Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1026 am EDT Monday Jul 28 2014
a strong middle-Summer low pressure and upper disturbance will bring
rain and embedded thunderstorms to the north country today. The
rain will fall heavy at times resulting in gradual main Stem river
rises. A few strong storms could develop across eastern Vermont
during the afternoon hours. This system exits into Quebec later
tonight with leftover showers confined to the mountains. The middle
to latter part of the week features isolated afternoon showers
under cool temperatures aloft. Highs will be a few degrees below
normal through midweek...trending closer to normal by later in the
Near term /until 7 PM this evening/...
as of 1014 am EDT Monday...minor update to capture latest trends
and increase 6hr quantitative precipitation forecast grids across central Vermont and lower CT River
Valley. Have noticed 1 hour quantitative precipitation forecast amounts between 0.30 and 0.60"
associated with band of heavy rainfall lifting across
central Vermont at this time. Rutland received 0... North Hartland
lake hads reporting a 3 hour total of 1.16 inches. This band will continue
to move north and impact all of central/northern Vermont through 18z
today. Also...a batch of moderate rain will continue across northern
New York...including the slv with lighter rainfall rates. Expecting
middle/upper level dry slot to develop across southern Vermont zones late this
morning...which will provide region with temporary break in
action...but as potent short wave energy and associated moisture across
central New York approaches the region...additional showers with embedded
storms will redevelop by noon today. These storms will be convective
in nature and localized gusty winds and very heavy rainfall will
be likely. Latest hrrr models shows this idea very well...especially
with regards to developing some weak instability and modest 0 to 6
km shear...to support thunderstorm activity. The soundings show a
tall skinny cape profile with the potential for some localized
flash flooding...mainly across Rutland/Windsor and Orange counties.
Will watch radar trends and rainfall rates very carefully this afternoon. Otherwise...
temperatures will be below normal today with values ranging from the l60s
dacks to m70s lower CT River Valley.
Previous near-term discussion issued at 415 am EDT Monday
Active Monday weather-wise for the north country...featuring a
dynamic storm system producing several issues to contend with
including heavy rainfall and potential for strong storms in
eastern Vermont. Frankly...the upper- level pattern and related degree
of large- scale forcing resembles Spring more than late July.
Big picture...surface low has developed near kroc along a baroclinic
zone which extends down across the Alleghany plateau and northward
to St. Lawrence Valley. Aloft...a negatively tilted shortwave
trough is located over Northern Ohio with associated strong 500 mb
jetstreak at trough base (evident in WV imagery by a pronounced
dryslot punching into western pa). There's not a very clear
consensus in 00z guidance where the surface cyclone tracks
today...with the NAM and sref mean being further to the west (an
Adirondacks to Montreal track) and global models taking more of a
central/southern New England to western New Hampshire track. I've tried to
split the difference between solutions for now.
Regarding heavy rainfall potential: ongoing band of moderate/heavy
rain and embedded thunder continues to track northward...aligned
roughly on 850-500 mb deformation axis. That band of rain will
spread northward across the north country. Categorical probability of precipitation
through today with rain falling heavy at times. Think the heaviest
rainfall amounts will fall across the eastern 'dacks and east-
facing Green Mountain slopes aided by southeast upslope. Main Stem rivers are
running low so I don't anticipate there being widespread Hydro
issues. However expect gradual river rises today...with perhaps
minor nuisance flooding especially in thunder and enhanced
rainfall rates. Forecast quantitative precipitation forecast through 12z Tuesday is a heavy model
blend - which brings a general 1" but amounts up to 1.5" are shown
from the eastern 'dacks...northern Champlain Valley and higher
peaks of The Greens.
Strong/severe thunderstorm potential: this is more conditional on there
being enough breaks in overcast - which may happen in eastern Vermont as
dryslot moves across later this afternoon. Prognosticated convective available potential energy are as high
as 1000-1200 j/kg in NAM/WRF across eastern Vermont...less so in the GFS.
Shear parameters are higher further south but still have around
30-35 kts of 0-6 km shear. Throw in good synoptic ascent which
could overcome low instability and I could see there being a few
strong storms across eastern Vermont. Storm Prediction Center has this area outlined in a
see text area today. Though there is some uncertainty in
instability...opted to add enhanced wording for gusty winds and
heavy rain for this area during the afternoon hours.
Temperatures today are tricky. Expect temperatures to rise only a few degrees across
northern New York and the Champlain Valley under overcast and rain
through the day. Highs in this area generally in the 60s/around 70
to the middle 70s in southern Vermont where potential for some breaks
in clouds exist.
Short term /7 PM this evening through Wednesday/...
as of 415 am EDT Monday...
For tonight: prognosticated sub-1000 mb surface low lifts into Canada.
Moderate rain still expected early tonight but expect probability of precipitation to
generally decrease. A good signal for northwest upslope/blocked flow
showers (e.G. Sub-critical Froude numbers per 00z nam) keeps highest
probability of precipitation after midnight to the mountains. 850 mb temperatures fall to +7 to
+9c tonight and partial clearing should bring lows in the middle 40s to
Tuesday through wednesday: both days are fairly similar in terms of
sensible weather. Large-scale lift diminishes...with cyclonic flow and
cold air aloft producing diurnally-driven clouds/showers -
generally dissipating with loss of daytime heating. Slight chance
to chance probability of precipitation indicated...generally highest across the mountains
and across northern New York closer to upper troughing. Highs
generally in the upper 60s-70s Tuesday and Wednesday with upper 40s
to middle 50s for lows Tuesday night.
Long term /Wednesday night through Sunday/...
as of 415 am EDT Monday...a slow warming trend to near normal late
Summer temperatures is expected with partly sunny skies and an
average chance of an afternoon/evening shower or thunderstorm.
Models in good agreement that the upper trough weakens but remains
in place Thursday then retrogrades a few degrees westward over
the weekend. A building Atlantic ridge aloft, rising heights over
the East Coast with a Bermuda high strengthening at the
surface...which is fairly typical for late Summer...leaves US in a
weak but mild southwest flow aloft. Some small chance of showers and
thunderstorms will continue each after/evening as area remains locked into
the eastern side of the upper trough.
Slightly below normal maximum temperatures are expected Thursday with partly
sunny skies. High temperatures mainly 75 to 80 with 850 temperatures
around 10-12c. 850 mb temperatures warm a couple degrees 12-14c Friday and
little change expected over the weekend day should be 12-14c. With
partial sun under diurnal cumulus clouds expect highs moderating to
near normal - upper 70s lower 80s. Low temperatures will be generally in
the 50s to lower 60s trending milder over the weekend. Looks like
winds will be light through the period so River Valley fog is likely
as we move toward our our peak fog season.
Aviation /14z Monday through Friday/...
through 12z Tuesday...a wide variety of varying flight conditions trending
MVFR locally IFR in moderate to heavy rain with embedded
thunderstorms as low pressure tracks eastward across New York then
northeast along a frontal system through central New England to
western ME/southern Quebec by 06z Tuesday.
Rain...moderate to heavy at times with embedded thunder beginning
10-12z from SW to NE. Expect conditions to lower to MVFR area-wide
with possible IFR at times. Thunder possible from mainly south and
east of btv/mpv indicated with thunderstorms in the vicinity at rut this afternoon.
Light winds early today gradually becoming northerly 10 to 15 kts
today at btv/pbg. Winds NE becoming north at mss/slk and could be some
g15-20kts. At rut/mpv light east/southeast winds will become west/northwest later
Outlook 12z Tuesday through Friday...
12z Tuesday - 12z Thursday...mainly VFR. Possible IFR/lower visibility in
overnight fog/mist mpv and slk.
12z Thursday Onward...mainly VFR although brief periods of MVFR
possible in a shower or thunderstorm.