Marine Weather and Tide Forecast for Lewiston, NY

NEAR TERM /THROUGH SUNDAY/
During this period a frontal boundary will remain stalled out to the south of our region...while additional weak waves of low pressure ripple eastward along this boundary. While the vast majority of the convection attendant to these waves and the frontal boundary itself will remain to our south...the presence of a weak inverted trough extending along our southeastern periphery may still be enough to generate a few showers at times across the Southern Tier and interior portions of the Finger Lakes/North Country. Have covered these with a mix of slight chance to chance (20-40 percent) PoPs in the forecast for now...with areas further north and west expected to remain dry.

Otherwise the rather stark nortwest-southeast bifurcation in cloud cover currently seen on satellite imagery will tend to remain in place through the rest of the day...with lower clouds hanging tough across the Southern Tier owing to greater amounts of low level moisture there...while clear largely skies will be found across portions of the Niagara Frontier and North Country. Tonight nocturnal cooling/moistening within the pool of lingering low level moisture in the vicinity/south of the inverted trough will likely result in the lower clouds expanding back somewhat northwestward again...with some lower stratus/areas of fog expected to redevelop across the higher terrain...especially across portions of the Southern Tier where it rained last night and this morning. On Sunday...the lower clouds should then tend to thin and lift from northwest to southeast again with renewed diurnal heating and mixing.

SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/
Canadian sourced high pressure will slowly loosen its grip on our region this period as it migrates eastward, extending from Quebec to the northwestern Atlantic by Tuesday before moving entirely offshore Tuesday night. Meanwhile, a mid-level shortwave crossing into the Ohio Valley from the central Mississippi Valley will cause a stalled frontal boundary in the region to begin lifting back northwards towards the eastern Great Lakes as a warm front. While stronger forcing for showers and thunderstorms won't arrive until the shortwave and warm front move in on Tuesday, we may contend with some spotty light showers at times through Monday night with weak isentropic lift and weak low-level convergence in the vicinity. NBM is much drier than global ensemble guidance for Monday in particular, with the former showing null QPF and the latter (mainly the GEFS/ENS) showing 60-80% for measurable rainfall over our region. Have hedged above NBM though still only spotty light QPF amounts given the nebulous forcing in place.

LONG TERM /WEDNESDAY THROUGH SATURDAY/
A phasing shortwave pattern will carve out a deeper longwave trough across the Great Lakes Wednesday through Thursday. A strengthening wave of sfc low pressure ahead of this trough will track northeast from the Upper Midwest to Quebec in tandem. This will lift the previously stalled frontal boundary even further north and firmly place the forecast area in the system's warm sector, with much more summer-like air advecting into the region. The increased heat, humidity, and instability will be accompanied by stronger LLJ forcing to also increase chances for showers and thunderstorms across the area. Details remain murky at this range, mainly in regards to track of the low and timing of the system's cold front, but the general setup could be supportive of heavy rainfall and more robust convection should all the parameters favorably align.

Overall activity should begin to wind down Thursday night, though could be some lingering showers as the upstream trough looks to hang back quite a bit and not cross the region until later Friday. There are indications that much stronger ridging (and thus warmer and drier weather) may build across the central/eastern CONUS over the weekend, though confidence is low in this being preceded by some "ridge runner" shower/tstorm activity Saturday.

AVIATION /19Z SATURDAY THROUGH THURSDAY/
Through Sunday a frontal boundary will remain stalled out to the south of our region...while additional weak waves of low pressure ripple eastward along this boundary. While the vast majority of the convection attendant to these waves and the frontal boundary itself will remain to our south...a weak inverted trough extending along our southeastern periphery may still generate a few showers at times across the Southern Tier and interior portions of the Finger Lakes/North Country
Meanwhile
areas further north and west will remain dry.

This being said...the presence of the inverted trough and lingering low level moisture along and to its south will allow the mix of IFR/MVFR ceilings along our southeastern periphery this afternoon to expand back northwestward a bit and lower again tonight as nocturnal cooling/moistening of the lower levels takes place...with areas of low stratus and fog expected to redevelop across the higher terrain of the Southern Tier and Finger Lakes. Further north and west conditions should remain VFR through tonight...though some lower-end VFR ceilings will probably still make it into KBUF-KROC-KART for at least a time. On Sunday renewed diurnal heating and mixing should then result in improvement to higher-end MVFR/lower-end VFR across the Southern Tier and interior of the Finger Lakes...with VFR conditions prevailing elsewhere.

Outlook...

Sunday night and Monday...Mainly VFR with a chance of showers and isolated thunderstorms mainly across the Southern Tier and Finger Lakes.

Tuesday...Mainly VFR with a chance of showers and thunderstorms, especially southern portions of the area.

Wednesday and Thursday...VFR/MVFR with showers and thunderstorms likely.

MARINE
High pressure will slide from Quebec to offshore of the Canadian Maritimes through the rest of the weekend...while several waves of low pressure ripple along a stalled out frontal zone across Ohio and Pennsylvania. The pressure gradient between these features will maintain northeasterly winds on Lake Erie and Lake Ontario, with a moderate chop on both lakes.

As the high shifts further eastward Sunday night and Monday...winds will veer southeasterly and weaken on both Lakes. The weakening and offshore flow component will allow waves to subside, with little to no chop expected for the start of the new work week.

BUF WATCHES/WARNINGS/ADVISORIES
NY...None.
MARINE...None.