Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
742 PM EDT Tuesday Jul 22 2014
a weak area of high pressure will be off the New England coast overnight.
A cold front will move south from Canada on Wednesday. This cold front
will bring showers and thunderstorms to the north country Wednesday
and Wednesday evening. Some of the thunderstorms will produce
strong gusty winds and locally heavy rainfall. A high pressure area
will build into the region on Thursday bringing cooler and drier air
to the north country...with high temperatures in the 70s on Thursday.
Near term /until 6 am Wednesday morning/...
as of 736 PM EDT Tuesday...after reaching 90f at btv this
afternoon...daytime cumulus clouds have largely dissipated early
this evening with onset of diurnal cooling cycle. Will have a
quiet albeit moderately humid overnight period with just some
prevailing thin cirrus clouds...mainly across the northern half of
the forecast area. Surface winds will continue light south to
southwest. These factors will hold overnight lows near 70f in the
Champlain and St. Lawrence valleys...and generally middle-upper 60s
elsewhere across the forecast area. Similar to last night...anticipate
some patchy fog development after midnight in the CT valley and
nearby river valleys.
Short term /6 am Wednesday morning through Thursday night/...
as of 402 PM EDT Tuesday...a cold front will be entering the
Saint Lawrence valley in northern New York Wednesday morning.
Conditions still remain favorable for strong to severe
thunderstorms across the region on Wednesday...with 0-6km bulk
shear values of 30-40 kts and convective available potential energy of 1000-2000 j/kg. Precipitable water values
of around 1.8 to nearly 2.0 inches. Wet bulb zero values are well
above 11000 feet and approach 12000 feet...so hail threat is minimal.
The main threat from some of the stronger thunderstorms on
Wednesday will be for strong gusty winds and locally heavy
rainfall. Unidirectional flow of 30-40 knots aloft also suggests
these storms will be moving along...so not concerned with any
flash flooding issues at this time. Could see some ponding of
water in poor drainage areas. Have included enhanced wording in
the forecast for Wednesday for strong gusty winds and locally
heavy rainfall. Still expecting some showers and storms to linger
into early Wednesday evening...but expecting most of the activity
will be done by midnight Wednesday night.
High pressure to build into the region on Thursday and remain through
Thursday. Much cooler and drier air will move into the region on
Thursday with highs only in the 70s. Lows Thursday night will be
in the 40s to lower 50s.
Long term /Friday through Tuesday/...
as of 318 PM EDT Tuesday...moving on into Friday and
Saturday...partly sunny and pleasant conditions continue with
just a slight chance for a shower across the higher terrain
Friday afternoon as we remain under cyclonic flow aloft from a
upper low to our north. Highs will range right around normal in
the middle 70s to low 80s...and lows in the 50s. Pattern becomes a
bit more unsettled and uncertain from Saturday night Onward with
latest medium range guidance at odds in the handling of a
shortwave entering the Canadian prairies Friday interacting with
the upper low/trough over eastern Canada. Overall the GFS phases
the shortwave into the trough much faster than the
European model (ecmwf)...shifting it into the Great Lakes region Sunday morning.
European model (ecmwf) solution supports this idea as well...just only 24 hours
later. For now will split the difference on timing and continue
to offer chance probability of precipitation for Sunday/Sunday night.
Better support for more widespread showers and storms comes
Monday with good model agreement as the upper low over James Bay
retrogrades westward and deepens over the Great Lakes Sunday
night leaving the north country unsettled in southwest flow
aloft. System is slow to shift east so we could be looking at a
wet few days to start the work week. Overall...right now dynamics
not overall strong so not thinking anything too
significant...just some garden variety showers thunderstorms.
Aviation /00z Wednesday through Sunday/...
through 00z Thursday...generally VFR overnight...with brief
period of MVFR possible at kslk. Diurnally driven cumulus clouds
dissipating this evening...with some high cirrus clouds gradually
lifting northward. Surface ridge weakening as pressure gradient
increases ahead of a surface cold front...currently over the central
Great Lakes region. So in the waning hours of ridging high
pressure...expect mostly clear skies by 06z/Wed...and light winds
around 5kts or less. Clouds begin to encroach upon the region
from the west...with broken/overcast skies reaching kmss around 12z.
After 12z...cold front shifts towards the region with rain showers and
thunderstorms and rain possible after 15z at kmss...progressing eastward through
the afternoon. With tightening gradient...winds will quickly
increase out of the south-southwest-SW at 8-12kts with gusts of 15-25kts by
Rain showers/thunderstorms and rain ahead of cold front expected to reach cpv and kmpv between
16z and 19z...reaching krut last as the front progresses southeastward.
Rain showers/thunderstorms and rain will be capable of heavy downpours and gusty
winds...deteriorating conditions to MVFR/IFR at times. Kmss
likely to see precipitation ending towards end of taf period.
Outlook 00z Thursday through Sunday...
00z Thursday - 06z Thursday...VFR with brief period MVFR/IFR in heavy
showers/T-storms with frontal passage. Storms could be
strong...capable of turbulence and heavy downpours with limited
risk of small hail.
06z Thursday - 12z Thursday...most tafs VFR. However...possible IFR or
lower visibility in fog/mist at slk and possibly mpv pending
12z Thursday - 00z Monday...VFR under high pressure. Late night and early
morning IFR or lower visibility in fog/mist at mpv and slk
possible. An isolated afternoon shower over the higher terrain is