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  Thursday July 19, 2018

 

NWS Area Forecast Discussion


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FXUS61 KBTV 161745
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
145 PM EDT Mon Jul 16 2018

.SYNOPSIS...
Hot and humid weather is expected today as high pressure shifts
to our east. A cold front will approach from the west tonight
and push eastward through the forecast area through Tuesday
evening. Along and ahead of the front, showers and a few
embedded thunderstorms will develop tonight and become more
widespread Tuesday during the frontal passage. A few stronger
storms are possible, containing heavy rainfall and dangerous
cloud to ground lightning. Once the front exits to the east
Tuesday evening, surface high pressure and ridging aloft will
keep the area mainly dry through Friday. Unsettled weather
returns for the weekend as the upper-level ridge overhead
breaks down.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 1029 AM EDT Monday...Going forecast remains in good shape
for today with only a slight adjustment made to lower PoPs for
this morning through early afternoon. Still appears as if deeper
moisture doesn`t arrive until after 00Z with perhaps an
isolated terrain driven shower possible beforehand. Otherwise,
another mainly dry and hot day still looks good.

Previous Discussion...
Upper-level ridge axis is right overhead this morning, which is
supplying favorable conditions for some effective nocturnal
radiational cooling. As the ridge axis and surface high pressure
shifts eastward today, will see flow becoming southwesterly,
supporting increasing warm air/moisture advection. 925 temps
will climb to around 25C today. Should see some increasing cloud
cover throughout the day as instability and moisture increase,
but still expecting high temperatures to top out in the low 90s
in lower elevations and upper 80s elsewhere. In addition to the
well above normal temperatures today, the "mugginess" factor
will also be on the increase as we tap into the tropical air
mass that has been lingering over the southeastern United
States. Dewpoints will climb to the low to mid 60s today,
supporting heat indices that will approach the mid 90s for an
hour or two in the Saint Lawrence and Champlain Valleys. While
we will be close to heat advisory criteria, thinking enough
drier air will be mixed down from aloft during the afternoon
hours such that dewpoints will drop a few degrees during peak
heating. This will limit heat indices to just below heat
advisory criteria, but a hot and muggy day is still expected.
Prepare accordingly if you have outdoor plans today, limiting
time in the sun and drinking extra water.

We could see a stray afternoon convective shower or two pop up
today, particularly along the mountains, but expecting coverage
to be fairly limited as forcing is not great. That changes
overnight though, with increasing warm air and moisture
advection along with height falls aloft supporting more
widespread coverage of showers. We will also see increasing
elevated instability overnight, so some thunderstorms are not
out of the question. Lows tonight will be quite warm...low 70s
in the Champlain and Saint Lawrence Valleys and upper 60s
elsewhere. Along with the warm overnight temperatures, dewpoints
will climb through the night and it will feel fairly humid and
uncomfortable for sleeping.

Tuesday morning, a cold front will approach the Saint Lawrence
Valley from the west, providing more focused precipitation for
northern New York through the morning hours. By early afternoon,
the front will move into Vermont, and move east into New
Hampshire by the evening hours. The general setup Tuesday
continues to look favorable for widespread rainfall and some
thunderstorms along and ahead of the frontal boundary.
Instability won`t be overly impressive under mostly cloudy
skies, but forecast values of 500 to 1500 J/kg will be
sufficient to support convective showers and thunderstorms. Due
to the impressive amount of moisture in the atmosphere, a deep
warm cloud layer as indicated by forecast soundings, and the
tall, skinny CAPE profiles, continuing with the thinking that we
could see locally heavy rainfall within any thunderstorms that
develop. The upper level trough will lag slightly behind the
front, so the best shear will not be collocated with the frontal
passage. However, still expecting 20+ kts of 0-6 km Bulk Shear
along the front, so we could see some storms organize into
multicells. The best chance for organized convection looks to be
in central and eastern Vermont in the late afternoon/evening
hours as the upper level wave starts to catch up with the front.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 312 AM EDT Monday...Mid/upper level trof will deepen
across the ne conus behind sfc cold front. CWA is under modest
low level caa on Tue Night with some gradient from building high
pres and departing cold front. Best potential for fog
development would be across northern NY on Tues Night and maybe
some patchy development toward sunrise on Weds across central VT
valleys. Lows mainly in the upper 40s to upper 50s. 1022mb high
pres over the central Great Lakes will build into our cwa on
Weds with much cooler and drier air on northwest winds. Progged
850mb temps range btwn 10-12c on Weds, supporting highs in the
lower 70s mountains towns to m/u 70s warmer valleys with
northwest winds 5 to 10 mph. Deep dry layer from building high
pres and subsidence aloft will promote mostly sunny skies,
except a few fair wx cumulus clouds over the trrn during peak
heating as convective temps are reached. High pres will provide
cwa with clear skies and light winds on Weds night, supporting a
sharp drop in temps once the sunsets. This will allow sfc temps
to reach cross over values with patchy fog developing in the
deeper/protected valleys of northern NY and central/northern VT.
Have trended toward the ECE guidance, which shows a 38f for
slk, which seems reasonable. Expecting lows to range from the
upper 30s NEK to mid 50s cpv on Weds night. Fog development will
limit rate of temp fall during the early morning hours.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 312 AM EDT Monday...The combination of building mid/upper
level ridge and 1020mb high pres will keep our cwa dry through
Friday with warming temps. Expecting a large swing in daily
temps from cool overnight lows and mild afternoon highs, as deep
dry layer remains overhead. 925mb to 850mb thermal profiles warm
1 to 3c everyday, supporting highs upper 70s to l/m 80s on
Thursday, with lower 80s mountains to near 90 warmest valleys on
Friday. These warmer temps are supported by progged 850mb temps
near 15c on Friday with 925mb values btwn 22-23c. These values
warm another degree or two on Saturday with 16c at 850 and 24c
at 925mb, supporting another very warm day across the region.

Latest trends in guidance shows mid/upper level ridge slowly
breaking down on Saturday into Sunday, as northern stream short
wave energy helps to deepen trof across the central Great Lakes.
Still plenty of uncertainty on magnitude/timing of mid/upper
level trof, along with potential impacts across our cwa. Deep
southerly flow ahead of trof will help to advect higher
atmospheric moisture back into our fa by Sunday as pws surge to
near 2.0. In addition, strong short wave dynamics with trof and
associated boundary will provide synoptic scale lift for showers
and storms, especially on Sunday into Monday. Therefore have
trended pops toward high chc for Sunday, based on good agreement
in models of available moisture/forcing across our fa. Still
some question if trof is deepen enough to produce secondary
coastal development along boundary and if this could enhance
rainfall across our fa. Temps with clouds/precip will hold in
the 70s to lower 80s, but higher humidity values are likely
especially on Sunday into Monday of next week.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
Through 18Z Tuesday...VFR conditions will largely persist
through 12Z Tuesday with low/mid clouds increasing after 00Z as
a cold front approaches from the west. Some widely scattered
showers remain possible during the overnight, but the bulk of
precipitation associated with the front comes after 12Z where
brief MVFR/IFR in TSRA is possible, especially from the
Champlain Valley eastward. Variable winds less than 10 knots
this afternoon trend light and variable overnight before
shifting out of the south/southwest after 12Z and increasing to
10-15kts.


Outlook...

Tuesday Night: VFR. Slight chance SHRA, Slight chance TSRA.
Wednesday: VFR. NO SIG WX.
Wednesday Night: VFR. Patchy BR.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. NO SIG WX.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. Chance SHRA.

&&

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

&&

$$
SYNOPSIS...RSD
NEAR TERM...Lahiff/RSD
SHORT TERM...Taber
LONG TERM...Taber
AVIATION...Lahiff



 
 
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