Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1022 am EDT Wednesday Aug 20 2014
a ridge of high pressure will move east of the region this afternoon.
A low pressure area over the western Great Lakes will bring
increasing clouds to the north country today...with a chance of showers
and a possible thunderstorm across northern New York late this
afternoon. Skies will become cloudy across north country tonight
with the best chance for showers and possible thunderstorms across
northern New York. Showers will overspread the remainder of the
region on Thursday...with a chance of thunderstorms across
northern New York on Thursday.
Near term /until 6 PM this evening/...
as of 1022 am EDT Wednesday...radiational fog in the eastern Vermont
river valleys has burned off. Regional radar continues to show a
slow northeastward motion to showers and embedded thunderstorms in
western NY/PA. Early morning hi-res reflectivity guidance has
struggled with its timing...though more recent runs point to area
of showers/storms not making it into the St. Lawrence Valley until
later this afternoon...and not until after 00z for the Champlain
Valley area. Adjusted probability of precipitation to match these general trends. Still
think threat of thunder will exist especially with a later timing
allowing for a little better instability (generally at or below 1000
j/kg). It also is a fairly moisture-laden airmass with precipitable waters per
buf/alb radiosonde observations between 1... not excessively so. So
could be a few downpours in steadier rain showers across northern
I did adjust highs up a couple degrees across Vermont as skies
remain mostly clear...and lowered a bit across northern St.
Lawrence Valley area. With surface warm front anchored along the
northern St. Lawrence Valley...slightly cooler/drier air near the
mouth of the St. Lawrence River may filter down on northeast surface
flow. Highs in the 70s for northern New York...and upper 70s to
Lower/Middle 80s in the Champlain Valley.
Short term /6 PM this evening through Friday/...
as of 450 am EDT Wednesday...models in somewhat better agreement
tonight in bringing showers and possible thunderstorms into
northern New York tonight. MOS probability of precipitation look too high across Vermont
tonight...so have gone below MOS guidance from the Champlain
Valley eastward. Thus...have a sharp pop gradient from the
Connecticut valley to the Saint Lawrence valley tonight. The
lowest probability of precipitation over eastern Vermont with the highest probability of precipitation across the
Adirondacks and Saint Lawrence valley in northern New York. Models
in better agreement in bringing showers into Vermont on Thursday.
Thus...have increased probability of precipitation across Vermont on Thursday. Have kept
in a chance of thunderstorms across northern New York on
Thursday...as this is where the best instability will be. On
Friday...upper low slides south of the region with an upper ridge
building south from Quebec. Thus...decreasing chance for showers
on Friday. Have just gone with slight chance probability of precipitation on Friday. The
upper ridge building south from Canada on Friday Marks the start
of a Rex block developing across the region for this weekend.
Long term /Friday night through Tuesday/...
as of 400 am EDT Wednesday...large scale pattern will feature a
blocking type scenario developing across the eastern Continental U.S.. both
European model (ecmwf)/GFS shows a developing closed 500 mb cyclonic circulation over the western
Atlantic and building hght ridge across the central Continental U.S. Into the
Great Lakes by Sunday. This pattern will result in mainly dry conditions
for days 4 through 7 with near to slightly above normal temperatures. Surface
high pressure building down from eastern Canada will push slightly
cooler temperatures into our central/eastern County Warning Area over the
weekend...associated with easterly flow and 850 mb temperatures between 8-10c.
These temperatures support highs mainly in the 70s across our region with
this cooler maritime air will have the greatest impacts on eastern
Vermont...associated with low level easterly follow. Surface high pressure remains
nearly stationary into next week...with building hghts aloft. This
will slowly allow temperatures to climb...with best thermal ridge and
warmest low level temperatures across the Central Plains into the Ohio Valley.
This very warm air mass...has difficulties advecting into our
County Warning Area...given placement of surface ridge and northwest follow aloft...but should
by the middle to end of next week. Prognosticated 850 mb temperatures will warm between
12-14c by next Wednesday...with highs in the M/u 70s mountains/nek to l80s
warmer valleys. Will continue to keep forecast dry as best ulvl support and
middle level moisture is located to our west through the middle of next
Aviation /14z Wednesday through Sunday/...
through 12z Thursday....LIFR in fog will prevail at mpv until
13z...before gradually dissipating. Middle/upper level clouds will spread
from west to east across our taf sites this morning ahead of an
approaching warm front. These clouds will produce scattered showers
across northern New York taf sites by 21z today...and spread into Vermont
by this evening. Initially given the very dry llvls...expecting
some of the moisture to fall as virga. Some MVFR ceilings could
develop at slk by this evening...as moisture increases on
southerly winds. Otherwise...look for light terrain driven winds this
morning...to become south/southeast at 4 to 8 knots today...with
easterly follow at mss.
Outlook 12z Thursday through Sunday... additional showers are
likely into Thursday with periods of MVFR cigs/vis...especially
at slk/mpv. Fog/br will be limited by the increasing clouds and
threat for showers. Surface high pressure across northern Maine will build
into our taf sites on Saturday into Sunday with VFR conditions
likely. The combination of clear skies and light winds will result in
fog/br at slk/mpv both Sat and sun mornings with IFR conditions