Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 190858 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 358 AM EST Mon Feb 19 2018 .SYNOPSIS... Periods of showers and steadier rainfall will develop later today 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 next weekend. && .NEAR TERM /THROUGH TUESDAY/... As of 250 AM EST Monday...Quiet weather is expected through the first half of the day as building western Atlantic ridge evolves off to our east. Increasing south/southwest flow is expected over time with gusts topping out in the 10 to 20 mph range by afternoon. Higher gusts from 25 to 35 mph are expected in the Champlain Valley as low level channeling effects take shape in the 975-925 mb level. As the afternoon progresses a warm front and associated deeper moisture advect quickly north and east into the forecast area with an increasing threat of showers and/or periods of light rain, especially south and west. High temperatures a blend of available guidance supporting seasonably mild values in the upper 30s to lower 40s east and lower to mid 40s from the Champlain Valley west. By tonight into Tuesday the start of another, near-record breaking period of warmth surges into the area under strengthening southwesterly flow aloft. An unusually strong Bermuda-like subtropical high with 500 mb heights to in excess of 590dm will be the driving force during this period. The warm front will pivot northward to a position near or just north of the international border during this time with periods of showers and/or steadier rainfall expected across central and northern counties in proximity to better lift along the frontal zone. Temperatures take on a classic non-diurnal trend tonight as values trend steady or slowly rise under continued light to modest south/southwest flow. By sunrise Tuesday readings should range from the upper 30s to lower 40s across eastern VT, and in the 40s further west. By Tuesday afternoon readings should climb solidly into the 50s for most spots with a few spot 60f readings possible south where some partial sunshine is expected. Dewpoints will also climb considerably during this time (into the 40s), fostering a 24-36 hour period of rapid snowmelt as condensation processes begin in earnest on the snowpack. See climate and hydrology sections below for specific details. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
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As of 355 AM EST Monday... ...Record-breaking maximum temperatures in the 60s to around 70 are forecast on Wednesday with a near complete snowmelt in many areas with ice jam breakup and river/stream flooding possible... The warm front will push well to our north Tuesday night so any rain across the north will taper off with chances of showers lingering mainly in the northern sections of our area. The region will be well entrenched in the warm sector through midday Wednesday before a cold front pushes southeast across northern New York by early afternoon and into Vermont mid to late afternoon and finally evening in southeast VT. The front will be accompanied by a period of showers, mainly over the north which could end as snow showers with little if any accumulation. QPF during this Tue-night through Wed period looks to be a quarter to half inch in the north, highest near KMSS, and just a tenth or inch or less in southern VT. With the warm front well north of the border on Wed, there may be a period of just high cloud cover through midday except perhaps near the international border where more cloud cover is expected before clouds increase during the afternoon from northwest to southeast with the approaching cold front. Temperatures will be steady or rising all night Tuesday night with the 00Z temperatures as the lowest readings in the mid 40s to mid 50s. Guidance seems a bit cool for Wed with models limiting boundary layer mixing with surface cooling, so have raised blended temps about 3 degrees closer to the EKD MOS. GFS boundary layer forecast looks best with better mixing right off the surface. If we to realize full mixing from 850/925mb (9C/15C) would yield high temps even warmer into the lower 70s further north to BTV but for now just hedged them up a bit. See Climate section below for existing record temperatures. Dewpoints will also rise through the 40s, exacerbating snowmelt from the warm temperatures. Runoff from snowmelt and rainfall will be peaking Wed afternoon and evening. This when area rivers and streams will be most at risk to ice jam and/or river flooding. See Hydrology section below for more details.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
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As of 355 AM EST Monday...Look like the cold frontal passage will be through most of our region early Wed evening with some light rain showers possible ending as some snow showers over the higher terrain with little in the way of accumulation. Maximum runoff from snowmelt and rainfall will have peaked Wed evening but should still continue through at least part of the night, so area waterways will still be rising even once temperatures drop back below freezing. Record high minimum temperatures for Feb 21 are possible but not likely as temperatures are expected to be cooling off by midnight. For Thursday through Sunday...looking cooler and fairly active as the northeastern CONUS remains under fast zonal Westerly flow as subtropical ridge over the southeast is suppressed. Thursday looks quiet right now with the frontal zone to our south but with the flow still WSW southern VT still could be at risk of rain or snow showers depending upon how far the front ends up. Otherwise a couple more short waves and associate low pressure systems progged to move through Fri/Fri night and again late Sunday into Sunday night. While temperatures will be cooler than what we`ll see in the middle of the week, they`ll still be above normal, generally in the mid 30s to mid 40s during the day, overnight lows in the teens and 20s. Since temperatures will be either side of freezing, precipitation will fall as rain and/or snow...so have stayed close to a model blend on temperatures which resulted in a lot of rain/snow mix through the end of the week, so stay tuned as the forecast gets refined.
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&& .AVIATION /08Z MONDAY THROUGH FRIDAY/... Through 06Z Tuesday...VFR through 21Z, lowering to a mix of mainly MVFR/VFR thereafter as periods of rain showers move into the region from the south and west. SCT/BKN high cigs above 100 AGL expected through 18Z, trending BKN/OVC in the 035-060 AGL range from 18-00Z, then lowering further thereafter. Some patchy IFR possible at KMSS late. Winds south/southwesterly and increasing to between 8-15 kts this afternoon into tonight. Exceptions at KBTV and KPBG where low level southerly jet will push speeds into the 14-20 kt range with gusts to 30 kt in the 14-00Z time frame. As the stronger southerly flow moves in aloft some brief LLWS to 40 kt possible at KSLK in the 09-13Z time frame. Outlook... Tuesday: Mainly MVFR, with areas IFR possible. Definite RA. Tuesday Night: Mainly MVFR, with local IFR possible. Chance RA. Wednesday: Mainly MVFR, with local IFR possible. Chance RA. Wednesday Night: Mainly VFR, with local MVFR possible. Chance SHRA, Chance SHSN. Thursday: VFR. Slight chance SHSN. Thursday Night: VFR. NO SIG WX. Friday: VFR. Slight chance SHRA, Slight chance SHSN. && .HYDROLOGY... As of 250 AM EST Monday...A 48-hour period of anomalously warm temperatures will affect the region from Monday 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 Monday night 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 late tonight through Wednesday evening for VTZ001>012-016>019. NY...Flood Watch from late tonight through Wednesday evening for NYZ026>031-034-035-087. && $$ SYNOPSIS...JMG NEAR TERM...JMG SHORT TERM...Sisson LONG TERM...Sisson AVIATION...JMG HYDROLOGY...TEAM BTV CLIMATE...TEAM BTV

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