textproduct: Gaylord

KEY MESSAGES

- Showers likely and chance of thunderstorms this afternoon/evening. A few strong storms possible. - Quiet Wednesday-Thursday

- Unsettled again Thursday night into this weekend.

DISCUSSION

Issued at 236 PM EDT Tue Aug 18 2026

Pattern / Forecast Synopsis:

Disheveled longwave troughing over northeastern North America to be the primary influence of the region over the forecast period, with occasional shortwave trough passages to move through the region, most of which will be maturing / closed off, and may have some hangtime across the Great Lakes owing to standard stagnant August jet dynamics.

Currently, a mature upper low over Hudson Bay to continue an eastward trek, with antecedent SW return flow drawing in warmer and (to an extent) more moist air across the Great Lakes. Surface dewpoints have already ballooned to the 60 to 66 range across the region as of the noon hour, with evidence of prefrontal clearing building into northern Michigan. Surface cold frontal boundary roughly stretching from James Bay through Marquette and WSW through Minnesota just north of the Twin Cities. Evidence of some mixing trying to manifest just ahead of this cold frontal boundary... which may be something to watch for across our neck of the woods. Nonetheless, frontal boundary to pass through the region with just enough instability to force a convective response across Wisconsin, eventually leaking into northern lower late this afternoon into the evening, with showers and storms gradually clearing through the evening / night from WNW to ESE.

Surface high pressure to build on the backside of the front, yielding an aggressive drying NW wind regime (in conjunction with 500mb height rises / shortwave ridging) through the day Wednesday that will bring back sunnier skies and seasonable warmth during the day and again Thursday... but with the dry nature of the airmass and calming winds overnight, cooler nights to return Wednesday and Thursday nights. Next wave digs from the NNW starting Friday, with current trend pointing to this wave occluding / closing off overhead through the course of the weekend, bringing back cooler and unsettled conditions for at least the start of the weekend (and perhaps a renewed severe threat Friday?). High pressure / 500mb shortwave ridging to follow through the day Sunday and into Monday before the next wave passes through at the end of the forecast period.

Details:

Shower / Storm Potential This Afternoon / Tonight: Aforementioned frontal boundary to traverse the region this evening into tonight, which looks to suffice in the forcing department (albeit, to a limited extent... as pointed out by previous forecaster, frontal convergence leaves a bit to be desired). Latest CAMs seem bound and determined to have an aggressive prefrontal mixing regime, particularly across northeast lower with downsloping WSW winds. Will have to see how aggressive this trends as it will be pivotal to the generation of this evening's instability, and thus the evolution of any convection. Nonetheless, the other thing CAMs are persistent with is deeper moisture right along / ahead of the front pooling across the region, and thus giving us instability in the order of 500 to 800 J/kg of MLCAPE. Several fascinating aspects to this setup to unpack... first and foremost, most modeled soundings showcase a pseudo-inverted-V profile that usually comes with gustier storms that don't really produce much in the way of rainfall... but with largely unidirectional flow, anticipate it is possible if (and it's a BIG ole "if") we can maintain instability following any intial convection, which could support increasingly heavier rainfall in any additional storm formation. A majority of CAMs seem to find this idea possible, but I admittedly have my doubts.

Aforementioned unidirectional flow will be a big player in any potential convective evolution. Hodograph shape this evening will largely be linear, and as such, while this does eventually favor an outflow dominant multicellular / linear mode... should be noted that upon convective initiation (when storms are most discrete), this does favor splitting cells... with potential for an initial left mover dominant regime before transitioning into a linear mode with time... and select CAMs have this down to a tee across the NW lower shoreline, perhaps scraping the very southern reaches of Mackinac County... As such, there is potential for an intial hail dominant severe threat across the aforementioned regions before transitioning to a linear, more wind / outflow dominant mode this evening. Should note... we probably only achieve the most marginal of severe conditions at best if we can hold onto progged instability trends... but in the event we trend more downward with instability, the threat may become much more muted. Nonetheless, enough is there for SPC to expand the inherited Day 1 Marginal Risk (1/5) across all of northern lower, butting up right against eastern upper. Primary highlighted hazard is damaging wind gusts (5%), though in this morning's most recent outlook, a 5% hail risk has been introduced to NW lower (GT Bay and south), cutting off to the east roughly at I-75 / US 127... which matches well with a majority of evening / overnight convective episodes... most robust west, a bit more isolated / weaker east.

Final piece of the puzzle is hydro based concerns. Recent drier weather has allowed our soil to revert back to its more normal porous sandy character... but with an increasingly moist profile during the frontal passage, coupled with some borderline echo training potential (unidirectional flow!) within PWATs swelling closer to 1.50, in the event repeated storms can manifest, suppose there is potential for some localized heavy rainfall totals. In particular focus by CAMs is the NW lower corridor, including the Grand Traverse Bay / TVC area, which has a handful of CAMs laying down a strip of quick 1.50-2.50"+ of rain. Pending on how quickly this can occur (and to what extent), suppose there could be a quiet flood concern, especially if this can manifest over the Traverse City urban corridor... with more stratiform / isolated convective modes driving lower rainfall totals the farther east one goes across northern lower.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 133 PM EDT Tue Aug 18 2026

-SHRA AND -TSRA will sweep across all TAF sites this evening, resulting in temporary reductions in CIG's and VSBY's. Mainly VFR with periods of MVFR will persist between 1822 to 1903Z tonight followed by VCSH and patchy BR overnight. Winds veer to the NNW Wednesday with SKC expected through the remainder of the forecast period.

APX WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory until 11 PM EDT this evening for LHZ345. Small Craft Advisory until 8 PM EDT this evening for LHZ346. Small Craft Advisory until 11 PM EDT this evening for LMZ323- 342-344>346.