Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 301850

Area Forecast Discussion
National Weather Service Burlington VT
250 PM EDT Fri Sep 30 2016

Upper level low pressure over the Ohio Valley will weaken as it
slowly lifts across New England over the upcoming weekend. Mostly
cloudy skies and scattered showers will result, though pronounced
periods of dry weather are also expected. With the abunance of
clouds temperature ranges will be narrower than normal with
seasonably cool daytime highs and relatively mild overnight lows
through Monday.


As of 245 PM EDT Friday...A relatively quiet night remains in
store for the forecast area. The blocking high pressure across
central Quebec which has provided our area with ideal early fall
weather will continue to slowly weaken while increasing mid to
high level moisture increases in advance of upper level low
pressure across the Ohio Valley. There has been some light shower
activity associated with this latter feature across southern New
England and portions of central/upstate New York this afternoon,
though the abundance of dry air in the lower levels has largely
inhibited this activity across our area. In regard to pcpn threat
tonight I stayed close to inherited guidance with some emphasis on
the latest CAM output which suggests the primary threat of light
pcpn should occur across our western counties (mainly western
Dacks/SLV) this evening, transitioning to areas of
central/southern VT later tonight as better moisture plume rides
northward. Areas across the northern Champlain Valley and in
general the northernmost tier of counties should remain largely
dry overnight. Low temperatures should be similar to last night
given thickening upper cloud cover will limit raditional processes
- mainly 40s to around 50.

By tomorrow a mainly persistence forecast will be offered as upper
low pressure will remain nearly stationary across the Ohio Valley
allowing modest south to southeasterly flow to continue into our
area. Deeper moisture and better threat for scattered light showers
will be tied to either 1)a weak plume across central/upstate New York
on the upper low`s eastern periphery, or 2)across
southern/southeastern New England where a maritime airmass with PWATs
to 1.5 inches will reside. Further north across the intl border and
northern Champlain Valley conditions should again remain largely dry.
Only notable larger-scale change was to lower high temperatures by
several degrees over prior forecast. This is consistent with over
half of the consensus blended output and in closer agreement with
latest MOS guidance which show values mainly from the mid 50s to
lower 60s (perhaps a few mid-60s in the SLV).


As of 249 PM EDT Friday...

Little substantive change noted in today`s 12z guidance suite
pertaining to the forecast for Saturday night through Sunday night.
A very slow-evolving upper low over the Ohio Valley begins to pivot
north-northeastward through the period, and beginning to deamplify
as it does so. The system will continue to advect Atlantic moisture
northward, but will run into lingering weak subsidence associated
with a weak ridge across our northern counties. Forecast challenge
remains timing a period when PoPs may be highest. While PoPs are
generally in the Slight Chance to Chance range through this period,
overall forecast QPF is kept very low - on the order of a few
hundreths. It looks at this point that Saturday night may be a
period where a greater coverage of showers may exist, with a break
Sunday before ramping up late Sunday night. While temperatures still
trend above-normal compared to 30-year normals, blanket of overcast
skies through the weekend will lead to narrow diurnal ranges with
cooler highs and "milder" lows. Highs Sunday in the 60s, though may
struggle to climb much above 60 in eastern VT. Lows Saturday night
in the 40s to lower 50s and Sunday night upper 40s to mid 50s.


As of 249 PM EDT Friday...

Continuing a trend with last night`s 00z global guidance, today`s
12z guidance suite continues to indicate that Monday would offer the
best chance at widespread, if light, rain. This is as the
deamplifying upper-level low from the previous period evolves into
an open wave trough and gets entrained in the broader belt of
westerlies. While PoPs are the highest in the Monday period - high
Chance to low Likely - precipitation is expected to be showery
driven mainly by cold pool aloft and any weak instability that can
be generated. Temps still in the 60s for highs and lows in the
40s/around 50.

A period of generally dry conditions is then anticipated Tuesday
through the remainder of the period, as CONUS 500 mb pattern becomes
more amplified with a large upper level ridge over the eastern third
of CONUS with a digging trough over the central US. Anticipating
more sunny skies and larger diurnal temperature ranges (milder than
normal highs in the mid 60s to low 70s and cooler but seasonable
lows 40s to low 50s). Will be looking at how Matthew evolves over
the next several days in the Caribbean/Bahamas, but at this point
in time guidance does not suggest any impact to our area. See the
latest forecasts at NHC`s website for more details on Matthew`s
current and forecast evolution.


.AVIATION /19Z Friday THROUGH Wednesday/...
Through 18Z Saturday...Generally BKN/OVC mid to high level VFR
cigs over the next 24 hours as upper low pivots to our distant
southwest. Cigs mainly above 100 AGL until later tonight into
Saturday when some patchy bkn cigs in the 050-090 AGL range may
encroach into southern VT/KRUT terminal with a threat of light
showers/sprinkles. Remainder of forecast area should remain
largely dry/pcpn free through the forecast period. Winds generally
light east to southeasterly with occasional gusts to 20 kts
possible at KRUT through 00Z due to downsloping effects.

Outlook 18Z Saturday through Tuesday...

18z Sat - 12z Tue: Mainly VFR with brief bouts of MVFR/sct showers
as upper low drifts into the region while weakening over time.
Much of the period will remain dry.

12z Tue onward: Mainly VFR with building high pressure.




SHORT TERM...Loconto
LONG TERM...Loconto
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