Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 190245 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1045 PM EDT Tue Sep 18 2018 .SYNOPSIS... A few showers are possible this evening as a strong cold front pushes south through the area. Behind this front, variable clouds and cooler, more seasonable weather is expected tonight into Thursday. The next chance of showers comes Thursday evening ahead of a warm front which will pass through the region by Friday morning. It will be windy and warm Friday before another strong cold front brings another chance of showers or a thunderstorm by Friday night. A much cooler Canadian airmass and its associated high pressure moves in for Saturday. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... As of 1043 PM EDT Tuesday...Late evening update included adding patchy fog across s-central VT, promoted by the shower activity occurring mainly 23-01Z. May see the fog become more intermittent as cold front settles southward into Rutland/Windsor counties next 1-2 hrs, with developing northerly wind shift and increased mixing potential. Previous Discussion...We did it again. Another 80 degree day at BTV which puts us at 82 for the year and second place all time behind 86 back in 2016. In fact, we`ve hit 86 at BTV and close to our record high of 87 set last year. Shallow cold front continues to progress swd across the forecast area this evening, draped across the Northern Adirondacks into the southern Champlain Valley and newd across central/nern VT. Much of the low-level cold advection appears to be originating from the Gulf of St. Lawrence and St. Lawrence Valley, with strong nely flow noted across srn Quebec. In fact, temperatures are only in the mid 40s in the Quebec City area and nwrn ME...so definitely a marked air mass change overnight. Winds shift to northerly and increase to 10 to 20 mph locally a bit stronger indicated around lake Champlain with good mixing as cooler air moves over the unseasonably warm lake waters in the lower 70s. Temps will fall back through the 70s to around 60 by sunset in the the far northern higher terrain. A few lingering showers across southern Rutland county will depart to the south late this evening. Based on satellite trends to the north, will see an increase in low cloudiness overnight as frontal inversion sharpens. May even see some patchy drizzle across far n-central into nern VT late given maritime origin of the air mass. Some patchy drizzle may also be possible in the higher terrain. Overnight lows tonight should range from the upper 40s to mid 50s north and mid to upper 50s south. Morning stratus in most areas early Wednesday will slowly lift and break up by afternoon as mixing processes deepen and the aforementioned inversion weakens as high pressure moves eastward across southern Quebec and heights rise aloft. With 925 temps ranging from 10 to 14C looking for highs in the mid 60s to lower 70s. High pressure ridging down into the area from Canada and the upper level shortwave ridge crests of the region Wednesday night it should be mainly clear and cool leading to dense valley fog in the usual places but it could be more widespread. Expect lows in the upper 40s to low 50s in Vermont, and upper 30s to upper 40s in northern New York. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... As of 304 PM EDT Tuesday...500 mb heights will be increasing throughout the day on Thursday as a result of a a deepening upper level trough over the upper Midwest. This should help to make Thursday a bit warmer than previous days with high temperatures increasing into the mid 60s to lower 70s (which is a few degrees above climatological normal). The aforementioned upper level trough will continue to deepen throughout the day and as a result, a surface low pressure system will quickly develop over the Great Lakes region on Thursday. A warm front associated with this low will skirt the North Country late Thursday afternoon and through the overnight period into Friday. Isentropic lift ahead of the warm front should help bring some light rain to northern New York and the northern half of Vermont. One thing to keep an eye on will be an increasing southwesterly low level jet Thursday night. This could easily create some upslope and downslope precipitation patterns with westerly facing slopes see higher rainfall amounts while the Champlain Valley could see little rainfall. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 304 PM EDT Tuesday...Following the warm front that works through the region Thursday night, Friday looks to be a bit warmer with high temperatures in the upper 60s to around 80 degrees with the warmest temperatures being in the Champlain and St Lawrence Valleys. The temperature forecast is subject to change as the forecast is very dependent on the timing of a cold front that is expected to move through the region Friday night. The surface low associated with this system will track well north of the North Country, which is typically not favorable for widespread rainfall or strong thunderstorms. In addition, there will be the passage of a pre-frontal trough out ahead of the cold front which piecemeal upper level support even further. However, given that there is around a 50-60 kt 850 mb jet, there will be strong shear present. The amount of instability is yet to be determined but is worth monitoring since this front looks to be a pretty strong one. This cold front will bring quite the pattern change to the region with a strong Canadian high pressure system lingering behind the front. Initially, a strong burst of southerly winds is expected Friday afternoon out ahead of the front as the pressure gradient tightens with high pressure to our south and a deepening low pressure system to our north. Widespread winds in the 10 to 20 mph range with gusts upwards to 40 mph in some locations will be possible. The strongest winds look to occur over Lake Champlain where sustained winds of 20 to 30 mph with gusts to 40 mph look likely at this moment. Following the cold front on Saturday, both high and low temperatures are expected to be below climatological normals. High on Saturday through Monday will generally be in the upper 50s to mid 60s with lows around 40 to the lower 50s. Saturday night looks to be the coldest night as Canadian high pressure will linger overhead with clear skies prevailing due to lack of moisture and increased subsidence. It looks quite likely that parts of the Northeast Kingdom and northern Adirondacks will see a good frost or possibly even a freeze Saturday night while other locations linger in the upper 30s to upper 40s. Any chances of rainfall after Friday look pretty slim as high pressure continues to reign supreme through the beginning of next week. There will be another deepening trough over the western half of the U.S. during the beginning of next week which will bear watching as it will be the next big system to impact us sometime during the middle of next week. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Through 00Z Thursday...Mainly VFR conditions early this evening, but as sfc cold front progresses southward, anticipate an increase in post-frontal cloudiness overnight. Most TAF sites will see a trend toward BKN-OVC015-030 with HIR TRRN OBSCD after 04Z or so. Winds have shifted N-NW at all TAF locations, and will continue N-NW 8-12kts thru the overnight hrs as colder air mass filters into the region. Vsby generally unrestricted, but could see some patchy drizzle/6SM BR late (08-12Z). Currently thinking stratus layer will gradually break and lift 15-18Z with light northerly winds for the daylight hours on Wednesday. Thus, should see a gradual trend back to VFR conditions by late morning or the early afternoon hours on Wednesday. Outlook... Wednesday Night: VFR. Patchy BR. Thursday: Mainly VFR, with local MVFR possible. Slight chance SHRA, Patchy BR. Thursday Night: Mainly VFR, with areas MVFR possible. Likely SHRA. Friday: Mainly MVFR, with local IFR possible. Likely SHRA. Friday Night: Mainly MVFR, with areas VFR possible. Likely SHRA. Saturday: Mainly VFR, with local MVFR possible. NO SIG WX. Saturday Night: VFR. NO SIG WX. Sunday: VFR. NO SIG WX. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Sisson NEAR TERM...Banacos/Sisson SHORT TERM...Clay LONG TERM...Clay AVIATION...Banacos/Sisson

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