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  Monday August 20, 2018

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 190547
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
147 AM EDT Sun Aug 19 2018

.SYNOPSIS...
High pressure will build into the region tonight through early
next week with fair and dry weather expected. The next chance of
rainfall occurs toward the middle of next week as a frontal
system crosses the area. Temperatures will average near to
slightly above normal through the period.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1212 AM EDT Sunday...Quick midnight update to bring in
fog slightly faster than anticipated. Many locations have
already cooled to or are near to cooling to their crossover
temperatures (upper 50s to low 60s), so expecting fog to become
more widespread over the next couple of hours. Some areas will
see patchy dense fog, but this should be fairly localized. The
Burlington Airport continues to report 1/4 sm visibility, but
webcams show other areas of Burlington fog-free. Looking at
observations and webcams throughout the forecast area, patchy
fog, dense in some places, seems to be the rule throughout. With
high pressure building in, calm winds, saturated soils...see no
reason for much improvement in visibilities overnight. Morning
sun will likely do the trick...so have fog persisting through
sunrise, then improving shortly thereafter. No other edits
needed.

.PREVIOUS DISCUSSION...
After a mainly cloudy and seasonably cool day, skies should
trend partly cloudy to mostly clear in most areas tonight as
surface high pressure builds east from the Great Lakes/southern
Ontario. Some clouds may linger far south through about midnight
as yesterday`s cold front continues to pull southward through
the southern portions of NY and New England. Outside a stray
light shower or sprinkle in these far southern counties through
early evening, dry weather is expected. Patchy fog will also be
a good bet, especially across central and northern counties
where clearing will occur sooner. Leaned close to most recent
NAM 3km output in this regard, which typically handles lower
boundary layer moisture profiles the best among CAMs under these
conditions. Low temperatures a blend of bias- corrected MOS
output showing readings bottoming out mainly in the 50s, though
locally around 60 in mildest spots of the Champlain/Lower CT
River Valleys.

By tomorrow into tomorrow night fair and dry weather continues as
the aforementioned surface high bridges atop the region. The only
subtlety will be a developing kink/gyre in the mid level flow across
southern New England during this period which may act to through a
few clouds back into our eastern counties through the
daylight/evening hours. Dry air in the lower levels associated with
the surface high should prevail north and west with mostly
sunny/clear conditions expected. High temperatures should range from
the upper 70s to lower 80s in most spots which is supported nicely
by model blended 925 mb thermal progs. Lows Sunday night to be quite
similar to tonight with some slight variability as is customary
under light wind/mainly clear sky regimes.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
As of 251 PM EDT Saturday...The period of drier and cooler weather
will continue on Monday and the first half of Tuesday with both
high pressure aloft and at the surface residing over the North
Country. The drier air will continue to keep skies mostly clear
which will help warm Monday and Tuesday into the mid 70s to
lower 80s. Neither showers nor thunderstorms are expected to
develop during the beginning of the week as instability will be
non-existent. This is due to a lack of moisture and a very
strong subsidence inversion around 825 mb will keep the
environment extremely stable.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 251 PM EDT Saturday...The weather pattern begins to get more
active Tuesday night as a warm front approaches from the
southwest. Between 21Z Tuesday and 06Z Wednesday, precipitable
water will increase from around 0.75 inches to about two inches
as southerly flow aloft will tap into a very moist air mass.
The main axis of moisture will lag about 6 hours behind the
baroclinic zone ahead of developing surface low tracking across
the Great Lakes region and moves northeast toward Montreal. This
should initially keep rainfall rates pretty light initially
with heavier rainfall developing after midnight on Tuesday and
continuing into Wednesday. Looking at how moist the air mass is
becoming and how quickly it will be doing so, have opted to
remove the mention of thunder as lapse rates throughout the
entire column shift to moist adiabatic values. Nevertheless,
upper level support becomes quite favorable as much of the North
Country is under upper level diffluence and the left exit
region of the jet which could create some locally heavy rainfall
as high precipitation rates will be possible. That being said,
it wouldn`t be surprising to see rainfall amounts between a
quarter and three quarters of an inch with some locally higher
amounts.

Rainfall will taper off late Wednesday with a strong push of drier
air following a frontal passage. This should allow for skies to
rapidly clear overnight Wednesday into Thursday with mostly clear
skies expected on Thursday. We will remain in the influence of the
upper level trough Thursday and Friday which will give much of the
North Country a nice northerly wind component and will help to keep
temperatures in the mid 70s to around 80 degrees. The trough looks
to exit the region on Saturday and a high amplitude upper level
ridge will replace this feature and allow for temperatures to warm
above normal values once again. Overall, following the rain late
Tuesday and Wednesday, the long term looks like a nice period of
weather for late August.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Through 06z Monday...The combination of high pressure building
in overnight, clear skies, calm winds, and recent rainfall will
support ongoing fog, dense at times through the night. Expecting
LIFR conditions to develop/continue through 12Z at KBTV, KMPV,
KSLK. Visibilities/ceilings at KMSS/KPBG will bounce between IFR
and VFR through the night. Mid to low-level cloud deck over
southern Vermont will keep fog from developing at KRUT, however
if they are able to clear out overnight, the potential for fog
exists. Confidence is lower in clearing at KRUT, so have kept it
out of the TAF for now. Throughout the forecast area, fog and
IFR conditions improve to VFR after 14Z. Winds will be calm
overnight, becoming easterly/northeasterly during the day.

Outlook...

Monday: VFR. NO SIG WX.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. Chance SHRA.
Tuesday Night: Mainly MVFR, with areas VFR possible. Definite
SHRA.
Wednesday: Mainly MVFR, with local IFR possible. Chance SHRA.
Wednesday Night: Mainly VFR, with areas MVFR possible. NO SIG WX.
Thursday: VFR. NO SIG WX.

&&

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

&&

$$
SYNOPSIS...JMG
NEAR TERM...JMG/RSD
SHORT TERM...Clay
LONG TERM...Clay
AVIATION...RSD



 
 
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