Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 201432 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 932 AM EST Tue Feb 20 2018 .SYNOPSIS... Unseasonably warm, near record setting temperatures are expected across the area through Wednesday along with periods of showers or light rain. A cold front will swing south through the area Wednesday evening with cooler temperatures in its wake for late week. An active weather pattern continues into the upcoming weekend with renewed chances for light rains and snows. && .NEAR TERM /THROUGH WEDNESDAY/...
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As of 923 AM EST Tuesday...Overall forecast in good shape this morning with current radar showing bands of light to moderate rain moving from the SLV/western Dacks into extreme northern VT along a warm front. This boundary will continue to slowly lift north of our cwa by this afternoon...along with the best moisture and 5h...so expect the areal coverage of precip to decrease. Temps are tricky this morning with low level cold air trapped east of the greens with readings only in the 30s with fog...while parts of the western dacks/cpv are in the upper 40s to lower 50s. Already 54f at the base of Whiteface Mountain...with 48 at Lake Placid...while PBG is 38f. Have adjusted to capture latest temp trends and added areas of fog for parts of central/eastern vt and northern NY. Sfc obs and radar estimates show between 0.25 and 0.75 has fallen across the SLV and parts of the northern Dacks. This rainfall combined with very warm temps...we expect to start seeing rises on the Ausable and Salmon Rivers shortly. Given cooler temps and less rainfall so far over VT...river rises will occur later this evening into the overnight hours. Prior Discussion...The overall forecast picture remains largely unchanged over the next 42 hours as a dominant +590 dm subtropical ridge centered between Bermuda and the northern Bahamas controls the deep-layer synoptic flow across the eastern third of the nation. Deep southwesterly flow aloft will advect an unseasonably mild airmass into the region beginning today and persisting into early Wednesday afternoon. Numerous showers with periods of light rain will continue across central and northern counties today, lifting slowly north to the intl. border and northward tonight into Wednesday morning as a strong warm front lifts through the area. Back trajectory analysis at 500m suggests source air this afternoon originated across the northern Gulf Coast States yesterday, with tomorrow`s air wrapping around the ridge from the subtropical Atlantic near Grand Bahama Island. With mean 925 mb temperatures surging above +10C a period of extreme warmth by February standards will evolve during the period. Highs today should mainly top out in the 50s, with a few spot 60F readings in the southern St Lawrence/Champlain Valleys and a few upper 40s in far northeastern VT and near KMSS. Wednesday will be a record- setting day as 925 mb temperatures surge into the +12 to +15C range, pushing highs into the 60s to locally near 70F. If KBTV can surpass 62F (I currently have a high of 69F) it will be the second warmest February temperature on record, surpassed only by the 72F set just last year! I wonder what the statistical odds of that happening in the Queen City`s 134 year period of record? As the temperatures warm a surge of higher dewpoint air, (upper 40s to lower 50s) now poised off to our southwest across western NY/PA will advect northeastward into our area fostering a period of rapid snowmelt and robust river rises. By later Wednesday most, if not all snow cover below 2000 feet should be essentially erased leading to heightened concerns over ice breakup on area rivers. Given the broad consensus in the guidance the Flood Watch remains in place with this package (see hydro discussion below). By Wednesday afternoon the surface boundary will swing southward through the area as a cold front. The baroclinic zone with this feature is quite sharp, so hourly temperature drops could be quite noticeable within the hour of its passage (> 10F). Scattered to numerous showers will drop south into the bulk of the forecast area during this time, through trend more scattered in nature as one progresses toward early evening winds veer to northwesterly.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 400 AM EST Tuesday...The cold front will exiting southeast VT at the start of the short term period with any lingering light showers tapering off by midnight. Despite strong cold advection and temperatures falling into the 20s by Thursday morning, rivers will be still running high and cresting Wednesday evening but a few of the slower responding rivers may still be rising overnight and not crest til Thu morning. On Thursday, the frontal boundary becomes nearly stationary over the mid-Atlantic region as it runs into the anomalously strong ridging over the southeast. A weak wave aloft and surface low will move along the front on Thursday and develop some light overrunning precipitation with the west southwest flow aloft. ECMWF, CMC, and SREF mean are furthest north and most bullish on QPF with a tenth to quarter inch in southern VT and as far north as MPV/BTV, while NAM/GFS keep it south of the region with little more than flurries or sprinkles. For now just keeping a chance of light snow or mixed wet snow/light rain in the forecast with the split in the model solutions. Temperature profiles mostly cold enough for snow though the lowest valley locations may have some light wet snow or light rain mixed in with high temperatures in the mid to upper 30s. Perhaps the models will come into better agreement today. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 400 AM EST Tuesday...Slightly cooler but still warmer than normal conditions will prevail through early next week. The region will also remain in an active pattern with a fast WSW flow aloft as southeast ridging continues to dominate aloft. The first in a series of low pressure systems will bring a mix of rain and snow to the region Friday afternoon into Friday night, followed by another late Sat night and Sunday. Although there are slight differences in the tracks of each of these lows, overall it looks like temperatures will be cold enough for some snow especially in the higher elevations and northeast VT, but temperatures will be marginal so some valley mix or change to rain look likely. Latest indications is the system on Sunday might bring some stronger and gusty southeast winds. High temperatures will generally be in the mid 30s to mid 40s with lows in the 20s through the period. Later next week things look quite interesting with the development of a blocking pattern with cutoff lows and highs, something we haven`t seen in a while. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... Through 12Z Wednesday...Conditions have continued to deteriorate overnight and early this morning and should continue to do so through 18Z to 21Z. The worst conditions will be observed over northern New York where colder temperatures at the surface have created a low-level inversion and trapped moisture right off the surface. KMSS will be the first to gradually improve after 21Z but KSLK will likley remain IFR through much of the forecast period. KBTV remains the stubborn site this morning as nice cross-barrier flow over the Adirondack mountains continue to hinder the development of ceiling below 2800 ft. As moisture continued to advect northward today, ceilings will gradually fall below 2kft for a brief while before steadily improving during the evening. KMPV and KRUT have seen fog with visibilities 1 mile or less but these conditions should improve throughout the day but should see increasing ceilings and vsbys by late morning. Outlook... Wednesday: Mainly VFR, with areas MVFR possible. Chance SHRA. Wednesday Night: VFR. NO SIG WX. Thursday: VFR. Slight chance SN. Thursday Night: VFR. NO SIG WX. Friday: VFR. Chance RA. Friday Night: Mainly MVFR, with local IFR possible. Chance SN, Chance SHSN. Saturday: Mainly MVFR, with areas IFR possible. Chance SHRA, Chance SHSN. && .HYDROLOGY... As of 245 AM EST Tuesday...A 42-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 period. The model consensus shows rainfall totals averaging from 0.5 to 1.50 inches across far northern VT into the northern Adirondacks and St Lawrence Valley with the highest totals in the latter location. 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 this 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 including the Ausable R. at Au Sable Forks, NY, Missisquoi R. at North Troy, VT and the Winooski R. at Essex Junction, VT. 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 through Wednesday evening for VTZ001>012-016>019. NY...Flood Watch through Wednesday evening for NYZ026>031-034-035- 087. && $$ SYNOPSIS...JMG NEAR TERM...JMG/Taber SHORT TERM...Sisson LONG TERM...Sisson AVIATION...Clay HYDROLOGY...TEAM BTV CLIMATE...TEAM BTV

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