Area Forecast Discussion
Issued by NWS Burlington, VT

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466 FXUS61 KBTV 181125 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 625 AM EST Sun Feb 18 2018 .SYNOPSIS... Light snow across portions of the region this morning will quickly end as low pressure off the southern New England coast pulls offshore and high pressure begins to build in. Drier conditions develop for this afternoon and tonight before a significant warming trend is expected Monday through Wednesday of next week, along with periods of rain. Record high temperatures are possible Tuesday and Wednesday, with highs well into the 50s and possibly lower 60s. && .NEAR TERM /THROUGH MONDAY/... As of 625 AM EST Sunday...Quick update to adjust for snow coming to an end across the region. Otherwise, previous forecast is in good shape. Previous Discussion...Low pressure just southeast of the benchmark combined with a weak shortwave trough moving east out of the Great Lakes early this morning will continue to provide the North Country with light snow through sunrise before building high pressure over the Ohio Valley brings an end to precipitation. Despite high pressure building in and significant drying aloft, an abundance of low level moisture combined with blocked west- northwest flow will keep skies cloudy to mostly cloudy through much of the day, especially in the northern mountains. Could see some breaks of sun by mid-afternoon in the Champlain and St. Lawrence Valley, and potentially right around sunset for the remainder of the region though. Highs will remain above seasonal normals ranging through the 30s. For tonight, high pressure builds over the Northeast with skies clearing briefly after sunset but increasing moisture in the 400-500mb layer aloft will bring some mid-high clouds over the region after midnight. This cloud deck is already visible on CONUS IR/WV imagery over Minnesota and Wisconsin where an overcast layer around 25,000 feet is being reported. With mild afternoon temps and increasing cloud cover into the night, low temps are expected to be mild again, only dropping into the upper teens to mid 20s. High clouds exit the region to our east Monday morning with sunny skies developing by mid-morning and temperatures warming well above normal into the 40s area-wide. This is in response to the aforementioned high shifting offshore and a warm southerly return flow developing in advance of a warm front lifting northward from the Ohio and Tennessee Valleys through the day. Most of the day will remain dry, but chances for showers increase during the late afternoon into evening hours, especially across northern New York where rain looks to move in around the evening rush hour. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... As of 300 AM EST Sunday...Confidence remains high on an extended period of anomalous warmth during the Monday night through Wednesday time frame. This morning`s models are consistent in showing an usually strong subtropical ridge building across the eastern third of the nation into Tuesday night before a gradual erosion of its northern edge allows the polar front, in modified form to sink south through the area by later Wednesday. Deep southwesterly flow will transport near record warmth and high dewpoint air across our area during this time frame leading to rapid snowmelt and significant river rises. Blended QPF output also maintains consistency with prior forecasts in showing the greater threat of 0.50 to 1.5 inch two- day totals will lie across the northern third of the forecast area in closer proximity to the surface front lying across southern Canada. Further south QPF amounts are much less and generally under a half an inch. With the increased confidence in large-scale snowmelt and resultant river rises, ice break-up and/or potential ice jam flooding remains the greatest threat with this event and a Flood Watch has been issued for our entire area from Monday night into Wednesday (see hydro section below). As discussed above, temperatures will climb near or exceed record maxes or min-maxes during the period with Tuesday highs in the 51-58 range, and Wednesday`s values even milder from 55 to 65. If any partial sun can be realized on Wednesday 70F is not out of the question ahead of the front across southern counties. See climate section below for more details. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... As of 300 AM EST Sunday...By Wednesday night the aforementioned cold front will sink south of the area with any lingering evening showers transitioning to snow showers before ending overnight. Lows by Thursday morning remaining above normal, but much more reasonable from 25 to 35 degrees. Dry weather then returns to the area for Thursday into Friday as a modified airmass of eastern Pacific origin advects atop the northeast. This will keep temperatures well above normal, though not as extreme as the Tuesday/Wednesday warmth. Daily highs should range through the 30s on Thursday, then mid-30s to lower 40s by Friday as southerly return flow becomes re-established. Looking further out, another round of mild and potentially wet weather returns for next weekend as the sub-tropical ridge builds north once again. Low pressure riding northeast out of the Central Plains will push into the the Upper Great Lakes Friday night and toward the central Ontario/Quebec border by Saturday. Deepening southerly flow should provide the impetus for decent moisture transport into our area with chances of showers/light rainfall blossoming over time. High temperatures to respond accordingly, topping out mainly in the 40s to locally near 50 in milder valley locales. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... Through 06Z Monday...Snow is quickly diminishing across the region with just a few sites holding onto IFR visibility and MVFR ceilings at this hour, but a gradual climb to VFR is still expected at all sites by 18Z as high pressure builds into the region. Variable winds less than 10 knots currently turn WNW shortly with some gusts near 20 knots through sunset before winds decouple to nearly calm Sunday night. Outlook... Washingtons Birthday: Mainly VFR, with local MVFR possible. Chance RA. Monday Night: Mainly MVFR, with local IFR possible. Likely RA. Tuesday: Mainly MVFR, with areas IFR possible. Definite RA, Chance SHRA. Tuesday Night: Mainly MVFR, with local IFR possible. Likely RA, Chance SHRA. Wednesday: Mainly MVFR, with areas VFR possible. Likely RA, Chance SHRA. Wednesday Night: Mainly VFR, with areas MVFR possible. Chance SHRA, Chance SHSN. Thursday: Mainly VFR, with local MVFR possible. NO SIG WX. && .HYDROLOGY... As of 300 AM EST Sunday...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. Still some variability shown in this morning`s modeled 48-hr QPF, though the general consensus is for totals to average from 0.5 to 1.5 inches across far northern VT into the northern Adirondacks and 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. With numerous ice jams in place from the substantial thaw this past January, localized high water/flood concerns near these features remains a real concern as ice break-up occurs. Taking this all into account we`ve gone ahead and issued a Flood Watch for the entire forecast area from late Monday night through early Wednesday evening. && .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 Monday night through Wednesday evening for VTZ001>012-016>019. NY...Flood Watch from late Monday night through Wednesday evening for NYZ026>031-034-035-087. && $$ SYNOPSIS...Lahiff NEAR TERM...Lahiff SHORT TERM...JMG LONG TERM...JMG AVIATION...Lahiff HYDROLOGY...JMG CLIMATE...TEAM BTV is the U.S. government's official web portal to all federal, state and local government web resources and services.