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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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223 FXUS63 KGRR 151747 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 147 PM EDT Mon Jul 15 2024 .KEY MESSAGES... - Showers and storms move off to the east this morning - Another round of strong/severe storms this evening/tonight - Mainly dry after Tuesday && .UPDATE... Issued at 1113 AM EDT Mon Jul 15 2024 Much of the Grand River basin saw 1 to 2 inches of rain overnight and many of the smaller streams are elevated. Another round of storms with heavy rain are anticipated tonight. Runoff will be efficient. As a result, we issued a flood watch for the region near and south of I-96, from Muskegon to Lansing. Also, river levels are elevated, especially around Jackson. The added rainfall tonight could push them up to near flood stage. As for the severe weather tonight, there has been a slight northward shift of the axis of strongest convection in the morning model runs. Thus the southern half of the CWA looks to be at risk for a fast moving line of storms with damaging winds. There is now good consistency amongst the models on this scenario and the 12z HREF supports this as well. The 12z ABR sounding showed a deep EML with 45 to 55 knot westerly flow 700 mb through 400 mb. The latest upstream VWP`s 500 mb pressure level plots are showing the 50 knot winds around 500 mb persisting at KFSD and KMPX. From SPC`s meso page, the current and forecast Effective Bulk Shear values are shown to be strong as mid to upper level wave seen on WV imagery over the upper Plains moves into the Great Lakes Region tonight. MU CAPE values were already up to 3000 J/kg in southern WI and over 4000 J/kg in IA. Visible imagery shows strong heating will continue through the afternoon. The southwesterly low level jet is shown to strengthen ahead of the convection through the evening. Based on all this, confidence for a line of storms with damaging winds has increased for southern parts of Lower MI tonight. && .DISCUSSION... Issued at 408 AM EDT Mon Jul 15 2024 - Showers and storms move off to the east this morning A very long lived mesoscale convective vort is moving through the forecast area this morning. This vort was formed last night in the northern plains and it reinvigorated convection yesterday evening on the Mississippi near the IA/WI line. It has not produced severe weather in our area, but it has produced flooding and a lot of lightning. We remain concerned about flooding in the Lansing metro area early this morning as the ground there has been saturated from recent rains and this activity has been producing 1-2 inch per hour rainfall rates. We do have areal Flood Advisories and Warnings that carry into the 800am to 1000am time frame. Flooding should recede fairly quickly this morning as it is more urban and small stream related. The showers and storms will likely clear to the east out of the GRR forecast towards 12z. In the wake of this activity we expect some clouds to linger much of the morning over at least half the forecast area from near and just north of I-96 southward. This will put a lid on how much heat we see today as the clouds do not clear out until towards midday. - Another round of strong/severe storms this evening/tonight The next focus is on our next round of thunderstorms which could be strong to severe. The HREF 4 hour max reflectivity which does well most of the time shows a surge of convection moving in after 800pm. It sweeps through the forecast area between 800pm and 600am. This round looks to hit many of the same areas as the current round (near and south of I-96). There is a signal for some severe weather in the same area given quite a few updraft helicity swaths moving through the area. MUCAPE values hit 2000-3000 j/kg along with 30-40 knots of deep layer shear so we will be monitoring once again for severe weather. We are in a slight risk from the SPC for the southwest half of the area (MKG to GRR to LAN) and points to the south. Can envision the slight line being bumped a bit north today, possibly up towards Alma to include points south down U.S. 127. - Mainly dry after Tuesday The front will progress south on Tuesday as an upper trough settles into the area. We have chance pops for showers in the forecast across the south on Tuesday. We may see some scattered showers on Wednesday with the upper trough, otherwise much of the rest of the week looks dry with high pressure settling in. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 147 PM EDT Mon Jul 15 2024 Leftover moisture evaporating off the ground is creating a few to broken layer of cumulus around 2500 feet early this afternoon. This is expected to gradually mix out with drier air over the next several hours, and it should be mainly VFR until thunderstorms arrive later this evening. The 12Z HREF member models arrived with a fair amount of agreement on the time of arrival of the thunderstorms. Confidence in TS with heavy rain and sudden wind gusts 40 or 50 knots is highest around AZO and BTL. Confidence is a little less but still medium for TS at MKG, GRR, LAN, and JXN. After the storms, MVFR ceilings are likely through Tuesday morning with gradual improvement during afternoon. && .MARINE... Issued at 408 AM EDT Mon Jul 15 2024 An overall fairly slack gradient is in place through Tuesday night, so wave height overall will be on the low side. The exception is the potential for a short duration burst of wind tonight associated with thunderstorms expected to sweep across Lake Michigan. Thunderstorms look likely this evening over the lake, which will likely kick up a wave field. This is one of our top problematic scenarios as the wind is short lived, but can be strong with overnight thunderstorm complexes and low level jets. We could be looking at waves that over perform into Tuesday morning. As of right now we have 2-4 footers in the forecast and we will have to see tonight what actually sweeps across the lake. Our next time frame of concern will be on Wednesday in a north flow behind a frontal passage. NAM winds look to be in the 10-20 knot range which should keep us just below advisory. The GFS however is showing more 15-25 which would push us into a Small Craft Advisory and Beach Hazards Statement. We will be watching for more consensus in speeds as this event closes in. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Flood Watch from 9 PM EDT this evening through late tonight for MIZ050-056>059-064>067-071>074. MARINE...None. && $$ UPDATE...MJS DISCUSSION...Duke AVIATION...CAS MARINE...Duke