Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 200800 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 300 AM EST Fri Jan 20 2017 .SYNOPSIS... Relatively quiet weather will persist across the region through the upcoming weekend with mainly cloudy skies and very mild temperatures. A more significant weather maker is looking more likely to affect the region Monday night into Tuesday with potential significant accumulations of snow or mixed precipitation. Behind this system continued mild temperatures with on and off chances of rain and snow shower activity are expected by the middle to later portions of next week. && .NEAR TERM /THROUGH SATURDAY/... As of 300 AM EST Friday...Quiet conditions continue today as pronounced and blocking upper ridge remains parked across the northeast. With lingering moisture trapped beneath a semi- permanent subsident inversion the timing and coverage of any partial clearing today will remain the biggest forecast challenge. Background flow does trend southerly over time however, and with the inversion weakening slightly the prior idea offering at least some breaks in the overcast still appears reasonable by afternoon in many spots. Time will tell though as we`re still near the annual bottom in regard to weakness in insolation. As has been the case over the past few days temperatures will remain remarkably steady, climbing only some 4 to 6 degrees from our overnight lows - generally from 35 to 41. By tonight into Saturday we`re still advertising a weakening impulse and associated spotty light precipitation to arrive from the southwest over time. Mid-level warm thermal advective processes are rather unimpressive and with the described weakening trend as system runs into our blocking ridge I expect rather scant, very light QPF at best across the area. Some minor concern that where surface temperatures do drop near or slightly below freezing some spotty very light -fzra and/or -fzdz will be possible. Indeed FRAM model output does show a light glaze of a few hundredths of an inch here and there across the SLV into portions of the Dacks and Vermont later tonight into the morning hours on Saturday. However, given the expected spotty, light QPF coverage will only mention in our Hazardous Weather Outlook at this point. As boundary layer temperatures warm by late morning on Saturday any threat of spotty light icing will end. With little airmass change very uniform temperatures will continue with overnight lows in the upper 20s to lower 30s (mid 20s northeast VT) and highs on Saturday in the upper 30s to lower 40s. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY/... As of 330 PM EST Thursday...Relatively quiet weather continues into the Friday night/Saturday time frame. An upper level ridge will be building into the North Country which should block some of the energy that will be heading into the Great Lakes. The strong inversion that will be trapping low level moisture will become eroded on on Friday evening and so low level clouds begin to move out of the area but a persistent mid deck will keep the area mostly cloudy through the day. There will be some light warm air advection that pushes into the region and so it wont take much to generate some light stratiform rain/snow especially in the higher terrain. Temperatures will remain above normal in the continue very mild with lows Friday night from the lower 30s and Saturday highs in the upper 30s to lower 40s. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 330 PM EST Thursday...The end of the weekend should remain quiet before the weak upper level ridge breaks down. Then we move into a more uncertain time period from Monday through Wednesday. The one certainty is that we should be well above normal for temperatures to start the week. The most significant portion of the forecast is the potential for a phased low pressure system that will impact us early in the week. A southern stream upper level trough will dive south of the mid-Atlantic region over the Carolinas while a surface low develops over the DelMarVa peninsula. By Monday evening the GFS and EC show the system phasing and increasing in intensity. The trend in the guidance has been to bring the low close to the coastline Monday Night into Tuesday sliding the surface low inside of the benchmark. If that scenario plays out then we would trend colder than previous runs and we will see a wintry mix. I`m hesitant to go straight snow, however, because 1000-500mb thicknesses remain closer to 542-545 dam. So I chose to use a thickness based approach for precip type for the event leading to a mix of snow and sleet. The big take away is that the trend was more from rain and freezing rain to more of a wintry mix. This will be something continue to keep an eye on moving forward. I agree the previous forecaster in that there is some concern based on the potential for gusty southeasterly downsloping winds, especially along the western slopes of the Green Mountains later Monday afternoon into Monday night as mean 925-850 mb flow may exceed 40 knots. This will eventually predicate some adjustment of model qpf fields as valley/terrain shadowing/enhancement effects will be magnified. Higher-res guidance will certainly provide more detail as we draw closer in time. Variable conditions are expected behind that system as with synoptic flow stays southwesterly. This results in no significant change in our airmass through the mid week. Expect several shortwaves to pass through the area but at this point there isn`t a significant amount of confidence in timing. The idea of a daily threat of scattered rain/snow shower activity seems the way to go so I continued that from the previous forecast. Temps will continue in the mid 30s to lower 40s during the day time with overnight lows averaging in the upper 20s to lower 30s. && .AVIATION /08Z Friday THROUGH Tuesday/... Through 06Z Saturday...MVFR conditions expected at all TAF sites with periods of IFR at MPV and SLK. SLK also experiencing light snow with IFR conditions expected to end between 09z-11z. Low level moisture trapped under inversion will persist into Friday with MVFR cigs. BUFKIT model soundings indicate inversion weakens in the afternoon with less moisture available, allowing for breaks in cloud cover and period of VFR conditions. Heading into Friday evening, expect MVFR cigs to return for Friday night. Light to calm winds this morning will pick up slightly on Friday, but generally around 5 kts or less. Outlook 06Z Saturday through Tuesday...Areal coverage and cigs heights associated with plenty of low level moisture continues to be the aviation focus for Friday night into Saturday. A few sprinkles or flurries possible Saturday with general mvfr mountains to vfr valleys. Next system spreads a wintry mix across our taf sites late Monday into Tuesday with widespread mvfr to ifr conditions likely...along with breezy southeast downslope winds possible at Rutland. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...JMG NEAR TERM...JMG SHORT TERM...Deal LONG TERM...Deal AVIATION...KGM is the U.S. government's official web portal to all federal, state and local government web resources and services.