textproduct: Gaylord

KEY MESSAGES

- Weakly forced convection overnight/Friday?

- Precipitation chances along passing cold front Friday night/ Saturday morning...and more showers Sunday.

- Rain continues Monday (heavy rain possibility Lower Michigan).

DISCUSSION

Issued at 308 PM EDT Thu Aug 6 2026

Pattern Synopsis/Forecast: High latitude Rex block across much of Canada impacting the pattern across the northern tier of states: low pressure portion of the block centered over Hudson Bay extends south into the northern Plains/upper Midwest/Great Lakes. Upper level highs centered over the southwest U.S. and off the mid Atlantic coast...with the remnants of an old low still meandering near the Florida panhandle. Several short wave troughs rotating through the norther tier cyclonic flow; one crossing the upper Lakes this afternoon...a second digging southeast across the Dakotas...and a couple of embedded circulations over northern Saskatchewan and northwest Ontario. Northwest-southeast oriented moisture gradient across the upper Lakes: precipitable water values at or below 0.75 inch across Upper Michigan...and near 1.50 inches across southeast Lower. At the surface...lingering boundary is draped across southern Lower Michigan...extending southwest across Illinois/ northern Missouri to a 1014mb frontal wave over eastern Kansas. Broad subtropical high over the western Atlantic keeping the humidity up into southern Lower Michigan but as mentioned earlier low levels dry out a bit to the west and north.

Great Lakes will remain on the southern periphery of the upper low in the vicinity of Hudson Bay through the weekend...with height falls/short wave trough and cold frontal passage expected Friday night/Saturday. A little more influence from zonal Pacific-origin flow Sunday...though there will still be short waves zipping by along the jet axis. Given this zonal flow set up there should be a persistent east-west frontal boundary that sets up likely south of the Great Lakes for most of the extended forecast period. Forecast trends suggest the upper low may make a more concerted push southward around this time next week.

Primary Forecast Concerns:

Weakly forced convection overnight/Friday?: Beyond anything that pops along the Lake Huron breeze this afternoon...some subtle things to watch tonight across the southeast third of the forecast area or so. Low level theta-e advection/convergence and elevated CAPE (>500J/kg MUCAPE) may be just enough for some scattered convection to pop. Probabilities may be boosted by weak mid level short wave trough/PV anomaly overnight into Friday morning. Low probability event but probably not low enough to leave out of the forecast. Diurnal heating during the day Friday and increasing low level moisture will result in MLCAPE values at or above 1500J/kg developing. Forcing is pretty minimal outside of localized convergence and Lake Huron lake breeze. Any storms that do develop will have a pulsey-downburst wind threat with them.

Precipitation chances along passing cold front Friday night/ Saturday morning...and more showers Sunday: A better organized/more strongly forced band of showers/thunderstorms expected to cross northern Michigan later Friday night/Saturday morning before the forecast trends drier for Saturday afternoon. Respite from precipitation chances look to be short...combination of an approaching jet streak and increasing low level theta-e advection will bring a renewed threat for showers/thunderstorms late Saturday night through Sunday.

Rain continues Monday (heavy rain possibility Lower Michigan): Frontal boundary to the south of the Great Lakes with a low level deformation axis across the upper Lakes and a few ripples in the upper level flow will increase the chances for more widespread rain Monday. Lots of mesoscale details to work out...but QPF probabilities across northern Lower showing some potential (20-40%) of exceeding 1 inch with some low probabilities exceeding 2 inches Monday through Tuesday morning.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 703 PM EDT Thu Aug 6 2026

VFR. Stationary front to the south may send some lower clouds to MBL later tonight into Friday morning, but cloud bases to remain above 3500ft there... and holding higher the farther north one goes. Bigger concern will be potential for fog at MBL later tonight, which could easily lead to flight category reductions. Other item of note will be shower / storm potential at APN Friday afternoon. Not enough to nail specific timing down at this juncture, but included VCSH for them 18z and beyond. Light south to southwest winds, perhaps gusting past 15kts at MBL Friday afternoon.

APX WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...None.