Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/10/24
Area Forecast Discussion
National Weather Service Burlington VT
1009 PM EST Sat Mar 9 2024
.SYNOPSIS...
A powerful late winter storm will impact the North Country with a
wide varied of weather, from heavy wet mountain snowfall to a mix of
rain and snow in the valleys and breezy wind along the Western
Slopes. Given the heavy wet snowfall, scattered to numerous power
outages are possible, especially in the mountain towns above 1000
feet. A prolonged upslope accumulating snowfall is likely late
Sunday through Monday with significant additional snowfall expected.
Temperatures fall to near normal values for Sunday and Monday.
&&
.NEAR TERM /THROUGH SUNDAY/...
As of 954 PM EST Saturday...The storm is ongoing with a few
adjustments needed. The main message of a long duration,
elevation dependent heavy snow with periods of gusty winds
continues to be unchanged. However, some temperatures are warmer
than expected across northern New York and northern Vermont the
last few hours due to compressional warming from a downsloping
wind. This resulted in decreasing snow potential for locations
like Saranac Lake and midslope/foothills of the far northern
Green Mountains. Elsewhere like Rutland, precipitation
efficiency has been heavy enough to overcome downsloping with
snow occurring. East/along the southern Greens, upsloping has
been producing 1" per hour snowfall rates with rain occurring
for most valley locations. Mesoscale models bring the upper low
over the North Country overnight allowing winds to shift and
filter some colder air into the Adirondacks - more meaningful
snow will begin after midnight. Winds were lowered with gusts
dropping quicker than expected as wet profiles dampen the wind.
Otherwise, the forecast remains on track.
Previous Discussion...Main adjustment concerned tapering winds
gusts down a little with precipitation loading tamping speeds by
5-10mph for most spots. Still, gusts 30-40 mph possible through
midnight for portions of the Highway 11 corridor across far
northern New York. Winds shifting more southeasterly overnight
will favor stronger gusts along the west slope of the Greens as
the lljet moves across the North Country. We`re still on tap to
see some gusts 40-50 mph in Rutland and eastern Addison
counties. Snow is ongoing above 1000ft elevation with rain/rain-
snow mix elsewhere. The forecast remains on track for a decent
shot of mid-high elevation snows with lower elevations
accumulating tomorrow evening/overnight into Monday.
Previous Discussion...All winter storm warnings and advisories
continue for our cwa, with very little change made to snowfall
and expected impacts.
Did issue wind advisory for central/southern Western Slopes from 00z
to 12z Sunday for localized gusts 45 to 50 mph.
Hydro continues to be watched very closely and is challenging to
determine amount of runoff with rain/snow event, but Otter Creek at
Center Rutland is now forecasted to reach minor flood stage on
Sunday aftn/evening and we are watching other lower elevation sites
like Winooski at Essex closely.
Greatest impact from this system wl be numerous power outages to
towns and cities above 1000 feet from the expected heavy wet
snowfall.
A large spread in the 10th and 90th percentile snowfall amounts
continues, indicating the challenge with this system, with
several sites increasing in the past 12 hours. We have continued
a conservative approach in our snowfall amounts toward the 25th
percentile, especially in the valleys.
Crnt radar and sfc obs indicate rain has overspread northern NY
this aftn, with snow occurring atop Whiteface and a temp of
27F. Without obs/webcams difficult to determine snow levels, but
feel they are pretty high and mostly above 2.5kft today. Winds
have been gusty from the south/southeast at 15 to 35 mph.
Have noted a slight shift in the RAP and latest HRRR/NAM 3km
guidance with track of sfc low pres, which pushes slightly
warmer air into VT and more potential for a mix of rain in the
midslope locations overnight.
Water vapor shows evolving full latitude mid/upper lvl trof with
elongated sfc low pres extending from the northern Great Lakes into
the southern Appalachian Mtns. As potent 500mb s/w energy
located over the MS Valley ejects northeast this evening,
primary low pres wl develop on leeside of the Appalachian mtns
tonight and track northeast toward SNE on Sunday. A strong sub-
tropical jet of 120 to 140 knots is helping with scale synoptic
ascent, along with advecting deep/rich moisture into our region,
as pw values surge btwn 0.75 and 0.90. This system wl have no
issue with available moisture, based on latest water vapor
trends, but initially lacks cold air making for an extremely
challenging and elevational dependent snowfall fcst.
The combination of dynamical and evaporational cooling wl help cool
the column just enough to support a heavy wet snowfall for towns and
cities above 1000 ft tonight. A strong elevational dependent
gradient is still anticipated from valley floors to mtn summits.
Soundings continue to show a large near isothermal layer near 0C
from sfc to 800mb for initial precip surge tonight, with strong
925mb to 850mb se flow helping to cool east side of the Greens just
enough, along with the eastern Dacks. Meanwhile, downslope warming
develops on western slopes, northern Dacks and parts of the NEK,
resulting in slightly warmer bl temps and a mix of rain/snow. I have
to admit its a been concerning to examine the 12z GFS output at MPV
and seeing 2.0" of qpf as heavy wet snow from 00z to 12z Sunday and
near 1.0" of qpf as snow for BTV. Given complexity of the system and
thermal profiles hovering near 0C, we are expecting some surprises
with this system in terms of areas under and overproducing on the
front end. Areas of greatest concerns are locally here in the CPV,
valley cities of central/eastern VT, including the NEK, and parts of
the northern SLV. As upper lvl dynamics and associated cool pocket
of air moves directly overhead btwn 09z-14z Sunday, expect a burst
of wet snow for most, including valley locations. Snowfall totals
have changed very little for first part, ranging from a dusting to
several inches in the valleys below 1000 feet to 6 to 12 inches
midslopes and summits. Temps hover either side of freezing
overnight. Total qpf for first part ranges from 0.50 to 1.25 with
localized higher amounts in the se favored upslope regions of the
central/southern Greens.
Have continued wind advisory for central/southern Western Slopes of
the Greens from 00z-12z Sunday. The core of strongest 925mb to 850mb
winds of 45 to 65 knots occurs btwn 03z and 09z, before axis shifts
to the east. Mixing is questionable as core of strongest winds are
colocated when precip is the heaviest, but examining sounding data
at RUT showed the potential for localized gusts 45 to 50 mph.
For Sunday, initial surge of deep layer moisture and associated fgen
forcing wl exit our northern cwa btwn 14z and 16z, with a decrease
in areal coverage of precip. Feel lingering snow showers wl be most
concentrated over the mtns on Sunday midday. With break in precip
and limited caa, temps should warm into the mid 30s to lower 40s,
with any slick travel quickly improving for a period of time. After
18z winds begin to shift to the northwest as deepening system
becomes vertically stacked to our east. Developing upslope flow and
associated caa and backside 700mb deformation zn wl enhance areal
coverage of precip again acrs most of the region. Initially bl temps
support all snow above 1500 feet, but as caa continues rain quickly
changes to all snow to the valley floors by 00z Monday. Additional
moderate to heavy snowfall is anticipated Sunday night into Monday,
with significant accumulation likely in the western slopes and
northern dacks.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 354 PM EST Saturday...Conditions look very favorable for a
prolonged and significant upslope event for the northern Dacks and
central/northern Greens during this time frame. A much drier and
fluffier snowfall is anticipated with additional snowfall amounts
varying greatly based on elevation. A dusting to 4 inches here in
the CPV to 6 to 12 inches likely Western Slopes, with localized
amounts from Mt Mansfield to Jay Peak of 12 to 18 inches possible.
Northern Dacks see similar type amounts of 6 to 10 inches with
localized amounts of 10 to 16 inches possible with 2 to 6 inches in
parts of the SLV. Much lighter in the lower CT River Valley
associated with downslope flow. Snow ratios wl quickly be changing
as thermal profiles cool and progged 850mb temps drop btwn -10C and
-14C by 03z Monday. Given deepening low pres near 985mb, expect
breezy to gusty northwest winds of 15 to 30 mph with gusts 30 to 45
mph possible acrs downslope areas of the mtns. Eventually vertically
stacked system slowly pulls away and upslope snow showers wl slowly
decrease in areal coverage on Monday night. Have pops/qpf and snow
amount grids to match this thinking. Temps are below normal on
Monday with northwest winds and precip.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 354 PM EST Saturday...Uneventful weather is expected Tuesday
through Thursday with a return to above normal temperatures and
possibly some rain showers as clouds tend to increase midweek. The
Friday - Saturday timeframe looks unsettled with a frontal boundary
likely in the vicinity with a weak wave or waves moving along it to
help produce mainly rain but possibly higher elevation snow
depending on the storm track.
Have PoPs in the likely category Friday night when best consensus
exists on a period of steady precipitation, but this pattern does
not lead to high confidence onset/cessation of rain and/or snow.
Also snow level uncertainty is large given that north of the frontal
boundary low level temperatures probably will be cold enough for
higher elevation snow. So while this precipitation event will likely
be rain for most locations as the latest forecast shows, the west-
east orientation of a thermal gradient will also mean wet snow could
fall if a wave passes to our south and would be more likely as one
goes northward for a given elevation.
The flow pattern looks rather zonal, especially compared to recent
storms, which will limit the potential precipitation amounts. The
latest NBM currently suggests a roughly 5 to 15% chance of exceeding
an inch of precipitation over this 48 hour period. That being said,
southwesterly low level flow looks moist enough such that NAEFS
water vapor transport and PWAT for that period is in the 90th
climatological percentile supporting heavy rain if other ingredients
line up. The 12Z global models do show a very low probability
scenario (9% of all ensemble members), driven mainly by the GEPS,
with a more amplified upper air pattern and chances of heavier
precipitation. It bears watching if this idea gains more support, as
it would change the forecast towards potentially heavier showers and
a more significant warm up that could lead to flooding given the
recent wet/snowy weather.
Overall, this period will be rather mild if not unusually so with
temperatures on Tuesday mainly in 35-45 range and mainly in the 45
to 55 range Wednesday through Friday, likely trending cooler over
the weekend especially if skies remain cloudy.
&&
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Through 00Z Monday...Overall trends through the next several
hours will be from VFR/MVFR to widespread MVFR by 05Z and
eventually IFR at all sites by 10-12Z. Precip type will mainly
be snow, though locally rain or rain/snow at KBTV/KMSS. After
12Z, precip tapers off but IFR/MVFR ceilings will persist
through the remainder of the period. Winds will remain brisk at
the surface and aloft tonight with areas of LLWS and local gusts
of 20-30kts from the SE at KRUT. After 12Z winds drop off
significantly below 10kts, before ramping back up from the W
after 18Z to 10-20kts.
Outlook...
Sunday Night: Mainly MVFR and IFR, with local VFR possible.
Definite SHSN.
Monday: Mainly VFR, with areas MVFR possible. Windy with gusts to
30 kt. Chance SHSN.
Monday Night: Mainly VFR, with local MVFR possible. Chance SHSN.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: Mainly VFR, with local MVFR possible. Slight chance
SHRA.
Wednesday Night: Mainly MVFR, with local IFR possible. Slight
chance SHRA.
Thursday: Mainly VFR, with local IFR possible. NO SIG WX.
&&
.HYDROLOGY...
A widespread mix of rain and snow will develop across the HSA
tonight with liquid precipitation amounts of 0.50 to 1.25 inches
expected in the valleys. It is very difficult to determine rain/snow
and potential runoff, but given high river flows currently our best
river forecasts indicate the Otter Creek at Center Rutland could
reach minor flood stage late Sunday. In addition, the Winooski at
Essex may reach action stage, with several other rivers rising to
bankful. It should be noted, if a warmer solution verifies with more
rain, additional minor flooding is possible.
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory until 8 PM EDT Monday for VTZ001>005-
007-009-011-021.
Winter Storm Warning until 8 PM EDT Monday for VTZ006-008-010-
016>020.
Wind Advisory until 8 AM EDT Sunday for VTZ011-018-019.
NY...Winter Weather Advisory until 8 PM EDT Monday for NYZ026-028-
035-087.
Winter Storm Warning until 8 PM EDT Monday for NYZ027-029>031-
034.
&&
$$
SYNOPSIS...Taber
NEAR TERM...Boyd/Taber
SHORT TERM...Taber
LONG TERM...Kutikoff
AVIATION...Lahiff
HYDROLOGY...
Area Forecast Discussion
National Weather Service Pittsburgh PA
955 PM EST Sat Mar 9 2024
.SYNOPSIS...
Rain transitions to snow showers on Sunday with highest
accumulations in the ridges. Impactful snow squalls are
possible as well which may lead to localized higher
accumulations in the lowlands. Gusty winds continue through
Monday when dry weather returns and temperatures moderate to
above normal by mid-week.
&&
.NEAR TERM /THROUGH SUNDAY/...
KEY MESSAGES:
- Rain comes to an end this evening transitioning to snow.
- Winter Storm Warning in effect for Eastern Tucker and Eastern
Preston Counties beginning at midnight Saturday night.
- Winter Weather Advisory in effect for PA/WV Ridges beginning at
midnight Saturday night.
- Wind Advisory in effect for areas north of Pittsburgh and the
PA/WV ridges beginning at 6am Sunday.
- Convective snow showers on Sunday may be impactful, especially
north of I-80.
-------------------------------------------------------------------
Rain has mostly exited the area this evening as the cold front
has pushed off to the east. Cloud cover will still hold firm as
low-level moisture remains entrenched, and the break in precip
won`t last long as strong cold advection ensues and low level
lapse rates steepen into the overnight hours and the day on
Sunday coincident with a strong upper trough passage as moisture
wraps around the back side of the departing low. This will lead
to a good setup for convective snow showers and orographically
aided snowfall in the ridges.
Starting with the ridges, upslope flow with upper trough passage
acting on a saturated profile into the dendritic growth zone will
result in a period of snow with highest amounts in Eastern Tucker
and Eastern Preston Counties. Given the nature of the steep lapse
rates, a moist DGZ, and some modest instability noted in the hi res
ensembles, snow liquid ratios should be on the order of 17-18:1
(slightly above NBM mean) with total QPF around 0.4-0.6" resulting
in probabilities >6" sitting around 80%, thus the decision to
upgrade to a Winter Storm Warning. For the remainder of the WV
ridges and PA ridges, totals will hold below warning criteria
with high confidence as probabilities of >3" sit at 60-90% and
only 20-30% for >6".
Elsewhere across the area, northwest flow off of Lake Erie with
steepening low level lapse rates, some marginal instability
(ensemble probability of >100 J/kg is around 40% locally), and
moisture extending into the dendritic growth zone will favor a good
setup for lake effect snow bands. The NAM and RAP snow squall
parameter is reaching up to values of 8-10 by Sunday late morning
(anything >1 is favorable for snow squalls). Most of the parameters
are there for a snow squall setup, but the one element in question
is surface temperatures which have been rather warm as of late.
Accumulations will likely be highest on grassy surfaces, but any
location that gets under a heavier band may see quick, impactful
accumulation and reduction to visibility on roadways as rates try to
overcome the warmer ground. It is important to note with this event
that totals are going to be localized and variable due to the
showery/squally nature of the snow and warmer surface temperatures.
Areas in the widespread 1-2" in the forecast for southwest PA (2-4"
in the I-80 corridor) may locally see less or greater than those
totals as it will be dependent on where localized heavier bands set
up, which even at this timeframe, is difficult to pin down.
Confidence in more widespread snow showers is highest along the I-80
corridor with proximity to the lake; probabilities of exceeding
advisory criteria (3") here sit around 40-60%, and coupled with
higher confidence in localized, higher impact effects from
squalls, a Winter Weather Advisory is in effect for this threat
with the best timeframe for snow squalls from 10am-7pm Sunday.
In addition to the snow, wind gusts will increase behind the
front ramping up Sunday morning and afternoon with a tightening
pressure gradient. Low level lapse rates will steepen in strong
cold advection in the wake of the front with an isallobaric
component resulting in around 1 mb/hour pressure rises. This
should lead to a period of gusty wind right before and after
frontal passage tonight and through Sunday with a tight
gradient, strong cold advection, and a 30-40 knot low level jet.
Peak gust forecasts across the lower terrain are still forecast
just under wind advisory criteria (40 knots), but a Wind
Advisory is in effect for the ridges where latest ensemble
guidance shows probability of hitting advisory criteria around
70-90%. It is possible that locations in the lowlands see
advisory criteria gusts within any heavier snow bands, but
confidence in any one location is too low to justify an
extension of the Wind Advisory.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
KEY MESSAGES:
- Dry weather returns Sunday night.
- Temperatures moderate to near normal for Monday.
-------------------------------------------------------------------
Snow showers will come to an end Sunday night as increasing
subsidence with drier air under building high pressure shallows the
depth of the moisture. Lows Sunday night will be the coldest, but
actually most seasonable, of the forecast period with widespread
readings in the 20s expected. Clouds will clear from west to east,
but with elevated wind, don`t expect the clearing to make that much
of a difference in lows even if it`s a bit quicker to occur than
expected.
We`ll see a nice rebound in temperatures beginning Monday as ridging
builds overhead returning plentiful sunshine, thicknesses increase,
and warm advection begins as flow gradually backs southwesterly.
Highs Monday look to top out around 50 degrees with lows Monday
night coming in a few degrees above average.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
KEY MESSAGES:
- Another warmup is expected through the week.
- High pressure will keep the area dry until late week.
- Rain chances return at week`s end.
----------------------------------------------------------------
Ridging persists through mid-week returning above average
temperatures and dry weather. There is some disagreement in the
ensembles on the strength of the building ridge, but with little
consequence as the chance of measurable precip remains very low
through Wednesday; there is a low probability chance of a few
isolated showers clipping the I-80 corridor on Wednesday among
the ensemble clusters that favor a slightly weaker ridge as a
weak wave slides by to our north, but NBM probability of
measurable precipitation is less than 10%.
High pressure pushes off to the east as troughing digs into the
central CONUS and low pressure develops somewhere across the
Midwest. Significant ensemble spread comes into play at this
timeframe in regard to the strength and timing of the responsible
trough, so forecast confidence is much lower to close out the week.
It`s increasingly likely that we`ll see an end to the dry spell by
week`s end as rain chances increase come Friday.
Otherwise, temperatures continue to warm up Tuesday as deep layer
southwest flow takes hold with 60s returning and even some 70s
look possible by mid to late week.
&&
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
The cold front is currently tracking east of AGC and will
likely be over Laurel Ridges in the next hour. MVFR conditions
will gradually build into the region from the west as drier
conditions advance from the northeast. Snow showers, currently
over the Great Lakes, will increase in coverage after 06Z as a
new trough approaches in the wake of the cold front. There may
be a brief period of -RASN before precip type transitions to all
-SN with advancing cold air.
Compacted gradient wind after 12Z Sunday will increase wind
gusts, especially with sfc heating after dawn, +20kts gusts will
continue throughout most of the TAF period. Snow showers will
be scattered through the early to mid- morning hours, providing
generally brief visibility restriction to IFR/low MVFR.
Between 15Z to 20Z Sunday, a passing shortwave may increase
snow shower activity and create intense isolated bands, TEMPOS
have been added for 1SM to 3/4SM vis for portions of the
afternoon. However, any squall does have the potential to have
lower vis restrictions, LIFR to even brief VLIFR visibility
(less than 1/2 mile) and stronger wind gusts, perhaps to 40 to
45 knots in the most extreme cases.
.Outlook...
Pressure height rises and increasing subsidence will aid the
end of snow showers, easing of wind, and improving area
restrictions early Monday and could carry into Wednesday.
Restrictions may return Friday as the ridge axis breaks down and
returns precipitation to the region with a passing low.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 2 AM EST Monday for PAZ007>009-
013>016-022-074-076>078.
Wind Advisory from 6 AM Sunday to noon EST Monday for PAZ074-
076-078.
OH...None.
WV...Winter Weather Advisory until 2 AM EST Monday for WVZ510-511-
513.
Wind Advisory from 6 AM Sunday to noon EST Monday for
WVZ510>514.
Winter Storm Warning until 2 AM EST Monday for WVZ512-514.
&&
$$
SYNOPSIS...MLB
NEAR TERM...MLB
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Hefferan/CL