Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
326 PM EDT Tuesday Jul 29 2014
upper level low pressure located over the jame Bay region today
will continue play a large role in the north country's weather
through the end of the work week. Temperatures through Thursday
night will run a little below normal...with chances each day for
an afternoon shower or thunderstorm. A return to more normal
Summer temperatures is expected Friday and into this weekend...
with a continued chance for afternoon and evening convection.
Near term /until 6 am Wednesday morning/...
as of 325 PM EDT Tuesday...pretty quiet and tranquil conditions
are expected for tonight as we remain under a dry cyclonic
northwest flow from upper level low pressure parked over the
James Bay region. Plenty of clouds out there this afternoon...but
should generally dissipate later this evening though not expecting
completely clear skies...especially across the northern Adirondacks
and Saint Lawrence valley. Should be enough to develop some
locally dense fog in the favored valley locales though after
midnight. With modest radiational cooling and unseasonably cool
temperatures aloft...overnight lows will run a bit below normal in the
middle/upper 40s across the Adirondacks and eastern Vermont...and
low/middle 50s in the valleys.
Short term /6 am Wednesday morning through Thursday night/...
as of 325 PM EDT Tuesday...short term period remains largely
dominated by the aforementioned upper trough/low over eastern
Canada which slowly retrogrades ever so slightly westward
Wednesday and then slightly southward towards the international border
Thursday. Some weak instability and step low level lapse rates
each afternoon will result in chances for isolated to scattered
showers and possibly a rumble of thunder...but overall coverage
will likely be limited with weak forcing aloft and limited
low/middle level moisture to work with. Best chance will be Thursday
with a decent shortwave and cold pocket aloft rotating through
northern portions of the County Warning Area. Timing of this feature will play a
large role in the amount of instability we see with latest
guidance hinting at an early arrival which will limit convective
potential. Nevertheless...will continue to mention high chance to
low likely probability of precipitation for showers with a chance of thunder. In
addition...with cold pool aloft moving overhead could see some
small hail with any stronger updrafts which do develop...but will
leave out for now and let further shifts assess.
Temperatures through the period will remain slightly below normal with
highs in the low/middle 70s...and lows generally in the 50s.
Long term /Friday through Tuesday/...
as of 310 PM EDT Tuesday...large scale features indicate a highly
amplified pattern will continue across the Continental U.S. With middle/upper level trough
across the Great Lakes and strong middle/upper level ridge over the
western Atlantic. This results in an active west to southwest follow
across our County Warning Area...with several embedded vorts expected to impact our
County Warning Area. Difficult to determine exact timing of individual
features...but pattern supports an unsettled weather scenario
going into the weekend and early next week. If trough digs deeper
across the Great Lakes/NE Continental U.S....then better moisture/instability
would be suppressed to our south and our County Warning Area would remain dry.
However...both GFS/GFS ensembles and European model (ecmwf) shows the potential for
daily showers/storms. Will mention highest probability of precipitation during the daytime
hours and taper off to slight chance at night. Prognosticated thermal profiles
change very little through the period with 850 mb temperatures mainly between
10-12c...supporting highs in the 70s mountains to lower 80s warmer
valleys. Lows will be highly depend upon cloud cover and
precipitation...but mainly 50s mountains to l/M 60s warmer valleys.
Aviation /20z Tuesday through Sunday/...
through 18z Wednesday...VFR conditions will prevail at all taf sites
through this evening. Aviation challenge will be areal coverage of fog
at slk/mpv and associated LIFR conditions. Thinking diurnally
driven cumulus clouds will dissipate with the loss of surface heating
this evening...with areas of fog develop at slk/mpv by 06z
tonight. Guidance suggests these areas will drop blw their cross
over temperatures...with clear skies and light winds...combined with recent
rainfall will result in fog. Have mention visible 1/2sm with ceilings overcast at
100 feet at both mpv/slk. Thinking some Winooski River Valley fog
could impact btv...especially northern and eastern side of the
Airport...especially if a light drainage follow can develop...per
local btv solution. Otherwise...winds of 15 to 20 knts at 200 feet
above ground level and terrain driven winds at Rutland of 3 to 7 knots will limit fog
potential. Otherwise...fog lifts between 12-13z on Wednesday with VFR
Outlook 18z Wednesday through Saturday...
scattered showers and thunderstorms will be possible Wednesday and Thursday
aftns with localized MVFR conditions in the heavier
showers/storms. In addition...brief gusty winds will be possible
with visible between 3-5sm in any shower activity. Clouds and winds
should limit fog/br potential...but locations that receive rainfall
during the daytime have the potential for IFR conditions in fog at
night. Surface high pressure with mainly VFR conditions will prevail Friday