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KEY MESSAGES

-Scattered showers and storms continue this morning with hot and humid weather through the afternoon.

-Cool and quiet weather returns Wednesday through the remainder of the work week with frost/freeze concerns tonight through Thursday night.

DISCUSSION

Issued at 313 AM EDT Tue May 19 2026

Pattern Synopsis:

Longwave midlevel troughing is currently positioned over the North American Plains today with a strong jet max over the Great Lakes Region. At the surface, low pressure positioned over Northern Wisconsin this morning will progress northeast today and drag a cold front across the CWA. Hot and humid air ahead of the front will continue to linger over the region before the strong thermal gradient rapidly drops temperatures overnight. Scattered showers and storms remain possible ahead of the frontal passage this morning as lingering instability settles across Northern Lower today.

Cool and quiet weather builds into the region this evening through the remainder of the work week. cP air influence will return climatologically cool surface temps ahead of an upstream midlevel ridging pattern that builds over the central CONUS this week, causing temperatures to slowly build back to the mid/upper 70s. Dewpoint temps falling near or below freezing with efficient radiational cooling will return overnight frost/freeze concerns. Additionally, another thing to monitor amidst the atmospherically dry and cool high pressure is the continuation of minimal RH values approaching critical thresholds for fire weather. Precipitation chances build this weekend as a secondary trough axis develops over the North American Rockies and lifts northeast. No impactful weather is expected at this time, but energy waves will continue to inject enough instability to keep rainfall in the forecast as we head into late May.

Forecast Details:

Scattered showers and storms continue this morning with hot and humid weather through this afternoon... Enough lift from the well- advertised frontal boundary will fuel scattered showers with embedded thunderstorms this morning into the early afternoon. Overnight loss of surface based instability combined with showers becoming detached from the cold front itself will keep any severe potential minimal across the CWA. While most locations can expect mostly cloudy skies with hot and humid temperatures this afternoon behind the decaying line, daytime heating processes will build the minimal CAPE and shear values to support one or two single-celled thunderstorms that could produce strong gusty winds and/or hail.

Cool and quiet weather returns through the remainder of the week with frost/freeze concerns Tuesday through Thursday night... Post- frontal northwest flow will pull cool and dry cP air into the Great Lakes Region tonight. Cold air advection combined with clear skies and radiational cooling processes will return potential frost development tonight followed by widespread frost/freeze Wednesday and Thursday nights. Surface high pressure will continue through the end of the work week, but surface temperatures are expected to slowly build as upstream embedded ridging shifts its axis over the Midwest. 850mb temps start near freezing and increase to around 10 degrees Celsius by the end of the week, resulting in adiabatic heating processes warming daytime highs from the 50s this Wednesday to the mid/upper 70s for most areas by the end of the week.

One other thing to monitor this week besides the frost/freeze concerns is the dry dew points near or below freezing, leading to minimal RH values dropping to near critical thresholds for fire weather. No wind is expected under aforementioned subsidence, but we will continue to monitor conditions this Wednesday and Thursday if any potential lake breeze processes occur.

Somewhat active weather returns this weekend as another trough develops surface low pressure lee of the Rockies and makes its way to the Midwest around the Saturday/Sunday timeframe. Latest guidance depicts strongest moisture advection to our south, likely leading to steady stratiform precipitation for the Northwoods. Additional waves of energy will keep slight to scattered PoPs in the forecast through the remainder of the forecast period, but no widespread precipitation or impactful weather is expected at this time.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 1154 PM EDT Mon May 18 2026

Fog/stratus is developing, especially in northern sites (CIU/PLN/APN). IFR to VLIFR expected at times overnight. This should improve as thicker clouds and showers return to the area toward and after daybreak. Still expect CIU to be IFR/LIFR for much of Tuesday, and PLN for Tuesday morning. MVFR elsewhere Tuesday with some showers, and perhaps a few TSRA. Breezy s to sw winds early Tuesday become w and nw late.

APX WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory from 8 AM this morning to midnight EDT tonight for LHZ345>349. Small Craft Advisory until midnight EDT tonight for LMZ323-341- 342-344>346. Small Craft Advisory from 8 AM this morning to midnight EDT tonight for LSZ321-322.