Marine Weather and Tide Forecast for Palmyra, NY

KEY MESSAGES
1) Warm with rounds of showers and thunderstorms through much of the week.

2) Marginal risk for isolated severe thunderstorms and locally heavy rainfall Tuesday and Wednesday.

DISCUSSION
KEY MESSAGE 1...Warm with rounds of showers and thunderstorms through much of the week.

Surface low pressure will move from the central Great Lakes this morning to the Saint Lawrence Valley by early this evening. A period of warm advection and moisture transport will cross the eastern Great Lakes this morning ahead of the low, enhanced on the nose of a 40-50 knot low level jet in the warm sector of the passing low.
Isentropic upglide and convergence near the nose of the low level jet will likely support an area of showers and scattered thunderstorms moving northeast across the area this morning.

A second line of convection may develop along the weak cold front trailing the low, which will cross the eastern Great Lakes from late morning through late afternoon. Convergence from the passing weak front may combine with convergence along the southern edge of enhanced flow off Lake Erie from the Southern Tier into the Finger Lakes and Central NY, where convection is most likely this afternoon. A gusty southwest wind off the cold Lake Erie and Lake Ontario waters will likely reduce the chance of afternoon storms on the lake plains.

Most of the showers and scattered thunderstorms will end early this evening with the exit of the weak cold front and loss of diurnal instability. This will leave mainly dry conditions through the first half of the night. Late tonight, a convectively augmented shortwave will move out of lower Michigan and across southern Ontario, approaching Western NY before daybreak with increasing chances of showers and thunderstorms from west to east during the pre-dawn hours. This cluster of thunderstorms, and the potential for additional rounds of showers and thunderstorms, will continue through Wednesday across the region.

Additional showers and sub-severe thunderstorms are likely to continue crossing into WNY and over to the North Country through the remainder of Wednesday night. A deeper, positively tilted mid-level shortwave moving into the Great Lakes from the Midwest will then cause the stalled boundary to briefly lift north of the region with a drying trend south of Lake Ontario as temps remain warm. The surface low attendant to the shortwave will then push a cold front through the forecast area sometime between Thursday and Thursday night with yet another round of showers and embedded thunderstorms.
Some mid to long range guidance suggests a secondary sfc wave developing along the boundary which could slow its progression.
Uncertainty in this solution leads to PoPs >30% being maintained through Friday, though temps should still cool several degrees compared to the midweek timeframe.

KEY MESSAGE 2...Marginal risk for isolated severe thunderstorms and locally heavy rainfall Tuesday and Wednesday.

Numerous rounds of showers and thunderstorms will cross the eastern Great Lakes today through Wednesday, with a few of these rounds potentially bringing a risk of isolated strong wind gusts and locally heavy rainfall.

The first round of convection in the warm advection regime this morning is not likely to become severe, with an initially stable boundary layer keeping instability rooted above the surface and keeping most of the stronger winds aloft. Thunderstorms will produce brief heavy downpours today through tonight with PWAT values reaching or exceeding 1.25", but strong flow and fast storm motions will limit the flood risk unless training convection occurs.

A weak cold front will cross the eastern Great Lakes from late morning through the afternoon today. Surface temperatures climbing into the 70s and surface dewpoints rising into the mid to upper 50s will support weak to moderate surface based instability by early afternoon. Strong flow in the 2K to 10K foot layer with largely unidirectional shear profiles will support the risk of isolated strong wind gusts in any stronger storms. Thunderstorms are most probable from late morning through the afternoon from the Southern Tier into the Finger Lakes and Central NY along the southern edge of enhanced flow over and northeast of the lakes. Stable lake shadows will expand northeast of Lake Erie and Lake Ontario in the afternoon, reducing chances for convection over the lake plains.

Any convection that develops this afternoon will end by early evening as the weak cold front exits and the boundary layer stabilizes. A convectively augmented shortwave will move across lower Michigan and southern Ontario overnight, approaching Western NY towards daybreak Wednesday. Forcing and persistent convergence along and east-west frontal zone may allow a cluster of showers and thunderstorms to persist overnight, with these storms moving into Western NY during the pre-dawn hours of Wednesday. A few of these storms may also bring a risk of locally strong wind gusts, particularly if bowing segments are able to persist through the overnight hours.

Wednesday, a decaying MCS in the vicinity of the Finger Lakes or North Country around daybreak will likely shuffle east and out of the forecast area by mid-morning. In its wake, the eastern Great Lakes will remain within the warm sector of a nearby stalled frontal boundary, with a short break in the shower activity expected. This should allow the environment to recover to some extent, especially if a few breaks in the cloud cover emerge. Signals from the short to mid-range guidance on convective evolution remain messy with the 18z REFS advertising a 30-65% chance for SBCAPE values >1000J/kg south of I-90 and west of the Finger Lakes, highest across southwestern NY. Steepening lapse rates and strong 0-6km bulk shear values around 45kts overtop the stalled boundary may cause a few strong to severe thunderstorms to develop as the next convective wave tracks into WNY from southern Michigan in the afternoon and evening. At this juncture the primary threat appears to be damaging wind gusts and small to marginally severe hail, though given potentially strong (>20kts) 0-1km shear profiles, cannot completely rule out an isolated tornado. The severe risk appears generally lower north of I-90 and in the North Country.

AVIATION /09Z TUESDAY THROUGH SATURDAY/
Areas of fog and low stratus will continue early this morning east of Lake Ontario with IFR/LIFR conditions.

Surface low pressure will move from the central Great Lakes this morning to the Saint Lawrence Valley by this evening. An area of showers and a few thunderstorms will cross the eastern Great Lakes from southwest to northeast this morning, with the greatest coverage likely to be across the northern portion of the area. A few more scattered showers and thunderstorms will develop this afternoon and early evening with daytime heating, mainly from the Southern Tier to the Finger Lakes, Central NY, and Tug Hill region. Any of the showers and storms today will produce brief VSBY/CIG restrictions.
Southwest winds off the cold lake waters will reduce the chance of afternoon and evening convection northeast of Lake Erie.

A variety of CIGS will continue today through tonight. MVFR/IFR CIGS will occur at times over and downwind of the lakes with high dewpoints over the cold water supporting a marine layer. Lower CIGS will also be found in areas of organized showers and across higher terrain at times.

A strong low level jet will remain in place today. This will initially support some low level wind shear early this morning, then gusty winds from mid morning through the afternoon. Expect gusts in the 20-30 knot range in most areas, and up to 35 knots northeast of Lake Erie including KBUF, KIAG, and KROC.

Outlook...

Wednesday through Thursday night...VFR/MVFR with some local IFR at times. Numerous rounds of showers and scattered thunderstorms.

Friday...VFR/MVFR with showers likely.

Saturday...Mainly VFR with a chance of showers later in the afternoon.

MARINE
Southwest winds will increase again today as a weak cold front crosses the eastern Great Lakes. The cold lake waters will tend to stabilize the boundary layer over the lakes, with stronger winds focusing on land. The most likely areas to see a period of Small Craft Advisory worthy winds today will be the Niagara River and the western end of Lake Ontario.

Rounds of showers and scattered thunderstorms will cross the lower Great Lakes today through Thursday. A few storms may produce locally higher winds and waves along with lightning strikes.

BUF WATCHES/WARNINGS/ADVISORIES
NY...None.
MARINE...Small Craft Advisory from 10 AM this morning to 7 PM EDT this evening for LEZ020.
Small Craft Advisory from 10 AM this morning to 7 PM EDT this evening for LOZ030-042.