Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1230 PM EST sun Dec 21 2014
an upper level low pressure system over New Hampshire this morning
will bring light snow to the southern half of Vermont with a
dusting to two inches expected. Dry weather will exist over the
remainder of the area along with below normal temperatures. The
pattern will change later Monday into Tuesday as moisture
increases from the south and a storm system moving into the Ohio
Valley will ultimately bring widespread rain to the area on
Wednesday along with windy conditions...especially Christmas evening
day and night.
Near term /until 7 PM this evening/...
as of 1230 PM EST Sunday...no changes to previous update with
main focus on light snow continuing to fall across parts of
central and southern Vermont. Previous discussion...small upper
circulation over New Hampshire having an impact on our area this
morning with light snow falling over south central Vermont...
generally south of Montpelier. This will continue through early
afternoon before upper circulation moves far enough east to have
less of an impact. Have added light snow to the forecast from
southern Addison and southern Orange counties south into Rutland
and Windsor counties. Looking at a dusting to two inches in this
area with just clouds over the remainder of the area.
Short term /7 PM this evening through Tuesday/...
as of 400 am EST Sunday...quiet dry seasonable weather will
continue through Monday as surface high pressure remains dominant
weather feature for tonight and Monday. Should see some clearing
tonight...followed by clouds on Monday as another shortwave
crosses the area. Flow will become more south and southeast on
Monday and Monday night. With some clearing tonight...especially
north...will see temperatures in the teens. Temperatures on Monday will
be near normal in the lower 30s. Will see some clearing Monday
night...but warm air advection begins ahead of next approaching
system. Very mild temperatures are expected with lows only in the
middle to upper 20s for our forecast area. Large scale low pressure
system will begin to approach our forecast area during the day
Tuesday. Warm air advection continues and clouds increase...a mild
day is expected with highs reaching the 40s in parts of our area.
There will be a chance for some rain and snow showers Monday night
and Tuesday across our southern zones as a shortwave and weak low
pressure system moves along the southern New England coast.
Long term /Tuesday night through Saturday/...
as of 445 am EST Sunday...latest guidance still supports the idea
of rainy and possibly windy conditions on Christmas evening day into
the morning hours of Christmas day.
Precipitation chances increase Tuesday night as high pressure
retreats across Canadian Maritimes and upper ridge axis slides
east of New England. Low level easterly flow combined with flow
becoming more southerly aloft will result in increased
frontogenesis over the region. Expect mostly light rain to become
rather widespread by Wednesday morning. Could be a few pockets of
snow or mixed precipitation Tuesday evening...especially in the
Northeast Kingdom...but soundings suggest mainly rain.
Chances for rain increase further Wednesday into Wednesday night.
Deep upper trough develops over the Midwest. Strong shortwave
rounds base of the trough early Wednesday then lifts northeast.
Deep and strengthening southerly flow in advance of the trough
will allow for good moisture advection into the north country.
850 mb winds not quite as strong as earlier model runs had
indicated...and flow now projected to be more southerly than
southeast. Still looking at a 40-50 knots 850 mb jet however. But
with less of an easterly component...downsloping would not be
quite as significant. Biggest area of concern for localized high
winds continues to be over the higher terrain and perhaps along
the western slopes of The Greens and the Adirondacks.
As far as quantitative precipitation forecast amounts for this system...we still expect total
amounts to range from 1 to 2 inches across much of the region.
Amounts will vary a bit due shadowing in some areas and orographic
enhancement in others. Highest totals likely along south facing
slopes of southern greens and Adirondacks...with lighter amounts
over northwest Vermont and far northern New York. With temperatures on
Wednesday expected to reach into the upper 40s and lower 50s...and
little drop off Wednesday night...the combination of rain and
mild temperatures will result in significant snowmelt. The snowmelt
combined with the 1-2 inches of rain could cause some localized
flooding in areas of poor drainage and in small streams. Right now
river gauges are showing river levels are quite low...so while
some minor flooding will be possible we don't expect significant
river flooding issues. Rain continues early on Christmas
day...then some drying expected with passage of cold front during
the morning. Lingering showers will continue during the
afternoon...and will transition to snow showers over the higher
terrain as colder air returns. Temperatures in valleys remain mild though
for much of the day with readings in the 40s.
Drier conditions expected for Thursday night and Friday...with
just some lingering mountain snow showers. Shortwave trough brings
a chance of snow/rain showers to the entire region Saturday.
Temperatures Friday and Saturday are expected to remain above
normal with highs each day in the middle 30s to around 40.
Aviation /18z Sunday through Friday/...
through 12z Monday...low level moisture remains over the forecast
area through the period with the result being lots of low clouds
and some patchy fog at times. IFR conditions early this morning at
most sites except rut/mpv where MVFR/VFR expected. During the day
today...areas with IFR improve to MVFR...and some locations may
see improvement to VFR for a time. More of the same for tonight
with low clouds and patchy fog. Expect MVFR conditions with areas
of IFR. Winds remain light and variable through the period.
Outlook 12z Monday through Thursday...
12z Monday-00z Tuesday...low clouds with mostly MVFR ceilings.
00z Tuesday-12z Wednesday...periods of MVFR in light mixed precipitation.
12z Wednesday-18z Thursday...periods of MVFR/IFR in rain. Gusty winds possible.
18z Thursday-00z Friday...mostly VFR with MVFR possible in scattered