Sunrise 5:55 AM   Sunset 9:12 PM Moonrise 5:29 PM   Moonset 3:32 AM

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LMZ323 Grand Traverse Bay South Of A Line Grand Traverse Light To Norwood Mi- 411 Am Edt Mon May 20 2024
Today - Southeast wind 5 to 10 knots becoming southwest early in the evening. Chance of showers and slight chance of Thunderstorms in the morning. Rain showers likely and a chance of Thunderstorms in the afternoon. Waves 2 feet or less. Tonight - Light winds. Chance of Thunderstorms and slight chance of showers. Waves 2 feet or less. Tuesday - Light winds. Scattered showers. Waves 2 feet or less. Tuesday night - South wind 10 to 15 knots with gusts to around 30 knots. Showers and a chance of Thunderstorms. Waves 2 to 3 feet.
winds and waves higher in the vicinity of Thunderstorms.
see the open lakes forecast for days 3 through 5.

LMZ300
No data

FXUS63 KAPX 201037 AFDAPX

Area Forecast Discussion National Weather Service Gaylord MI 637 AM EDT Mon May 20 2024

KEY MESSAGES

- Strong to severe storms possible this afternoon through this evening.

- Another round of strong to severe storms will be possible Tuesday night as a cold front passes through and brings a potential squall line passage through the region.

- Cooler and occasionally unsettled Wednesday into early Thursday.

SHORT TERM /THROUGH TONIGHT/
Issued at 355 AM EDT Mon May 20 2024

Southwesterly flow beginning to dominate the central CONUS...with bulk of convective activity crossing the central Plains into the Mid MS Valley early this morning in advance of a couple PV niblets deepening as they cross the central Plains...along a lingering BCZ stretching from central Quebec down through the OH Valley...and back into the central Plains...where anomalous moisture (pwats 1.5 inch or greater) looms in the vicinity of this boundary. Warm over the Great Lakes region
with 850mb Ts in the low to mid teens
and highs yesterday reaching well into the 70s over even northern Lower, with low and mid 80s from NE Lower down into central Lower where better downsloping aided in maxing out temps under the primary ridge axis
Dry here in northern MI though
with pwats on the very low end of climo at 0.25in from our 0z/20 sounding. Upstream convection over WI has been weak...but appears things are trying to hold together a little better as of 6z with IR satellite denoting a better showing of cooling cloud tops to our west in the last couple hours.

Anticipating leftover PV max from the central Plains/mid MS Valley to continue to trek NEward into the Upper Midwest/Great Lakes through today...ultimately dragging the boundary back northward toward central Lower with time today. Signals currently point toward an MCS/line of storms crossing central Lower MI during the late afternoon/evening during peak heating, with north central Lower most likely on the north end of this. However, it may be possible to develop some storms across NE Lower toward Saginaw Bay this afternoon, out ahead of the primary line from WI. Primary focus should be south of the Mighty Mac...and particularly toward M-72/M- 55 this afternoon into tonight, depending on how far north the boundary ends up getting today...though will expect rain and general thunderstorms to overspread the area tonight as well...most likely exiting the Sunrise Side toward daybreak Tuesday or later. Not a clear cut forecast by any means, though.

Primary Forecast Concerns:

Bottom line up front: potential severe threats today/tonight, if they materialize, will be damaging winds, large hail, heavy rain...and a tornado can't be ruled out. Primary focus for strong to severe convection will most likely be 1pm-midnight EDT from west to east...though not impossible we will deal with lingering rain/storms into the bulk of the night.

Strong to severe storms possible this afternoon into this evening...
Initial concern is how quickly precip will get into the area, given current dry air mass in the low-levels. Noting satellite imagery upstream is still trying to hold things together back over IA, and even into parts of SW WI...think it's not impossible this activity/convective debris holds together and gets in here to moisten up the atmosphere across NW Lower. There is also some suggestion that a lobe of moist air from the dying convection over the OH Valley may try to make it up into our SE (Saginaw Bay) area early in the day. Both of these ideas, if they verify, could suggest a greater potential for destabilization during the afternoon as deeper moisture and better forcing work in from the west with the niblet
Otherwise
it will take longer for convection to make it here and/or develop in the first place...with less instability to work with if it remains dry in the low-levels
However
noting that attm I'm struggling to find dewpoint guidance moist enough for what's actually going on right now...I'm becoming a little more suspicious that things could get beefy this afternoon.

Primary background flow in the low-levels could become south to southwesterly, which, if differential heating allows for lake breezes to develop, could suggest we may have to watch for pop-ups over NE Lower ahead of the primary line of storms coming out of WI which could produce some marginal hail. Given low-level veering flow potential along the Lake Huron lake breeze...anything that develops out this way could have a little spin with it
Additionally
will have to see how the incoming line of storms from WI interacts with any lingering boundaries from NE Lower, as this could produce anything from embedded spin-ups to very focused training convection and flash flooding. Given pwats are expected to approach the high end of climo, won't be shocked to see some areas get overly soaked...particularly noting a majority of the CWA may very well end up in the stratiform rain on the north end of the line, where storm motions would more likely end up being slow.

One thing that may work in our favor with regard to lowering severe potential today...is that wind fields aren't overly impressive with this system...noting deep-layer shear may run around 30kts...which tends to be just sufficient enough for storm organization. There currently appears to be a fairly narrow area of better shear, though, which could end up further north than where we currently expect the primary MCS to develop. This could either reduce severe potential...or shift it further north than currently expected (primary focus attm is along and south of M-72...but could end up as far north as the Bridge or the southern UP).

LONG TERM /TUESDAY THROUGH SUNDAY/
Issued at 355 AM EDT Mon May 20 2024

Pattern Synopsis / Forecast:

Potent 500mb wave ejecting from the Rockies into the central Plains set to utilize favorable jet streak dynamics to generate surface cyclogenesis. This wave and surface low will continue to deepen as it moves northeast into the western end of Lake Superior (likely sub 990mb), where it will largely become occluded / vertically stacked and eventually closed off by Wednesday. In response to this system developing and deepening considerably, southerly flow looks to force a warm frontal boundary northward across northern Michigan through the day Tuesday, settling somewhere near or just north of the north shore of Lake Superior. The passage of this frontal boundary will lead to lessened shower coverage (especially farther south in the CWA) Tuesday morning. Deep convective response anticipated across the heart of the Corn Belt region, and with potent SW flow aloft, should steer this area of strong to severe storms into the upper Great Lakes region later Tuesday night in conjunction with the cold frontal boundary. As the occlusion of the cyclone manifests and the cyclone itself slowly drifts eastward across Lake Superior on Wednesday, this should support additional showers (perhaps thunder?)
into Wednesday before the drier and cooler air behind the system finally makes its way into the Northwoods Thursday. Quick turnaround to milder temperatures Friday into Saturday as shortwave ridging ahead of another 500mb wave in the Canadian prairies moves overhead before another trough axis is forced eastward into the Great Lakes for the weekend, bringing more potential showers and perhaps some thunder too.

Primary Forecast Concerns:

Tuesday: Sub 990mb low moves into the west end of Lake Superior, which, based off of severe climo for APX, is in a favorable spot.
This system will be pumping a deeply moist airmass into the region in the wake of the northward surging warm frontal boundary. Diurnal heating may suffer a bit with high clouds, but instability is still progged to make an appearance, albeit with a capping inversion.
Deeper convection upstream likely becomes more of a linear mode (squall line / MCS) along the cold front as it moves through Wisconsin into Lake Michigan, and eventually, the Northwoods. Most CAMs are loaded with high amounts of CIN (+100J/kg), but the cold front will provide the necessary forcing to break through that cap as this activity progresses into the area, likely after midnight Tuesday night. Given the proximity of the surface low, atmospheric dynamics look to be pretty primed for activity if something can make it here (latest CAMs suggest that is well within possibility).

With the linear mode expected, probably looking at more of a wind threat as this feature passes through. The presence of the low pressure casts some wild cards into this setup, as shear will be rapidly increasing in conjunction with strengthening LLJ dynamics (850mb winds increase to 45-55kts, maybe higher?) and a 500mb wind max really acting to stretch out hodographs (Bulk shear up to 55- 60kts, as high as 30-40kts from 0-1km and SRHs potentially well over 400m^2/s^2). This opens the door for some embedded hailers in the stronger updrafts within the line, and even a quick spinup tornado along the line as it surges northeastward into northern Michigan.
WHILE UNLIKELY, any "renegade" updrafts that succeed in forcing through the capping inversion ahead of the main line could have a volatile environment to feast from (i.e. supercellular mode with all hazards on the table). Overall, latest CAM guidance hint at the best instability fading the farther north and east one goes across the APX footprint, which matches the latest SPC Day 2 outlook putting a Slight Risk (2/5) across much of northern lower Michigan and Marginal Risk (1/5) elsewhere. One final note- will have to monitor any convective trends downstate and points south during the day Tuesday, as any disruptions to the moisture advection regime may wipe out any instability across the region, and thus erodes severe potential as well.

Wednesday and Beyond: Following the passage of the cold front, the occluded nature and slow progression of the system will lead to the cooler air behind the system to be a bit slow to return to the region. Presence of the low pressure system over Lake Superior should help any diurnal instability to materialize into additional showers and perhaps some thunder too Wednesday. Drier air finally moves in behind the system, leaving cooler air overhead, with the area holding dry Thursday and Friday (outside of some lingering showers in the eastern Yoop Thursday owing to their proximity to the departing system).

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/
Issued at 637 AM EDT Mon May 20 2024

Primary timeframe attm for strong to severe storms will be 17-18z this afternoon through 4-5z tonight...especially across northern Lower MI
Least confidence in severe threat for CIU and PLN
but signals may be increasing for northward trends for this afternoon/evening
This being said
it is still a possibility that dying storms over WI could make it into northern MI this morning and reduce potential for strong to severe storms later in the day...therefore, some uncertainty in storm potential and have kept TS wording limited to TVC, mbL attm. Cigs/visbys also a bit uncertain but think we will transition to IFR/LIFR after 23z and 4- 6z, respectively, in the steadier rain and low stratus/fog. Winds generally south to southeast today under 15kts, though onshore flow may develop in the afternoon, esp at APN, mbL. Potential for a small low pressure center to track across the state tonight with the storms, which could lead to shifting surface winds. Higher gusts in/near thunderstorms. Winds to shift to west/northwest tonight behind the round of showers/storms.

APX WATCHES/WARNINGS/ADVISORIES
MI...None.
MARINE...None.

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