Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/21/24
AREA FORECAST DISCUSSION
National Weather Service Albany NY
916 PM EST Fri Dec 20 2024
.SYNOPSIS...
Light snow this afternoon into tomorrow morning resulting in
slippery travel, including today`s evening commute. After snow
ends tomorrow morning, winds turn breezy with clearing skies and
temperatures turning cold. Cold temperatures persist through
Monday before our next light snow event arrives Monday night
into Christmas Eve.
&&
.NEAR TERM /THROUGH SATURDAY/...
Key Message:
- Slippery travel this afternoon through early evening from
light snow. Motorists are encouraged to exercise caution while
driving and allow additional time to arrive at their
destination. Snow turns lighter this evening and may briefly
end overnight.
- Snow will likely turn briefly steady for the pre-dawn hours
into Saturday morning (4am to 10am) producing a quick 1 to 2
inches for the Capital District. Slippery travel is once again
expected.
Discussion:
Coverage of light snow is decreasing but there is a persistent
area of steadier snow in parts of the Taconics into the northern
Berkshires. Steady intermittent flurries occurring along and
north of I-90 with more scattered flurries elsewhere. The very
weak low level forcing is resulting in very chaotic forming and
dissipating areas of steadier snow, while weak isentropic lift
is supporting the larger area of light snow.
Some minor adjustments to snow chances, amounts in areas of more
persistent snow, and temperatures through the night. The best
chance at additional light accumulations are in areas of
terrain, especially the central Taconics and northern Berkshires.
PREVIOUS DISCUSSION:
Latest GOES16 water vapor imagery shows the parent trough
tracking through PA with a coastal low deepening off the mid-
Atlantic coast. Latest RAP analysis shows its central pressure
now sub-1000hPa. The approaching trough supported sufficient
warm air advection this afternoon which resulted in light snow
across much of eastern NY and western New England. Given that
weak forcing has remained below the DGZ, snowfall rates have
been well below 1" and snowflakes have been quite small yet
accumulated efficiently due to cold temperatures in the 20s. As
the trough exits off shore this evening (00 - 03 UTC), warm air
advection weakens and snow likely turns intermittent and even
stops at times, especially east of the Hudson. Areas at and
above 1000 feet, especially in the northern/eastern Catskills
should see snow persist thanks to upslope enhancements.
Otherwise, temperatures stay cold tonight in the teens and 20s.
As a secondary upper level trough approaches from western NY
late tonight (09-10UTC), a Mohawk Hudson Convergence (MHC)
signal identified in CSTAR research develops resulting in a
second period of snow over the Capital District through about
14-16 UTC. This will likely produce a quick 1-2 inches of
light/fluffy snow (SLRs 14-16:1) with snowfall rates briefly
reaching 0.5" per hour as the thermal profiles cool behind the
arctic front and forcing intersects the DGZ. Snow ends by
midday with northwest winds behind our cold front ushering in
much chillier air. Total snowfall amounts range 1 to 3 inches
with the highest amounts in the northern/eastern Catskills and
Schoharie County where amounts range 3-4 inches. There is 40 to
70% confidence for much of the region to receive at least 2
inches of snow but under 10% for greater than 4 inches. Some
upslope enhancements bring light snow for the southern Greens
and northern Taconics through tomorrow afternoon.
It then turns breezy tomorrow afternoon with northwest winds
becoming sustained 10-15kts and gusts up to 20-25kts. With
temperatures only in the 20s, the winds will make it feel even
chillier in the single digits and teens. Given how light/fluffy
the fresh snow will be, some blowing snow is not ruled out.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
Key Message:
- High confidence (greater than 75%) for cold temperatures this
weekend with frigid overnight lows both Saturday and Sunday
night. The combination of cold temperatures and light winds
Saturday will lead to wind chill or "feel-like" temperatures
ranging from -20C to 0C.
Discussion:
Clearing skies and northwest winds ushering in 850hPa isotherms
2 to 2.5 standard deviations below normal per the NAEFS (-15C
to -18C) will promote very cold overnight lows Sat night. With
the pressure gradient between the incoming high and exiting cold
front remaining tight enough, northwest winds remain sustained
5 - 15kts. The combination of a continued breeze plus plummeting
temperatures into the single digits and even sub-zero in the
southern Adirondacks, southern VT, and northern Catskills will
support wind chill values or "feel-like" temperatures between 0
and -20C. Some zones in the northern Catskills, Helderbergs,
Taconics and Berkshire County may approach cold weather advisory
criteria and we will continue to monitor trends.
Our 1035-1040 hPa Canadian high builds directly overhead Sunday
supporting clear/sunny skies. Winds will be decreasing through
the day as the pressure gradient weakens but still expecting a
slight northwest breeze (sustained winds 5-9kts). With the core
of our chilly air mass in place, daytime temperatures will
remain very cold as 850 hPa temperatures only range -12 to -18C.
This will result in temperatures only climbing into the teens
and single digits. Clear skies, decreasing winds, and a fresh
snow pack Sunday night will support ideal radiational cooling
conditions. Probabilistic guidance shows greater than 70% chance
for temperatures Sun night to fall below 10 degrees across eastern
NY and western New England and even 30 to 40% for temperatures
to fall below 5 degrees in the Hudson Valley. Thus, Sun night
will likely be the coldest night of the season as we expect
overnight lows to fall towards 0 in the valley with -10 to 0 for
areas at and above 1000ft. Some zones in the northern/eastern
Catskills, Taconics, and Berkshires are close to cold weather
advisory (-15F to -24F) and will be continue to evaluate
trends.
Staying dry into Monday as high pressure shifts into New England
with early sun fading behind increasing clouds as our next
disturbance approaches from the Great Lakes. Not quite as cold
as the weekend but still expecting below normal daytime highs
rising only into the 20s.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
Key Messages:
- Confidence is increasing for a widespread light snowfall Monday
night into Christmas Eve before drier weather arrives for Christmas
Day
Discussion:
A positively tilted upper level trough and weakening surface low
will cross the region Monday night into Christmas Eve bringing a
period of snow to the region. There still remains some uncertainty
with the amount of QPF with this system which would impact snowfall
totals. A current blend of the guidance suggests snowfall amounts of
a coating to 2 inches may be common. Southerly flow may result in
some upslope enhancement across the foothills of the southern
Adirondacks could receive 3 or 4 inches. Will continue to monitor
trends and fine tune snowfall totals over the coming days.
In the wake of this system, high pressure centered across Quebec and
northern New England noses into the region and looks to bring a
period of mainly dry weather for Christmas Day through the remainder
of the week. Highs each day will be in the 30s with some upper 20s
across the higher elevations. Lows will be mainly in the teens to
lower 20s.
&&
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Snow across the region has become lighter in intensity but
outside of the steadier snow, there are still persistent
flurries. Ceilings are varying between IFR and VFR at KALB and
that will continue through the evening, with the IFR occurring
during periods of steadier snow. KGFL, KPOU and KPSF have VFR
ceilings and KGFL and KPOU are outside of the steadier snow, so
visibilities are VFR. KPSF is within the zone of light snow and
flurries, so the visibility there is MVFR. There could be some
brief periods of MVFR ceilings and visibilities at KGFL, KPOU
and KPSF through the evening but predominantly VFR.
After about midnight, the steadier snow should end, but with
flurries around, continuing VCSH. Ceilings should become
predominantly MVFR at all TAF sites by then. One more round of
light snow is possible between midnight and about 12Z, so
including intervals of MVFR visibilities during that time
period.
After about 12Z, steadier snow ends but lingering flurries
suggests continuing VCSH at all TAF sites through about 17Z,
when any flurries should end. Ceilings and visibilities will be
VFR after 12Z and through Saturday afternoon.
Winds will be north at less than 10 Kt through tonight. Winds
become north to northwest at 10 to 15 Kt after 12Z-13Z, and will
gust near 20 Kt through Saturday morning and afternoon.
Outlook...
Saturday Night: Low Operational Impact. Breezy. NO SIG WX.
Sunday: No Operational Impact. NO SIG WX.
Sunday Night: No Operational Impact. NO SIG WX.
Monday: No Operational Impact. NO SIG WX.
Monday Night: Moderate Operational Impact. Chance of SN.
Tuesday: Moderate Operational Impact. Chance of SHSN...SN.
Tuesday Night: Moderate Operational Impact. Chance of SHSN.
Christmas Day: No Operational Impact. NO SIG WX.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.
&&
$$
SYNOPSIS...Speciale
NEAR TERM...NAS/Speciale
SHORT TERM...Speciale
LONG TERM...Rathbun
AVIATION...NAS
Area Forecast Discussion
National Weather Service Marquette MI
700 PM EST Fri Dec 20 2024
.KEY MESSAGES...
- Light to moderate lake effect snowfall continues into tonight,
shifting to the north wind snow belts by Saturday morning.
Best accumulations expected over north central Upper MI late
tonight/Saturday morning.
- Clipper moving through the Great Lakes could bring a
widespread snow Sunday night into Monday.
- Drier and warmer conditions expected behind the early week
system for Christmas Eve and Christmas Day.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 319 PM EST Fri Dec 20 2024
This afternoon`s RAP analysis shows the clipper system now beginning
to phase with another sfc low at ~1003mb located east of MD out over
the Atlantic. Meanwhile, a 1037mb high pressure is positioned over
southeast Manitoba and northern MN and a mid level trough is
beginning to dip over the UP. On the ground, sfc obs are showing
temps in the upper teens to 20s, likely our highs for the day and
lake sfc temps are averaging around 4.8C. Aloft, 850mb temps are
around -16C across Lake Superior yielding delta-ts of ~20C,
supportive of the lake effect clouds across the UP with light LES
mainly over the north central and east. The limiting factor for
snow is the dry air advecting in.
As the trough drops over the UP through this evening, 850mb temps
lower further to -18C to -20C over the east half of the lake
increasing the delta-Ts. With that bump in vertical motion alongside
increased delta-Ts, shower coverage looks to re-invigorate into the
evening hours. However, increasing sfc high pressure from the
northwest brings in drier air and lowers inversion heights to around
5kft or less. Also, moisture within the DGZ is not consistently
noted in the model soundings. As winds shift northerly, guidance
indicates a more dominant LES band supported by Lake Nipigon
upstream pretreatment developing this evening, then shifting west
overnight to Marquette County by Saturday morning. While this does
have support from low level convergence, an ideal fetch across Lake
Superior and assistance from Lake Nipigon, the increasing dry air
and diminishing cyclonic flow will limit accumulations and
associated impacts. The HRRR has been very consistent in yielding
advisory accumulations, however the QPF (approaching 0.15" to 0.2")
seems too high given the set up described above. The forecasted
total snowfall from this afternoon through tonight aligns with the
general solution among model guidance. This calls for an inch or
less of dry and fluffy snow, mainly north central and east. Isolated
amounts up to 2-3 inches can`t be ruled out into Saturday morning,
but placement of that band still is not solid.
Otherwise, northerly winds turn light tonight and lows settle into
the single digits around 0... except low to mid teens by the
lakeshores. Expect wind chills to dip below 0.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 254 PM EST Fri Dec 20 2024
Lake effect snow showers off of Lake Superior will taper off
Saturday as surface high presses into Wisconsin and dry air and
subsidence support drier conditions. Guidance suggests that lake
effect should be diminished across the forecast area by Saturday
evening. Before then though, additional snowfall amounts could climb
another inch or so, mainly from Marquette into western Alger.
Southerly flow will settle in Saturday night. Its possible this
could support light lake effect snow off of Lake Michigan into
eastern Delta, Schoolcraft, and Luce counties Sunday, perhaps
yielding an inch or two of snow.
Broad mid-upper level ridge to trough pattern stretching across
CONUS and Canada this weekend will gradually break down as a
shortwave digs southeast within the northwest flow over the western
Plains. As this clipper low presses across the northern Plains
Sunday night, a surface low will develop and press northeast into
Minnesota. By early Monday, general consensus among the various
deterministic packages suggests the now vertically stacked feature
will press eastward to near Menominee during the day and then
eastward overnight into Tuesday. There are some outliers though,
namely the NAM, which brings the system close to Thunder Bay. While
there is some support from a couple ensemble members of the EC,
GEFS, and GEPS, will treat the northern solution as an outlier in
this forecast package for the time being. The track of the consensus
would result in synoptic precip spreading into the area Sunday night
through Monday, followed by some lake effect potential into Tuesday.
The lake effect is less certain given the speed at which ridging and
WAA limits shower development. Despite the airmass aloft warming
with the system, it still should be cold enough for ptype to be
primarily snow. Snow would be wetter though, with NBM suggesting
snow ratios close to 10:1. QPF is less certain given the possibility
of lake enhancement off Lake Michigan into eastern Upper Michigan.
At this point though, 0.10 to 0.5 inches of liquid (highest east -
least west) looks possible, potentially yielding 1 to 5 inches of
snow with isolated higher spots being possible (highest east - least
west) Sunday night through Monday. There`s less support when
considering snow amount probabilities from the GEPS and EC though.
These suggest the east has a 10-30% chance of seeing at least 3
inches. This may have something to do with the track uncertainty or
the differences in warm air which will impact snow ratios. At this
point though, we`ll need to continue monitoring trends this weekend
to better identify amounts and potential impacts.
Warm air will press into the region after this system exits the
region. Deterministics suggests 850mb temps could warm above 0C by
Christmas morning, and then linger between +1 and 3C through at
least the following weekend. This warm airmass would support
temperatures climbing well into the 30s while overnight lows dip
only into the 20s. Some lakeshore areas may even stay above freezing.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 700 PM EST Fri Dec 20 2024
As high pres approaches from the nw, low-level flow will veer more
northerly tonight, and with a chilly air mass flowing across Lake
Superior, MVFR cigs and lake effect -shsn/flurries will be the rule
at IWD/CMX/SAW for most, if not all, of this fcst period. The -shsn
will be most frequent and a little heavier at SAW, likely resulting
in prevailing MVFR vis overnight thru Sat morning. Very brief IFR is
not out of the question. Only ocnl flurries are expected at IWD with
no vis restriction out of VFR. CMX may see a few periods of MVFR vis
during the night. MVFR cigs will scatter out to VFR at IWD late
Sat aftn and possibly at CMX near the end of the fcst period.
&&
.MARINE...
Issued at 254 PM EST Fri Dec 20 2024
Northwest 20 to 30kt winds will gradually taper this evening,
eventually falling below 20kts Saturday morning lake-wide. These
light winds will continue into early Sunday morning, when southerly
winds begin increasing as the next system approaches the Great
Lakes. There is some uncertainty in the track of the system, but the
current consensus agrees on pressure gradient increasing, which will
work to enhance low level southerly flow during the day Sunday and
Sunday night. 925mb winds among the guidance packages are southerly
winds of 30-40 kts, with the strongest winds across easterly Lake
Superior. There should be enough cold air aloft at this time to mix
stronger winds to the surface, but how strong is uncertain. Going
forecast is for winds to increase to near 30kts, but can`t rule out
some gales. Latest EC ensemble system suggests gale probabilities
between 10 and 40% across eastern Lake Superior. Model soundings
also suggest this could end up being a downsloping wind event near
the Upper Michigan lakeshores east of Marquette. So these nearshore
areas may not be removed from the stronger winds either.
Winds will settle west to east Sunday night into Monday. A warmer
than normal airmass will settle over the area afterwards. This looks
to help maintain light winds for a majority of next week.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...Jablonski
LONG TERM...JTP
AVIATION...Rolfson
MARINE...JTP