What has changed

Minor changes with this forecast update.

Messages

1.) Cool weather and periodic showers and thunderstorms, some of the lake-effect variety, are expected through Tuesday.

2.) Dry weather expected region-wide this Tuesday night through Wednesday.

Discussion

Key Message 1. Cool weather and periodic showers and thunderstorms, some of the lake-effect variety, are expected through Tuesday.

Aloft, a low should wobble ENE'ward from the northern Great Lakes to near the Gulf of St. Lawrence the rest of today through Tuesday. In response, cyclonic flow, initially SW'early to W'early over our region, veers to NW'early overnight tonight into Monday and then remains NW'early through Tuesday. Shortwave disturbances embedded in the cyclonic flow will continue to impact Western and Central NY. At the surface, a cold front was located near I-81 at 1:35 PM EDT. This front will continue moving E'ward and should exit the rest of our forecast area by 4 PM at the latest. Behind the front, a lake-aggregate trough is expected to persist through Monday night and then a high pressure ridge will begin to build from the western and central Great Lakes on Tuesday. Net low-level CAA will impact our region behind the cold front. Accordingly, late afternoon highs should reach the mid 60's to mid 70's today and Tuesday, respectively. In between, Monday is expected to feature highs only in the 60's to lower 70's courtesy of colder 850 mb temperatures and rather abundant cloud cover, including daily cumuliform clouds. Overnight lows should reach mainly the upper 40's to upper 50's around daybreak Monday, Tuesday, and Wednesday, respectively.

Outside lake-effect precipitation (details below), isolated to scattered showers and thunderstorms are expected the rest of today through Monday night as low-level convergence/moist ascent along the cold front and surface trough axes accompanying the shortwave disturbances release at least weak potential instability in the lowest ~1 km above ground and weak boundary layer storm energy stemming from daytime warming through this early evening and again late Monday morning through early evening. Behind the cold front, scattered lake-effect rain showers and thunderstorms have already developed over/downwind of Lake Erie and over much of Lake Ontario. Lake-effect rain showers and thunderstorms with periods of heavy rainfall will continue through Monday night as synoptic-scale low-level moisture remains deep/abundant and 850 mb temperatures around 8C to 10C continue to become established over/downwind of ~23C to ~24C Lakes Erie and Ontario, behind the cold front. Those factors will yield sizable lake-induced storm energy and lake-induced EL's around 20kft to perhaps 30kft above lake level.

The passage of the aforementioned shortwave troughs will cause mean low-level flow direction to vary over and downwind of Lakes Erie and Ontario. Accordingly, lake-effect precipitation should primarily stream ESE'ward or SE'ward from Lake Erie through Monday night. However, a period of W'early to WSW'early mean low-level flow should allow lake-effect precipitation to stream E'ward or ENE'ward from the lake during most of the predawn and daylight hours of Monday. This lake-effect precipitation should remain south of Buffalo. As for Lake Ontario, mean low-level flow should allow lake-effect precipitation to impact locations generally northeast of the lake through Monday afternoon, before the precipitation shifts S'ward and eventually settles southeast of the lake Monday evening through Monday night as a shortwave trough axis passage causes mean low-level flow to veer from SW'early to NW'early over/downwind of the lake. Note: lake-effect precipitation is expected to be most-organized tonight into Monday morning and again Monday night into Tuesday morning, when nighttime cooling will allow Lakes Erie and Ontario to be the primary sources of warmth, moisture, and instability.

On Tuesday, lake-effect rain showers and thunderstorms are expected to stream generally SE'ward from Lakes Erie and Ontario, but decrease in coverage/intensity and end by nightfall as the building surface ridge is accompanied by synoptic-scale low-level dry air advection, a lowering subsidence inversion, and increase in directional low-level vertical wind shear, which will all act to decrease lake-induced storm energy. Primarily dry weather is expected outside the lake-effect precipitation, but a few showers may accompany the passage of additional shortwave troughs/attendant surface trough axes coinciding with weak potential instability in the lowest ~1 km above ground.

Key Message 2. Dry weather expected region-wide this Tuesday night through Wednesday.