Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
945 PM EST Monday Nov 30 2015
another chilly night is expected across the region with mostly clear
skies and light winds through midnight...then clouds and southerly
winds will develop toward sunrise on Tuesday. The next system will
spread several rounds of occasional showers across the north country
late Tuesday into early Thursday. The showers may start as a brief
period of wintry mix on Tuesday afternoon and end on Wednesday
night into Thursday as a period of light accumulating
snowfall...especially in the mountains.
Near term /until 8 am Tuesday morning/...
as of 942 PM EST Monday...water vapor shows a complex pattern
across the eastern United States with confluent northwest flow aloft
over our County Warning Area...while closed 500 mb/7h circulation is located over the
Central Plains. This system will impact our forecast area late
Tuesday into Wednesday with several rounds of showers expected. Once
again the main forecast challenge tonight will be temperatures and
the areal coverage of clouds. Low level thermal profiles are
slightly warmer later tonight with southerly flow
developing...and some areas will continue to experience some
clouds. Coldest temperatures with lows near 10f will be over the
Northeast Kingdom with 15f in the slk/Lake Placid areas...and
upper teens to lower 20s elsewhere. Temperatures are dropping
slightly faster than expected but upper and middle level cloud cover
should be over a good portion of the region in the next couple
hours and help slow the temperature drop.
Short term /8 am Tuesday morning through Wednesday night/...
as of 315 PM EST Monday...deep closed cyclonic circulation over
the Central Plains will eject several embedded pieces of energy
our way...along with advection of some sub-tropical moisture.
First short wave energy and associated 925mb to 700mb warm air
advection lift arrives by 18z southwest area and quickly expands
northeast into the Northeast Kingdom by 22z Tuesday. The 850mb
flow will be from the southwest at 35 to 45 knots...while the
boundary layer winds will be from the southeast around backside of
high pressure...resulting in some downslope shadowing across the
Northeast Kingdom and Champlain Valley. Given some evaporational
cooling the initial surge of precipitation could feature a few sleet
pellets or some light freezing rain...especially in cold layer per
NAM soundings between 1200 and 2200 feet in the mountains. 925mb
to 850mb thermal profiles quickly surge above 0c by 00z and
approach +7c supporting all rain overnight into Wednesday.
Thinking most of the precipitation occurs overnight on Tuesday night into
Wednesday morning...before middle/upper level dry slot develops on
Wednesday. Have noted good rrq of 100 knot jet lifting across southern
Canada and nose of developing sub-tropical jet lifting over the
Appalachian Mountains on Tuesday night...helping to enhance a
period of deep layer lift over our region. This synoptic scale
lift combined with precipitable waters surging between 0.75 and 1.0 or 2 Standard above
normal will help to produce a widespread moderate rain event.
Thinking quantitative precipitation forecast values will range between 0.25 and 0.75 by Wednesday
with highest amounts over the high peaks of the northern dacks.
On Wednesday...some middle/upper level drying occurs over the Saint Lawrence
valley while initial lift and associated band of rain will lift
north of our County Warning Area. However....as closed system tracks across the
central Great Lakes by 18z Wednesday...another southern stream piece of
energy will round the trough base and help develop weak surface low
pressure near Washington District of Columbia. This low pressure will track northeast toward
the Gulf of Maine by 12z Thursday...while closed 500 mb/7h system moves
just north of our forecast area. The secondary coastal system will
help to pull deeper sub-tropical moisture back into our
central/eastern forecast area...while low level cold air advection
develops on north winds by 00z Thursday. Thinking rain redevelops
between 21z-00z...but turns to a period of accumulating snowfall on
Wednesday night...especially across the mountains of Vermont. Still some
uncertainty how much deep layer moisture is pulled north into this
system tracking to our north and how quickly secondary surface low
pressure develops along the coast. Will mention likely to Cat probability of precipitation with
several inches of snow accumulation possible. Helping promote
additional lift across our region is 250mb dual jet couplet at 00z
Thursday...but this feature quickly shifts north as progressive flow
aloft continues. The synoptic precipitation will transition to a period of
upslope precipitation late Wednesday night into Thursday before ending. Some
additional snow accumulation is likely along the western slopes and
northern dacks. Still too much uncertainty on amounts as feel
upslope quantitative precipitation forecast/moisture is overdone based on fast progressive pattern
and track of upper level system.
Temperatures will be very mild with highs in the 40s on Tuesday and
fall very little overnight on Tuesday night with southerly
winds...clouds and precipitation. As surface winds shift to the northwest
after 18z Wednesday...expect low level cold air advection to develop as
prognosticated 850 mb temperatures drop below 0c by 06z Thursday...along with 925mb
temperatures. This supports lows in the 20s mountains to upper 20s to lower
30s in the valleys by Thursday morning.
Long term /Thursday through Monday/...
as of 303 PM EST Monday...medium range guidance is in good
agreement in regards to the overall synoptic pattern for the long
term with only minor differences in timing and moisture forecasts.
Forecast period begins on Thursday where strengthening surface low
pressure will be over the Gulf of Maine while the parent closed
middle/upper level low will be on the btv County Warning Area doorstep shifting
eastward. Ample moisture wrapping around the surface low
interacting with lift/energy from the upper level low will
continue to produce scattered valley rain/snow showers through the
day with snow likely across the higher summits and northeast
Vermont. As we shift into Thursday night, the best lift and deep
moisture shift east of the region with a brief surface and upper
ridge building in, drying out conditions for the overnight.
For Friday and Friday night, a secondary upper trough and weak
surface low shift through the area with more scattered rain/snow
showers expected, but likely more widely scattered than on Thursday
with weaker overall upper dynamics. On Saturday a large scale upper
ridge and surface high build back into the area and dominate the
north country's weather with sunny/clear/dry conditions expected
through the weekend.
Temperatures through the period will be seasonal to slightly above normal
with highs ranging from the middle 30s to middle 40s, and lows in the middle
20s to low 30s.
Aviation /03z Tuesday through Saturday/...
through 00z Wednesday...generally VFR conditions expected through
the most of the period. After 11-13z Tuesday clouds increase
again from the south/southwest ahead of our next system but remain
VFR until around 18z. After that MVFR ceilings will start to move
in and could become IFR as some locations by the end of the
period. Along with this rain will move into the area around 15z-
17z and could have impacts on visibility very late in the period.
There is a potential for a short lived period of freezing rain at
mpv/slk as the rain first starts but should switch over to rain as
the temperatures warm slightly with the southwesterly flow. Winds
are light and variable overnight, then increasing to 5-10 knots
from the south/southwest after 14z Tuesday.
Outlook 00z Wednesday through Saturday... 18z Tuesday - 00z Friday...VFR
deteriorating to MVFR/IFR as low pressure system tracks through
the region. Rain Tuesday/Wednesday transitions to snow showers Wednesday night
through Thursday before ending.
00z Friday - 12z Friday...mainly VFR under brief high pressure.
12z Friday - 12z Sat...MVFR/local IFR in scattered snow showers.
12z Sat - 00z sun...trending to VFR under building high pressure.