Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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996 FXUS63 KGRR 250018 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 818 PM EDT Tue Sep 24 2024 .KEY MESSAGES... - Isolated Heavy Rain and Severe Potential into this Evening - Dry Wednesday through Friday with mild temperatures - Rain chances over the weekend and early next week && .DISCUSSION... Issued at 350 PM EDT Tue Sep 24 2024 - Isolated Heavy Rain and Severe Potential into this Evening AN area of persistent heavy rain across Muskegon County has resulted in 2 to 4 inches of rain today. More localized areas of heavy rain are expected this evening. Sfc low centered near southern Lake Michigan late this afternoon will track northeast across Lower Michigan this evening causing rain bands to pivot across the western zones. We have increased QPF to account for excessive rainfall along the Lake Michigan coast where hi-res models show the rain persisting this evening. Meanwhile, cellular convection across northern Indiana will be moving into the southern forecast area late this afternoon and early evening where marginal instability is present as dew points are peaking in the mid 60s. Deep layer shear is only about 20 to 25 knots, but 0 to 1 km helicity values are over 100 just north of the warm front which is expected to stay south of 1-94. Main threat is transient mesocyclones in isolated cells or embedded in small line segments with brief tornado potential. The severe threat will diminish this evening as sfc based instability wanes. The low moves east with the steadier rain exiting the eastern zones by midnight. Some lake effect rain showers could persist near Lake Michigan into early Wednesday before moving offshore out over the lake as the flow goes north. - Dry Wednesday through Friday with mild temperatures Once the current system moves entirely east of the area on Wednesday, we will see a nice and dry period set up for the area through Friday. That is because we will be under the influence of the upper ridge building over the area from the west. This ridge will be reinforced out ahead of the Tropical system that will be moving toward the Ohio Valley. This results in plenty of subsidence over the area, and moderating temperatures well into the 70s. - Rain chances over the weekend and early next week The ridge will hold for a bit, but will eventually allow some of the moisture up over the area beginning on Saturday, and lingering at least into Monday. The upper low that will be in place near Arkansas and will absorb the tropical system, will eventually continue to rotate in the region until a stronger system can boot it out. The upper low is expected to largely stay SSW of the area through the week, but will wrap moisture into the area from the SE and have short waves rotating through our area. Right now, it looks like there will be intermittent chances of rain showers and a chc of storms for the weekend into early next week. It does not look like a washout on any particular day, but could rain at just about any time. Temperatures will stay mild during this time frame as there is not really any cold air immediately available. It is looking like that around the Tuesday time frame, that a stronger northern stream system will dive SE out of Canada, and will be strong enough to kick the weekend low out. That will involve another chance of rain, and much cooler air behind it eventually. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 818 PM EDT Tue Sep 24 2024 Have removed thunderstorms from the TAFs as lighting has been sparse, mostly distant east of MKG and north of GRR. The heavy rain showers in the vicinity of AZO have not produced lightning in quite some time. Still good confidence in ceilings deteriorating to IFR overnight, possibly LIFR in spots, then gradually improving during the middle of the day Wednesday. && .MARINE... Issued at 350 PM EDT Tue Sep 24 2024 Waterspouts are possible this evening along convergent lines of showers and isolated thunderstorms. Rain will be heavy enough to lower visibility to below one half mile at times. Northerly winds through Wednesday night should remain below 20 knots but may produce some choppy waves near Big and Little Sable points. WInds go offshore on Thursday and Friday and waves in the nearshore should remain at a foot or below. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Ostuno/NJJ AVIATION...CAS MARINE...Ostuno