Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1015 PM EDT Tuesday Jul 7 2015
a cold front over the eastern Great Lakes will move eastward across
the north country overnight. This cold front will produce
scattered showers and isolated thunderstorms overnight. A high
pressure area will build slowly east from the Great Lakes on
Wednesday and will be over the north country through the end of
the week...bringing fair...dry and less humid weather to the north
Near term /until 7 am Wednesday morning/...
as of 1005 PM EDT Tuesday...very humid air mass in place across the
north country this evening with upper 60s to low 70s dewpoints in
advance of the surface cold front approaching from southeastern
Ontario/Ottawa Valley region. Despite high dewpoints...instability
is limited by marginal middle-level lapse rates (700-500mb values of
only 5.5-6.0c/km per Storm Prediction Center mesoanalysis and 00z alb sounding) and
onset of diurnal cooling cycle this evening...with very Narrow
Cape profiles on observed and NAM/rap model soundings.
Scattered shower activity associated with frontal rainband across
northern Franklin New York and St. Lawrence counties at 02z will continue
steady eastward movement overnight. Diminishing instability will cause
thunderstorm chances to gradually decrease during the overnight
period...and included just a slight chance of thunderstorms after 03z.
Frontal rainband will reach the Champlain Valley by 04z and across
central/eastern Vermont 05-08z. Two to four tenths of an inch of rain is
possible across northern New York into northern Vermont...aided by precipitable water values 1.8 -
1.9" along the frontal boundary. South winds will remain
moderately gusty (10-15 miles per hour with gusts to 25 miles per hour in the Champlain
Valley through midnight or so...and then shift northwesterly with frontal
passage overnight. Low temperatures generally in the middle 60s at
daybreak...but temperatures holding in the low-middle 70s in most areas through
midnight ahead of the frontal boundary.
Short term /7 am Wednesday morning through Thursday night/...
as of 411 PM EDT Tuesday...some light rain shower activity to
linger over the region early Wednesday morning before clearing
develops by midday on Wednesday...as models show a middle level dry
slot will be over the region by 18z Wednesday. High pressure over
the eastern Great Lakes will build slowly east from the Great
Lakes on Wednesday and will remain over the north country through
Thursday night. Have added a mention of patchy dense valley fog
after midnight Wednesday night...as combination of clear skies and
nearly calm winds will lead to ideal conditions for radiation fog
to form in the usual fog prone valleys of eastern and northeast
Vermont...as well as in the sheltered valleys of the Adirondacks.
Long term /Friday through Tuesday/...
as of 218 PM EDT Tuesday...overall very little change from
previous forecast thinking as medium range global models remain
very consistent in the extended pattern. Forecast period begins on
Friday with northwest flow aloft and surface high pressure over
the northeast as a middle-level high develops over the southeast
Continental U.S.. as the upper ridge builds westward and amplifies into the
central Continental U.S. Surface high pressure over the northeast is
reinforced by more middle-level subsidence resulting in prevailing
partly sunny/cloudy skies across the btv County Warning Area through Saturday.
Temperatures will be seasonal with highs in the 70s/80s and lows
in the 50s/60s. By Sunday some disparity in the models develops in
regards to the timing and strength of shortwave energy riding over
the aforementioned ridge and the depth of a trough dropping
southward from James Bay. The GFS continues to show the most
bullish shortwave and deepest trough entering into the btv County Warning Area
Sunday afternoon, and has shown this for several days. Meanwhile,
the European model (ecmwf) and Canadian-Gem are much weaker offering drier
conditions. The past few days i've leaned towards the drier
European model (ecmwf)/Gem solution as my gut tells ME the GFS is suffering from
convective feedback as the shortwave originates out of the Lee of
The Rockies but with will play it safe since we're talking 5 days
out and go with some low chance probability of precipitation.
Aviation /02z Wednesday through Sunday/...
through 00z Thursday...VFR conditions start the period with
increasing clouds ahead of approaching cold front. The front
reaches the St. Lawrence Valley around 02z along with some MVFR
ceilings/visibility in light rain, traverses the area from west to east
through 11z. MVFR low clouds will linger behind the front for
several hours, expecting low level moisture to remain into the
morning hours. Clouds will lift eastward, revealing VFR conditions
starting at kmss around 09z, spreading to the Adirondacks and
Champlain Valley around 12z- 13z and krut/kmpv between 13z-15z.
VFR conditions will prevail through the rest of Wednesday as
surface high pressure builds in.
For winds, south/southwest flow will continue at 8-16kts this
evening with some lingering gusts possible. Winds turn
north/northwest behind the front and persist throughout the day
Outlook 00z Thursday through Sunday...
00z Thursday - 12z Sun: VFR. Early morning IFR fog possible at
12z sun - 00z Mon: VFR. Chance MVFR showers. Slight chance thunderstorms and rain.
as of 340 PM Tuesday...a lake Wind Advisory remains in effect
through around midnight tonight. South winds from 15 to 25 knots
will continue into the nighttime hours before decreasing and turning
north after midnight and towards morning. Wave heights of 2 to 3
feet can be expected through midnight...especially across the
Broad Lake and along south facing shorelines. Winds and waves
lessen to 1-2' on Wednesday.