Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1030 PM EDT Monday Sep 15 2014
an upper-level disturbance approaching from the west will bring
increasing clouds this evening followed by scattered rain showers
during the overnight hours into early Tuesday morning. Skies will
remain mostly cloudy through much of Tuesday...with gradual
clearing Tuesday evening. Generally dry and seasonably cool
conditions return for middle to late week. A widespread frost is
expected Thursday night as strong Canadian high pressure builds
in across the region.
Near term /until 7 am Tuesday morning/...
as of 1030 PM EDT Monday...scattered light shower activity now
making steady progress east across southern Ontario and central/western
New York...with a few locations across northern New York/western Vermont also reporting a
brief sprinkle or light shower within the past hour or so.
Boundary layer remains a tad on the dry side with 5-10 degree tdd
values still noted across the area so alot of this initial
activity is falling as virga. Still fully expect that as planetary boundary layer cools
and nears saturation overnight showers will become more numerous
and have left areal probability of precipitation and precipitation amts largely unchanged however.
Lows remain on track...generally middle 40s to lower 50s for most
spots under light S/SW winds. Have a great night.
Short term /7 am Tuesday morning through Wednesday night/...
as of 318 PM EDT Monday...
on Tuesday...fast-moving shortwave trough will exit east of
Vermont between 12-15z Tuesday allowing most of the rain shower
activity to come to an end during the morning hours from west-
east. The NAM and btv-WRF 4km/12km runs all indicate bulk of the
shower activity east of the region between 12-15z...with just the
Prospect of a lingering sprinkle of two late in the morning. Probability of precipitation
lower quickly from around 70 percent at 12z down to 20-30 percent
by 15z. Near-saturated relative humidity conditions remain most of the day in the
925-875mb...and would anticipate skies remaining mostly cloudy most
sections for the balance of the day...with some afternoon peeks of
sun. High temperatures will generally be in the upper 50s to lower
60s...with light west winds in the wake of the associated surface
Tuesday night...a narrow surface ridge will build across New York
and New England from SW-NE with light winds in place. Probability of precipitation none. Main
question would be presence of any patchy low-level stratus...which
may be slow to dissipate...especially across the Adirondacks and
northestern Vermont. With degree of raditional cooling in question due to
cloud uncertainty...will stay relatively close to the MOS
consensus for now. Generally looking at lows around 40f in the
Champlain Valley and 30s elsewhere. Could see some additional
patchy/areas of frost away from the immediate Champlain Valley if
clearing skies can occur during the overnight period. Clearing
would also yield some locally dense nocturnal fog in the favored
river valleys of central and eastern Vermont...including the
Winooski...Connecticut...and lower Passumpsic.
Wednesday... we/ll be watching the approach of a reinforcing cold
front from Quebec and southeastern Ontario late in the day...with weakly
cyclonic flow in place in the mid-troposphere. Conditions should remain
dry during the daylight hours Wednesday...but will see some
increase in middle-upper clouds as the day progresses...especially
across the northern half of the forecast area. Temperatures will
continue unseasonably cool for middle-September with afternoon highs
generally in the low- middle 60s. Dewpoints in the upper 30s to lower
40s will make it feel somewhat crisp as well. Winds are generally
expected to be light from the west-SW south of the frontal
boundary...and generally 5-8 miles per hour across most of the lower
elevations across the north country.
A weak shortwave trough (with limited low-level moisture) and
secondary cold front will slide from northwest-southeast across the area during
Wednesday night. At this point...it appears this feature will just
be associated with mostly cloudy skies...a SW-northwesterly wind shift...and
a few light rain showers during the overnight hours. Will carry 20-30
probability of precipitation...highest across the northern mountains of Vermont and far northern New York. Low
temperatures Wednesday night generally in the lower 40s...with some
upper 30s in the northern Adirondacks and Northeast Kingdom.
Long term /Thursday through Monday/...
as of 345 PM EDT Monday...for the most part, no big changes in the
extended forecast period. Still looking for colder air to ooze in
Thursday, setting the stage for what appears to be a widespread
frost/freeze situation Thursday night. Dry weather continues
Friday. Models are a little bit more divergent Saturday Onward.
Looks like the trend is for a dry Saturday, with any showers
confined to Sunday and perhaps Monday. Looking for more? Well,
just keep on reading:
Thursday: region will be under cold air advection during the day.
Models do show deep layer drying as ridging starts to build in,
but there could be low level moisture/strato-cumulus that they
just can't resolve. At this point will go with a more optimistic
partly sunny forecast, but it could end up being more cloudy.
However, the primary thing we'll notice will be the temperatures.
925mb temperatures will be dropping during the day (7-10c at
daybreak to 2-5c by late day). So highs will only be in the 50s
for most areas -- perhaps 60f down in far southern areas. If it
ends up being more cloudy, then these temperatures might be too
warm. If not already clear, it will clear out for Thursday night.
Excellent radiational cooling situation setting up. Guidance has
been trending cooler, and I still went a bit below it especially
for normally colder locations. Bottom line, looks like most
outside of the immediate St Lawrence and Champlain valleys, there
will be a freeze -- some places a hard freeze with temperatures
into the middle 20s. Even the warmest valleys will likely see a
fairly widespread frost. To ME it looks like any actively growing
plants will be pretty much done with.
Friday: high pressure starts moving east, allowing slight warming
to commence. Still below normal temperatures. 925mb temperatures
of 5-7c will support daytime highs in the upper 50s to lower 60s.
Friday night could be a tricky temperature forecast. Warmer
southwest return flow should mean warmer in most areas. However
that flow always has trouble getting into areas east of The Greens
and especially the Northeast Kingdom. Have gone several degrees
cooler than guidance for eastern Vermont, and it should be another
frosty night there. In general, lots of 30s - with 40s in the
Champlain and St Lawrence valleys.
Saturday: 12 GFS and ensembles are all pointing to a dry day with
increasing southwest flow and warmth. The 00z Euro had showers
coming across. 12z Euro backed off on that, so have trended toward
the drier GFS solution. 925mb temperatures up to 11-14c, which
should support highs well into the 60s. Gradient tightens up as
well, so becoming breezy I would think in the Champlain Valley
especially. Do have some gusts to 20mph painted in, but could even
be a bit stronger. In sum, mild and breezy day.
Sunday/monday: models diverge more, so details are more fuzzy.
Euro wants to push a front through during the day, before stalling
it Monday. GFS is later with the front more like Sunday
night/early Monday. At this point feel the best course of action
is to maintain the chance of showers in the forecast. 925mb
temperatures warm even more and up to 12-16c or so. Uncertain
however how much sun we will see, so stuck with model blend which
indicates upper 60s/low 70s Sunday and 60s Monday. May still be
breezy, especially Sunday.
Aviation /03z Tuesday through Saturday/...
through 00z Wednesday...primarily VFR this evening and
overnight...lowering to a period of MVFR Tuesday morning...before
improving to VFR once again Tuesday afternoon. Ceilings will
gradually lower tonight as rain showers advance into the
region. Rain showers will be mainly light...so mostly VFR
visibilities are expected. However brief periods of MVFR are
possible...especially slk/mpv. Ceilings are then anticipated to
lower to MVFR for a period area-wide Tuesday morning...before
scattering out Tuesday afternoon. Light southerly winds tonight (5
knots or less) turn west/southwest on Tuesday from 5 to 10 knots.
Outlook 00z Wednesday through Saturday...
VFR nearly the entire period. Could be brief MVFR in a few showers
Wednesday night. IFR with late night patchy fog for slk and mpv is
also expected mainly Tuesday, Thursday and Friday nights.