Marine Weather and Tide Forecast for Farnham, NY

KEY MESSAGES
1) Locally dense fog is along the Lake Erie shoreline this morning.

2) Another round of widespread showers and embedded thunderstorms expected Saturday into Saturday night, some of which could be strong to severe across Western NY.

3) The very warm pattern continues through Saturday before much colder air moves in Saturday night.

DISCUSSION
KEY MESSAGE 1...Locally dense fog is along the Lake Erie shoreline this morning.

Dense fog has expanded onshore from Lake Erie early this morning.
Webcams show localized dense fog along the Lake Erie shoreline, including portions of Route 5 and Interstate 90. Due to the localized nature of the fog, a Special Weather Statement was issued for the morning commute for Niagara, Erie, and Chautauqua counties including the cities of Buffalo and Niagara Falls. Fog will slowly improvement through the morning hours, however a cool, northerly flow will hinder dirunal mixing this morning and low stratus and patchy fog will linger through the morning hours.

KEY MESSAGE 2...Another round of widespread showers and embedded thunderstorms expected Saturday into Saturday night, some of which could be strong to severe across Western NY.

Following a brief lull in the active weather today, the next widespread round of showers and storms will roll in from the west through the day Saturday. This batch will be forced by a strong cold front tied to a deepening closed low trudging across southern Hudson Bay Saturday night through Sunday. A secondary surface wave emerging on the leeward side of the Appalachians in the Mid-Atlantic states may slow the progression of the front, with the steadiest precip likely not exiting the North Country until Sunday morning. Basin averaged rainfall amounts of 0.5-1" seem plausible in most areas.

Severe weather potential Saturday...

Diurnal timing of the front combined with dewpoints in the upper 50s will likely form a conditionally unstable environment across WNY Saturday afternoon, with modeled MLCAPE values approaching 1000J/kg from the Genesee Valley westward. Strong unidirectional mid/upper level flow in this environment will contribute to peak effective shear values near 40kts, with strong 0-1km speed shear 20-30kts.
There will also be several potential limiting factors in this environment to consider. Convection will already be ongoing upstream headed into the day, the amount of surface-based instability and CIN remains in question as there will likely be a plethora of blowoff cirrus and mid-level clouds. Mid-level lapse rates also seem relatively poor, with 700-500mb rates only about 5.5C/km. In addition, while the low to the north will be in the process of deepening Saturday/Saturday night, the system's northeastern track will likely cause the stronger mid-level winds to begin pulling away from the region as or shortly before the onset of showers/storms.
While shear values will still be enough to pose some severe threat in any case, the window for optimal wind profiles may be short lived and not perfectly timed with peak instability. Current thinking is that for our forecast area, these variables will line up to be most favorable for severe weather in the western Southern Tier.

As of this update, local assessment is well corroborated by SPC's Marginal Risk (level 1/5) for Saturday across most of WNY, with a Slight Risk (level 2/5) for the far western Southern Tier.

KEY MESSAGE 3...The very warm pattern continues through Saturday before much colder air moves in Saturday night.

Temps will cool off several degrees today compared to the past few days behind a weak cold front, but still average about 5-10 degrees above climatology for mid-April. Strong southerly flow then returns Saturday with warmer temps closer to those observed earlier this week.

The more substantial pattern change will come behind the cold front described in Key Message (2) as deep upper level troughing crosses the Northeast. 850mb temps peaking around +15C Saturday afternoon will tumble to -4C to -6C by Sunday morning, then bottom out around -12C Monday morning. This will translate to surface high temperatures averaging 10-15 degrees (F) below normal Sunday through Monday night. Overnight lows will be similarly cold, with areawide temps dipping below freezing and potentially even into the teens across the higher terrain areas, depending on the amount of clearing that takes place.

The trough axis moving through the region, some minor lake enhancement, and upslope effects may support a few snow showers or flurries at times early next week. In general, the drier overhead airmass, warmer ground temps, and strong April sun should greatly inhibit the amount of accumulations in any one area. Some guidance (namely the CMC) suggests an embedded shortwave ripple at the base of the trough bringing a brief burst of snow to WNY Sunday night, though uncertainty is high in both the strength and track of this wave.

High pressure ridging at all levels cresting over and east of the region should cause a southerly flow to develop by Tuesday, causing temperatures to recover back to near or above climatological averages through midweek.

AVIATION /09Z FRIDAY THROUGH TUESDAY/
It's another impactful period for aviation with low stratus and fog across the eastern Great Lakes region through this morning. Areas of dense fog are mostly tied to the immediate lake shore, however visibility is expected to lower further inland towards daybreak.
Widespread low stratus will likely lead to IFR/LIFR at all TAF Sites through mid-morning. A caveat in the reduction of flight conditions, is an area of showers across eastern Lake Ontario and south of Buffalo this morning. The showers will likely disrupt flight conditions, allowing a brief period of improvement.

Surface high pressure will move overhead by this afternoon. Flight conditions will slowly improve today, with widespread VFR flight conditions this afternoon. A southerly wind will increase across the region tonight, limiting low stratus and fog development. VFR conditions are expected across the TAF sites.

Outlook...

Saturday
VFR in the morning
then deterioration to IFR/MVFR with showers and scattered thunderstorms developing during the afternoon and evening. Also breezy to windy.

Sunday/Sunday night...A mix of MVFR/IFR with upslope/lake effect rain showers mixing with and changing to snow showers.

Monday...Improvement to VFR/MVFR with leftover scattered lake effect/upslope snow showers ending.

Tuesday,,,Mainly VFR.

MARINE
Showers will end from west to east overnight. Winds will remain light on the marine zones this evening. A dense fog advisory is in effect for the eastern end of Lake Erie until 11am this morning.

Relatively light winds and minimal wave action are expected to continue today as high pressure builds across the Lower Great Lakes.
Winds are expected to increase out of the south Saturday through Saturday night in association with the approach/passage of a strong cold front. This may result in the next round of SCA conditions with the frontal passage also accompanied by another round of showers and storms...some of which could produce locally stronger winds and higher waves.

BUF WATCHES/WARNINGS/ADVISORIES
NY...None.
MARINE...Dense Fog Advisory until 11 AM EDT this morning for LEZ040-041.