Marine Weather and Tide Forecast for Lewiston, NY

KEY MESSAGES
1) Widespread, soaking rain will continue into this evening before tapering off from west to east overnight.

2) Unsettled weather is expected from late in the week through the beginning of next week.

3) Cool weather will support the potential for frost or freeze headlines Thursday night through Sunday morning.

DISCUSSION
KEY MESSAGE 1...Widespread, soaking rain will continue into this evening before tapering off from west to east overnight.

A deep mid level trough will become established across the Great Lakes through Thursday, with a well defined shortwave crossing the eastern Great Lakes this evening. An elongated surface low developing along the frontal zone will reach southwest NY this afternoon before moving to the Saint Lawrence Valley by late this evening. Large scale ascent ahead of the shortwave will maximize this afternoon and evening, and combine with a period of thermal packing and strong frontogenesis in the low/mid levels along and northwest of the frontal wave track to support widespread, soaking rainfall.

The most widespread rain over Western NY this afternoon will center on the Genesee Valley and Finger Lakes to the eastern Lake Ontario region this evening. The steady rain will taper off and end later this evening across Western NY, with the back edge of the rain exiting the eastern Lake Ontario region by around daybreak Thursday.
Rainfall totals will be in the 0.75" to 1.25" range for the bulk of the area. Far Western NY may be the only location that remains at or below 0.50" with a shorter period of soaking rain expected at the western edge of the deeper moisture and forcing from the frontal wave.

The steady rain will be gone by Thursday morning. A mid level closed low will stall just north of the Great Lakes, with cool cyclonic flow aloft, steepening low level lapse rates, and lingering boundary layer moisture supporting a few scattered showers in the afternoon and evening with modest daytime heating. The best chance of a few showers will be across Western NY and the North Country where somewhat deeper low level moisture will be found.

KEY MESSAGE 2...Unsettled weather is expected from late in the week through the beginning of next week.

An upper level trough will reside across the Great Lakes region from late in the week through the weekend. GOES water vapor imagery this afternoon shows a shortwave trough across the Northern Plains that will close off over the Northern Great Lakes through tonight. A cold pool aloft and daytime heating will support the chance for developing clouds and showers Friday afternoon through the weekend. Greater coverage in rain showers is expected Friday afternoon as a cold front approaches the region. Cold air advection is expected behind the front Friday night through Saturday with 850mb temperatures falling to -6C. Low freezing heights will support graupel/snow mixing with rain showers Saturday afternoon with any lingering showers briefing changing over to all snow showers across the higher terrain Saturday night. Little to no snow accumulation is expected during this time.

Westerly winds will be on the lighter side with modest wind gusts up to 25mph during the afternoon hours.

KEY MESSAGE 3...Cool weather will support the potential for frost or freeze headlines from late in the week through Sunday morning.

An upper level trough will bring an anomalously cold airmass for this time of year across the eastern Great Lakes region from late in the week through the weekend. Daily maximum and minimum temperatures will average 10 to 15 degrees below normal Thursday night through Saturday night. In particular, minimum temperatures are expected to fall into the 30s and even the 20s across the higher terrain on some nights. There remains high uncertainty regarding the amount of cloud cover through the weekend, which may impact how cold it gets. The growing season begins for the majority of the forecast area on May 1. This applies to areas with the exception of Cattaraugus, Allegany, Jefferson, and Lewis counties.

Behind the exiting trough, temperatures will climb closer to seasonal values Sunday night through Wednesday.

AVIATION /00Z THURSDAY THROUGH MONDAY/
An area of low pressure over the Finger Lakes region early this evening will continue moving north-northeast to the Saint Lawrence Valley by late this evening. Deep layer ascent and deep moisture will maintain a widespread soaking rain from the Genesee Valley to the North Country, with the back edge of the steadier rain tapering off across the Finger Lakes region by the early overnight hours, lastly tapering off across the North Country late tonight. MVFR/IFR VSBY can be expected in the steadier/ heavier rain from the Finger Lakes eastward, along with widespread IFR CIGS.

Although the steadier rain has tapered off across Western NY, areas of lighter showers will continue through late evening.
Expect this same scenario to translate east through tonight in the wake of the steadier rain shield. VSBY will improve to VFR from west to east for lower elevations as the rain ends, with some MVFR/IFR lingering across higher terrain overnight. CIGS will improve to MVFR/low VFR across the Niagara Frontier this evening, with IFR/MVFR hanging on for the remainder of the lower elevations through the overnight, and IFR lingering across higher terrain.

Thursday, a few scattered showers will linger across the North Country. A few additional scattered showers may develop across Western NY during the afternoon and early evening with steep low level lapse rates and cool air aloft working on lingering shallow low level moisture during modest daytime heating. MVFR/higher terrain IFR CIGS will slowly improve toward low VFR through the afternoon on the lake plains, with MVFR hanging on across higher terrain.

Outlook...

Friday through Sunday...VFR/MVFR with scattered rain showers at times. Some wet snowflakes may mix in across higher terrain, mainly Friday night through Saturday night.

Monday...Areas of MVFR with showers likely.

MARINE
A wave of low pressure will cross the Saint Lawrence Valley tonight before moving north across Quebec Thursday. Westerly winds will gradually increase on Lake Ontario and Lake Erie overnight through Thursday, producing choppy conditions on both lakes. The best chance of marginal Small Craft Advisory conditions will be on the east half of Lake Ontario Thursday afternoon through Thursday evening.

Looking further out through the end of the week, a continued unseasonably cool airmass and moderate pressure gradient may support additional periods of SCA conditions at times, particularly across Lake Ontario.

BUF WATCHES/WARNINGS/ADVISORIES
NY...None.
MARINE...Small Craft Advisory from noon Thursday to 2 AM EDT Friday for LOZ043-044.
Small Craft Advisory from 2 PM Thursday to 2 AM EDT Friday for LOZ045.