Marine Weather and Tide Forecast for Sault Ste. Marie, MI

SHORT TERM /THROUGH TUESDAY/
Issued at 334 AM EDT Mon Apr 28 2025

Pattern/synopsis: High pressure is moving east from Lakes Erie/Ontario. The primary surface low will move ene/ne from the northern plains, crossing Lk Superior this evening on the way toward the tip of James Bay. The trailing cold front will only get dragged into eastern upper MI by 12Z Tuesday. Return flow will gradually increase today and tonight, up until cold frontal passage late tonight/Tuesday.

Forecast: A lot going on. Fire wx first. Strong surface heating will be realized until midday, with convective debris clouds increasing w to e during the afternoon. A tightening pressure gradient and deep mixing will increase winds as the day proceeds. Gusts to 25-30mph in the afternoon. Surface dew points will start to climb in the afternoon, as moist advection wins out over mixing, and as cloud cover limits said mixing. But dew points and RH values will be quite low today, with increasing winds. Favored guidance in these scenarios (NBM10Pct for dry dew points, BcConShort for warmer temps) gets ne lower MI to marginal red flag conditions today (min RH at 25%). Nw lower, which moistens and clouds up a little faster, is 25-30%.
(This is excepting local downsloping locales like TVC, which will go slightly lower.)

Initial fire wx forecasts this morning will go out with elevated fire danger wording, as was agreed to in discussions with USFS/DNR yesterday. But a stronger response may need to be considered.

Return of rich BL moisture will take place west of Lake MI today. We don't see appreciable instability here during the daylight hours until very late, when the low level jet starts to develop and veer, allowing a bit of a tap off of WI. Weak elevated instability, on the order of a few hundred J/kg, could advect over and across the lake. Incoming decaying convection becomes more likely by then. After little/no precip thru early afternoon, pops do gradually increase nw of a mbL-GLR-Rogers line thru early evening. This is just residual showers (no thunder thru 00Z), with the highest pops in western Chip/Mack Cos.

1km winds ramp up to 55-65kt late evening/overnight, sw in the evening and wsw overnight. This will transport a drastically different airmass into the region...just aloft. MuCape values somewhat in excess of 1k g/kg overspread the forecast area in the evening and early overnight. Surface based instability will not be obviously present, but stability will become weaker late, when surface dew points climb into and thru the 50s.
Convection will become numerous to widespread tonight, in eastern upper, nw and n central lower MI. Given the prominent wind fields just above the surface, there is certainly some opportunity for convection that moves in from upstream tonight to pose wind/hail threats in particular (and in that order). A tornado is not out of the question either. Low-level directional shear is most substantial early tonight, when instability is just arriving. Wind fields are more unidirectional overnight.

Synoptic wind gusts will increase to 30-35mph tonight, reflecting the tight pressure gradient and much stronger winds just off the surface. Stability factors look to preclude us mixing down more than that.

Max temps today in the 60s in eastern upper MI, near 70f to the lower 70s in most of northern lower MI (TVC probably takes a run at 75f). Temps will relatively steady tonight, 60s in northern lower MI and 50s in eastern upper.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/
Issued at 334 AM EDT Mon Apr 28 2025

A cold front will progress across the region Tuesday morning and early afternoon, possibly accompanied by a few showers or storms.
There is a marginal risk for isolated severe storms. It will be windy Tuesday with gusts between 30 and 40 mph. Turning sharply colder during the afternoon with falling temperatures. Clearing and cold with diminishing winds Tuesday night. Wednesday will feature lots of sunshine along with seasonable temperatures as high pressure dominates the region. A developing area of low pressure will then likely lead to showers Thursday, with chances of showers possibly lingering into Friday. Temperatures will turn cooler once again.
Cool temperatures likely continue into Saturday followed by expected warmer readings Sunday. No precipitation is anticipated next weekend with high pressure in control at the surface and aloft.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
Issued at 144 PM EDT Mon Apr 28 2025

VFR conditions will persist through ~03Z tonight. S winds remain 15 to 20kts with G25 to 30kts during this time. Chances for TSRA after 03Z will linger through the period. W/S of 40 - 50+ mph at 2 kft overnight due to strong LLJ. Isolated TS chances from 03Z to 06Z, then more scattered TS coverage from 06Z thru 12Z as storms move from W-E across northern MI. A few could impact terminals, leading to MVFR/IFR cigs/vis and frequent lightning.
Damaging wind gusts and large hail are also possible hazards with storms. Chances for TSRA shift to NE lower Tuesday morning.

APX WATCHES/WARNINGS/ADVISORIES
MI...Red Flag Warning until 6 PM EDT this evening for MIZ016-020- 021-025>027-031>033-099.
Red Flag Warning until 8 PM EDT this evening for MIZ017-018- 022>024-028>030-034>036-041-042.
MARINE...Small Craft Advisory until 11 PM EDT Tuesday for LHZ345>349.
Small Craft Advisory until 8 PM EDT this evening for LMZ323- 341-342-344>346.
Gale Warning from 8 PM this evening to 11 AM EDT Tuesday for LMZ323-341-342-344>346.
Small Craft Advisory until 11 PM EDT Tuesday for LSZ321-322.