.5" of rain Sunday Night into Monday night is 40-60 percent and over 1 inch is around 10 percent. This weekend into into next week marks the start of a pattern shift as the ridge that has brought dry weather for over a week breaks. This change makes troughing the predominant upper-level setup. Several additional chances of rain are possible over this time period, however as is common with these setups, the timing of the shortwaves and associated rain showers is still not nailed down. Thermal troughing also causes 850mb temperatures falling to around 10C, translating to a near normal low to mid 70s for highs next week. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 100 PM EDT Thu Sep 19 2024 Much of this forecast period will see a continuation of the conditions over the past few days with mostly sunny/mostly clear skies and lighter winds. We will see some rain chances later in the period, with some potential MVFR conditions with the rain chances. Once again, mainly high clouds in place at the beginning of the forecast period. Cumulus clouds are starting to form, but will remain VFR. The cumulus clouds will be more concentrated for the eastern terminals. Those cumulus clouds will once again dissipate after sunset. Fog is not likely tonight with a light wind around 4-5 kts remaining at the sfc, and better winds 1-2k ft agl. We will see some mid level clouds start to move in just before sunrise Friday at KMKG and spreading east. Can not rule out a sprinkle with this, but the very dry lower levels should keep the sfc dry. The better chance of showers and isolated thunder will arrive at the western sites after 16z or so. The eastern sites will not see this potential until after the end of this period. Some MVFR will be likely with the showers and thunder, with some isolated IFR possible also. Will stick with the MVFR wording for now, and fine tune the forecast in subsequent issuances. && .MARINE... Issued at 252 PM EDT Thu Sep 19 2024 A weak cold front will bring a chance for scattered showers early Friday morning. Otherwise, expect offshore winds starting Friday with winds shifting southerly then westerly Friday afternoon following the passage of the front. Wave heights stay generally low through this weekend, with the highest waves to around 2 feet Sunday evening. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Thielke/Thomas AVIATION...NJJ MARINE...Thielke