Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
447 am EDT Friday may 29 2015
a ridge of high pressure will be over the north country tonight
and tonight. A strong cold front will move slowly southeast from
Canada on Saturday and move through the region Saturday night.
Another ridge of high pressure will bring drier cooler weather for
the beginning of next week.
Near term /until 6 PM this evening/...
as of 447 am EDT Friday...a ridge of high pressure will be over
the region today with mostly sunny skies expected with highs in
the 80s. Have gone a bit above MOS guidance for maximum temperatures
Short term /6 PM this evening through Sunday/...
as of 447 am EDT Friday...expecting dry weather to continue into
tonight across the region. Have leaned toward the lower NAM MOS
probability of precipitation for tonight. Btv 4km and European model (ecmwf) showing a mainly dry forecast
across the region for tonight. Have gone with just slight chance
probability of precipitation for showers for the Saint Lawrence valley closer to daybreak
on Saturday. Models a bit slow in bringing in showers and
thunderstorms into the region on Saturday...with the best chance
for showers and thunderstorms across northern New York late
Saturday morning. The showers and thunderstorms will move into
Vermont Saturday afternoon. Have gone with likely probability of precipitation on
Saturday. Storm Prediction Center has the region in a marginal risk for severe
thunderstorms on Saturday. However...0-6 km bulk shear at 18z
Saturday is only 20-30 knots...and wet bulb zero values around
11000 feet...so any hail that develops in any thunderstorm will
likely remain below severe criteria at this time. The main threat
from the thunderstorms on Saturday and Saturday night appears to
be locally heavy rainfall...as precipitable water values running
around 1.5 to 1.8 inches Saturday afternoon into early Saturday
Expecting rain showers to linger into early Sunday morning...but
expecting clearing skies to develop across the region by Sunday
afternoon as the cold front will be south of the region.
Long term /Sunday night through Thursday/...
as of 325 am EDT Friday...a strong 1039mb area of high pressure builds
into southern Canada behind surface cold front on Sunday night
into Monday. This will result in cool temperatures and dry
conditions. Given moisture profiles expect a large swing from
cool overnight lows on Monday morning to highs on Monday afternoon.
Still expecting some patchy frost in the colder valleys of the
dacks and nek on Monday morning with latest mex for slk showing a
30f. Prognosticated 850 mb temperatures between 4-6c on Monday support highs only in
the 60s to near 70f warmer valleys...with north winds.
Plenty of uncertainty develops for Monday night into Tuesday with
placement of deep layer moisture and development/movement of
middle/upper level trough. GFS keeps our County Warning Area dry with surface high pressure
overhead and best 850 to 500mb moisture and associated quantitative precipitation forecast well
south of our County Warning Area. Its interesting that the GFS shows potent 500 mb
vorticity and closed circulation moving across our northern County Warning Area on
Tuesday...but moisture is very limited and displaced way to our
south. Meanwhile...the European model (ecmwf) shows the 500 mb trough and associated
energy moving directly overhead...with surface low pressure tracking along
the eastern Seaboard for Tuesday. This would result in a widespread
rain event...with very chilly temperatures. Thinking the European model (ecmwf) is a bit
agressive with advection of moisture north and development of surface
low pressure...given position of high...so will continue to keep forecast dry
at this time. This is subject to change as the event draws closer and
models come into better agreement. Otherwise...prognosticated 850 mb temperatures
warm a degree or two a day...and support above normal temperatures by the
middle to end of next week. Expect highs back into the M/u 70s mountains
to l 80s warmer valleys by Thursday with lows mainly in the 40s
Aviation /09z Friday through Tuesday/...
through 06z Saturday...1028mb high pressure located over southern
Canada will building into our taf sites with clring skies and
light winds. This will allow for areas of fog/br to
develop...especially in locations that have received rainfall
recently...like slk. Have mention vlifr/LIFR conditions with fog
and visible around 1/4sm through 12z Friday. Difficult to determine
fog at mpv...with some clouds lingering...but given drying aloft
per water vapor...thinking fog/br will develop between 07-08z.
Similar conditions expected at mss with maybe a brief period of
IFR/MVFR in fog/br at pbg/btv/rut between 07-11z. Otherwise...fog/br
will lift between 11z-13z this morning with VFR conditions prevailing
at all taf sites. Light and variable terrain driven winds will
become south at 5 to 10 knots.
Outlook 06z Saturday through Tuesday...areas of patchy fog will be
possible at slk/mpv between 07-11z Saturday with IFR conditions.
Otherwise...a surface cold front will produce scattered showers
and thunderstorms on Saturday afternoon into Saturday night. Some
storms could be strong with localized gusty and erratic outflow
winds...heavy rainfall...and frequent lightning. Breezy south to
southwest winds of 15 to 25 knots can be expected on Saturday
afternoon...before switching to the northwest by 12z Sunday. Areas of
low level turbulence and wind shear is likely in and around any
thunderstorm activity on Saturday afternoon. Expecting the rain to
lower visible between 1-3sm in the heavier precipitation...with periods of IFR
likely at all taf sites. Surface high pressure with VFR conditions develop
Sunday through early next week. Some fog/br possible each morning
with IFR conditions.
as of 447 am EDT Friday...a cold front will move slowly southeast
from Canada on Saturday and move through the region Saturday
night...with a chance for showers and thunderstorms Saturday
afternoon into Saturday night. A lake thunderstorm advisory may be
needed for Lake Champlain Saturday afternoon and Saturday night.
South winds will increase to 15 to 25 knots late tonight and
remain south at 15 to 25 knots on Saturday. A lake Wind Advisory
for Lake Champlain may be needed tonight and Saturday.
as of 139 am EDT Friday...the automated surface weather observing
system (asos) at Saint Johnsbury Vermont (1v4) is not currently
reporting due to a communications line issue. No estimate is
available at this time as to when the 1v4 ASOS communications line
will be restored to service.