Area forecast discussion
National Weather Service Burlington Vermont
142 PM EDT Wednesday may 22 2013
Synopsis...
a warm front lifting northeastward across the region late this
afternoon and evening will bring the potential for isolated to
scattered showers and thunderstorms. Some thunderstorms may be
severe and produce large hail...damaging winds...and locally heavy
downpours. A slow-moving cold front will then approach from the
eastern Great Lakes region bringing additional widespread rainfall
and embedded thunderstorms during Thursday and Thursday night.
While it won't be raining continuously...periods of briefly heavy
rain associated with the showers and thunderstorms will generally
bring an additional 1 to 2 inches of rain across the north country
through Thursday night. Some minor flooding will be
possible...mainly Thursday into Thursday night with the most
widespread rainfall.
&&
Near term /until 8 PM this evening/...
as of 122 PM EDT Wednesday...Severe Thunderstorm Watch issued for
the entire forecast area through 10pm.
Unsettled pattern continues across the north country in vicinity of
east-west oriented frontal zone which remains draped across the region.
Surface trough and 850mb temperature gradient suggests synoptic frontal zone
is up near the international border...but given the widespread convection
that has occurred in several waves during the past 6-12
hours...the effective frontal position extends across the southern tier
of New York into northwestern CT where large mesoscale cold pool has been
established.
There are slight 700-500mb height rises this morning through early
afternoon...and absence of low-level convergence suggests additional
rainfall is unlikely through about 19z. Clouds but no precipitation through middle
afternoon...will trend sky cover from overcast to broken by noontime.
Thereafter...there is a southwesterly backing and strengthening of 850mb
flow across western PA into central New York per model guidance. Feel that
remnant outflow boundary across central New York will enhance
isentropic ascent late in the day across the Adirondacks and
S-central Vermont...allowing for development of shower and thunderstorm
activity. The 00z NAM shows development of MUCAPE of 500-1000
j/kg across all but northestern portion of the forecast area 21-00z. Rap
soundings show a bit more instability...up to 1500 j/kg...though
surface dewpoints may be a bit overdone here. Based on consensus of
the models including locally run 4km WRF...looking for
development of a few strong late day/evening thunderstorms as well. Storm Prediction Center
calibrated severe probabilities and day 1 outlook support a few
severe storms...and mentioned gusty winds and small hail in the
forecast and severe weather potential statement for late aftn/evening. Deep layer (sfc-6km)
shear exceeds 40 kts and is supportive of some long-lived
updrafts. 00z alb sounding showed precipitable water values of 1... northward
advection of this moist air mass will also yield locally heavy
downpours with the convection late this afternoon into this evening.
Afternoon temperatures today highly depend on some sunny breaks during the
late morning-middle afternoon period. Anticipate some intervals of sun
today...and with 850mb temperatures of +14c could warm quickly during
the early afternoon. High temperatures in the valleys generally in the
middle to upper 70s...but could reach 80f if we get a bit more
sunshine and insolational heating.
&&
Short term /8 PM this evening through Friday/...
as of 418 am EDT Wednesday...deep-layer southwesterly flow and warm
advection continues overnight...with best isentropic ascent
gradually shifting north and east. Have carried likely probability of precipitation for
widespread showers and continued embedded thunderstorms. Some decrease in
cape overnight...so kept enhanced wind/hail wording just through the
evening hours. Lows will be on the warm side tonight with 60s
dewpoints in place along with clouds and S-SW winds all night.
Low temperatures will mainly be in the upper 50s to lower 60s.
Thursday will produce our most widespread rainfall as cold front
and associated positive tilt 500mb trough begins to shift slowly
southeastward across the forecast area. Moist and marginally unstable air
mass will support several bands of slow moving convection
along/in advance of the cold front. Given the setup...most of the
nwp quantitative precipitation forecast looked on the low side given evolution and moist air mass
in place. Trended closer to higher European model (ecmwf) quantitative precipitation forecast with widespread 1+"
rainfall amts across the County Warning Area. Some of this heavy rain continues
into Thursday night...especially central and eastern Vermont. Can/T rule
out localized 2" rainfall amts before things lighten up early
Friday. Some minor flooding is possible...refer to Hydro section
below. Highs Thursday generally in the middle 70s. Episodes of
showers/thunderstorms expected under cloudy skies.
Friday...likely probability of precipitation for rain showers in the morning...then
slow/gradual drying from northwest-southeast across the region. Should see some
partial sunshine late in the day from the Champlain Valley westward.
Cooler temperatures with highs in the low-middle 60s.
&&
Long term /Friday night through Tuesday/...
as of 450 am EDT Wednesday...lots of uncertainty in forecast as we
head into the Holiday weekend...as latest trends show a much
deeper/slower system for Friday into Sunday. Have trended toward the
00z European model (ecmwf) and 12z GFS solutions for this forecast...which supports
the mention of rain on Saturday into Saturday night. If current
trends continue for a much deeper and slower system...additional
showers would be possible for Sunday. Latest 00z European model (ecmwf) shows
northern and southern stream interaction by 12z Sat...which helps
to produce a closed and slow moving 500 mb/7h circulation over the
Middle Atlantic States. While surface low pressure tracks from New Jersey coast to
the Gulf of Maine by 18z Sunday. Given the position and track of
closed system and associated surface low pressure...expect heaviest quantitative precipitation forecast
to be just south and east of our County Warning Area on Friday into Saturday.
However...backside deformation band of enhanced middle level relative humidity and
associated 850 to 500mb lift is expected to develop. Its
extremely difficult to determine exact placement and movement of
these bands and the associated precipitation...therefore will just mention
chance probability of precipitation for Saturday into Saturday night. Feel system will slide
just far enough east by Sunday to keep forecast dry at this time. On
Sunday...as surface low pressure tracks into the Gulf of Maine...look for
gusty northwest winds to develop. Latest soundings show 850 mb winds
between 35 and 45 knots...which with some mixing will support gusts
between 25 and 35 miles per hour..especially Sunday afternoon. Prognosticated 850 mb temperatures
support highs only in the l/M 50s mountains to u50s/l60s for Sat and
Sunday. Expect a raw/cloudy and breezy type day on Sunday...with
blw normal temperatures. Surface high pressure will finally build into our County Warning Area on
Monday into Tuesday...with a slow clring trend...along with warmer
temperatures. If skies clear and winds becm light...patchy frost will be
possible in the colder mountain valleys late this weekend or early
next week.
&&
Aviation /18z Wednesday through Monday/...
through 18z Thursday...showers and thunderstorms across the
region will generally move west to east. VFR conditions will
deteriorate to MVFR within showers and LIFR/IFR in and around
thunderstorms this afternoon through the evening hours. Some
thunderstorms will contain small hail and dangerous wind gusts in
excess of 50 kts. Kslk already experiencing some ts...with krut
seeing MVFR ceilings in rain showers. Kpbg/kbtv and kmpv will likely
see convection within the next 2 hours and continue through the
evening. Kmss just north of best instability...but will also
likely see some convection.
After the storms and showers taper off...mainly after
06z...moisture where is has rained will continue MVFR ceilings...but
winds will begin to pick up out of the S-SW with gradually
improving conditions towards middle morning.
Outlook 18z Thursday through Monday... unsettled weather with
occasional showers/storms will continue for Thursday into Friday across
our taf sites. The stronger showers/storms on Thursday afternoon/evening
associated with a surface cold front will produce MVFR conditions...with
brief periods of IFR likely. Also...any storms will have the
potential to produce gusty surface winds up to 40 miles per hour. Areas of fog
and low clouds will be possible on Thursday night...with some
localized IFR/LIFR likely. Scattered showers may linger into
Saturday/Sunday with MVFR...before high pressure slowly builds into
the region by early next weak. Gusty northwest winds will be possible
over the weekend...with areas of low level turbulence.
&&
Hydrology...
430am Wednesday...widespread 1.0" to 1.5" rainfall (with locally
higher amts) has occurred across the north country during the
past 24-30 hours associated with several episodes of heavy
showers and thunderstorms. An additional 1-2" rainfall is forecast
between late afternoon/evening showers and thunderstorms and the more
widespread rain and embedded thunderstorms on Thursday. While antecedent
soil conditions have been dry...and vegetation is fully
active...the additional rainfall will eventually bring the
potential for street/poor drainage flooding. Associated minor
flooding would most likely occur during the day Thursday and into
Thursday night. Main-Stem river flooding is not forecast...but
may need to watch some of the smaller rivers and streams that
could locally exceed bankful later Thursday and Thursday night.
&&
Btv watches/warnings/advisories...
Vermont...none.
New York...none.
&&
$$
Synopsis...banacos
near term...banacos/neiles
short term...banacos
long term...Taber
aviation...kgm/Taber
hydrology...
