Area Forecast Discussion

KEY MESSAGES

- Freeze conditions expected tonight with lows from mid 20s to around 30.

- Low chances of rain return for Tuesday night but only light precipitation amounts are expected which will not have a significant impact on flooding concerns.

- After a cool start to the week, temperatures trend warmer starting Tuesday.

DISCUSSION

Issued at 244 PM EDT Sun Apr 19 2026

Water vapor imagery this afternoon depicts a strong upper level vort max dropping southeast across the western Great Lakes. Low levels have mixed out nicely in advance of this feature with dew points bottoming out to around 20 degrees in spots. These low level dew point trends should make instability a bit more of a struggle with max sfc based CAPES expected around 100 J/kg for a few hours this afternoon. Despite limited instability, would expect a few higher based showers to develop given strength of mid/upper level forcing and a strong mid level cold pool (-18 to 20 deg C at 700 mb). Some enhancement to frontal convergence with flow off Lake Michigan could help initiate these showers, and these low rain chances should be progressive from west to east following the stronger vorticity advection with the upper trough. Given large dew point depressions, any rainfall amounts will be light.

Some low clouds may linger into this evening downwind of Lake Michigan with some weak lake response possible, but otherwise clearing skies are expected as a broad low level anticyclone eventually shifts across the region overnight. The orientation of the low level thermal trough from southeast Canada into the eastern Great Lakes and portions of the Ohio Valley still suggests coldest mins in mid 20s across south central Lower Michigan into far northwest Ohio. Confidence is still on the high side that all areas should be below freezing for mins tonight, so no changes planned to the Freeze Warning at this time.

Monday will be a quiet transition as southern Great Lakes/Ohio Valley become positioned in upper level inflection zone between eastern CONUS trough/western CONUS ridge. Broad synoptic scale subsidence in this pattern will provide mostly clear skies with below normal temperatures continuing. Some patchy frost is possible again Monday night across the far east, but given departure of low level ridge axis, low level gradient should be strong enough during the overnight hours into Tuesday morning to limit this potential.

Tuesday will feature a better mixing day as low level southwest flow increases downstream of a weak, low amplitude northwest flow short wave trough and the low level ridge axis shifts off the Mid Atlantic coast. Breezy/windy conditions are expected on Tuesday and deep mixing combined with stronger WAA should lead to above normal temps back into low-mid 70s for most locations. A southward sagging frontal boundary Tuesday night and some pooling of moisture in pre-frontal zone should lead to some light rain showers shifting north to south across the area Tuesday evening, but precip amounts should be less than one quarter of an inch.

For the remainder of the work week, medium range guidance does suggest more significant western CONUS troughing developing but this will occur in the backdrop of a somewhat stable longwave pattern with only a slow eastern progression of central CONUS upper ridge. This evolution should keep primary moisture/instability axis west of the local area on Thursday with likely cold frontal passage as system occludes well to the northwest across Northern Plains/south central Canada. Rain showers and perhaps a few storms may accompany this front. Much above normal temps Thursday and Friday will give way to more seasonable temperatures by early next weekend.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 130 PM EDT Sun Apr 19 2026

A strong upper vort lobe will drop across the region this afternoon. Good low level mixing and dry airmass has led to sfc dew points bottoming out this afternoon. This should limit strength of surface based instability. Given strength of vort lobe and strong mid level cold pool would still expect isolated-scattered showers to progress through northeast Indiana but will be short-lived if they occur and in a brief temporal window from 19Z to 23Z. Winds will relax this evening with loss of boundary layer mixing, eventually becoming light and variable as a broad low level anticyclone drops across the Great Lakes and Ohio Valley.

IWX WATCHES / WARNINGS / ADVISORIES

IN...Freeze Warning from midnight EDT /11 PM CDT/ tonight to 11 AM EDT /10 AM CDT/ Monday for INZ005>009-012>015-017-018-020- 022>027-032>034-103-104-116-203-204-216. OH...Freeze Warning from midnight tonight to 11 AM EDT Monday for OHZ001-002-004-005-015-016-024-025. MI...Freeze Warning from midnight tonight to 11 AM EDT Monday for MIZ078>081-177-277. MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ043- 046.