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  Tuesday August 20, 2019

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 201348
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
948 AM EDT Tue Aug 20 2019

.SYNOPSIS...
Plenty of sunshine with comfortable temperatures and humidity
levels can be expected today across the North Country. Highs
generally in the mid 70s to lower 80s with light winds. An
active day is anticipated on Wednesday with showers and
thunderstorms likely, especially during the afternoon hours. A
few stronger storms are possible, which will be capable of
producing gusty winds, small hail, localized heavy rainfall, and
frequent lightning. Cooler and drier weather returns toward the
end of the week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 943 AM EDT Tuesday...No changes needed to the forecast
this morning with full sunshine and high pressure building in. Previous
discussion follows.

North Country Chamber of Commerce weather today with plenty of
sunshine and mild temperatures, along with lower humidity
levels. A weak cold front has passed through our cwa overnight,
resulting in advection of drier and slightly cooler thermal
profiles. Highs today generally in the mid 70s to lower 80s,
maybe a few mid 80s cpv, given deep mixing with such dry
profiles.

The aforementioned cold front will lift back north as a warm
front late tonight into early Weds. This boundary, along with
some increase mid level moisture and weak embedded 5h vort
sliding across our fa, may produce just enough ingredients for a
few showers/embedded storms. Have pops increasing to chc by 12z
Wed with some isolated mention of thunder, due to increasing
instability parameters above shallow inversion. Temps tonight
mainly in the upper 40s to l/m 60s with comfortable humidity
values.

Expecting an active Weds with development of showers and
thunderstorms likely during the aftn/evening hours. SPC has
placed most of our cwa in slight risk for severe, but still some
uncertainties on degree of instability and limited convergence
as a series of boundaries swing across our fa. It seems
ingredients look very favorable a day or two out, but when event
is here, several factors combine to limit the intensity and
coverage of storms of so far this convective season.

Thinking warm front lifts north of cwa by 15z, with most of our
region well established in the warm sector with climbing bl
temps/dwpts. Temps will warm well into the 80s with dwpts
approaching 70f in the slv/cpv by mid aftn. This will help to
destabilize our atmosphere with sfc based cape ranging from 1500
to 2500 j/kg, with highest values in the CPV on Weds aftn.
Meanwhile, developing low level jet of 25 to 30 knots, along
with increasing 700 to 500mb wind fields from approaching
mid/upper level trof will enhanced favorable 0 to 6 km shear of
35 to 45 knots. These ingredients all support severe storms with
some organization on Weds, along with sounding data indicating
an EML of 6 to 7 C/km lapse rates btwn 700 and 500mb.
Furthermore, good height falls are expected with approaching
trof. However, still some uncertainty on amount of sfc
instability due to potential clouds and limited low level
forcing, as a series of boundaries will be crossing our cwa. The
00z NAM NEST composite reflectivity progs are not all that
impressive across our cwa either, but ARW and HRW WRF NSSL are
much more robust, indicating the potential for strong/severe
storms. Sounding thermodynamics and wind profiles would support
some organized convection with bowing line segment/multi-cell
convective mode. Gusty to localized severe winds would be
primary threat, with some low level turning of profiles,
especially where trrn (SLV/CPV) influences the local wind
direction. Have mention potential threat in HWO for now, but
given uncertainty on forcing and instability have not placed
enhanced wording in forecast yet. Still plenty of time for
dayshift or mid shift to add wording and fine tune
location/timing of convection in the next 12 to 24 hours. As
with any convection, localized heavy rainfall and frequent
lighting is anticipated with any storms on Weds.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 320 AM EDT Tuesday...The main weather feature for Thursday will
be the passage of a cold front associated with a deepening low
pressure system across Quebec. Still some timing differences among
the models on when the front will pass with ECMWF slowest of the
solutions and GFS the fastest. Have settled on a blend between the
two, very similar to NAM timing with FROPA arriving between 12-18z
from west to east. Winds aloft will turn out of the west advecting
in lower dewpoints but better cold air advection does not arrive
until overnight Thursday into Friday with the passage of a secondary
cold front. Temperatures Thursday will still be ~6-10 degrees cooler
from Wednesday with highs in the mid 70s mountains and St Lawrence
Valley to around 80 elsewhere. As mentioned by previous forecaster
the passage of this front should be relatively uneventful with some
showers and possibly isolated embedded thunderstorm. Model progs
indicate very narrow band of moisture with this feature and weak
elevated instability and meager SB CAPE around 300-600 J/kg. Have
generally offered 30s-50s PoPs with highest chances across St.
Lawrence valley and International Border with lowest chances for our
southern counties.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 320 AM EDT Tuesday...No real changes made to the extended
forecast with upper level troughing remaining in place through
Friday/Saturday. Secondary cold front and reinforcing shot of cold
air arrives Friday with a slight chance of showers possible across
the northern mountains and Northeast Kingdom of Vermont. Partly
cloudy skies are expected with temperatures topping out in the mid
60s to around 70. Overnight lows will drop below normal into the mid
40s to mid 50s. Similar conditions are expected for Saturday under
mostly sunny skies. After this, upper level pattern becomes highly
amplified across the eastern US with high pressure and dry weather
expected trough midweek. Temperatures warm a couple degrees each day
with near normal highs in the mid 70s to around 80 to lows in the
low to upper 50s.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
Through 12Z Wednesday...Very limited fog last night with SLK
only reporting VLIFR in fog, which will lift shortly. Otherwise,
high pres will produce vfr conditions for the next 12 to 24
hours. Mid level clouds overspread our taf sites after 06z
tonight which may limit fog/br development. Light winds become
south 3 to 6 knots today and light trrn driven overnight.

Outlook...

Wednesday: VFR. Likely SHRA, Chance TSRA.
Wednesday Night: Mainly VFR, with local MVFR possible. Chance
SHRA, Slight chance TSRA.
Thursday: Mainly VFR, with local MVFR possible. Chance SHRA.
Thursday Night: VFR. Slight chance SHRA.
Friday: VFR. Slight chance SHRA.
Friday Night: VFR. NO SIG WX.
Saturday: Mainly VFR, with local MVFR possible. NO SIG WX.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.

&&

$$
SYNOPSIS...Taber
NEAR TERM...Duell/Taber
SHORT TERM...LaRocca
LONG TERM...LaRocca
AVIATION...Taber


 
 
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