Area Forecast Discussion
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FXUS61 KBTV 211750
Area Forecast Discussion
National Weather Service Burlington VT
150 PM EDT Fri Oct 21 2016
Rain event persists over the North Country as a mid-level
longwave trough continues to dig south and east from Canada. This
trough will become negatively tilted late Friday into early
Saturday, keeping frontal boundary, associated surface low
pressure system and rain over the region through Saturday
night/early Sunday. Colder air will filter in behind this system
along with northwest flow producing upslope rain and snow showers
Sunday through Tuesday. Another surface low pressure system looks
to affect the Northeast Thursday.
.NEAR TERM /THROUGH SATURDAY/...
As of 1024 AM EDT Friday...Precip continues to shift more
westward with more widespread breaks across the Adirondacks this
morning, before eastward momentum and additional moisture shift
eastward later this afternoon.
Previous discussion...Bulk of precip over Nrn NY and NW VT this
morning. With mid-level trough expected to become negatively
tilted this afternoon, precip shield looks to pivot NW providing
break in rain to VT and portions of Champlain Valley late morning
to early afternoon. At the same time, NAM and GFS indicate strong
low level deformation producing moderate to heavy rain at times
over Nrn NY, before weakening as we head into the evening hours.
For this afternoon, the most uncertainty lies with exact
positioning of surface low pressure and, therefore, wind direction
as there will be a markedly sharp wind shift over the region.
Models continue to indicate moisture from coastal system will feed
into the NE low pressure system latter half of today into tonight.
This combined with diffluent mid-level flow will result in
possible periods of moderate rain over VT, especially during the
Saturday morning, models find more consensus on surface low
positioning along the southern New England coast, traversing
northward during the day. This means deep NW flow over the North
Country will bring in colder air and terrain enhanced rain
.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 400 AM EDT Friday...Rain will gradually change to snow over
the higher elevations of the Adirondacks and Green Mountains
Saturday night as a closed upper low moves over the region which
will provide dynamical cooling aloft with a change to snow over
the higher elevations. Have leaned toward the warmer GFS MOS
guidance for min temperatures Saturday night, as the NAM MOS
guidance looks too cold. Also, combination of cloud cover and
gusty west winds will help to keep air well mixed and will help to
keep temperatures up. Thus, have lowered snowfall amounts a bit
from the previous forecast given a slower changeover to snow in
the higher elevations.
Models showing precipitation winding down across the region Sunday
morning, with most of the activity done by midday on Sunday.
Models show the region will still be under cyclonic flow Sunday
night from the departing surface low pressure area over Quebec
Sunday night. Have kept in some slight chance pops for rain or
snow showers Sunday night.
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 400 AM EDT Friday...The north country remains under
cyclonic flow from the departing surface low pressure area over
eastern Quebec Monday and Tuesday. Thus, have kept in slight or
low chance pops for rain or snow showers for Monday and Tuesday.
High pressure will build slowly east from the Great Lakes Tuesday
night, with mainly fair and dry weather from Tuesday night through
early Thursday. On Thursday, a warm front will approach the region
from the Great lakes and the Ohio valley. Have put in a chance of
rain showers into the forecast for mainly Thursday afternoon.
.AVIATION /18Z Friday THROUGH Wednesday/...
Through 18z Saturday...Varying flight conditions across the North
Country with persistent low clouds/IFR/MVFR in NY and rains at
KMSS with VFR/MVFR in VT. However...surface cold front moving
south across Champlain Valley has brought IFR/LIFR cigs and this
trend will continue elsewhere.
Precipitation will be in rounds...except at KMSS where it will be
peristent through period. Showers moving North into Taf sites this
afternoon and exiting by evening then just some isold/sct showers
til 15z Sat when more persistent showers/rain returns.
Primarily IFR/LIFR tonight with clouds/drizzle and IFR Saturday
with clouds and showers/rain.
North winds in NY and Champlain Valley will move into rest of VT
and eventually shift to NW for Saturday with 10 knots or less
tonight but increasing and gusty by late Saturday.
The end result...deteriorating conditions with little no changes
Outlook 18z Saturday through Tuesday...
18z Saturday through 00z Monday: A prolonged period of unsettled
conditions is expected with widespread MVFR/IFR in periods of
00z Monday through 00z Wednesday: A mix of VFR/MVFR with upslope
showers in NW flow.
As of 425 AM EDT Friday...Rainfall amounts ranging from 1-1.5
inches have already fallen across the St Lawrence Valley,
northeastward across the northern Champlain Valley this morning.
Rain will continue today through Sunday, being most persistent
over the St Lawrence Valley and Adirondacks. An additional 1 to 3
inches is expected. Given most of the region is in moderate to
severe drought...we are not anticipating any widespread hydro
issues. However...some minor urban and street flooding is possible
associated with the heavier rainfall rates on Friday with leaves
clogging storm drains. Otherwise...some modest rises in local
rivers and streams are likely this weekend...but no widespread
flooding is anticipated.