Area Forecast Discussion
Issued by NWS Burlington, VT-- Highlight Changed Discussion --
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FXUS61 KBTV 201446
Area Forecast Discussion
National Weather Service Burlington VT
1046 AM EDT Wed Jul 20 2016
Ridge of surface high pressure will remain over the North Country
through Thursday, providing the region with sunny and dry weather.
Temperatures will warm above seasonal normals again towards the
end of the week. Periods of showers and thunderstorms are
expected Thursday night through Saturday as a frontal system moves
slowly through the region.
.NEAR TERM /UNTIL 11 PM THIS EVENING/...
-- Changed Discussion --As of 1046 AM EDT Wednesday...No changes for 1030 am update.
Another sunny and dry day is expected today. There may be just
some scattered fair weather cumulus clouds around, especially
around the mountains and NEK but no precipitation is expected.
Prevailing flow is northwest aloft with surface high pressure off
to our south and west today. 850 temps rise to to 10-13 deg C by
21z so expect surface temperatures will rise quickly and reach
upper 70s to lower 80s which is just about normal for late July.
Another mainly clear night is expected tonight as flow aloft
becomes more westerly and surface high pressure drifts to the
mid-Atlantic region. Some warm air advection starts aloft so some
high clouds may show up after midnight. Some patchy fog is
possible but depends on the clouds so left it out for now. Low
temps not as cool as this morning mainly in the 50s with perhaps a
few cold spots in the upper 40s such as SLK.
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.SHORT TERM /11 PM THIS EVENING THROUGH FRIDAY NIGHT/...
As of 425 AM EDT Wednesday...0z guidance suite did not offer too
much in the way of changes, though there are differences between
models on some of the specific details. for thursday, NAM was more
aggressive with afternoon convection across northern NY and have
discounted that aspect. for Friday, I stuck with an overall blend
of models. So details are still on the fuzzy side given the
averaging method of these differences. Some of the forecast
thoughts are as follows:
Thursday: surface high moves off to the east, so a low level
south/southwest flow develops. mid level flow is still from the
west/northwest, however some of the fringes of the intense heat
found across the Central US will be leaking into the region on that
westerly flow. 925mb temperatures will rise to around 22C & 850mb
temperatures to about 16C, and given a good deal of sun, we`ll
easily be able to develop a deep mixed layer. Rough rule of thumb in
these situations is to add 10C to the 925mb temperature and 15C to
the 850mb temperature to estimate the high temperature in the
valleys. Thus the math gives us 31-32C (or 88-90F), which is more
for the Champlain & St Lawrence Valleys. Slightly cooler elsewhere
due to elevation. Despite the warmth, we should see mainly sunny
skies thanks to the warm layer aloft/inversion. However by late in
the day, guidance indicates an elevated mixed layer (EML) advecting
in from the west. Could mean an isolated shower/storm across
northern NY, though chances are generally less than 20%. The NAM is
more aggressive with this feature and thus develops more
scattered late afternoon t-storms across the western half of the
forecast area. As mentioned above, have discounted this.
Thursday Night: EML and associated instability aloft moves across
the area. We should see scattered showers and isolated thunderstorms
develop because of this. It will be turning more humid, and with all
of the clouds, lows will not drop much -- mid/upper 60s.
Friday: Interesting day. Still looking like we could see some
strong or isolated(?) severe t-storms. However, the various
ingredients don`t quite come together all at the same time. Models
also have timing differences between them which makes the confidence
a little lower. Best guess at this point is we`ll have surface
instability (temperatures well into the 80s, perhaps 90F
again)resulting in CAPE values pushing 2000 J/kg. We`ll also have
increasing shear aloft of 35-45kts which is good for storm
organization potential. We`ll have still a little bit of an EML
around. We`ll also have a good amount of dry air aloft, which will
both act to reduce the overall coverage of convection but to enhance
the downburst potential. We`ll also be having a shortwave skip
through at some point during the day. Model soundings also indicate
high equilibrium levels and semi-low wet bulb zero (10-11k ft)
levels which suggest a hail threat.
What I`m thinking right now is that we`ll see scattered
thunderstorms develop by late morning or early afternoon. Although
there won`t be widespread coverage, those that do form could be
strong. NAM indicates scattered convection will continue well into
the evening as well. At this point kept PoPs in the 55-65% range.
Did not include any enhanced characteristics to the weather at this
point. However, Friday is a "Stay Tuned" kind of weather day,
especially if you are planning to do outdoor things.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 425 AM EDT Wednesday...Stuck with a blend of model guidance
as there is general agreement. The weekend will continue to be
warmer than normal. 850mb temperatures Saturday will be in the
15-17C range, and perhaps a degree warmer on Sunday. Went a couple
of degrees warmer than the blend, as I like the values shown by
the 00z GFS MEX guidance as we should be solidly in the 80s,
perhaps touching 90F here and there. A shot of a thundershower
across Vermont Saturday and Northern NY on Sunday.
Monday could be another active thunderstorm day. Fairly robust
shortwave embedded in the westerly flow aloft should be coming
through during the time of peak heating. At the surface, low
pressure will pass by well to our north, but a cold front will sweep
through the region probably late in the day. Both the 00Z GFS and
ECMWF indicate decent amounts of instability (CAPE of 1000-1500
J/kg), and increasing 0-6km shear later in the day. This far out,
subtle changes in timing could mean big differences in what we
actually see. Thus will not go crazy with things, and just paint
in 30-45% chance of thunderstorms. Depending on how much sun we
get, it could be another day where we make a run for 90F.
Tuesday - looks dry and cooler, with temperatures back to near
.AVIATION /15Z Wednesday THROUGH Sunday/...
Through 12z Thursday...VFR today under high pressure. Local
MVFR/IFR possible SLK/MPV 07-12Z in fog tonight. Expect some lake
breeze interaction around Lake Champlain, with KPBG turning
easterly and westerly component at KBTV. Scattered cumulus at 5-6K
ft expected to develop over the mountains and NE VT. Should be
mainly clear and calm tonight through 06Z with some increase in
high clouds toward 12z Thu as the high moves south of region and
wind become south to southwest.
Outlook 12z Thursday through Sunday...
Thu...VFR under high pressure. Overnight IFR fog
possible, especially at KSLK and KMPV.
Thu night-Sat...VFR, with scattered MVFR in showers and
Sun...Mainly VFR under weak high pressure.