Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
628 am EST Wednesday Nov 25 2015
variable cloud cover will erode today as high pressure builds
across and east of the area. With a return of southerly winds,
expect temperatures to moderate by later today, and especially on
Thanksgiving when seasonably mild and dry weather is expected. The
next chance of precipitation will occur by later Friday into
Friday night as a cold front crosses the region. Behind this front
a return to dry and seasonably cool weather is expected by this
Near term /through tonight/...
as of 628 am EST Wednesday...forecast remains in good shape as of
600 am. Did make some minor adjustments to hourly temperature and
dewpoint trends through late morning, otherwise little adjustment
needed as we progress toward sunrise. Have a great day.
Prior discussion from 325 am EST Wednesday...
strengthening surface high pressure will build overhead today and
east into the Maritimes by tonight with mainly dry weather and
light winds expected. Pesky moisture trapped beneath the extant
synoptic inversion at middle levels will allow variable cloud cover
and perhaps a stray flurry here and there to linger through the
morning hours, though a general trend toward partly sunny skies is
expected by this afternoon as planetary boundary layer mixing processes increase with
arrival of southerly return flow. Leaned on the cool side of
guidance given clouds will limit insolational heating through a
portion of the morning hours, though readings should be milder
than yesterday generally topping out from the upper 30s to middle
By tonight southerly return flow continues to increase across the
area in response to a tightening pressure gradient between departing
1050 mb surface high and a developing longwave trough across the upper
Midwest. Temperatures will be a tad tricky depending on degree of
mixing and/or decoupling across the area. As is typical during
nocturnal return flow events, mildest readings to occur in the
Champlain/St Lawrence valleys (mid to upper 30s) where readings will
remain nearly steady or slowly rise after midnight whereas eastern
Vermont and Adirondack communities will see values fall into the evening
hours (upper 20s to lower 30s) before trending steady late.
Short term /Thursday through Friday/...
as of 351 am EST Wednesday...as the intensifying surface high
pressure moves over Nova Scotia the pressure gradient between it
and the weak low pressure system over Ontario will be nearly 30mb
and will lead to rapidly increasing southerly winds on
Thanksgiving day. Those southerly winds will bring strong warm air
advection and thus we will be looking at daytime maximum temperatures in the
upper 40s to near 50 for Thanksgiving day under mostly clear
skies. With the strong southerly flow continuing to increase
expect temperatures Thursday night to remain high and thus i've got middle
40s as the forecast for overnight lows. Temperatures on Friday
will be quite similar to Thursday as the low pressure system
shunts north of the region into northern Quebec. As the parent
system passes well to the north expect increasing cloudiness with
showers looking likely to enter the Saint Lawrence valley some
time in the middle afternoon to early evening Friday. Temperatures in
the vertical will stay warm enough to melt everything and thus
rain will be expected through Friday.
Long term /Friday night through Tuesday/...
as of 351 am EST Wednesday...thankfully, the guidance this
morning is more in line with the 12z data from yesterday in that
there is increasing continuity of timing. Both the GFS and European model (ecmwf)
continue to drag the front through the north country bringing rain
showers through Friday night with the GFS still remaining slightly
more progressive. Thermal profiles show the rapidly cooling air
under cold air advection moving into northern New York shortly
before midnight on Friday producing some wintry mix over the Saint
Lawrence valley and upslope regions on the Adirondacks for about a
3-4 hour period then transitioning to mainly periods of snow
showers through early Saturday morning. After midnight the rest of
the north country should be looking at rain transitioning to snow
as well but we will be fighting a losing battle with available
moisture. The GFS remains the more favourable solution due to how
progressive the upper level flow will be and thus if we use the
GFS as the basis for timing the moisture source will be existing
between 06z and 12z Saturday morning. I do anticipate as we get
into the northwest flow there will be some upslope snow potential
but that will stay highly localized along the western slopes of
the northern greens.
Behind that front, temperatures will fall rapidly under strong cold air
advection and thus I anticipate temperatures on Saturday to only warm
into the middle 30s and fall to the middle 20s overnight. As the surface
high builds in on Sunday into Monday expect more seasonable
temperatures with maximum temperatures in the upper 30s to around 40 with
overnight lows in the middle 20s. The next good chance for precipitation
will be middle week as an upper level low with a surface closed low
develops over the Great Lakes. As has been consistent this fall,
the surface low is expected to push north into southern Quebec
producing rain showers by middle week.
Aviation /11z Wednesday through Sunday/...
through 12z Thursday...sct/bkn mainly VFR ceilings expected through
18z, trending scattered/sky clear thereafter and into the overnight hours.
Brief MVFR possible at northern New York terminals through mid-morning. Winds
variable 5 knots or less through 18z, trending south 5 to 10 knots
later this afternoon into tonight and locally higher at krut/kbtv.
Increasing flow aloft will likely lead to low level wind shear concerns at
kpbg/kslk and possibly kmss after 00z. No precipitation expected.
Outlook 06z Thursday through Sunday...
12z Thursday - 18z Friday...VFR under high pressure.
18z Friday - 12z Sat...trending to MVFR in rain showers as a cold
front drops into the region. Some MVFR/IFR -shsn possible 00-12z
Sat as precipitation ends.
12z Sat - 00z Monday...trending VFR with high pressure.