Marine Weather and Tide Forecast for Plattsburgh, NY

KEY MESSAGES
As of 234 PM EDT Saturday...

1. This afternoon's rain moves out this evening, but additional showers are expected tonight into Sunday morning.

2. Brief ridging combined with an upper trough will keep Monday and Tuesday chilly but mainly dry.

3. Gradual warming through mid to late next week to near normal temperatures with a few chance for light rain showers.

DISCUSSION
As of 234 PM EDT Saturday...

KEY MESSAGE 1: Rain has spread across mainly central and southern VT this afternoon, with a few showers lifting into the eastern Adirondacks and portions of the Champlain Valley. This precipitation will continue to shift eastward through the day, with any additional rainfall less than a quarter of an inch. Our next round of showers arrives this evening into the overnight with a prefrontal trough and cold frontal passage. This activity can be seen on upstream radars, moving across lower Michigan and into Ontario. These showers will arrive into the St Lawrence Valley before midnight, and there could still be enough elevated instability for a rumble of thunder or two.
Showers should wane in coverage as they move eastward into Vermont late tonight/early Sunday. However, the cold front will quickly follow Sunday morning, bringing a renewed chance for additional showers, especially across central and eastern VT. Much drier air follows the cold front, and precipitation should quickly end by late morning/early afternoon, so Mother's Day won't be a complete washout. However, expect good mixing behind the front as well due to cold air advection and clearing skies, allowing winds to become gusty during the afternoon. Dewpoints will fall as well, with minimum relative humidity values dropping into the 25 to 35 percent range. Winds will be gusting to around 20 mph, though the highest gusts will be in northern NY, which will also see the highest relative humidity values due to cooler daytime temperatures. Highs will range from the mid/upper 50s in west of the Champlain Valley, while 60s will be much more common from the Champlain Valley eastward.

KEY MESSAGE 2: Surface high pressure will edge into the area Monday and Tuesday, ushering in a cool and dry airmass. However, an upper shortwave trough will swing overhead on Monday. Much like what we saw on Friday, the cold pool aloft combined with daytime heating will lead to steep low level lapse rates. While this should generally lead to daytime clouds, there could be just enough moisture and instability to allow afternoon showers to develop, particularly over northern NY. This upper trough will give way to ridging by Tuesday though, so no precipitation is expected. Both days will be chilly, with highs around 10 degrees below normal; most spots should top out in the 50s. Sunday night and Monday night will feature frosty conditions as lows dip into the low to mid 30s. Frost Advisories may need to be issued, especially since the growing season for the St Lawrence Valley and all of Vermont except the Northeast Kingdom officially starts on May 11.

KEY MESSAGE 3: Early week surface ridging accompanied by upper level troughing will start the extended on a cooler note, before more persistent ridging under southwest flow gradually warms the region to near normal temperatures by late next week. Cool and dry conditions will start off the extended Tuesday night with chances for Frost across eastern Vermont as surface high pressure aided by 540mb thickness lines will drop temperatures into the low to mid 30s in eastern Vermont. The climatological growing season for eastern Vermont (outside of the NEK), begins Monday May 11th, so Frost headlines may be needed if cloud cover becomes conducive for radiational cooling.

Into the middle and late portions of next week, strong ridging across the western CONUS will trend our flow pattern towards troughiness with an upper level low still in place across the Hudson Bay. There is good agreement in a long wave ejecting out of the Great Lakes which should help dislodge the upper low, however, the evolution of the surface system remains somewhat uncertain. Models are not handling the deepening of the long wave trough well, with the duration of any shower activity in question. A blocking high in the north central Atlantic will delay the propagation of a surface low Wednesday into Thursday, however, models such as the EPS keep cyclonic flow and shower activity into Friday as the low stalls and becomes embedded in a baroclinic zone off the New England coast. The GEFS/GEPS are a bit more progressive with the low also a bit north which would reduce the chances of the system occluding over New England. Behind the mid to late week system, ridging should make its return for the weekend with warming temperatures to at or perhaps above normal with GEFS 925mb temperatures to 15C, supporting temperatures in the 70s. The one caveat would be if the mid to late week system becomes blocked, temperatures may be cooler than currently forecast due to shower activity, northeast cyclonic flow and clouds for the weekend. For now, we can hope for a warm, and drying weekend.

AVIATION /18Z SATURDAY THROUGH THURSDAY/
Through 18Z Sunday...A coastal low to the south of the region will bring continued light rain to RUT/MPV with lowering ceilings for the next 4-5 hours, before precipitation taper off. Breezy south southwest winds will also continue through the daylight hours.
Ceilings will trend towards MVFR at BTV/EFK in association with the passing coastal low, however, there is still some uncertainty how soon ceilings trend lower, thus have used TEMPO groups for later this afternoon into this evening. To the west, conditions should remain VFR at MSS/PBG/SLK for at least the next 2-3 hours, with ceilings lowering towards MVFR between 20-22Z at SLK, and 00-03Z at MSS. A cold front will bring some shower activity to MSS between 02-04Z, with perhaps some 5SM showers and a brief rumble of thunder, but the front will be weakening as it approaches MSS, thus leading to lower confidence in thunder and lower vsbys and just a mention here in the discussion. The front will bring just isolated to scattered showers as it moves across the region overnight. By daybreak, some reinvigorated showers will be possible in the vicinity of BTV/MPV/EFK through the morning hours. Behind the front by late morning tomorrow, winds will shift to the west southwest.

Outlook...

Sunday Night: VFR. NO SIG WX.
Monday: VFR. Slight chance SHRA.
Monday Night: VFR. Patchy frost.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: VFR. Slight chance SHRA.
Wednesday Night: Mainly MVFR, with areas VFR possible. Chance SHRA.
Thursday: MVFR. Chance SHRA.

MARINE
A Lake Wind Advisory is in effect this afternoon and overnight.
South winds of 15 to 25 kt will continue through the remainder of this afternoon. They will briefly subside this evening, then pick back up overnight. Waves of 2 to 4 feet can be expected.

BTV WATCHES/WARNINGS/ADVISORIES
VT...None.
NY...None.