Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
637 PM EST Thursday Feb 26 2015
Arctic high pressure will bring tranquil and cold weather
conditions through early Sunday morning. A trough of low pressure
approaching from the Great Lakes region will bring the potential
for a widespread light snow across the north country late Sunday
into early morning morning. Temperatures will remain well below
normal through early next week...but will trend milder Tuesday
night into Wednesday as a low pressure system tracks to our
west...bringing a chance for mixed wintry precipitation.
Near term /through Friday/...
as of 629 PM EST Thursday...with the early evening update, made
only minor tweaks based on last few hours of
satellite/radar/observation trends. Though radar does show
widespread light returns off to the south and west, it appears
that 97% of this are just clouds/virga. Have to go pretty far
south for any observations of light snow. Thus, though the chance
for a flurry across parts of the 'dacks and southern Vermont is
not zero, it is not all that high either. Cut back on the coverage
Otherwise, main forecast issue will be the low temperatures.
Currently considerable clouds across the region, though for
northern sections it's just high & thin cirrus which does not seem
to be holding back radiational cooling. Locations along the
Canadian border are starting to rapidly cool -- faster than
previously forecast as well. Have nudged low temperatures down a
few degrees in the far northern areas of New York and Vermont to
account for this quick drop off. May need to go even a bit lower
given that dewpoints are running -10 to -15f which is a good proxy
for the potential low temperature under good radiational cooling
Otherwise, i'll leave the previous discussion text as is for those
that want to read more...
Generally quiet weather expected tonight
and Friday. Low pressure passing well east of the middle- Atlantic
coast maintained middle-upper level cloudiness across much of the
north country today. There is a trailing upper trough and
associated 500-300mb pv maximum across Northern Ohio at 19z...which will
translate east-northeastward across central New York this evening. The 12z btv-4 and
btv-12km WRF runs suggest continued middle-upper clouds through
midnight...with a slight chance of a flurry across the northern
Adirondacks...mainly through 03z. No accumulation expected...but
did maintain 20 probability of precipitation for any flurry activity this evening mainly
Adirondacks into Rutland County Vermont. Once this upper trough
passes...we should trend partly cloudy to mostly clear areawide
after midnight. Surface high pressure will likewise be building eastward
across the region from the Great Lakes...so it appears we/ll have
light winds and good radiational cooling prospects after midnight.
The MOS consensus looked reasonable - with lows generally zero to
10 below...and locally 15 below in the northern Adirondacks and far
Northeast Kingdom. Just made some adjustments to the diurnal curve
to show more rapid temperature drop once clouds lessen late. Winds
generally north 5-10 miles per hour will generally lessen to less than 5 miles per hour
Surface ridge remains in place throughout the day Friday. Should see
mostly sunny skies...though temperatures will remain about 20 degrees
below late February normals with highs generally in the middle teens.
Short term /Friday night through Saturday night/...
as of 305 PM EST Thursday...strong surface anticyclone (1040-1044
mb) remains anchored across the northeastern Continental U.S. Through the
period bringing dry/mostly clear and seasonably cold conditions.
Air mass should gradually moderate over time. Didn/T see any
reason to stray significantly from the MOS consensus...with lows
zero to -15f Friday night...into the lower 20s for highs
Saturday...and then +5 to -5f for Saturday night. Winds will shift
light into the S-SW Saturday around 10 miles per hour...and generally light
and variable during the nighttime periods. Probability of precipitation none.
Long term /Sunday through Thursday/...
as of 309 PM EST Thursday...surface ridge slides eastward off the
Atlantic Seaboard with the north country in warming southerly flow
and increasing clouds from approaching upper level trough out of
the western/upper Great Lakes. At the surface, low is ill-defined
but come late Sunday we will be in the warm sector of this system
with snow showers spreading SW to NE. Sunday night a cold front
will traverse across the region...shifting winds to the northwest and
allowing residual moisture to produce some upslope snow showers on
High pressure builds in briefly Monday night through most of
Tuesday. What may possibly be a major storm will affect the region
Tuesday night through at least Wednesday. Strengthening surface
low will move across the Great Lakes and track to our west and
north. Main concerns with this storm are as follows: with fetch
off the Gulf of Mexico, GFS showing precipitable waters half an inch to one
inch, which could lead to heavy precipitation mainly Tuesday night.
Strong S-SW jet of 40-55kts at 850mb Tuesday night into Wednesday
will likely lead to precipitation enhancement on southwest to westward
facing slopes and shadowing on eastern slopes and valleys, as well
as strong gusty winds at the surface, especially across the higher
terrain. Models show tight pressure gradient, further supporting
strong wind potential. Warming Tuesday night into Wednesday will
likely lead to mixed precip, but timing and just how warm is
uncertain at this time. European model (ecmwf) lagging behind GFS in timing of this
system and therefore timing and strength of warming which will
affect possibility of mixed ptypes. These models have also not
showed run to run consistency yet. This far out, have mentioned
snow mix with/to rain in southern valleys, mixing back to snow
Wednesday night as the cold front moves acr0ss the region.
Thursday will see the upper trough move through the area...keeping
clouds and possibly some more snow showers behind the cold front.
Near to slightly below normal temperatures in the upper teens to
around 30 Sunday through Tuesday will see warming to above normal
temperatures...some areas reaching the m30s Wednesday. Both GFS
and European model (ecmwf) show significant warming aloft with positive single
digits at 850mb some point on Wednesday.
Min temperatures will be mild Sunday night, but behind the first
cold front Monday night temperatures will be back in the single
digits. Warming ahead of the more significant system Tuesday night
with min temperatures in the teens lasting through Wednesday night.
Aviation /00z Friday through Tuesday/...
through 00z Saturday...VFR with light winds through the period.
Scattered/broken middle to high level clouds to persist through 12z with
passage of upper trough, then trend sky clear at most terminals by 00z
Saturday. Winds light west to northwesterly and less than 10 kts.
Outlook 00z Saturday through Tuesday...
00z Saturday-18z Sunday...mainly VFR with high pressure.
18z Sunday-06z Tuesday...developing warm front and associated
weak area of low pressure will increase the clouds with snow
likely by 00z Monday. Expect MVFR with periods of IFR.
06z Tuesday Onward...VFR conditions under high pressure.
Increasing chance for MVFR/IFR late Tuesday as warm front
approaches from the southwest.