Jamestown, NY 14702 Weather

What Has Changed

No major changes with this forecast update.

Key Messages

1) Dry and tranquil weather will prevail through this weekend.

Discussion

KEY MESSAGE 1...Dry and tranquil weather will prevail through this weekend.

High pressure at the surface and aloft will remain in place across the Ohio Valley and eastern Great Lakes through Wednesday night, maintaining dry weather and clear to mainly clear sky across Western and Central NY. However, a shortwave trough aloft should approach from the northern Great Lakes Wednesday night as the disturbance advances SE'ward. The only consequence is expected to be the development of isolated to scattered mid/upper-level cloud cover amidst moist isentropic ascent ahead of the shortwave trough axis above a much drier low-level tropospheric column. Clear to mainly clear sky and light or calm surface winds should contribute to the development of localized steam fog in the Black River Valley and Western Southern Tier river valleys through about daybreak this morning and again overnight Wednesday night through about daybreak Thursday. This fog is expected to be shallow amidst scarce synoptic-scale low- level moisture.

The shortwave trough aloft and attendant cold front will sweep SE'ward across the eastern Great Lake and vicinity on Thursday. The majority of the isobaric height falls aloft and large-scale forcing for ascent will be displaced well northeast of our area across Quebec, leaving a weakly-forced and moisture-starved cold front passage across our region. Besides the aforementioned increase in mid/upper-level cloud cover ahead of the shortwave trough axis aloft, a continued dry low-level tropospheric column is expected to permit a dry cold front passage. Behind the front, and east of the axis of a ridge at the surface and aloft that will approach from the Upper Great Lakes and vicinity, a cooler air mass will yield some increase in lake- induced instability. However, the lack of synoptic-scale low- level moisture will likely only support a few lake-effect stratocumuli over and south, and then over and southwest of the ~16C eastern Great Lakes later Thursday into Friday morning as mean low-level flow veers from N'erly to NE'erly. The N'erly mean low-level flow should also yield a few upslope stratocumuli generally south of the eastern Great Lakes.

Late afternoon highs are expected to reach the 50's to lower 60's today and Thursday. Daily lows should reach mainly the upper 20's to upper 30's around daybreak today through Friday. The high pressure ridge at the surface and aloft will continue to build E'ward and settle over the Northeast United States and vicinity on Friday through this weekend. Dry weather and clear to mainly clear sky are expected as stabilizing subsidence accompanies the ridge. Daily highs should moderate from mainly the 50's to 60F on Friday to the mid 50's to mid 60's on Sunday as our region eventually becomes located in a WAA regime along the western flank of the low-level ridge. Lows should reach mainly the mid 20's to mid 30's around daybreak Saturday and mainly the lower 30's to lower 40's around daybreak Sunday. Note: the environment should remain favorable for localized and shallow steam fog development in the Black River Valley and Western Southern Tier river valleys between about 12 AM and 9 AM EDT this Friday through Sunday.

Aviation

A strong surface high pressure ridge will continue to impact the eastern Great Lakes and vicinity, and be accompanied by light and variable or calm regional surface winds through 12Z/Thurs. Dry weather and mainly VFR will prevail. The one exception should be localized and shallow steam fog with MVFR to LIFR in the Western Southern Tier river valleys and Black River Valley through ~13Z/Wed and again after ~03Z/Thurs through 12Z/Thurs. The vertical wind profile in the lowest 2kft AGL is still expected to be unfavorable for the fog to reach KJHW.

Outlook...

Thursday through Sunday...Dry weather and mainly VFR expected. However, localized steam fog with MVFR to LIFR is possible in the Black River Valley and Western Southern Tier river valleys each morning.