textproduct: Detroit/Pontiac

KEY MESSAGES

- A Frost Advisory is in effect tonight for most of Southeast Michigan with lows in the 30s.

- Some rain and/or snow showers possible Sunday afternoon and evening with gusts above 30 mph at times; a rumble of thunder cannot be ruled out.

- A Freeze Watch is in effect Sunday night for most of Southeast Michigan with lows in the 20s.

- Temperatures warm back toward normal Tuesday, climbing well above normal through the rest of the week.

DTW THRESHOLD PROBABILITIES

* High for ceilings aob 5000 ft through about 09Z tonight. Then high again tomorrow morning/afternoon.

PREV DISCUSSION

Issued at 350 PM EDT Sat Apr 18 2026

DISCUSSION...

An extensive and potent cold front, extending from 980 mb surface low pressure stalling over southern Hudson Bay, has cleared east into the southern Ontario peninsula this afternoon. As expected, 2m temperatures dropped in the wake of the boundary, from morning readings in the 60s to afternoon readings in the 40s/50s. Post- frontal winds veered accordingly, and should persist from the west overnight with a slow decay of the pressure gradient. The ensuing cold advection has steepened low-level lapse rates and allowed for efficient mixing of the still shallow boundary-layer winds. Gusts of 20-30 mph should taper off overnight as a weak nocturnal inversion emerges, while prevailing winds drop below 10 mph, late. A Frost Advisory was issued for tonight until Sunday morning for all counties where the growing season has begun. Temperatures drop into the mid 30s, but could briefly drop below freezing around sunrise, should skies fully clear out and winds trend near calm. After a week of intermittently heavy rainfall, high soil moisture may help slow the rate of cooling for near-surface vegetation.

The composite longwave trough axis will bisect Lower Michigan Sunday morning. Although the jet streak and its strongest dynamics will have departed, a cyclonic flow regime will persist overhead throughout the day. Evidence of low-level convergence passing across Lake Huron and perturbed mid-level geopotential heights support scattered shower activity during the day. Moisture advection is unremarkable, and the lake contribution to moistening should be minor given relatively cold water temperatures. However, forecast soundings indicate deep surface-based mixing potential with the cloud-bearing layer residing within a portion of the DGZ, generating areas of precipitation. While temperatures will climb into the 40s during the day, drying within the lowest 3-5 kft AGL may favor evaporation/shedding of meltwater on snowflakes upon descent. Sounding data varies greatly with the height/depth of the saturated layer which has consequential impacts on final hydrometeor state. Should the maximized DGZ and deeper/drier boundary layer solutions win out, any snowfall would be non-accumulating, melting on contact. Additionally, potential exists for a few rumbles of thunder given the steepness of low- and mid-level lapse rates. This also supports blustery diurnal conditions with winds veering northwesterly and gusting above 30 mph at times.

Showers should quickly wane after sunset Sunday, ahead of a very chilly night by mid-late April standards. High confidence exists in overnight lows dropping into the 20s as 850 temperatures plunge below minus 10C late Sunday night. Issued a rare Freeze Watch for all areas in which the growing season has begun given the heightened sensitivity of early season vegetation and well-advertised cold airmass.

Height rises build in Monday with longwave ridging spreading east of The Rockies and a shorter wavelength ridge axis dropping across the Upper Midwest from the northern stream jet. Surface high pressure races southeastward with the northern anticyclone on Monday, with central high pressure of 1030 mb settling over Lower Michigan Monday afternoon. The surface high moves east Monday night, leading to a return flow setup and above normal temperatures. A cold front stalls out just to the south Tuesday night and Wednesday offering a chance for showers and/or thunderstorms near the Michigan/Ohio border. Much warmer to close out the week with highs in the 70s and dewpoints back into the 50s. Isolated showers/storms possible before expanding in coverage with the next FROPA Friday or Saturday.

MARINE...

Cold air advection is gaining traction this afternoon which will maintain higher mixing depths and persistence of gusty W to NW winds to 20 to 25 kt tonight. A secondary cold front passes through on Sunday, resulting in an uptick in wind magnitude during the afternoon and evening. Small Craft Advisories have been issued for western Lake Erie and Lake St. Clair with this forecast and additional advisories are likely for the Lake Huron nearshore late Sunday into Sunday night as wave heights build over 4 feet within gusty NW flow to 25-30 kt. High pressure builds directly into the Great Lakes on Monday allowing winds and waves to subside. Gusty south wind then develops Monday night into Tuesday ahead of the next cold front tracking across the upper Midwest.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Frost Advisory from 2 AM to 10 AM EDT Sunday for MIZ053-060>063- 068>070-075-076-082-083.

Freeze Watch from Sunday evening through Monday morning for MIZ053- 060>063-068>070-075-076-082-083.

Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422.

Lake St Clair...Small Craft Advisory from 10 AM to 8 PM EDT Sunday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 10 AM to 8 PM EDT Sunday for LEZ444.