Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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674 FXUS63 KGRR 180631 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 231 AM EDT Tue Jun 18 2024 .KEY MESSAGES... - Hot and humid with p.m. chances for storms through Tuesday - Heat, humidity, predominantly dry Wednesday through Saturday - Unsettled beginning Saturday then cooler beginning Sunday && .DISCUSSION... Issued at 315 PM EDT Mon Jun 17 2024 - Hot and humid with p.m. chances for storms through Tuesday No changes will be made to the going Heat Advisory with this forecast package. We have had a few isolated cells pop up this afternoon along a line of slightly enhanced convergent flow roughly from south of Grand Rapids to Saginaw Bay away from the Lake Michigan shoreline. This slightly enhanced convergence looks like it is the result of the flow off of the lake, but not a lake breeze with SW flow. This is interacting with an atmosphere with 3500 J/kg of MU CAPE available. Obviously plenty of instability, but little to no shear under the upper ridge to help sustain any updrafts. Thus far, we have had some winds of 30 mph out of cells. These will continue to be possible through sunset, when any leftover convection should come to an end. The potential for additional diurnal convection looks a little better for Tuesday afternoon and evening as compared to this afternoon. Instability looks to be a little less tomorrow afternoon, but values will still be up around 3150 J/kg. The difference for Tuesday afternoon is that a short wave riding up the backside of the upper ridge is forecast to move through the area Tuesday afternoon. This will provide as a better focus for convective development. Deep layer shear is still expected to be quite low around 15-20 knots, so we are anticipating pulse type storms with some small hail, winds to 40 mph, and locally heavy downpours. Once again, convection should come to an end toward sunset Tuesday evening. - Heat, humidity, predominantly dry Wednesday through Saturday No substantive changes to the forecast. We continue to expect highs in the low 90s and maximum apparent temperatures in the upper 90s. The Heat Advisory looks good at least through Friday with decent prospects for eventually expanding this into Saturday. As noted previously, there are slightly better chances for showers and storms farther north towards US-10 in the Wednesday into Thursday timeframe, but overall chances remain low. - Unsettled beginning Saturday then cooler beginning Sunday We continue to see a signal for a pattern change over the weekend. There are timing differences with the approach of an upper PV max and attendant cold front and convection. Some guidance has this as early as Saturday afternoon while other guidance has this as late as Sunday afternoon. Generally speaking, is is hard to transition out of hot spells like these without some type of severe weather. Even if convection was to move through our area Sunday morning around the time of minimum diurnal instability, there still could be plenty of residual conditional instability given the very ripe, warm and humid airmass we will have developed over the preceding days. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 229 AM EDT Tue Jun 18 2024 VFR weather is occurring across the TAF sites at 06z. A line of thunderstorms were located over Central Lower Michigan, but these are moving away from the TAF sites. We expect the rest of the night to be precipitation free at the TAF sites with VFR weather prevailing. The next weather concern is the chance for showers and thunderstorms during the day on Tuesday. Models are hinting at the threat of showers and storms lifting northward out of Indiana this morning and impact the area between 15z and 22z. At this point do not feel coverage or confidence is enough to include in the TAFs. Winds will be gusty from the southwest today at 10-20 knots with peak gusts around 25 knots. && .MARINE... Issued at 315 PM EDT Mon Jun 17 2024 We are issuing a Small Craft Advisory and Beach Hazards Statement for the northern half of the lakeshore starting Tuesday morning, going through most of Wednesday. The better gradient between the sfc ridge to our SE, and the low to our NW will be located over the northern half of our nearshore/lakeshore areas. It looks to be strong enough to generate 3-5 ft waves from around Whitehall to Manistee, especially near Little and Big Sable Points. This will continue into much of Wednesday, before the gradient weakens enough to not require them. The rest of the work week looks like it will be calmer with a weaker gradient in place. The gradient is not forecast to tighten up until toward Saturday as a front approaches. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from 8 AM EDT this morning through Wednesday afternoon for MIZ037-043-050. Heat Advisory until 8 PM EDT Friday for MIZ043>046-050>052- 056>059-064>067-071>074. MARINE...Small Craft Advisory from 8 AM this morning to 4 PM EDT Wednesday for LMZ847>849. && $$ DISCUSSION...NJJ/TJT AVIATION...Duke MARINE...NJJ