Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
758 am EDT Wednesday may 27 2015
there is a chance for rain showers across the north country this
morning. Strong to severe thunderstorms are likely across Vermont
and northern New York this afternoon. Some thunderstorms will
produce locally heavy rainfall...strong gusty winds...small hail
and frequent lightning. There is a chance for rain showers on
Thursday as a cold front moves through the region. Drier weather
is expected across the north country Thursday night and Friday.
Near term /until 6 PM this evening/...
as of 758 am EDT Wednesday...have made adjustments to sky grids
to cover partly to mostly sunny skies across the region at this
time. Composite radar lopp showing some scattered rain showers
over the Saint Lawrence valley in northern New York at this time.
Previous discussion from 432 am EDT Wednesday...composite radar
loop already showing some scattered showers across the northern
Champlain Valley and northern Vermont at this time. Expecting
conditions to destabilize by early this afternoon with convective available potential energy
values ranging from 500-1500 j/kg this afternoon. 0-6km bulk shear
will be around 30-40 knots this afternoon. Also...BUFKIT forecast
soundings showing precipitable water values will range from 1.5 to
1.9 inches across the region this afternoon...so locally heavy
rainfall will be possible with these thunderstorms. Strong gusty
winds will also be the main threat with any thunderstorms that
develop. Wet bulb zero levels are above 11000 feet...so feel any
hail reaching severe criteria looks marginal at this time. Have
used the btv 4km model for timing as to when thunderstorms will
develop and move through the region this afternoon. Storm Prediction Center has the
region in a slight risk for severe thunderstorms today.
Short term /6 PM this evening through Friday/...
as of 432 am EDT Wednesday...expecting any thunderstorm activity
to be mainly over eastern and southern Vermont early this evening.
Expecting a lull in shower activity overnight...before more shower
activity develops toward daybreak on Thursday as a cold front
moves through the region. Expecting temperatures to be mainly in
the 70s for highs on Thursday under cloudy skies. Have gone a bit
above MOS guidance for min temperatures tonight...as air mass will
still be warm and fairly humid. Have also gone with a slight
chance for thunderstorms on Thursday from the Champlain Valley
eastward. A ridge of high pressure will build in the region
Thursday night and Friday...with fair and dry weather expected.
Long term /Friday night through Tuesday/...
as of 430 am EDT Wednesday...another active day is expected on
Saturday afternoon/evening associated with surface cold front and potential
for showers and thunderstorms. The magnitude/intensity of storms
will depend upon frontal passage time...which models still
disagree on. GFS is showing frontal passage during peak heating Saturday
afternoon with surface based cape values between 1000 and 1500 j/kg...while
European model (ecmwf) is 6 to 12 hours slower and has less instability. Will
continue to mention chance to low likely probability of precipitation for this time
period...with the potential for some strong to severe
thunderstorms. Latest trends off the GFS continue to show the best 500 mb
vorticity associated with digging middle/upper level trough...approaching our
western County Warning Area during maximum instability...along with a sharp surface cold
front. If this timing would verify...a line of storms would be
likely...with wind profiles suggesting bowing line segments as the
primary convective Mode. Will continue to monitor latest timing for
potential changes in the forecast...but Sat afternoon/evening looks active.
Still some lingering showers on Sunday morning...before surface high
pressure builds into our County Warning Area. This will result in surface boundary
dropping south of our forecast area...into the Middle Atlantic States along with
best forcing/moisture. Will keep Sunday afternoon through early next
week dry at this time. Prognosticated 850 mb temperatures between 14-16c support highs well
into the 80s on Saturday...but will drop sharply by Sunday into
Monday...as prognosticated 850 mb temperatures fall back into the single digits.
Have noted latest mex has a 28f for slk on Monday morning...which
looks reasonable given clear skies...light winds...and prognosticated low level
thermal profiles. Some frost highlights maybe needed.
Otherwise...temperatures will rebound to near normal levels by middle week
with highs back into the 70s to near 80f.
Aviation /12z Wednesday through Sunday/...
through 12z Thursday...aviation challenge today will be timing of
convection. Scattered strong to severe thunderstorms will impact
our taf sites this afternoon. VFR conditions will prevail this
morning...with a light shower possible at slk/mss through 14z. Expect
showers/storms to increase in areal coverage/intensity after 16z
today...with periods of IFR ceilings/visible in the heavier storms. Visible
will range between 1-3sm and ceilings 1500 to 2500 feet above ground level. In
addition...any storms will be capable of strong and gusty outflow
winds...which will create areas of low level turbulence and wind
shear. Dangerous cloud to ground and cloud to cloud lightning will
accompany the storms this afternoon. Expect activity to shift east of
our terminals by 00z Thursday...with generally improving
conditions expected. Some patchy fog/br will be possible toward
06z at slk/mpv and maybe mss.
Outlook 12z Thursday through Sunday... additional storms will be
possible Thursday across our central/southern taf sites of
mpv/rut with a period of MVFR/IFR conditions. Surface high pressure with
VFR conditions develop on Friday...before another front with more
storms occur on Sat afternoon into Saturday evening. These storms will
contain localized gusty winds...brief heavy down pours...and
frequent lightning. Look for breezy south to southwest winds at 15
to 25 knots to develop ahead of approaching surface boundary on
Saturday. A wind shift to the northwest will occur behind the
boundary on Sunday.
as of 432 am EDT Wednesday...strong to severe thunderstorms will
develop across the region this afternoon. Some thunderstorms may
produce locally heavy rainfall...strong gusty winds...small hail
and frequent lightning. A lake thunderstorm advisory for Lake
Champlain may be needed this afternoon. If threatening weather
approaches...seek safe Harbor immediately. Winds and waves will be
locally higher in the vicinity of any thunderstorms. There is also
a chance for some rain showers this morning.