Lancaster, NY Weather

What Has Changed

No major changes with this forecast update.

Key Messages

1) Dry and tranquil weather is expected to continue through this Monday.

Discussion

KEY MESSAGE 1...Dry and tranquil weather is expected to continue through this Monday.

Aloft, a high pressure ridge builds from the Upper Midwest today and settles over the Northeast United States and vicinity, including our CWA, tonight through Sunday night. At the surface, the ridge continues to affect Western and Central NY as the embedded high pressure center wobbles generally S'ward from central QC to the Mid-Atlantic states. Dry weather persists in our CWA as stabilizing subsidence accompanies the ridge.

Clear to mainly clear sky is expected through most of the time period. However, isolated to scattered lake-effect stratocumuli over and downwind of the ~16C eastern Great Lakes are expected to persist through this late morning as a sufficiently-cold mean low-level flow veers from N'erly to ENE'erly. Lake-induced CAPE will remain limited as synoptic-scale low-level moisture remains scarce. These stratocumuli should dissipate by midday as daytime heating of surrounding land and overlying air causes the eastern Great Lakes to no longer be the primary source and warmth, moisture, and instability. Scattered to widespread upslope stratocumuli over the Western Southern Tier and vicinity should dissipate by daybreak this morning in response to the veering mean low-level flow and continued low-level dry air advection. The lake-effect and upslope stratocumuli are expected to remain too shallow to produce precip. Otherwise, variable amounts of mid/upper-level cloudiness associated with moist isentropic ascent preceding shortwave trough axes embedded in the NW'erly to W'erly flow aloft are expected, especially during today's mid-morning hours through the first few predawn hours of Saturday morning and Sunday afternoon through Sunday night.

Lows should reach mainly the upper 20's to upper 30's around daybreak this morning and be followed by highs in the 50's to lower 60's late this afternoon as weak low-level CAA continues in the wake of Thursday's cold front passage. Tonight's lows should reach mainly the mid 20's to mid 30's around daybreak Saturday as clearing sky, weak or calm surface winds, and low humidity promote efficient radiational cooling. Late afternoon highs should reach the mid 50's to lower 60's on Saturday 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 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.

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 9 AM EDT today through Monday, respectively.

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. Behind the front, another high pressure ridge should build from central Canada and vicinity through the evening. Late afternoon highs should reach mainly the mid 50's to mid 60's.

Aviation

Dry weather and mainly VFR are expected across Western and Central NY through 12Z/Sat as a surface ridge continues to affect our region and the embedded high pressure center moves generally S'ward from central QC to near Lake Champlain. Our regional surface winds are expected to veer gradually from NE'erly to SE'erly and be around 5 knots through the TAF period. However, surface winds will likely become calm periodically, especially this morning and again this evening through 12Z/Sat. Variable amounts of mainly mid/upper-level cloudiness are expected through the TAF period, in association with disturbances embedded in NW'erly to N'erly flow aloft.

Note: clear sky or sufficient cloud breaks and weak or calm surface winds will contribute to localized steam fog with MVFR to LIFR in the Black River Valley, Western Southern Tier river valleys, and lake valleys of the Finger Lakes Region through ~14Z/Fri and again from ~03Z/Sat through 12Z/Sat. A marginally- favorable vertical wind profile in the lowest 2kft AGL may allow fog to impact KJHW at times through ~14Z/Fri. Fog is not expected to impact that location overnight tonight into Saturday morning due to an unfavorable vertical wind profile in the same atmospheric layer. Black River Valley steam fog may impact KART between ~08Z/Sat and 12Z/Sat.

Outlook...

Saturday through Tuesday...Dry weather and mainly VFR are expected. However, localized steam fog with MVFR to LIFR should impact the same areas noted in the above discussion each late evening through about mid-morning.