FOUS11 KWBC 230810
QPFHSD
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Sat Mar 23 2024
Valid 12Z Sat Mar 23 2024 - 12Z Tue Mar 26 2024
...Northeast... Day 1...
This morning, heavy snow is underway from northern New York to much
of interior New England. Strong 850-700mb FGEN aloft coinciding
beneath the right-entrance region of a strengthening 250mb jet
streak over southern Quebec is aiding in the formation of distinct
heavy snow bands setting up from the Tug Hill and Adirondacks to
the Green and White Mountains. As the day unfolds, another jet
streak along the Mid-Atlantic coast will intensify and place its
diffluent left-exit region over New England through Saturday
evening. This "kissing jets" setup forces vertical ascent at mid-
upper levels of the atmosphere to become exceptionally strong,
while simultaneously, a 40-50 knot southerly 850mb jet is
directing copious amounts of moisture poleward towards New England.
Add in a sufficiently cold air-mass from the Tug Hill on north and
east through central and northern Maine, and the stage is more
than set for prolific snowfall rates producing a heavy, wet
snowfall over northern New England.
It is worth noting surface temperatures are likely to remain <32F
from the southern tier of New York and even as far south as the
Poconos to result in some minor ice accumulations. Latest guidance
has the surface-925mb layer remaining colder longer and thus
allowing for a longer period of freezing rain. The areas with
moderate-to-high chances (50-70%) for ice accumulations greater
than a tenth of an inch are the Berkshires, the Green, the
Monadnock and Merrimack Valley of southern New Hampshire, and
south-central Maine. Ice accumulations will be most likely confined
to trees, bushes, and power lines, while sidewalks and side roads
may also see some slushy accumulation during the day. The bigger
impact lies in the snowfall, however, as the WPC Snowband
Probability Tracker (SPT) shows snowfall rates of 2-3"/hr are
anticipated Saturday afternoon and into Saturday night across
northern New England. The WSSI shows Major Impacts (largely due to
Snow Amount and some cases of Snow Load) from the Adirondacks and
the Green and White Mountains through the heart of Maine. Areas
under Major impacts can expect considerable disruptions to daily
life that include dangerous, to even impossible, travel conditions,
widespread closures and disruptions, and given the dearth of
heavy, wet snow expected, the potential for tree damage and power
outages. WPC PWPF shows high chances (>70%) for snowfall totals
12" across Vermont's Northeast Kingdom, northern New Hampshire,
and northern Maine. Snow will conclude shortly after midnight as
high pressure builds in from the west on Sunday.
...The West... Days 1-3...
An upper low barreling into the Pacific Northwest will accompany a
second upper level disturbance tracking into southern California
to direct a slug of Pacific moisture into California and as far
north as the Cascades. The combination of upper level diffluence
along with strong topographically-enhanced snowfall rates will
result in periods of heavy snow along the Sierra Nevada and in the
Northern California mountain ranges (Siskiyou/Salmon/Trinity) at
elevations >5,000ft. Periods of heavy snow will also occur in parts
of the Cascades (>5,000ft) and in the Great Basin (elevations
7,000ft). By Saturday night, snow will advance east towards the
Wasatch, the Mogollon Rim, the western Colorado Rockies, and
northern New Mexico Rockies. Heavy snowfall along the Mogollon Rim
will generally occur at elevations >7,000ft, while the Wasatch,
Uinta, Colorado and northern New Mexico Rockies will witness heavy
snow at elevations >8,000ft. The Sierra Nevada and Northern
California ranges sport locally moderate-to-high chances (50-70%)
per WPC PWPF for snowfall totals >12". There will likely be some
portions of these mountains ranges that surpass two feet of snow as
lingering upslope flow continues into Sunday. Snow will also
linger through Sunday in the Four Corners region at elevations
7,000ft before gradually dissipating by Monday morning.
...Northern Rockies & High Plains, Central Rockies, Upper Midwest...
Days 1-3...
**Major Winter Storm Set to Impact Northern/Central Rockies to
Upper Midwest Beginning This Weekend**
The upper low in the Pacific Northwest will spawn a new surface
low in central Wyoming later this afternoon, while a strong dome
of high pressure over south-central Canada and lower pressure in
the Intermountain West maintains persistent easterly low-level
upsloping flow into the northern High Plains and northern Rockies.
This will keep periods of light snow falling in parts of eastern
Montana and the western Dakotas, but snow accumulations will be
more likely to occur on grassy surfaces, sidewalks, and side roads
during the day. By Saturday night, low pressure will rapidly
deepen over eastern Colorado. In response to the rapid pressure
falls in the central High Plains, the 850mb LLJ will exceed 50kts
over eastern Kansas and eastern Oklahoma. These southerly 850mb
wind speeds are above the 99th climatological percentile and
ushering in copious amounts of Gulf of Mexico moisture poleward
into the Northern Plains and Upper Midwest through Sunday.
By Sunday morning, heavy snow will be blanketing much of Montana
with the main shield of snow gradually overtaking the Dakotas. The aforementioned 850mb moisture will wrap around the northern and
northwestern flank of an elongated 700mb low located in central
Nebraska. Strong 850-700mb FGEN over the Upper Mississippi Valley
will result in heavy snow over southern Minnesota and northern Wisconsin
that could produce 1-2"/hr snowfall rates Sunday afternoon and
into Sunday evening. As the day unfolds the Central Plains will lie
beneath the divergent left-exit region of a 250mb jet streak
centered over northern Mexico, while to the north, the right-
entrance region of a 250mb jet streak in southern Ontario further
maximizes the intense vertical ascent atop the atmosphere. This
will allow for the surface low on Sunday to deepen to
exceptionally deep levels (sub 980 by Sunday evening). NAEFS at 00Z
Monday shows much of southeast Colorado, the OK/TX Panhandles, and
western Kansas sporting MSLP values that fall outside the observed
1979-2009 CFSR database.
Monday morning will see the strong 850mb warm air advection in the
Upper Mississippi Valley ultimately lead to a changeover from snow
to an icy wintry mix at first, then to all rain in southern
Minnesota, northern Wisconsin, and the U.P. of Michigan. This will
cut down on snowfall totals but the icy wintry mix in some areas
could still cause hazardous travel Monday morning. Meanwhile, in
central South Dakota, southeast North Dakota, and northern
Minnesota, snow will remain the primary p-type with strong wind
gusts >40mph causing blizzard conditions through Monday afternoon.
Snow will liner along the Red River of the North and northwest
Minnesota Monday night but rain will be the primary p-type in
northern Wisconsin and the Michigan U.P..
The latest WSSI shows Major Impacts in eastern South Dakota,
southeast North Dakota, central Minnesota, and northwest Wisconsin.
These areas sport moderate-to-high chances (50-70%) for snowfall
totals >12" for the event, while areas near the northwest South
Dakota and western Minnesota border have moderate chances (40-60%)
for >18" of snowfall. WPC PWPF also shows high chances (>70%) for
8" of snowfall in central South Dakota, along the Minnesota
Arrowhead, and in northern Wisconsin. Farther south, as a strong
cold front pushes through and upslope flow ensues, periods of
moderate-to-heavy snow have moderate-to-high chances (50-70%) for
producing >4" along the Colorado Front Range, the Palmer Divide,
and on south along the Sangre De Cristo. Light snow accumulations
are also possible in the High Plains of eastern Colorado and but
wind gusts topping 50 mph could lead to significant blowing snow
impacts. For more details on impacts, please review our latest Key
Messages below.
Mullinax
***Key Messages for Northern Plains Winter Storm***
--A significant March winter storm begins today
An extensive and high impact storm system will produce widespread
heavy snow and gusty winds over the Northern Plains into the Upper
Midwest beginning today and lasting into early next week.
--Widespread heavy snow expected
Heavy snow will spread across much of central and eastern Montana
by Saturday night, then expand into the Northern Plains and Upper
Midwest on Sunday and continue into Monday. There is a high chance
70%) of at least eight inches of snow extending from portions of
the Dakotas and north-central Nebraska northeastward through
Minnesota into northern Wisconsin.
--Hazardous impacts due to snow, snow load, and wind
Heavy snow and gusty winds will produce areas of blowing and
drifting snow and possible blizzard conditions Sunday into Monday.
Hazardous travel, along with some disruptions and closures are
expected late Saturday into early next week. Strong winds and
heavy, wet snow on trees and power lines may result in tree damage
and power outages.
--Strong wind gusts in the Central and Southern Plains
Blustery wind gusts in excess of 50 mph on Sunday may result in
power outages, blowing dust that causes reduced visibility, and
damage to property.
$$
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