FXUS61 KBTV 232330
AREA FORECAST DISCUSSION
National Weather Service Burlington VT
730 PM EDT Tue Apr 23 2019
After another sunny day across the North Country, cloud cover will
build back into the region this evening. A cold front will sweep
through the region during the overnight hours with widespread
rainfall amounts ranging from a quarter to a third of an inch. Rain
showers will continue behind the front on Wednesday but will likely
be confined to the higher terrain. Showers will then taper off
Wednesday evening with drier conditions expected to continue through
Friday morning before another cold front approaches the region from
.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
As of 730 PM EDT Tuesday...Going forecast is in great shape
with only a slight tweak needed to precip onset and end timing.
Showers are moving into western portions of the CWA currently
and latest trends show the bulk should clear northern New York
during the 03-05Z hours and eastward across Vermont from 06-09Z.
Some question with the latest 18Z guidance as to how much
upslope precipitation develops after 09Z, but have left the
forecast intact for now and will assess the upcoming 00Z
guidance for any potential changes. Other change was to remove
mention of any thunder as this afternoons activity has all but
gone away with no convection noted in the upstream obs/radar.
Previous Discussion...Skies cleared nicely throughout the day
with the axis of mid-level ridging moving across the North Country.
The subsidence can be seen nicely on satellite imagery and even
continues to suppress any cumulus from forming given temperatures
once again in the mid 60s to near 80 degrees. RAP soundings suggest
100 to 400 J/kg of CAPE yet CIN of -50 to -70 J/kg hints at why
diurnal cumulus has been hard to come by. That all will change
tonight as rather dynamic shortwave interacts with a developing
upper level low tracking across the international border. Convection
with this system can already be seen across western New York and
western Pennsylvania and all CAMs show the system entering a more
"energetic" air mass that hasn`t been capped by cloud cover.
As this happens, the frontal boundary associated with the upper
level trough will begin to pick up some speed and develop additional
convection as it crosses New York. While there is some CIN in place,
it looks like the front will be able to lift surface parcels above
the subsidence inversion and allow for some convective showers and
maybe even a thunderstorm or two to track into northern New York
after sunset. The loss of diurnal heating will limit convection
heading into the overnight period across Vermont but enough mid-
level forcing should still allow for convective showers to continue,
albeit a near nil chance for thunderstorms. Overall rainfall amounts
through tonight will be widespread quarter to a third of an inch of
As the upper level low tracks eastward toward Newfoundland, recycled
Atlantic moisture will wrap around the low and move back into the
North Country. In addition, with cold air advection behind the low,
we will see in increase in mid-level lapse rates which will help
produce additional showers on Wednesday; especially during the
morning and afternoon hours. The majority of these showers will fall
on the western slopes of the Adirondack and Green Mountains with
Froude numbers near 1. Some showers could back build throughout the
day into the Champlain Valley but most rainfall accumulations will
be restricted to the western slopes where an additional tenth to
quarter of an inch of rainfall will be possible. This rain won`t be
enough to cause any significant impacts on area rivers as levels
have dropped nicely after the two precious heavy rain events.
.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
As of 318 PM EDT Tuesday...Weak default ridging then builds
briefly across the area during Thursday with partly sunny skies,
light winds and seasonal temperatures from the upper 50s to mid
60s. Should be a really nice day for outdoor activities. By
Thursday night our next system in the pipeline approaches with
moisture streaming northeastward ahead of a sharply digging
upper trough across the Great Lakes. The idea of thickening
clouds later at night with increasing chances for showers across
the southwestern half of the forecast area toward morning looks
reasonable for now. This morning`s QPF/mass fields from the GFS
seem overdone at this point and as such have largely ignored
its output. Low temperatures to range from the upper 30s to mid
40s, slightly cooler far northeast where partial clearing will
persist most of the night.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 318 PM EDT Tuesday...Much uncertainty exists in the
extended portions of the forecast in regard to chances of
rainfall. Complicating matters will be persistent and fast semi-
zonal flow north of 40N at and above 500 mb which typically
leads to large model spread in timing/strength of systems. Today
is no exception with the GFS and Euro at odds with one another
during much of the period and at times 180 degrees out of phase.
For the sake of simplicity have downplayed pops into the lower
probability ranges, especially from Sunday onward until more
consistency is realized. The most confidence thus lies during
the front end of this period (Friday/Friday night) when the
aforementioned shortwave swings through the region with
scattered/numerous showers. Otherwise the main theme for now
with be variable clouds with on and off periods of partial
clearing with temperatures averaging near or slightly below
normal (mainly 50s and 30s).
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Through 00Z Thursday...Conditions will be deteriorating
overnight from VFR currently to MVFR this evening and through
the much of TAF period with isolated IFR possible at KSLK and
KMSS. Showers will shift across the area from 00-09Z with
additional upslope showers possible at KSLK after 12Z.
Restrictions in flight category will primarily be due to
ceilings, but in some heavier showers brief MVFR visibilities
are possible. Variable winds will shift to the south/southwest
this evening and eventually west/southwest overnight with gusty
winds to 25 knots possible Wednesday morning and afternoon.
Wednesday Night: Mainly VFR, with local MVFR possible. Chance
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. Slight chance SHRA.
Friday: Mainly VFR, with areas MVFR possible. Definite SHRA.
Friday Night: Mainly VFR, with areas MVFR possible. Likely SHRA.
Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA.
Saturday Night: VFR. Slight chance SHRA.
Sunday: Mainly VFR, with local MVFR possible. Chance SHRA.