Area Forecast Discussion

WHAT HAS CHANGED

As of 311 AM EDT Tuesday...

No significant changes.

KEY MESSAGES

As of 311 AM EDT Tuesday...

1. Primarily dry and seasonable through midweek. A period of rain is likely in southern portions of the region on Thursday, followed by another cold front that brings cooler and breezy conditions for Friday.

2. Chances for showers return Saturday night into Sunday, cool temperatures expected from Friday night through Tuesday night.

DISCUSSION

As of 311 AM EDT Tuesday...

KEY MESSAGE 1: A ridge of high pressure is centered near the International Border early this morning, providing us with ideal conditions for frost in the Adirondack region and far northeastern Vermont. The center of high pressure is expected to become positioned over the Gulf of Maine by this afternoon, leading to southerly channeled flow. Given dry and relatively cool air in place, Lake Champlain should once again have rather breezy conditions beginning this afternoon with a long duration of south winds through tomorrow morning.

Aside from the local terrain effects and modest low level jet tonight, no significant weather is expected as a weakening cold front approaches from the west tonight. Other than increasing clouds and milder conditions, there will be spotty light showers possible, with a broad consensus on the timing being in the early Wednesday morning hours and slightly greater chance of measurable rain in southern portions of our northern New York zones. Because the front largely washes out over/just south of our region, a large area of cloudy skies will probably be present during the day, which will possibly limit heating on what otherwise would be the warmest day of the week given fairly warm temperatures aloft. 925 millibar temperatures especially over our southern areas will likely be above normal (near the 75th percentile) during the afternoon, supporting highs near 80 in the Upper Valley especially with mainly sunny skies or breaks in the clouds. With dewpoints increasing back into the low 60s, it will be another short-lived bout of summer weather.

The next more substantial rainfall chance remains on track for Thursday associated with weak overrunning, as high pressure remains to our north and a wave of low pressure passes to our south. The thermal gradient and dynamical support for rain looks modest at best, so the footprint and intensity of rain should likewise be limited. Trends in the data show better chances of showers generally in the afternoon/evening and across southern/central Vermont and southern portions of the Adirondacks. Rain cooled air will complicate the temperature forecast especially with an earlier onset of precipitation, but for many locations Thursday looks like the last day for a while to see temperatures reach the 70s.

A trough passing through Quebec will force a cold front through our region Thursday night with little fanfare yet again, but bring in another round of refreshing air on northwest flow. Nothing particularly noteworthy with this air mass appears in the data at this time with only modest advection; even in the global ensemble cluster with the lowest temperatures they only drop a bit below seasonal normals. As such, high temperatures ranging from the mid 60s to low 70s amidst full sunshine look reasonable at this time. The most cool and dry air appears to be timed for Friday night as high pressure builds in from the northwest.

KEY MESSAGE 2: Focus for the longer term portion of the forecast continues to be the low pressure system bringing rain to our region Saturday night into Sunday. Surface low will track from the Great Lakes region northeastward just north of our area. There are still some differences between models with this system, but general thought is for rain to spread into our region Saturday night, continuing into Sunday with most areas having a wetting rain. ECMWF does keep this system mostly south of our area, but GFS solution shows most areas having rain. WPC has placed our region in Marginal risk for the excessive rain outlook.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Through 06Z Wednesday...Aviation forecast challenge tonight will be extent of fog as it develops. Mainly expecting valley fog, roughly 06z-13z. The most likely sites to see IFR/LIFR in fog will be MPV/EFK/SLK, but it can't be ruled out at any terminal. Have gone with 1/2-1SM in FG at MPV/SLK where confidence is highest, with 3-6SM in BR at EFK/MSS. SKC skies tonight give way to increasing mid/high level clouds during the daylight hours Tuesday. Otherwise, light terrain driven winds overnight will turn towards S at 5-10 kt after 14z Tue.

Outlook...

Wednesday: VFR. NO SIG WX. Wednesday Night: Mainly VFR, with local MVFR possible. NO SIG WX. Thursday: Mainly VFR, with areas MVFR possible. Chance SHRA. Thursday Night: Mainly VFR, with areas MVFR possible. Chance SHRA. Friday: VFR. NO SIG WX. Friday Night: VFR. Slight chance SHRA. Saturday: VFR. Chance SHRA.

MARINE

After a period of light winds this morning, channeled south winds are expected to rapidly increase towards noon. They should ramp up on the broad waters into the 20 to 25 knot range by late afternoon, and near 20 knots over the northern waters. As a result, waves will markedly increase into the 1 to 3 feet range this afternoon. During the evening, they will likely reach the 3 to 4 feet range in the vicinity of Colchester Reef and 2 to 3 foot range in the Inland Sea as winds will likely peak in intensity. Elevated south winds will likely persist into Wednesday morning before sharply diminishing by Wednesday afternoon.

BTV WATCHES / WARNINGS / ADVISORIES

VT...Frost Advisory until 8 AM EDT this morning for VTZ004. NY...Frost Advisory until 8 AM EDT this morning for NYZ030-031-034.