706 FXUS61 KBTV 191741 AFDBTV AREA FORECAST DISCUSSION National Weather Service Burlington VT 1241 PM EST Sat Jan 19 2019 .SYNOPSIS... A major winter storm is on tap for the North Country tonight through Sunday as low pressure over the southern Plains this morning tracks through the the Tennessee Valley today and up the East Coast Sunday. Steady snow will develop across the region late this afternoon and evening, and become heavy at times tonight into Sunday morning. Snowfall rates of 1 to 2 inches per hour are possible, making for hazardous travel. As low pressure departs to our east across the Gulf of Maine and Canadian Maritimes, blowing snow will increase throughout the day Sunday as north winds increase. Frigid temperatures and very low wind chills are expected in the wake of the storm for the Sunday night through Monday night period. Temperatures will moderate back into the teens on Tuesday, and into the low to mid 30s for Wednesday of next week. && .NEAR TERM /THROUGH SUNDAY/... As of 943 AM EST Saturday...Strong sfc anticyclone anchored across swrn Quebec this morning. Arctic air continues to filter in from sern Ontario and srn Quebec on northerly winds 5-10mph. At 1430Z, temperatures are hovering near zero in the BTV area, and closer to -5F near the intl border with dewpoints in the teens below zero. Widespread wind chills 10 to 20 below and mid- upper level cloud deck will make for very cold remainder of the daylight hrs areawide. Mosaic reflectivity already showing tendency toward mesoscale banding along the I-90 corridor into srn VT with strong 850-700mb frontal zone near our southern CWA border. Added in snow flurries next several hours across Rutland/Windsor counties and parts of the nrn Adirondacks to account for this mesoscale forcing axis well in advance of the sfc low over the lower Ohio Valley. Everything else remains consistent with previous fcst. Previous Discussion...Really only noise level changes made to the previous forecast with very good model consistency persisting and no changes made to current winter weather headlines. Early morning water vapor shows our impending winter storm across the southern plains with several lines of convection and lightning noted across TX/AR/LA/MS. Overall track of the system today through Sunday remains the same moving east-northeast into the Tennessee Valley this afternoon, to around D.C. by 12Z Sunday, and eventually into the Gulf of Maine by 00Z Monday. Ahead of system, quiet and cold conditions will be in place across the North Country this morning with temps in the single digits and teens as high pressure over James Bay filters southward into the region. Some concern remains across northern areas where drier/arctic air will be in place when snow arrives later this afternoon and evening, and this is shown well in the NAM low level RH fields which don't fully saturate until later tonight into Sunday morning. As such, we continue to highlight a sharp gradient in the snow totals, especially across the St. Lawrence Valley into the northwest Adirondacks. On the flip side, across central/southern Vermont, we continue to see the potential for strong frontogenetic forcing in the 850-700mb layer late tonight through Sunday morning, where within a mesoscale band we could see 1-2"/hr snowfall rates from around 06-15Z Sunday. All that said, only minor changes were made to the storm total snowfall amounts with a general 6-12" across northern New York, least in the St. Lawrence Valley, and 10-18" across Vermont with the lowest totals near the Canadian border. Additional threats during the storm will be cold temperatures and winds. Temps won't budge out of the single digits north to low teens south through the period with just some slight cooling across the St. Lawrence Valley tonight into the single digits below zero. Add in some increasing northerly winds Sunday in the 15 to 25 mph range and gusts to 35 mph in the Champlain Valley, and we'll be looking at areas of blowing snow and wind chill values of -5F to -20F. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 415 PM EST Friday...Dangerously cold wind chill expected Sunday Night into Monday morning with values between -20 and -40 below zero. Areas of blowing and drifting snow continue into Monday. The combination of departing 988mb low pres over eastern Maine and building 1038mb high pres will create brisk northwest winds and bitterly cold wind chills Sunday Night into Monday, as 925mb temps drop btwn -25c and -30c. Expect wind chill values btwn -20 and -40 below across the entire North Country, with the core of the coldest values btwn Midnight and 10 AM Monday. Wind chill highlights will be needed for this time period. Lows range from -5f to -20f overnight with highs on Monday +5f to -10f depending upon location. Synoptic setup shows deepening and closing off 5h circulation across western/central NY, while sfc low pres moves into the Canadian Maritimes. This creates north/northwest 925mb to 850mb upslope flow of 35 to 45 knots, as deeper 925mb to 700mb rh rotates back across our northern and central CWA Sunday Night into Monday. My experience tells me we low level caa, upslope flow, and lingering moisture with closing off system its going to take awhile to shut down the snow machine, especially eastern CPV and northern/central Green Mountains. The meso-scale setup is very interesting, as moderate to extreme instability will be present off Lake Champlain as very cold air moves over relatively warmer waters, while north/northwest flow will enhance low level convergence on eastern side. BTV4km shows strong, but shallow lift thru 15z Monday from cpv convergence on brisk northerly winds. Froude numbers show strongly blocked flow with values >0.50, supporting additional snowfall. The big question, given the extremely cold thermal profiles and snow growth layer near the sfc, what are the snow ratio's? My initial thoughts it will be needles with very small flake size, but reduce visibilities in the 1 to 2sm range across the western slopes/northern dacks and eastern cpv thru 18z Monday. Have noted 00z BTV 4km shows additional qpf of up to 0.10 at BTV from 00z Monday thru 18z with model progged snow ratio's of 25 to 30 to 1, which would support an additional 2 to 4 inches locally. For now, I have increased pops into the likely/cat range with additional snowfall of 1 to 3 inches. Meanwhile, away from the upslope snow showers and cpv convergence, lingering flurries and light snow shower activity will persist, but accumulations will be limited. Monday night 1039mb high pres builds toward northern NY and winds should gradually diminish toward 12z Tues. If winds decouple with fresh snow pack and clear skies, expect temps to quickly fall toward sunrise. Crntly have -10f to -25f, but some colder sites in the southern SLV/dacks could be near -30f, if winds decouple. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 240 PM EST Friday...Active period of weather continues with next system arriving on Weds, with the potential for an additional wave developing along sharp boundary on Thursday into Friday. This period is highlighted by plenty of uncertainty with regards to large scale synoptic pattern and associated low level thermal profiles. Models in decent agreement with a period of waa snow on Weds, with strong 850mb jet of 50 to 60 knots, producing some localized shadowing in the cpv. Expect a general 1 to 3 inches for this event with localized higher amounts in the high peaks and northern Greens. Initially thermal profiles are cold enough for all snow, but warm just enough toward the end for maybe a light mix, especially western dacks and southern CPV. Overall pattern for late week shows deepening mid/upper level trof across the central conus, while potent short wave energy rounds base and enhances sfc low pres across the se conus. This general idea looks reasonable, but uncertainty remains with the system tracking either to our west or along the coast. GFS/FV3 and CMC show a more eastern track and cooler, while UKMET is the western outlier and the ecmwf is the eastern outlier. For now have utilized superblend guidance and will mention high chance/low likely with thermal profiles supporting mostly snow. Will continue to fine tune the forecast over the next couple of days. Otherwise, temps warm into the mid 20s to mid 30s on Weds, before cooling back below normal by the end of the week. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... Through 18Z Sunday...VFR conditions this afternoon will give way to widespread MVFR-IFR conditions as slight snow moves into the region from the southwest after 22Z. Conditions will to worsen after 06Z as heavier bands of snow move in bringing widespread LIFR conditions throughout the overnight hours. By morning, snow begins to lighten but northerly winds increase to 10-20 knots and with that blowing snow conditions are expect at most terminals with after 15Z, with RUT seeing it much earlier as they will see an easterly wind after 06Z. Outlook... Sunday Night: Mainly VFR, with areas MVFR possible. Chance SHSN, Areas BS. Martin Luther King Jr Day: Mainly VFR, with local MVFR possible. Chance SHSN. Monday Night: VFR. NO SIG WX. Tuesday: VFR. NO SIG WX. Tuesday Night: VFR. Chance SHSN. Wednesday: Mainly MVFR and IFR, with areas VFR possible. Likely SHSN, Likely SHRA. Wednesday Night: Mainly MVFR, with local IFR possible. Chance SHSN. Thursday: MVFR/IFR conditions possible. Chance SHSN. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Winter Storm Warning from 4 PM this afternoon to 4 PM EST Sunday for VTZ001>012-016>019. NY...Winter Storm Warning from 4 PM this afternoon to 4 PM EST Sunday for NYZ028>031-034-035. Winter Weather Advisory from 4 PM this afternoon to 4 PM EST Sunday for NYZ026-027-087. && $$ SYNOPSIS...Lahiff NEAR TERM...Banacos/Lahiff SHORT TERM...Taber LONG TERM...Taber AVIATION...Verasamy