Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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798 FXUS63 KGRR 181859 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 259 PM EDT Sat May 18 2024 .KEY MESSAGES... - Warm Weekend Continues - Unsettled Weather at Times Monday through Wednesday - Drier and cooler Thursday and Friday && .DISCUSSION... Issued at 258 PM EDT Sat May 18 2024 - Warm Weekend Continues "Cold" front over Wisconsin slips our way tonight but it is really nothing more than a wind shift line. High temps will actually be similar or even a few degrees warmer on Sunday despite its passage. A band of showers and thunderstorms along the front in WI weakens considerably as it drifts southeast and arrives in our area later tonight, and may even dissipate completely before getting here. Will maintain 20-30 pops toward/after midnight for areas north/west of GRR but latest CAMs look to be decreasing the threat of convection since the shortwave stays well northwest of us over the Lk Superior region and instability wanes quickly. A few showers and storms may redevelop by Noon Sunday south and east of GRR where the frontal boundary stalls out and sfc instability rebuilds. RAP has SBCapes rising to near 2000 J/KG where sfc dew pts near 60 will be present along with some weak sfc convergence. Pops only 20-40 pct again (highest near JXN), and any storms will be the pop-up/pulse-variety in weakly sheared environment. Any diurnal showers/storms will dissipate with sunset although returning warm front late Sunday night could touch off a few storms again by daybreak Monday. - Unsettled Weather at Times Monday through Wednesday The ridge that will be over the area on Sunday will slip east of the area by Monday. This occurs as a long wave trough will dig and amplify across the western half of the country. Our area will end up under deep flow from the SSW which usually results in a warm and humid/wet period. This period looks about as expected with periods of showers/storms, although it will not be raining all of the time by any means. The first chance of rain will come as early as Monday as the leading short wave ejecting from the long wave trough skirts by to our NW. Ahead of this wave, we will see a surge of warm and moist air ahead of it with a low level jet. Showers and storms look like a decent bet into Monday night before that wave moves away from the area. We are expecting another more significant wave to lift NE around the long wave trough in the Tue/Wed time frame. A front will remain over the southern half of the area behind the Mon system, and will then move back north as a warm front on Tue ahead of the stronger wave. This will bring additional chances of showers/storms. This system is the center of the SPC DY4 outlook that clips the area. It appears that the main threat may stay SW of the area with the entire system wrapping up a bit to the west. We will remain out ahead of the cold front on Wednesday, leaving the area in the warm sector for at least a part of the day. Getting out that far, details are a bit gray. Timing of features with this system with respect to peak heating as late as Wed may ultimately determine the severe weather threat. The potential does exist with some strong wind fields aloft and plenty of warm and humid conditions present. - Drier and cooler Thursday and Friday It does look like the front should sweep out the heat and humidity by late Wednesday, leaving a mild and drier air mass in it`s wake. The instability and showery weather with the cold pool aloft should stay north, while the front moves SE of the area. This leaves some ridging in place, and it looks likely to stay dry through at least Friday. There remains some small chances of rain in the NBM, but we are thinking it is more likely to stay dry. Rain chances will increase some by Saturday, but nothing significant is on the horizon yet for the beginning of the upcoming holiday weekend. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 124 PM EDT Sat May 18 2024 There is only one minor noteworthy event in the forecast period through 18z. That is a frontal passage overnight into the Sunday morning hours. We currently have cumulus development with the boundary layer moisture left from this morning that is lifting up. We expect that this moisture will mix out this afternoon. These clouds are VFR, and should remain that way until sunset when they diminish. We will see a frontal boundary start to move through overnight, and exit the area Sunday morning. At this time, it looks like a period of 5-7k ft clouds will accompany this, with a few sprinkles expected. Behind the front, clouds will scatter out a bit and winds will turn to become from the NW. Some diurnal cumulus can be expected once again. && .MARINE... Issued at 258 PM EDT Sat May 18 2024 Winds and waves remaining below advisory levels through the remainder of the weekend, although a frontal boundary slipping through tonight will shift the winds from southerly this afternoon and tonight to northwesterly on Sunday. There may be a period Sunday afternoon where the NNW winds increase to near 15 kts or so for a time. The fog threat appears to have ended over the lake. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Air Quality Alert until midnight EDT tonight for MIZ050-056-057- 064-071. MARINE...None. && $$ DISCUSSION...Meade/NJJ AVIATION...NJJ MARINE...Meade