textproduct: Detroit/Pontiac

KEY MESSAGES

- Low temperatures dip back into the low to mid 30s tonight, but increasing surface winds and clouds overnight helping to limit widespread frost development.

- A slight chance of thunderstorms late Tuesday/Tuesday evening south of M-59. No severe weather is anticipated.

- Temperatures climb above seasonal normals on Tuesday (forecasted highs in the upper 60s to lower 70s), with even warmer air expected for the end of the workweek.

- Rain showers likely by Friday evening with possible thunderstorms.

DISCUSSION

Near-record cold was observed across Southeast Michigan this morning. The 12z KDTX sounding sampled a very chilly air mass with -10C at the 850 mb level. Under the influence of a sprawling high pressure system, clear skies and calm winds provided ideal radiational cooling conditions, allowing minimum temperatures to bottom out in the mid-to-upper 20s. These values were only a couple of degrees shy of the daily record lows at both MBS and FNT. Full April insolation has since allowed for a respectable recovery, with temperatures reaching into the 40s late this afternoon.

The synoptic pattern shifts tonight as surface high pressure slides toward the Atlantic coast. While low temperatures will dip into the low-to-mid 30s, increasing southerly winds and thickening cloud cover should mitigate widespread frost development. The exception may be the Thumb region, where calmer winds persist longer; however, with the growing season not yet officially underway for those northern counties, no frost/freeze headlines are planned.

A much warmer air mass is progged to surge into the region for Tuesday and Wednesday. As an elevated warm front lifts through late tonight and toward sunrise Tuesday, a strengthening low-level jet (LLJ) of 35-45 knots will drive a corridor of solid moisture advection, as 850-700 MB specific humidity reaches near 5 g/kg. High- resolution guidance (including the 3km NAM) suggests this forcing will be sufficient to trigger isolated to scattered sprinkles/light showers, primarily between 09z and 14z.

By Tuesday afternoon, the region will be firmly within the thermal ridge, with 850 mb temperatures approaching 10C. This supports widespread highs in the upper 60s to lower 70s toward the Ohio border. We will be monitoring for modest instability to develop along the southern Michigan border by late afternoon as a narrow theta-e plume advects into the region. Model soundings show MUCAPE values of 200 to 500 J/kg, which should be enough to support a chance of showers and a slight chance of thunderstorms for the southern tier of counties through Tuesday evening as a subtle shortwave trough tracks through the western Ohio Valley.

The thermal ridge holds firm through mid-week, though a shallow cold front may attempt to sag south from Lake Huron, keeping the Thumb several degrees cooler than the rest of the region. High confidence remains for a more significant warm-up toward the end of the workweek as the upper-level ridge axis amplifies. EPS members indicate highs potentially reaching the upper 70s by Friday, though timing of a significant cold front and associated shortwave likely bring showers and thunderstorms back into the forecast by Friday evening.

MARINE

High pressure maintains light wind and waves across the central Great Lakes this afternoon and evening. As the high moves east overnight, southerly return flow will set up and increase in magnitude through the morning Tuesday. Low-level stability is forecast to cap wind gusts at 20 to 30 kt, highest over central Lake Huron. Small Craft Advisories have been issued for the Lake Huron nearshore waters where confidence is highest in periods of 25+ kt wind gusts between 2am and 2pm. A cold front then settles southward across the region Tuesday night, bringing a chance of showers and thunderstorms mainly in the south. Lighter wind follows on Wednesday as weaker high pressure settles in. The next low begins to take shape over the upper Midwest midweek, eventually sending a warm front into the Great Lakes late Thursday into Friday. This brings moderate southeast flow and the next chance for showers and storms.

PREV DISCUSSION

Issued at 1257 PM EDT Mon Apr 20 2026

AVIATION...

With ample daytime heating and mixing ongoing this afternoon, still expect a few northwest wind gusts this afternoon upwards of 15-20kt. Otherwise, northwest winds relax later this afternoon and back westerly and then south-southeastly through this evening as high pressure drops through the region.

Scattered to broken mid to high clouds move in overnight from the northern Great Lakes region. These clouds are associated with the next wave of energy progged to track south across the area Tuesday into Wednesday. Could be a few sprinkles or very light rain showers around Tuesday morning, but confidence was not high enough to include mentions in the forecast at this time. South winds increase around daybreak Tuesday, then veer more southwesterly with gusts upwards of 20-25 knots ahead of a weak front sagging south across the area. Tuesday evening there is a chance for showers and thunderstorms, mainly for areas near and south of KDTW/KYIP/KDET. Have no mentions of storms in the TAFs at this point, but those details may need to be added in subsequent forecast updates.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms between 2100Z Tuesday and 0600Z Wednesday.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 2 AM to 2 PM EDT Tuesday for LHZ421-422- 441>443.

Lake St Clair...None. Michigan waters of Lake Erie...None.