Saint Bonaventure, NY Weather

What Has Changed

Isolated rain showers may accompany the passage of a cold front this Monday, especially across far-northern portions of North- Central NY, including the Thousand Islands. Otherwise no major changes were made to the forecast.

Key Messages

1) Dry weather is expected the majority of the time through early next week. However, a few rain showers may accompany the passage of a cold front this Monday.

Discussion

KEY MESSAGE 1...Dry weather is expected the majority of the time through early next week. However, a few rain showers may accompany the passage of a cold front this Monday.

Aloft, a ridge continues to build from the western Great Lakes and vicinity through tonight and then settles over the Northeast United States and vicinity this Sunday through Sunday night. At the surface, the ridge continues to affect our region as the embedded high pressure center wobbles generally S'ward from southern QC to the Mid-Atlantic states. Dry weather persists in our CWA as stabilizing subsidence accompanies the ridge. Sky will be clear during most of the time period, but passing cloudiness, primarily in the mid/upper-levels, is expected at times as moist isentropic ascent precedes the axes of shortwave troughs embedded in the primarily W'erly to NW'erly flow aloft, especially before daybreak this morning and again Sunday afternoon through Sunday night. Lows should reach mainly the mid 20's to mid 30's around daybreak this morning as clearing sky, weak or calm surface winds, and low humidity promote efficient radiational cooling. Highs should reach the mid 50's to lower 60's late this afternoon as weak WAA begins to develop along the western flank of the low-level ridge. Overnight lows mainly in the mid 20's to upper 30's are forecast around daybreak Sunday due to another round of efficient radiational cooling. Warmer highs, mainly in the upper 50's to upper 60's, are expected on Sunday and should be followed by overnight lows mainly in the mid 30's to upper 40's around daybreak Monday as the WAA regime strengthens somewhat along the western flank of the low-level ridge.

On Monday, cyclonic W'erly to WNW'erly flow aloft and embedded shortwave troughs are expected to impact our region. Variable amounts of mainly mid/upper-level cloudiness are expected amidst moist isentropic ascent ahead of the shortwave trough axes. At the surface, the aforementioned ridge will exit generally SE'ward and be followed by the SE'ward passage of a weak cold front during the late morning through early afternoon. A rather dry low-level atmospheric column should permit a dry cold front passage across most of our CWA. However, forcing for ascent along the front may coincide with sufficient amounts of low-level moisture to permit the development of isolated and light rain showers across far-northern portions of Jefferson and Lewis Counties, including the Thousand Islands. Behind the front, another high pressure ridge builds from central Canada and vicinity. Late afternoon highs should reach mainly the mid 50's to mid 60's.

During Monday night through Tuesday, the surface ridge will continue to affect our region as the embedded high pressure center moves from northern ON toward southwestern QC, while the ridge aloft builds from the Upper Midwest and eventually the western and central Great Lakes. Dry weather is expected as stabilizing subsidence accompanies the ridge. Low-level CAA behind Monday's cold front passage will contribute to lows reaching mainly the lower 20's to mid 30's around daybreak Tuesday and highs reaching the 40's to 50's late Tuesday afternoon.

Note: Clear sky or sufficient cloud breaks and weak or calm surface winds should contribute to localized steam fog in the Black River Valley, Western Southern Tier river valleys, and the lake valleys of the Finger Lakes Region during the predawn hours through about 10 AM EDT today through Tuesday, respectively.

Aviation

Mainly VFR flight conditions will continue through the 06Z TAF period. Periods of mid and upper level cloud will continue to pass over eastern portions of the region through the late night/early morning hours, followed by mainly SKC conditions for today.

Otherwise, the only issue will continue to be the possibility for late night/early morning river valley and inland lake fog that will bring localized flight restrictions where it is able to form. With mid and upper level decks possibly hanging on through a good chunk of the early morning hours across eastern portions of the area, the best possibility for any localized fog will be across the western Southern Tier and upper Genesee valleys late tonight, persisting through mid morning or so. Looking back at conditions yesterday morning, KJHW saw flight restrictions for around 30 minutes. With the very dry airmass and very similar conditions remaining in place, other than a subtle wind shift to SE'erly through the early morning hours, only brief impacts at worst are expected for KJHW again late tonight into the first part of this morning.

Outlook...

Tonight through Wednesday...Mainly VFR. However, localized flight restrictions will be possible each late night/early morning owed to river valley and inland lake fog.