Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
148 am EDT Sat may 23 2015
partly cloudy skies will give way to clear skies overnight. A
very cold air mass will be over the north country overnight with
low temperatures by daybreak on Saturday in the upper 20s to lower
to middle 30s. A weak ridge of high pressure will build into the
region on Saturday and remain through Sunday. A warm front will
approach the north country on Monday and bring a chance of rain
showers to the region.
Near term /until 7 am this morning/...
as of 1034 PM EDT Friday...isolated late rain showers (and higher
Summit snow showers) continue to diminish across central Vermont at
0215z...and infrared imagery indicates clearing skies across the St.
Lawrence Valley and points north and west moving into the north
country. Strong low- level cold air advection continues as well...with gusty northwest
winds in place...but temperatures already falling into the middle-upper 30s
along the international border (36f at Newport Vermont at 02z). As such...freeze
warnings look on track with no changes made at this time.
Slightly above freezing for early am lows expected in the frost
advisory area across the Champlain Valley (with moderating
influence of Lake Champlain and stronger low-level mixing). Frost
may actually be mitigated a bit by continued moderate winds...but
more sheltered locations will see some patchy frost formation with
lows 33-36f in the Champlain Valley. 850 mb temperatures already
down to -6c along the international border per latest RUC analysis...and
should drop to around -7 to -8c during the pre- dawn hours.
Definitely a chilly night for late may...but temperatures will
begin a strong moderating trend beginning on Saturday.
Short term /7 am this morning through Sunday night/...
as of 400 PM EDT Friday...a weak ridge of high pressure will
build into the region on Saturday and remain through Sunday.
Expecting temperatures to climb into the upper 50s to 60s on
Saturday after a cold start with sunny skies expected. Not as Cold
Saturday night with lows from the upper 30s to the 40s.
Temperatures will climb into the 70s on Sunday with highs in the
70s. A warm front will approach the southwest Saint Lawrence
valley late Sunday night...so have gone with slight chance probability of precipitation
for rain showers for the southwest Saint Lawrence valley in
northern New York.
Long term /Monday through Friday/...
as of 320 PM EDT Friday...large scale pattern will feature
developing middle/upper level ridge across the eastern Continental U.S. By
midweek. This synoptic scale setup will result in much above
normal temperatures and daily chances for afternoon/evening
showers/storms. No widespread wetting rain events are anticipated
through the middle of next week. Have continued to mention chance to
low likely probability of precipitation Monday afternoon into Tuesday...associated with surface
warm front. This feature will have good 500 mb vorticity traveling from northwest
to southeast across our region...while a ribbon of enhanced 850 to 500mb
relative humidity moves from southwest to northeast. Still some timing
differences between the GFS/Euro...but overall idea of a period
of rain showers looks good. Quantitative precipitation forecast will generally be <0.25 for this
warm front feature.
For Tuesday through Friday of next week our County Warning Area is well
established in the warm sector...as ribbon of enhanced middle level
moisture and associated vorts lift north of our region. Prognosticated
925mb temperatures range between 18c and 22c during this period...supports highs
well into the 80s with maybe a few readings near 90 in the
Champlain and Saint Lawrence valleys...especially given dry surface
conditions. The lack of forcing and deep layer moisture will limit
areal coverage/intensity of storms...along with an organized
convection. Thinking daily airmass type storms will be
possible...especially across the higher terrain during the peak
surface heating. Daily maximum cape values range between 800 and 1500
j/kg with shear profiles supporting pulse type storms during the
Wednesday through Friday time period. Otherwise...better chances for
storms arrives next weekend associated with a cold front.
Aviation /06z Saturday through Wednesday/...
through 06z Sunday...VFR expected through the period. Scattered-broken
5000-8000 foot cloud deck contniues to dissipate but still hanging
in a bit with northwest upslope flow across Vermont. Early this morning...gradually
dissipates overnight leading to clear skies at all taf sites and
continues through today with only some scattered middle level clouds
moving in later today and increasing to broken Sat night/Sun morning.
Northwest winds 5-10 knots early this morning and west/northwest
this morning to 8-12 knots with gusts 15-22 knots...highest mpv.
Winds turn west/southwest Saturday afternoon with gusts 15-25
knots...highest at mss slowly diminshing tonight.
Outlook 06z Sunday through Wednesday...VFR conditions continue
for Sunday into Monday...before a weak warm front will produce a
period of light rain showers on Monday afternoon into Tuesday. A period
of MVFR ceilings will be possible...especially in the mountains. The
chances for afternoon showers and thunderstorms will continue for
Wednesday...with brief MVFR ceilings/visible in the heavier storms...mainly
during the peak heating hours.
a very dry period continues across our region with many locations
4 to 6 inches below normal precipitation year to date. The latest
US drought monitor has the Saint Lawrence valley and parts of
southern/central Vermont in moderate drought conditions with
abnormally dry elsewhere. These dry conditions have produced very
dry dead fuels per coordination with Vermont dept of Forest, Park,
and recreation. These dry fuels combined with breezy southwest to
west winds Saturday and minimum afternoon relative humidity values
between 17 and 25% will increase fire weather concerns. The
strongest winds will occur between noon and 7 PM...while rh's
will be the lowest between 2 PM and 6 PM on Saturday. Localized
wind gusts between 20 and 25 miles per hour will be possible in the southwest
to northeast aligned Saint Lawrence valley and parts of central
and eastern Vermont. Given the expected weather conditions and
very dry fuels...we will issue an Special Weather Statement to
highlight the fire weather concern...as winds are marginal and
keetch Byram drought index is < 300 across our region.
However...given the conditions above any fires that do occur could
spread quickly...burn intensely and be difficult to contain on
as of 306 PM EDT Friday...a lake Wind Advisory is in effect for
Lake Champlain tonight. Northwest winds have generally been in the
10 to 20 knot range. Strengthening pressure gradient should be
able to push lake winds to lake Wind Advisory criteria, in the 15
to 25 knot range, through at least the first half of tonight.
Thereafter, a slackening pressure gradient should allow for lake
winds to subside under criteria towards the morning hours. Expect
waves to be in the 1 to 3 foot range with a moderate chop. Highest
waves will tend to be in areas exposed to the north.
Vermont...freeze warning until 8 am EDT this morning for vtz003-004-
Frost advisory until 8 am EDT this morning for vtz002-005-009-
New York...freeze warning until 8 am EDT this morning for nyz026-027-
Frost advisory until 8 am EDT this morning for nyz028-035.