Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1030 am EDT sun Apr 19 2015
high pressure building into the region today will provide dry and
seasonal conditions to finish out the weekend. This will be the
last nice day we see for awhile unfortunately, as a prolonged
period of unsettled weather is expected next week with widespread
rain Monday and Tuesday, followed by on and off showers through
Near term /until 6 PM this evening/...
as of 1027 am EDT Sunday...only very slight adjustments for 1030
am update this morning. Refreshed first few hours to match current
observations and interpolate out. As expected clouds are
dissipating this morning and the rest of the day looks like sunny
skies. Previous discussion follows.
Previous discussion...better get out there and enjoy today
because it might be the last one like this for awhile. High
pressure builds into the region with dry conditions, light winds
and seasonal temperatures expected. We're still seeing some pesky
low stratus across a good portion of northern and central Vermont
this morning from cyclonic flow around low pressure exiting off
the Nova Scotia coastline. As high pressure settles over the north
country this morning we should see these clouds dissipate to
clearer skies by this afternoon. 925-850mb temperatures are a few degrees
cooler than yesterday so despite full sunshine this afternoon
highs will top out in the middle 50s to low 60s.
Short term /6 PM this evening through Tuesday/...
as of 420 am EDT Sunday...dry weather continues through the first
half of tonight as well, but then turns unsettled for all of next
week and into next weekend as a digging upper trough over the
central Continental U.S. Develops into a vertically stacked closed low and
takes residence over the Great Lakes. As the surface low takes
shape, a warm occluded front will approach the north country late
tonight into early Monday morning and traverse the northeast
through Tuesday. Strong southeasterly flow along the boundary will
tap into rich Gulf moisture with precipitable waters approaching 1" supporting
moderate rainfall which could cause some Hydro issues as snowmelt
continues from deep snowpack across the higher elevations. In
addition, confidence continues to increase that a moderate to
strong southeasterly downslope wind event will materialize along
the western spine of the Green Mountains and portions of the
Adirondacks Monday afternoon. Local 4km WRF shows a strong
925-850mb jet moving across the area Monday afternoon through late
evening with the latest run indicating 50-60kts at 925mb over the
favored downslope regions along the western slopes of the northern
from Killington to Jay Peak. Forecast sounding shows the low level
inversion is just below 925mb so while not all of these winds will
mix to the surface, confidence is increasing at we'll see gusts in
excess of 40mph and likely up towards 50mph which would warrant a
Wind Advisory. Will hold off for now and allow further shifts to
assess, but it's looking like it's in the cards.
Occlusion shifts through the region late Monday night into
Tuesday morning with a middle level dry slot developing over the area
Tuesday which should end the widespread precipitation. As the front
shifts through models are indicating a little bit of elevated
instability and Storm Prediction Center sref calibrated ts forecasts show a slight chance
for some thunder so have opted to include this in the forecast.
Anticipate it will turn out much like yesterday with just a
handful of strikes, nothing really to worry about.
Long term /Tuesday night through Saturday/...
as of 353 am EDT Sunday...unsettled weather conditions with
relatively cool temperatures will characterize much of the
extended forecast period. Good run-to-run and model-to-model
consistency observed between European model (ecmwf)/GFS/GFS ensemble mean. Quasi-
stationary...equivalent barotropic upper low over the northern Great
Lakes and Ontario will very slowly drift eastward...reaching our area
early Friday morning...and then slowly pivot northeastward across S-central
Quebec. This will be the main feature of interest...and the north
country will remain within the deep-layer cyclonic flow associated
with this system throughout the extended period. A shortwave
trough prognosticated to translate through the southern/southeastern periphery of the
upper low will bring our most widespread rain chances during
Wednesday into Wednesday night. Thereafter...activity will be less
organized...and potentially driven by diurnal heating with more
widespread coverage of shower activity during the daylight hours
Thursday and Friday. With thermal trough in place (850mb temperatures - 6
to -8c Thursday night...and -4 to -6c Friday night)...may see some
snow shower activity mixing in...especially during the nighttime
hours and over the higher terrain. May see some light snow
accumulations Thursday and Friday across the higher summits.
Daytime highs Wednesday-Friday will range from the middle-upper 50s on Wednesday...and
low-middle 50s for Thursday and Friday. Overnight lows will range
from the middle-upper 30s Tuesday night...to the low-middle 30s Wednesday
night through Friday night...and locally in the upper 20s above
1500 feet. Best potential for sunshine appears to be Saturday...as
upper low shifts northward across central Quebec. Prevailing west-northwesterly flow
will maintain cool thermal regime...with highs remaining in the
Aviation /15z Sunday through Thursday/...
through 12z Monday...VFR through the period. Broken-ovc035-045 layer
across central/northern Vermont (including btv/mpv) will erode 12-14z
leaving mainly sky clear for the balance of the day. Will see some
cirrus clouds (sct-bkn250) advance from SW-NE after 00z this
evening...and eventually altostratus layer (bkn-ovc120-150) toward
09-12z Monday. Winds generally north 5-10 kts...becg light southeast (5
kts or less) tonight...except locally southeast 10-13kts at rut after
Outlook 12z Monday through Thursday...
12z Monday - 00z Wednesday...frontal system brings periods of
MVFR and IFR rainfall west/ hir terrain obscured. Leading warm front will
bring first frontal rain band into the region during Monday
morning. Moderately strong pressure gradient may also result in
gusty winds potentially in excess of 25 kts from the south-southeast...and
briefly up to 40 kts at krut during Monday afternoon. Low level wind shear also
possible during Monday and Monday night. Second band of rain moves
in late Monday night through Tuesday morning. Hir terrain obscured through
much - if not all - of the period.
00z Wednesday - 00z Friday...broad upper trough remaining in
place. MVFR possible in scattered showers throughout the period.