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  Wednesday May 22, 2019

 

NWS Area Forecast Discussion


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573
FXUS61 KBTV 221422
AFDBTV

AREA FORECAST DISCUSSION
National Weather Service Burlington VT
1022 AM EDT Wed May 22 2019

.SYNOPSIS...
Surface high pressure building in from southeast Ontario and
western New York will crest across the North Country, bringing
fair and seasonable weather conditions today. The dry weather
will be short-lived as an upper level disturbance brings
scattered showers and thunderstorms to the region late in the
day Thursday, into Thursday night. A few strong to severe
thunderstorms are possible late in the day Thursday, mainly
from the Champlain Valley westward across northern New York.
Another frontal system will bring renewed prospects for rain
late Saturday into Saturday night, with drying conditions on
Sunday as the frontal system shifts east of New England.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 1015 AM EDT Wednesday...Current forecast for today is well
on track with mostly sunny skies prevailing across the North
Country. Winds are slightly stronger and gustier than initially
thought as we mix down some winds from around 900 mb but all
models show this core of stronger winds exiting to the east by
noon which should put an end to the gusty winds. Expect cloud
cover to begin building during the afternoon hours from the west
as we see cirrus blow off from convection further west work it`s
way into the region.

Previous Discussion...Low of 28F at KSLK early this
morning. Temperatures will rebound quickly under mainly clear
skies. Synoptically quiescent conditions today as low-mid level
ridge axis crests over the North Country. Winds will be lighter
compared to yesterday, but still continuing north at 5-10 mph,
and locally nely across far nrn NY. After a chilly start early
this AM, temperatures will moderate with highs 65-70F (about
8-10deg warmer than yesterday) aided by full morning sunshine
and filtered sun thru increasing cirrus layer this afternoon.
PoPs NIL.

As sfc ridge axis shifts ewd into the Gulf of Maine tonight,
will see developing light S-SE low-level flow, and a sfc-850mb
warm front developing across w-central NY. Within the frontal
zone, a few showers are possible late tonight, though moisture
and absence of deep-layer forcing for ascent will be limiting
factors. Weak isentropic ascent is best from the Adirondacks
sewd into s-central VT. Accordingly, placed a slight chance of
rain showers in this area 06-12Z Thursday. Otherwise, just
expecting partly to mostly cloudy conditions with increasing
mid-level cloud cover. The clouds will help keep overnight lows
in the 40s.

Thursday looks to be an interesting day. Weather conditions
begin quiet with increasing south winds. Could see some gusts
20-30 mph across nrn NY into the Champlain Valley by early
afternoon as p-gradient increases. Vigorous 700-500mb shortwave
trough moving rapidly ewd across the northern Great Lakes region
will result in increasingly cyclonic flow field and strong mid-
level height falls across nrn NY into VT between 21-00Z. The
North Country will also be in a favored left exit region of a
70-75kt 700mb jet moving ewd in conjunction with the shortwave
trough, and flow up to 125kt at 250mb toward early evening.
Appears a pre-frontal trough will develop across central/nrn NY
late in the day in response to daytime heating and increasing QG
forcing upstream, and should serve as a focus for initiating
convective cells. Storms could be fast-moving, given strength of
background flow field. Thermodynamically, conditions are a bit
marginal for strong convection, as duration of low-level
moisture return is limited to 12-18 hrs. Appears PBL dewpoints
will only recover into the 50s Thursday afternoon, except
locally near 60F dewpoints across St. Lawrence County NY. While
moisture will be a limiting factor, mid-level lapse rates appear
favorably steep (7-7.5 C/km), with small residual plume of
elevated mixed layer air making it into the region with the fast
flow regime, per 00Z GFS solution. This will aid in updraft
intensity. Also, modest sfc- 850mb thermal ridge axis, with
valley temps warming into the low-mid 70s, should be sufficient
to develop near 1000 J/kg of surface-based CAPE across the
western half of our forecast area. Given very strong low- mid
level wind fields, including sfc-6km bulk shear around 60kts,
these modest CAPE values should be sufficient for the
development of a few strong to severe thunderstorms across nrn
NY mid-late Thursday afternoon, perhaps moving into western VT
toward the late afternoon and evening hours. As such, included
mention of small hail and gusty winds in the forecast, and have
included a mention of potential strong to severe storms on
Thursday in the morning Hazardous Weather Outlook. PoPs increase
to 60-70 percent as best forcing moves through 21-00Z Thursday,
when combination of forcing and instability should be maximized
over much of the forecast area.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/...
As of 316 AM EDT Wednesday...A compact upper-level shortwave
with a surface low reflected at the surface will track from
southern Quebec southeastward to the Gulf of Maine Thursday night.
Instability over the forecast area will increase with 500+ J/kg
of CAPE expected to develop Thursday evening into early Friday
night within the warm sector of the fast-moving cyclone. A pre-
frontal trough will move eastward through the area during the
early overnight hours, and although the nocturnal timing of the
trough isn`t ideal, good dynamic support aloft (DPVA, favorable
jet dynamics) coupled with the expected instability will
support some thunderstorms continuing into Thursday night.
Relatively steep mid-level lapse rates, dry air in the mid-
levels, and a 40-50 kt low/mid-level jet will support a threat
for gusty winds and small hail in any of the stronger storms.

Precipitation and thunderstorm chances will significantly decrease
after midnight behind the trough with the loss of instability
and moisture. The remainder of the night will be quieter with
just some residual orographic showers tapering off over higher
elevations as the system`s cold front passes uneventfully
through the area. Lows will be in the low to mid 50s.

Friday will be drier and breezy behind the cold front. Forecast
soundings are indicating low-level moisture getting trapped
under a building subsidence inversion through the morning, so
the day will start off with plenty of low clouds over the area.
However, much of the low-level cloud cover will mix out through
the afternoon, and it should turn into quite a pleasant, partly
sunny day. Highs will be in the low to upper 60s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 316 AM EDT Wednesday...The progressive weather pattern
will continue through the long term as we remain in fast, zonal
flow on the northern fringe of a strong ridge of high pressure
centered over the southeastern US.

Friday`s dry weather will continue into Friday night, but a warm
front pushing into the area Saturday will bring the next round
of precipitation to the North Country. The warm front is
associated with an upper-level shortwave and attendant surface
low passing well to our north over James Bay, Canada. With the
upper-level forcing so far removed to our north, upper-level
support with this system won`t be strong over our area.
However, what stands out about this system is the impressive
moisture advection into the North Country Saturday through
Saturday night, with PW values progged to reach over 1.5".
Isentropic ascent will drive precipitation starting during the
daytime hours Saturday. There will be a brief window for some
embedded thunderstorms to develop Saturday evening through early
overnight, but once again the potential will be limited by the
nocturnal timing of the best forcing moving through.

The system will quickly depart Sunday morning. There may be a
few lingering residual showers during the morning hours, but for
the most part Sunday should be dry with increasing sunshine
through the day. The progressive pattern continues into next
week, with Monday looking to be the next potential for a quick
shot of rain followed by drier weather Tuesday. Temperatures
through the long term will be near to slightly above seasonal
normals.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Through 12Z Thursday...VFR with SKC this morning and increasing
mid-upper level clouds this afternoon through tonight. A
developing warm front to our south tonight will bring a slight
chance of a rain shower to SLK/RUT 06-12Z Thursday. Winds
continue north 5-10kt today, except locally nely PBG/MSS after
12Z today.

Outlook...

Thursday: VFR. Chance SHRA, Chance TSRA.
Thursday Night: Mainly VFR, with areas MVFR possible. Likely
SHRA, Slight chance TSRA.
Friday: Mainly MVFR, with areas VFR possible. Slight chance SHRA.
Friday Night: VFR. Slight chance SHRA.
Saturday: VFR. Likely SHRA.
Saturday Night: MVFR/IFR conditions possible. Chance SHRA, Slight
chance TSRA.
Sunday: Mainly VFR, with local MVFR possible. Slight chance SHRA.

&&

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

&&

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



 
 
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