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-- Discussion containing changed information from previous version are highlighted. --
999
FXUS61 KBTV 251718
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
118 PM EDT Sun Jun 25 2017

.SYNOPSIS...
Scattered showers and thunderstorms are expected to develop
later this morning and afternoon across the North Country. Gusty
winds and small hail will be possible with any of the thunderstorms.
The showers and storms will taper off tonight...but the potential
for additional showers or storms will develop once again Monday
afternoon. High temperatures will be right around seasonal
normals today and a few degrees below normal on Monday.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 1020 AM EDT Sunday...Forecast remains in good shape and
no changes needed as of 1000 am. Approaching robust shortwave
across the eastern Great Lakes still on track to arrive later
today forcing scattered showers and storms, a few of which may
be strong. Best forcing along PVA axis to occur across northern
tier of counties this afternoon. Have a great day.

Prior discussion...Deep layer shear has developed over the area
and will persist through tonight...and even into Monday for
that matter. Instability is expected to develop as temperatures
warm into the 70s and temperatures aloft cool a couple of
degrees. This will create a nearly dry adiabatic lapse rates in
the 850-500 millibar layer...thus producing sufficient
instability for convection. Meanwhile dynamic support will also
be increasing over the area as a pronounced shortwave trough
moves out of the eastern Great Lakes and into our area tonight.
These conditions will all be sufficient to create scattered
showers and thunderstorms later this morning and afternoon
across the area. Forecast soundings show low wet bulb zero
values and drier air in the sub cloud layer. As a result...the
potential for gusty winds and small hail will exist and will
include in the forecast from midday into early evening.

For tonight...convection will decrease in areal coverage toward
midnight as we lose instability and dynamic forcing shifts north
and east of the area. Should be relatively dry during the
overnight hours.

Deep layer shear remains over the area on Monday and instability
should develop during the afternoon hours. Temperatures will be
a few degrees cooler than Sunday...thus instability will not be
as favorable as Sunday. And there will be less of a forcing
mechanism on Monday...thus looking at only a chance for showers
or storms during the afternoon hours. Activity should not get
organized enough to become strong...so no enhanced wording at
this time.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 325 AM EDT Sunday...not much change in the overall
forecast for this period - still more unsettled weather. The
first half of Monday night will have a weak shortwave push
across the region. Models all show some disorganized convection
associated with the shortwave lifting southwest to northeast
through 08z, so have aligned the PoPs with a blend of some of
the hi-res models to show the evolution. One little feature to
see if it comes to pass will be the potential for a little bit
of lake effect showers come off Lake Ontario into the St
Lawrence Valley area first thing Tuesday morning thanks to some
cooler air aloft. A stronger upper trough approaches the area
Tuesday. Although there will be plenty of clouds and
temperatures on the cool side (upper 60s to lower 70s), the
temperatures aloft (around 500mb) are rather cold (near -22C),
so that should result in some instability to produce another
round of afternoon/evening showers and perhaps a few t-storms.
With the cold air aloft, wet bulb zero heights are quite low
(7000-8000ft), so chance for some small hail in any deeper
convection.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 325 AM EDT Sunday...00z model suite still pointing toward
a continued lengthy stretch of unsettled weather. Not that it
will be cloudy and rainy continuously, rather we will see short
dry periods of 12-18 hours followed by 12-18 hour long periods
where scattered showers and t-storms will be around. At upper
levels, we will be in a region of fast mainly zonal (west to
east) flow with embedded shortwaves zipping through. It will be
these shortwaves, combined with daytime heating, that will be
the primary triggers for the convection. Given the uncertainty
in timing these shortwaves, it`s best to take a bit more of a
general approach to the forecast and use a model blend for day-
to-day PoPs. At this point, I don`t see anything indicating any
widespread severe weather through Friday.

GFS and ECMWF continue to show a more significant upper trough
develop to our west on Saturday, resulting in a deeper southerly
flow which brings in some very moist air (precipitable water
closes in on 2.0"). If this does come to pass, we could have
some hydro related issues by then, especially if we have enough
convective activity repeat across the same areas during the
week. Just something to watch at this point.

In general, temperatures will be slightly below normal through
much of the week though trending closer to normal late week as
the more southerly flow develops. Again, stuck with model blend
for temperatures, and there is considerable error potential if
we end up having much more sunshine than currently expected.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Through 18Z Monday...Mainly VFR through the period with
scattered showers and thunderstorms through early evening.
Shortwave pushing across the area this evening driving scattered
showers and thunderstorm activity across the area. No severe
weather is expected though a few of the more robust storms could
produce small hail, gusty winds into the 30-40 mph range,
enhanced low level turbulence and brief MVFR/IFR conds.
Coverage of storms to wane this evening and overnight with loss
of surface heating and as shortwave exits east. Winds west to
southwesterly 6 to 12 kts and occasionally gusty into the 15-20
kt range through sunset, abating to light overnight. After 12Z
Monday VFR continues, but with an increasing threat of showers
and thunderstorms once again as we approach the 18Z time frame.
Given this will occur toward the very end of this forecast cycle
have omitted specific mention at this point. Winds continue
light west/southwesterly 5 to 10 kts.

Outlook...

Monday Night: VFR. Chance SHRA...Slight Chance TSRA.
Tuesday: VFR. Chance SHRA...Slight Chance TSRA.
Tuesday Night: VFR. Slight Chance SHRA...Slight Chance TSRA.
Wednesday: VFR. Chance SHRA...Slight Chance TSRA.
Wednesday Night: VFR. Slight Chance SHRA.
Thursday: VFR/MVFR. Likely SHRA.
Thursday Night: MVFR. Likely SHRA...Slight Chance TSRA.
Friday: VFR/MVFR. Chance SHRA...Slight Chance TSRA.

&&

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

&&

$$
SYNOPSIS...Evenson
NEAR TERM...Evenson/JMG
SHORT TERM...Nash
LONG TERM...Nash
AVIATION...JMG