Area Forecast Discussion
Issued by NWS Burlington, VT-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KBTV 200910
Area Forecast Discussion
National Weather Service Burlington VT
510 AM EDT Thu Oct 20 2016
-- Changed Discussion --Stregthening surface low pressure system will bring widespread
rainto the North Country Thursday afternoon through Sunday.
Occasionally heavy rainfall expected, especially this evening into
early Friday. As the front pushes east of the area by early next
week a return to seasonably cooler weather is expected.
-- End Changed Discussion --
.NEAR TERM /THROUGH FRIDAY/...
-- Changed Discussion --As of 510 AM EDT Thursday...Today looks to be the beginning of a
pattern change as 500mb trough continues to dig south and
gradually east over the central USA. Rain will encroach upon the
St Lawrence Valley and Adirondacks in the early afternoon
associated with frontal system moving in from the SW. Question
remains how far north and east it will spread before the deepening
trough and surface low riding up the frontal boundary causes area
of rain to pivot north and west sometime on Friday.
Strong low level deformation associated with front moves into St
Lawrence this afternoon into tonight, leading to heavier rainfall
for Nrn NY, before weakening on Friday. Another consideration for
Friday is sub-tropical system weakening as it heads north far off
the Carolina coast, but moisture looks to get absorbed or wrapped
into the low affecting the Northeast, and could result in
resurgence of heavier precip over eastern VT late Friday into
Friday night, per the 00Z ECMWF. This may be dependent on when the
500mb trough becomes more neutral or negatively tilted late
Winds another concern as strong low level jet enters the region
this afternoon. Southerly jet of 40-55kts at 850mb stays over the
North Country through Friday. This will lead to strong winds
across the higher terrain. Best chances for strong winds to mix
into the valleys would be early Friday as the precip shield pivots
slightly NW, allowing for breaks in precip over VT. Have gusts up
to 15-25kts across most of the area on Friday, before the surface
low tracks over the area.
In summary, cloudy and wet pattern expected throughout the near
term with temperatures in the mid 50s to mid 60s today as we
remain in the warm sector. Tonight temperatures remain mild in the
mid 40s to upper 50s. Forecast max temperatures tricky on Friday
as the surface low and associated front traverse across the North
Country. Timing of FROPA will dictate wind shift of NW-N and
colder air filtering in.
-- End Changed Discussion --
.SHORT TERM /FRIDAY NIGHT/...
As of 351 PM EDT Wednesday...Still expecting a widespread 1 to 3 inch
rainfall during this time period with initial heavy rain axis
across northern NY...but shifting into VT by the weekend. On
Thursday night potent short wave energy will be curving out deep
mid/upper level trof as deep moisture advection takes places
across our region associated with southwest flow aloft. Initially
our cwa will be in the warm sector associated with deep southerly
flow and pws surging to 1.50 inches which is 2 to 3 std below
normal. Both GFS/NAM show low level thermal gradient tightening on
Thursday Night into Friday across Northern NY as weak elongated
surface low pressure develops. This fgen forcing will be enhanced
by nose of 40 to 50 knot low level jet and right rear quad of
departing 250mb of 140 knots over southern Canada. These strong
dynamics combined with abundant moisture will produce an axis of
moderate to heavy rainfall during this time period. Still some
uncertainty to the exact placement of this band...along with
movement on Friday into Friday Night. Thinking heaviest rain
occurs across the Saint Lawrence Valley and Northern Dacks
Thursday Night into Friday Morning...then shifts into northern
Vt/northern Champlain Valley on Friday...before weakening. Have
mention pops at 100% western cwa...and tapered off to high chc/low
likely eastern VT...as models indicate potential mid/upper level
dry slot impacting this area. Also...expecting a tight west to
east qpf gradient...with 1 to 3 inches Saint Lawrence Valley/Dacks
to <0.25" Southeast VT through Friday Night. Exact placement and
amount of qpf in these tight precip gradient forecasts can be very
challenging. Temps start very warm on Thursday night with reading
mainly in the 40s to mid 50s...but as northeast winds developing
on Friday...expect a large gradient between highs only in the
upper 40s to lower 50s west to mid 60s lower CT River Valley. This
gradient could be even stronger depending upon amount of sun in
the CT River Valley on Friday and potential temps near 70f
associated with progged 850mb temps near 10C. Progged 850mb temps
drop below 0c by 12z Saturday across the dacks and into extreme
northern VT...supporting some mix of rain with snow. Have trended
temps aloft toward the cooler guidance...which supports lows near
30f dacks to near 50F CT River Valley....with mainly 40s
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 351 PM EDT Wednesday...Still plenty of uncertainty during this
time period with evolution of mid/upper level system...associated
track of surface low pres...how quickly cold air advects on
backside and amount of qpf. This uncertainty also presents
complication in snow levels for Saturday into Sunday...along with
potential impacts. Using a blend between the faster gfs with the
cold air advection and warmer ecmwf solution and later arrival of
cold air...still supports some accumulating snowfall across the
higher terrain this weekend.
A prolonged upslope/backside deformation precip event is expected
Saturday into Sunday with additional precip amounts of 0.50 to 1.5
across our region...with highest amounts in the
mountains...especially northern dacks and northern/central vt
mountains and parts of the Northeast Kingdom.
The 12z Ecmwf is stronger and closes off 5h/7h circulation over
eastern PA by 12z Saturday...with our cwa still in the warm
sector...until 00z Sunday...delaying arrival of mountain snow.
Meanwhile...gfs is quicker with progged 850mb temps dropping below
0c by 12z over the dacks and across the entire region by 18z
Saturday. Given closed 5h/7h circulation...expecting plenty of deep
layer moisture advecting back into our region...with very favorable
upslope signatures present. This includes northwest between 925mb to
850mb of 35 to 45 knots...strong 850 to 700mb uvv`s...and good 850
to 500mb moisture. The difficult question is how quickly the cold
air advects into the region and associated lowering snow levels.
Current forecast shows snow developing between 12z-15z dacks summits
and between 18z-21z for the northern Green Mountain Summits. NAM/GFS
bufkit soundings show freezing levels dropping to 1500 feet
overnight Saturday into Sunday...with snow levels lowering to base
areas. How much snow will stick with extremely warm ground
temps...and potential impacts with leafs on the trees and power
outages is still too early to tell. The potential for 6 or more
inches is possible at summits with several inches of heavy wet snow
across the higher mountain towns of the northern dacks/green
Eventually the vertically stacked area of low pres lifts toward the
canadian maritimes by early next week and moisture profiles
dissipate. Will mention pops near 100% for Saturday into Sunday in
the favorable upslope areas...and taper off to chance by early next
week. Expecting a large temp contrast from valleys to summits with
highs mainly 30s mountains and 40s valleys on Saturday and upper 20s
mountains to mid 40s valleys on Sunday. Slightly warmer weather
arrives by early next week...as clouds and precip dissipate.
.AVIATION /09Z Thursday THROUGH Monday/...
Through 06z Friday...VFR conditions except at KSLK with IFR to
VLIFR possible this morning. MPV could see brief period of
LIFR/VLIFR centered around 10Z. In the late morning ceilings
lower to around 4000-5000 feet as a front will bring rain showers
to most terminals. Expect rain to affect MSS/SLK/PBG/BTV by early
afternoon. Possible periods of MVFR with confidence of MVFR cigs
and vsbys at MSS/SLK around 19Z onward. PBG/BTV/MPV could see MVFR
conditions after 00Z Friday.
Winds vary greatly due to proximity to front. Overall expect
southerly winds, possibly gusting at times in the afternoon as low
level jet moves over the North Country late this afternoon into
evening. Cannot rule out possible LLWS, especially heading into
Outlook 06z Friday through Monday...
06z Friday through 00z Monday: A prolonged period of unsettled
conditions is expected with widespread MVFR/IFR in periods of
00z Monday through 00z Tuesday: A mix of VFR/MVFR...with VFR/IFR
possible in showers.
-- Changed Discussion --As of 510 AM EDT Thursday...A widespread and long duration
rainfall of 2 to 4 inches with isolated higher amounts expected to
start midday Thursday and ending Sunday. There will be some breaks
throughout the event, especially across portions of Vermont. 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.
-- End Changed Discussion --