textproduct: Burlington

WHAT HAS CHANGED

As of 152 AM EDT Thursday...

Frost Advisories and Freeze Warnings were issued for Thursday night/Friday morning.

KEY MESSAGES

As of 152 AM EDT Thursday...

1. Strong high pressure will support a widespread frost and freeze tonight. Localized hard freeze conditions are possible.

2. Chances for rain increases on Sunday as a warm front pushes into the area.

3. Somewhat unsettled for Memorial Day and into the work week, with seasonable temperatures expected.

DISCUSSION

As of 152 AM EDT Thursday...

KEY MESSAGE 1: Focus for the late week period will be on temperatures, especially potential for sub-freezing lows tonight. In a pattern like this where we expect mainly clear skies, calm winds, and an anomalous dry air mass (characterized by precipitable water near the 5th percentile), Model Output Statistics tend to be fairly skillful compared to the National Blend of Models and we have heavily leaned the forecast towards this data. While there is some possibility of mid-level clouds currently over the Midwest leaking out into our region, most model guidance shows clear skies. As such, confidence is fairly high that we should achieve some of the lowest temperatures possible with this air mass. Therefore, we have issued freeze warnings for the Adirondacks and far northeastern Vermont where coverage of sub-freezing temperatures will be widespread. Many locations within the northern Adirondacks could also see temperatures drop below 28 degrees, resulting in a hard freeze. Coverage of freeze conditions elsewhere in north central/ northeastern Vermont is somewhat patchy that warnings were not issued, but potential for expansion exists. For example, the latest MET MOS guidance at the Montpelier Airport in Berlin is 27 degrees for a low temperature but 33 from the MAV MOS. Similarly, while most of the Champlain Valley does not have a Frost Advisory at this time due to limited coverage, frost is expected anywhere temperatures drop into the mid 30s. As such, advisories could be issued if forecaster confidence in temperatures falling into this range overnight increases closer to Lake Champlain.

Low temperatures Friday night also trended lower along with a decrease in sky cover, given preference for much of the deterministic guidance showing skies remaining mainly clear again as a sprawling high pressure area remains overhead. The low level temperatures will have increased substantially (850 millibar temperatures near 0 Celsius on Thursday night are progged to be near 5 Celsius Friday night), which will limit coverage of frost quite a bit with lows mainly in the upper 30s to mid 40s. Frost looks primarily in the northwestern Adirondacks and eastern Essex County, Vermont. However, the large scale pattern favors northeastern Vermont seeing localized frost conditions, where low temperature forecasts are only slightly above the needed threshold.

KEY MESSAGE 2: Model guidance supports higher chances for rain areawide on Sunday, with even the driest ensemble scenario showing at least likely rainfall at some point during the day. It appears a relatively organized wave of weak low pressure will accompany a warm front such that forcing for precipitation overcomes the strong upper level ridging out ahead of the system. Expect stratiform, soaking rain spreads northeastward during the morning hours with some lingering rain in the afternoon before the frontogenesis exits. The intensity of the rain is rather questionable, although hydrologically speaking rainfall still looks light. However, amounts still are uncertain in particular given precipitation distributions skewed by some unlikely, very wet scenarios. Realistic driest scenarios lead to totals as little as a trace to a few hundreths of an inch of rain, most likely in northeastern Vermont. As of now, the consensus idea shows about a quarter inch of rain is possible in the Champlain Valley and central Vermont, and a third to half inch of rain in southern portions of Vermont into much of northern New York.

KEY MESSAGE 3: High pressure attempts to build in from the west while the upper trough swings across the region on Memorial Day. There's considerable spread in both deterministic and ensemble solutions in how quickly rain exits to our east and make way for the drier airmass associated with the incoming high. It's roughly split between a mostly dry Memorial Day and a wetter one, especially during the morning hours. Current thinking is perhaps the NBM/WPC forecast is a bit overdone, but given the uncertainty, have stayed with their PoPs/wx for now. Drier weather does seem to take hold by Monday night, but then shower chances increase again later Tuesday into Tuesday night as an upper shortwave trough swings around low pressure centered near the Gaspe Peninsula/Canadian Maritimes. It's after this system moves by that we could get into stronger ridging, with temperatures rising back above normal toward late week.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Through 12Z Friday...VFR conditions will prevail through the entire TAF period. Other than KEFK with BKN030 through 14z Thu, expect decreasing high clouds through the morning hours, becoming FEW- SKC by 18z and remaining so through the remainder of the forecast period. N/NW winds of 5-10 kt today will occasionally gust to 18 kt at KMPV and perhaps KEFK, trending a bit more toward the NW after 18z. Winds then light and variable after 00z Fri.

Outlook...

Friday: VFR. NO SIG WX. Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. Saturday Night: VFR. Chance SHRA. Sunday: VFR. Chance SHRA. Sunday Night: Mainly MVFR, with local VFR possible. Chance SHRA. Memorial Day: Mainly MVFR, with local IFR possible. Chance SHRA.

BTV WATCHES/WARNINGS/ADVISORIES

VT...Frost Advisory from 11 PM this evening to 8 AM EDT Friday for VTZ003-006>011-016>021. Freeze Warning from 11 PM this evening to 8 AM EDT Friday for VTZ004. NY...Frost Advisory from 11 PM this evening to 8 AM EDT Friday for NYZ026-027-087. Freeze Warning from 11 PM this evening to 8 AM EDT Friday for NYZ029>031-034.