Area Forecast Discussion
Issued by NWS Burlington, VT

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987 FXUS61 KBTV 200035 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 735 PM EST Mon Feb 19 2018 .SYNOPSIS... Periods of showers and steadier rainfall will develop later tonight into Wednesday as a strong warm front lifts through the area. Unseasonable, near record breaking warmth is expected for Tuesday and especially on Wednesday fostering river ice breakup and potential flooding concerns. Temperatures trend cooler by Thursday onward into next weekend, though remain well above late February norms. Additional precipitation will move into the area by the weekend. && .NEAR TERM /UNTIL 7 AM TUESDAY MORNING/...
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As of 644 PM EST Monday...No significant changes from previous forecast. First off, not expecting any hydro/flooding issues overnight...with any significant river rises not beginning until the daylight hrs Tuesday. Looking for a mild night with temperatures steady in the upr 30s to lower 40s...and generally slowly rising toward daybreak on continued southerly winds. Synoptic warm front has lifted north of the intl border, but it appears secondary warm front and E-W boundary with richer moisture across nern OH, srn tier of NY into srn VT, will continue to provide the primary focus for periods of light to moderate rainfall overnight. Generally expecting precipitation to focus northward across the St. Lawrence Valley, nrn Adirondacks, and n-central VT toward daybreak on Tuesday as 925mb theta-e gradient shifts nwd. Rainfall amts will generally range from 0.1-0.25" overnight, except locally 0.50" or so across St. Lawrence and Franklin NY counties. With dewpoints pushing above freezing, will see patchy fog develop, mainly in sheltered locations with continued low- level mixing with south winds 10-15mph in more open valleys.
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&& .SHORT TERM /7 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... As of 500 PM EST Monday...Lots of interesting aspects to the forecast from Tuesday through Wednesday night. I`ll try to touch on all of them in this discussion. Very warm system impacting the region with a surface front stationary to our Northwest just across the International border. This will be the focus for several waves of energy and precipitation over the 48 hour forecast period. Record breaking maximum temperatures are forecast for Tuesday and Wednesday. Dewpoints will also be surging into the 50s. Temperatures and dewpoints result in thawing degree hours off the charts, we expect much of the snow to melt across the region. On top of this, a quarter of an inch to an inch and three quarters of rain is forecasted, highest in the Saint Lawrence valley and lowest in Southeastern Vermont. Losing much of our snowpack will release 3 to 7 inches of snow water equivalent into the river basins. The rainfall and snowmelt together have led to high confidence that we will have flooding across much of the area. The northern Adirondacks and Northern portion of the Vermont, as well as the Saint Lawrence valley have the highest chances for flooding. Also, any locations that still have ice jams in place from the January event will be especially susceptible to flooding. Temperatures on Tuesday, firmly in the warm sector, will surge into the 50s, dewpoints will be approaching the 50s as well. Unprecedented wet system with pwats surging to about 1.4 which is also near record breaking for Feb. Thawing degree hours have already started to accumulate, and will continue until sometime Wed night. Thawing degree hours reach 850-1200 which is huge, passing the 300 mark sometime Tuesday afternoon across our Western zones, and Tuesday night across the entire area. This is when I`d expect problems to start cropping up on the rivers as far as ice movement goes. Once again temperatures will not fall too far Tuesday night, lows in the upper 40s to lower 50s. Max temperatures on Wednesday will be even warmer, widespread 60s. Cold front will finally start moving and cross our area Wednesday night, by the time the cold front moves across the region, precipitation should have ended therefore not expecting much snow on the backside of this system. There may be a brief break in the precipitation Wednesday morning as the front briefly drifts even further north from the border. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 405 PM EST Monday...Cooler but still warmer than normal conditions will prevail through early next week. The region will also remain in an active pattern as fast zonal flow dominates aloft. High pressure will keep the weather dry Thursday and Thursday night. Then the first in a series of low pressure systems will bring a mix of rain and snow to the region Friday into Friday night, followed by another later Saturday into Saturday night. The third rain/snow system arrives Sunday into Monday. Although there are still differences in the tracks of each of these lows, overall it looks like temperatures will be cold enough for snow at night, while daytime highs will allow most areas to change over to rain. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
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Through 00Z Wednesday...Warm frontal zone weather with mix of VFR/MVFR ceilings across the North Country early this evening... generally lowering into the MVFR category areawide after 03Z, with HIR TRRN OBSCD. Will see periods of light/moderate rain and BR thru the period, and localized IFR ceilings are expected to develop at SLK after 03Z this evening. Winds will remain from the south, with gusts locally to 25kt at BTV through 06Z with valley channeling. Local valley channeling will also keep MSS locally NE winds at 5-10kts. Winds slacken somewhat toward daybreak, and will see some Low-Level Wind Shear (LLWS) issues at SLK/MSS/RUT after 08Z, as winds near 2000ft strengthen to 40-50kts. Outlook... Tuesday Night: VFR/MVFR conditions possible. Chance SHRA. Wednesday: Mainly MVFR, with areas VFR possible. Chance SHRA. Wednesday Night: VFR. Chance SHRA, Chance SHSN. Thursday: VFR. Slight chance SHRA, Slight chance SHSN. Thursday Night: VFR. NO SIG WX. Friday: VFR. Chance SHRA, Chance SHSN. Friday Night: MVFR/IFR conditions possible. Likely SN. Saturday: Mainly MVFR, with local IFR possible. Scattered SHRA, Scattered SHSN.
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&& .HYDROLOGY... As of 400 PM EST Monday...A 48-hour period of anomalously warm temperatures will affect the region through Wednesday afternoon. Periods of rainfall, modest winds and dewpoint temperatures climbing into the 40s to lower 50s will foster rapid snowmelt and ice break-up across the entire area. Also boosting confidence are extremely high thawing degree hour totals - averaging 900 to 1200 over the Tuesday/Wednesday time frame. The model consensus continues to show totals to average from 0.5 to 1.75 inches across far northern VT into the northern Adirondacks and SLV with the highest totals in the SLV. Lesser amounts generally under a half an inch are expected across central and southern VT. Taking this all into account, modest to substantial river rises look highly probable starting Tuesday afternoon and continuing into Wednesday, supported by NAEFS/SREF MMEFS hydrograph data. While widespread open water flooding is not expected, several rivers may approach minor flood. More importantly numerous ice jams remain in place from the substantial thaw this past January, so the potential for localized high water and/or flooding near these features remain a real threat as ice break-up occurs. && .CLIMATE... Here are the current record high temperatures for February 20th and 21st: Record High Temperatures: ............Feb 20th....Feb 21st.... BTV.............58 (1981)...59 (1981)... MPV.............56 (1994)...57 (1953)... MSS.............63 (1994)...62 (1953)... St. Johnsbury...60 (1981)...62 (1981)... Record High-Minimum Temperatures: ............Feb 20th....Feb 21st.... BTV.............50 (1981)...49 (1981)... MPV.............47 (1981)...47 (1981)... MSS.............47 (1994)...41 (1981)... St. Johnsbury...40 (1981)...46 (1981)... && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Flood Watch from 1 AM EST Tuesday through Wednesday evening for VTZ001>012-016>019. NY...Flood Watch from 1 AM EST Tuesday through Wednesday evening for NYZ026>031-034-035-087. && $$ SYNOPSIS...Neiles NEAR TERM...Banacos/Neiles SHORT TERM...Neiles LONG TERM...Hastings AVIATION...Banacos HYDROLOGY...TEAM BTV CLIMATE...TEAM BTV

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