Scientific Forecaster Discussion

000 fxus61 kbtv 191146 afdbtv Area forecast discussion National Weather Service Burlington Vermont 646 am EST Tue Feb 19 2019 Synopsis... a large area of high pressure across the Great Lakes region will build eastward into the northeast, bringing dry, mostly clear, and seasonable cold conditions through Wednesday. Quick moving low pressure passing to the north and west of the St. Lawrence River will bring developing snowfall Wednesday night, ending as a wintry mix early Thursday morning. Snow and sleet amounts will range up to a couple of inches from the Champlain Valley westward across northern New York, with 2 to 5 inches of snow and sleet excepted across north-central into northeastern Vermont. Some melting of this snow and sleet is expected as Thursday afternoon valley temperatures rise into the 40s. Temperatures will remain above normal with drier weather to end the week. && Near term /through Wednesday/... as of 636 am EST Tuesday...a chilly start this morning, as decoupled planetary boundary layer during the pre-dawn hours has allowed 2-M temperatures to fall quickly, especially across southern St. Lawrence County. This includes 11z temperatures of -17f at Edwards and -18f at Bullhead Pond. Temperatures aren't quite as cold across Vermont owing to continued light winds and areas of stratus across N-central and nern Vermont. These factors have kept temperatures generally in the single digits above zero at sunrise, except zero to -10f across Rutland County. Have made minor adjustments to sky cover and temperatures based on recent trends, but overall forecast is on track for dry and seasonably cold conditions today. Previous discussion... synoptically quiescent conditions prevail across the north country as large sfc anticyclone builds ewd from the Great Lakes into the nern conus, and eventually shifts east of New England on Wednesday. Some residual stratus clouds persist across N-central into nern Vermont early this morning per GOES-16 fog product, and could see a few lingering flurries in Vermont's Northeast Kingdom. However, dry north-northwest low-level flow will result in clearing conditions areawide toward daybreak with sunny skies expected today. Northwest winds increasing to 10-15mph will keep temperatures on the chilly side, with highs only in the 15-20f range, except 20-25f across the srn valleys. High pressure builds directly overheard tonight with diminishing winds. Should be ideal radiative cooling conditions with lows in the single digits above zero, and locally zero to minus 10f across the northern Adirondacks and Vermont's Northeast Kingdom. As high pressure shifts to our east on Wednesday, a southerly return flow develops, allowing afternoon highs to reach the mid- upr 20s. Should see a trend toward filtered sunshine Wednesday aftn as mid-upr level cloudiness increases from SW-NE late. Pops none through the near-term period. && Short term /Wednesday night through Thursday/... as of 104 am EST Tuesday...little overall change in expected minor snow to mixed precipitation event expected Wednesday night into early Thursday morning. Primary low is still expected to track to our north and west, and secondary low development occurs late and too far east to have any significant impact on our forecast area. Thus, strong 850-700mb warm air advection will drive isentropic ascent with developing snowfall from SW-NE, likely during the 00-03z period from btv south and west, and between 03-06z across north-central into nern Vermont. Periods of warm air advection snows will continue during the overnight hours (pops 80-90%), but will see SW 850-750mb winds of 50-60kt advect above freezing/warm layer into the region late. This warm layer results in a transition to sleet across nrn New York and south- central Vermont 06-09z, and into the Champlain Valley 09-12z. Far northeastern Vermont remains mainly snow based on current NAM/GFS vertical profiles. May see a few pockets of light freezing rain as well, but not expecting much in the way of ice accumulation (trace to a few hundreths). Also appears that synoptic mid- level dry slot works into the region quickly 10-13z, with a rapid end to any steady precipitation from west-east around or just after daybreak Thursday. The remainder of Thursday will feature isold rain/Summit snow showers, with valley temperatures warming well into the 40s. With overall quantitative precipitation forecast mainly 0.20-0.35", not looking at a major winter event Wednesday night early Thursday morning. General snow/sleet totals of 1-2" expected from the Champlain Valley wwd across nrn NY, and 2-5" of snow/sleet for central into nern Vermont with colder temperature profiles expected. May see some slow travel for the morning commute on Thursday, especially east of The Greens. Current trends suggest winter weather advisories may be needed for Wednesday night into the morning commute time frame, mainly for central into nern Vermont. Should see melting and improving Road conditions with partial sunshine later Thursday morning into the aftn and temperatures rising into the 40s. Gusty south to southwest winds are also expected Thursday. In the Champlain Valley and nrn NY, will see S-SW winds 15-25 mph with gusts to 35 mph possible with steepening lapse rates and good low-level mixing. && Long term /Thursday night through Monday/... as of 301 am EST Tuesday...surface cold front and shortwave energy aloft shift through the region Thursday night with precipitation generally waning through the night with some upslope snow showers possible across the higher terrain. High pressure follows for Friday and Saturday with dry and pleasant weather expected with temps ranging through the 30s for highs and teens/20s for lows. Next system moves in for Saturday night through Monday and appears to be a rinse and repeat from the mid-week storm with primary low pressure once again tracking from the Lee of The Rockies northeast through the Great Lakes Sunday and into southern Quebec Sunday night. Latest GFS/fv3/ECMWF are all in fairly good agreement showing little coastal development which leads to warm air intruding into the region on strong south/southwesterly flow creating some ptype issues. Soundings indicate precip starts as snow Saturday night and briefly changes to a mix of sleet/snow and perhaps freezing rain Sunday morning before transitioning rapidly to all rain by the noon hour as surface temps rise into the 40s area-wide. Could see a break in precip in the warm sector depending on the strength of the mid- level dry slot Post warm front passage, and if that does occur it could allow for a period of gusty winds to mix to the surface before the cold front passes Sunday night. Behind the cold front precipitation transitions back to snow and gradually becomes more terrain focused heading into Monday. && Aviation /12z Tuesday through Saturday/... through 12z Wednesday...dry/VFR conditions expected at the taf sites thru the period. Lingering broken-ovc030-040 across far N-central into nern Vermont should dissipate toward 13-15z. Likewise, localized sct013 at kslk should dissipate next 1-2 hrs. Winds will continue north-northwest 7-10kts today, becoming light and variable tonight. Outlook... Wednesday: VFR. No sig weather. Wednesday night: mainly VFR, with areas MVFR and IFR possible. Likely sn, definite pl, likely freezing rain. Thursday: mainly MVFR, with areas VFR possible. Chance ra, likely freezing rain. Thursday night: mainly VFR, with local MVFR possible. Slight chance shsn. Friday: mainly VFR, with areas MVFR possible. No sig weather. Friday night: mainly VFR, with areas MVFR possible. No sig weather. Saturday: VFR. Slight chance shsn. && Btv watches/warnings/advisories... Vermont...none. New York...none. && $$

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