Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/24/22
AREA FORECAST DISCUSSION
National Weather Service Albany NY
1101 PM EST Fri Dec 23 2022
.SYNOPSIS...
Dangerously cold wind chills will be in place tonight,
especially over the higher terrain, with snow showers over the
Taconics, southern Greens and western Adirondacks. Snow showers
should come to an end by morning. Drier and cold weather will
persist through the Christmas weekend. Then, a more organized lake
effect snow band looks to impact the western Adirondacks Sunday
night into Monday.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
.Winter Weather Advisory issued for Bennington, western Windham,
eastern Rensselaer, and eastern Columbia Counties until 1 AM
EST Saturday...
.Wind Advisory in effect for all of western New England and
eastern New York through 7 AM Friday...
.Wind Chill Advisory in effect for the eastern Catskills,
southwestern Adirondacks, the central and southern Taconics, and
portions of western New England through noon Saturday...
The main items of concern for the near and short term periods are:
1) Dangerously cold wind chills through Saturday morning, 2)
Blustery winds out of the west, 3) Some upslope snows over
southern Vermont and the northern and central Taconics tonight,
4) Accumulating lake effect snows that will only clip our very
northwestern sections (Herkimer and Hamilton Counties) Sunday
night into Monday.
As of 11pm, our powerhouse closed low continues to track into
Ontario with a current central pressure analyzed to be
impressively at 970hPa per the latest RAP guidance. The Rap
shows a tight pressure gradient still overhead and since it is a
slow moving low (likely slower than what the models project),
we extended the wind advisory until 7am Saturday. Latest
observations from ASOS and NYS mesonet observations show wind
gusts of 35 - 45mph which also supports extending the wind
advisory through morning. We will continue to evaluate
observations/trends and can cancel the advisory earlier if
needed.
Winds should gradually weaken after Midnight with snow showers
also winding down along the Taconics and southern Greens as
westerly winds shift to the southwest and we lose the upslope
component. Total snowfall amounts in these areas based on
trained spotter and social media reports range from 3 to 6
inches with an additional 0.5 inch or so still possible before
the snow showers end. The western Adirondacks will likely be
the exception with lake effect snow showers continuing overnight
in northern Herkimer and Hamilton Counties resulting in
additional 1 to 2 inches of snow.
While the steepest drop in temperatures have already taken
place, as the winds gradually weaken after Midnight,
temperatures will likely drop a few more degree. Expecting the
morning lows to fall into the single digits and even sub-zero
single digits in the southern Green, eastern Catskills and
southern Adirondacks. These temperatures combined with breezy
westerly winds will lead to dangerous wind chills ranging -25 to
-5 degree.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
Through the Christmas Holiday Weekend, the main show will
continue to be the LES event out west over western New York
impacting our northwestern zones especially Sunday into Monday
as winds shift more out of the west. Otherwise, a dry and cold
period for the remainder of the area can be expected.
Daytime high temperatures on Saturday (Christmas Eve) are progged to
be in the teens most places (single digits higher elevations north).
These values are well below normal on the order of about 20F
degrees. Saturday night overnight lows are expected to be in the low
double digits over the valleys to single digits higher elevations.
Temperatures moderate slightly on Christmas Day as the cold vortex
retreats north. Daytime highs are expected to be in the mid 20s
along the river valleys (teens higher elevations), still colder than
normal on the order of about 10F degrees. Christmas night, overnight
lows are expected to fall into the teens over the river valleys (low
double digits to high single digits over the higher
elevations). On Monday, daytime highs are expected to climb only
in the mid to upper 20s along the river valleys (teens higher
elevations).
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Long term period will begin Monday night with mainly dry conditions
across the area except for a possibly a few lake effect snow showers
lingering across northern Herkimer County. During the Monday night
and Tuesday timeframe, large-scale pattern will feature troughing
over the east coast with ridging in the west. Northern stream
disturbance may bring some light snow showers to northern zones,
while southern stream shortwave tracks well south of our area. Given
lack of interaction between these two features, any snow showers are
expected to be on the lighter side and isolated to scattered in
nature.
As the upper trough moves off to the east of our region Tuesday
night, heights rise aloft as weak upper ridging builds over our
region. Upper ridging should remain in place through the end of the
week per latest deterministic and ensemble guidance. During this
period, generally dry and tranquil weather is expected with ridging
in place aloft and high pressure overhead at the surface.
Temperatures through Wednesday night will remain below average,
especially at night with high pressure overhead. As the high moves
off the east coast towards the end of the week, temperatures moderate
to above normal levels. The next chance for any meaningful precip
comes does not look to be until at least next weekend.
&&
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
Precipitation has ended at KPOU and precipitation will end at the
other TAF sites over the next hour or two although some snow showers
could linger at KPSF through 04Z. Cigs may remain in the MVFR range
tonight due to very cold air aloft. Ceilings are expected to vary on
Saturday between MVFR and VFR and a few snow flurries are possible
on Saturday.
Southwest Winds at 10-20 kt with gusts to 30 kt tonight through
Saturday.
&&
.HYDROLOGY...
Several rounds of heavy rain overnight and into the day combined
with snowmelt to cause ongoing high water and isolated river
flooding. Flood warnings currently in effect for the Williams River
at Rockingham, VT and Schoharie Creek at Gilboa Bridge, NY. Flooding
on the Hudson River at the Poughkeepsie, NY forecast point is
receding however the tidal surge continues to affect the Hudson
River, with an action stage crest (around 7 feet) currently underway
at the Albany forecast point. Attention turns to the Mettawee River
at Granville, NY and points along the Housatonic River in
Connecticut, where minor flooding is still possible, depending on
just how much snowmelt materializes. With the end of rainfall and
steep temperature drops cutting off snowmelt, additional flooding is
not forecasted.
For details on specific area rivers and lakes, including observed
and forecast river stages and lake elevations, please visit the
Advanced Hydrologic Prediction Service /AHPS/ graphs on our
website.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...Wind Chill Advisory until noon EST Saturday for CTZ001.
Wind Advisory until 7 AM EST Saturday for CTZ001-013.
NY...Wind Chill Advisory until noon EST Saturday for NYZ032-033-047-
051-058-061-063-066-082.
Wind Advisory until 7 AM EST Saturday for NYZ032-033-038>043-
047>054-058>061-063>066-082>084.
Winter Weather Advisory until 1 AM EST Saturday for NYZ054-061.
MA...Wind Chill Advisory until noon EST Saturday for MAZ001-025.
Wind Advisory until 7 AM EST Saturday for MAZ001-025.
Winter Weather Advisory until 1 AM EST Saturday for MAZ001.
VT...Wind Chill Advisory until noon EST Saturday for VTZ013.
Wind Advisory until 7 AM EST Saturday for VTZ013>015.
Winter Weather Advisory until 1 AM EST Saturday for VTZ013-014.
&&
$$
SYNOPSIS...Evbuoma/Speciale
NEAR TERM...Evbuoma/Speciale
SHORT TERM...Evbuoma
LONG TERM...Main
AVIATION...SND
HYDROLOGY...
Area Forecast Discussion
National Weather Service Boston/Norton MA
1042 PM EST Fri Dec 23 2022
.SYNOPSIS...
The arctic front sweeps through the region late this afternoon
followed by plummeting temperatures this evening and ocean effect
snow showers developing over the Cape/Islands and immediate south
coast. Cold and dry holiday weekend, but scattered ocean effect
snow showers will impact the Cape/Islands Saturday. Dry weather
is expected next week with a gradual warming trend.
Temperatures could reach the 50s by the end of the week.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Forecast remained largely on track. Did try to better time out
the arrival of the colder air this evening, along with the winds
subsiding. Ocean-effect snow showers underway across the
southern coastal waters, as well as portions of Cape Cod and the
islands. Also watching a mesoscale band of snow across north
central MA. The latest few runs of the HRRR and the 18Z 3-km NAM
appeared to have a good handle on the present locations of
precipitation, and were leaned on heavily for this update.
Also seeing rivers respond to the combination of rainfall and
upstream snowmelt. A River Flood Warning has been issued for the
Wood River at Hope Valley. Also canceled the River Flood Warning
for the West Deerfield River at West Deerfield per latest
observations.
630 PM update...
The arctic front has moved through southern New England as of
6:30 PM with winds shifting to the SW. While we saw a surge of
50-60 mph wind gusts with the frontal passage, wind gusts have
generally settled around 35 to 45 mph for most locations. The
cold air has made its way into western MA (Pittsfield is
reporting a temp of 21) which has allowed the exiting precip to
end as snow or sleet in the Berkshires and Worcester hills.
Previous Discussion...
* Windy with plummeting temps this evening
* Ocean effect snow showers developing over Islands
Arctic front moving into the CT Valley and will quickly sweep
across rest of SNE and move off the coast by 5-6 pm. One area of
heavier convective showers are lifting to the north and east of
SNE. Additional showers assocd with the front and strong
shortwave moving across SNE and this activity will sweep across
eastern areas through late afternoon. As colder air rushes in
from the west, a brief period of snow showers expected across
portions of western MA and particularly the Berkshires where up
to an inch accum is possible. Elsewhere, the rain may end as a
brief period of snow showers before ending with no accum.
Strong winds...
Another pulse of strong winds expected for a few hours along and
behind the cold front into the evening after the wind shift to SW.
The strongest gusts which could briefly reach 50-60 mph will likely
be across eastern MA with the secondary low level jet. The jet is
weaker, 50-60 kt, but inversion will be mixing out with strong cold
advection and deepening boundary layer so should be able to mix a
lot of this wind down, especially given strong pressure rise fall
couplet with the front. Winds will diminish later this evening as the
strongest cold advection diminishes overnight, but winds will remain
gusty through the night.
Temps/Wind chills...
Expect 20-30 degree temp drop in about a 6 hour period behind the
front assocd with the strongest cold advection. There will be a 1-2
hour window late this afternoon in western MA/CT for a few icy spots
on roads, especially with any snow showers, but not expecting a
significant impact as the strong winds and rapid drying takes hold.
Dewpoints will be falling through the 20s and into teens within a
few hours after the colder moves in and roads will dry out quickly.
Lows tonight will range from the single numbers in central/western MA
and higher terrain in CT to low/mid teens elsewhere, except lower
20s outer Cape/Islands. Wind chills will drop to zero to -10F late
tonight, except single number wind chills SE MA and Cape/Islands.
Portions of the Berkshires could briefly get down to -15F
Ocean effect snow...
The strong cold advection will bring 850 mb temps down to -18C with
deepening boundary layer. This will result in extreme instability
over the warmer SST with delta T approaching 30. We expect ocean
effect snow showers to develop south of Long Island within the SW
flow with bands of snow impacting the Islands and possibly up to the
immediate south coast. Forecast confidence on snow amounts is low
but thinking an inch or 2 is possible over Nantucket and a coating
on Cape Cod. Some of the hi-res models also indicating some minor
accum immediate south coast of RI but confidence here is low. More
persistent snow bands may end up south of Nantucket but this will
need to be monitored if it ends up further N.
Coastal flooding...see section below
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Saturday into Saturday night...
Deep trough over the NE will lead to cold and dry conditions with
diurnal CU in the interior, and ocean clouds along the south coast.
Ocean effect snow showers will persist south of New Eng within the
SW flow which will impact the Islands and especially Nantucket.
Another inch or 2 is possible over Nantucket which could bring total
accum to 2-4 inches but our confidence is not high and this would be
over a 36 hour period so not planning on any advisory at this time.
Highs teens interior to lower 20s near the coast, with lows Sat
night in the single numbers and teens. Still blustery Sat with gusts
25-35 mph creating daytime wind chills of zero to 10F.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Highlights...
* Dry and chilly through Christmas, then remaining dry with
moderating temperatures next week.
Details...
Sunday the low pressure continues it exit into northern Quebec,
relaxing the pressure gradient and bringing a break from the gusty
winds. Christmas Day will be quiet and dry, with plenty of sun under
building high pressure. Moving into the week between Christmas and
New Years` we`re looking at more of the same with dry and quiet
weather beneath a sprawling area of high pressure that builds in
from the south and east. As a trough digs into the western U.S. mid
to late week it pumps up a mid level ridge over the east coast,
supporting moderating temperatures. Highs surge into the 40s
Thursday and even the 50s by Friday and New Year`s Eve. EPS ensemble
guidance gives a 50-60% chance of temps over 50 F next Friday and
even higher odds by New Year`s Eve.
&&
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight...High confidence.
Improving to VFR for most outside of the Cape/Islands. Will have
MVFR conditions linger with ocean-effect snow showers. Most
likely at ACK, but could leak into HYA/FMH from time to time.
Up to an inch of accumulation is possible at ACK. WSW/SW winds
at 15-25 kts with gusts of 35-45 kts in the evening. Gusts ease
to 25-35 kts after 06Z.
Saturday and Saturday night...High confidence.
VFR for most, but MVFR/borderline MVFR conditions linger across
the Cape/Islands due to ocean effect snow showers. Will remain
gusty out of the SW/WSW with speeds of 15-20 kts and gusts of
25-35 kts. Winds ease to 5-10 kts Saturday night with gusts of
15-25 kts. The highest gusts confined to the Cape/Islands.
Could see another 1-2 inches of new snow across ACK.
KBOS Terminal...High confidence in trends, moderate in exact
timing of strongest winds this afternoon/evening.
KBDL Terminal...High confidence.
Outlook /Sunday through Wednesday/...
Christmas Day: VFR. Windy with local gusts up to 30 kt.
Sunday Night through Monday: VFR. Breezy.
Monday Night through Wednesday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
High Confidence.
Storm Warnings continue into early Saturday morning. Gusts to
50 kt possible as the arctic air overspreads the coastal waters.
Winds will slowly diminish thereafter, with gale force wind
gusts overnight diminishing further Sat/Sat night. Rough seas
and areas of light freezing spray developing over the nearshore
waters as arctic air pours into the region.
Outlook /Sunday through Wednesday/...
Christmas Day: Strong winds with areas of gusts up to 30 kt.
Rough seas up to 12 ft. Slight chance of snow.
Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 10 ft.
Monday: Winds less than 25 kt. Seas up to 5 ft.
Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft.
Tuesday: Winds less than 25 kt.
Tuesday Night through Wednesday: Winds less than 25 kt. Seas
locally approaching 5 ft.
&&
.TIDES/COASTAL FLOODING...
We are not expecting any coastal flooding on the south or east coast
for tonight`s high tide. The astronomical tide is lower and surge is
expected to decrease to around 1 ft on the east coast and 1 to 1.5
ft on the south coast as winds shift to SW and pressures rise
rapidly. This will fall short of flood thresholds. There is a low
risk the surge in the upper reaches of Buzzards Bay could be around
2 ft with favorable SW wind, but the worst case in this scenario
would be minor splashover.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Wind Warning until 1 AM EST Saturday for MAZ022>024.
RI...None.
MARINE...Storm Warning until 1 AM EST Saturday for ANZ230>237-250-251-
254>256.
&&
$$
SYNOPSIS...KJC/BW
NEAR TERM...Belk/KJC/BW
SHORT TERM...KJC
LONG TERM...BW
AVIATION...Belk/KJC/BW
MARINE...Belk/KJC/BW
TIDES/COASTAL FLOODING...Staff
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
258 PM PST Fri Dec 23 2022
.SYNOPSIS...Mild temperatures with some light rain will occur
across the area through Monday. A powerful storm will impact
Northwest California with heavy rain, strong winds and high surf
Monday night through Tuesday. Additional storms are forecast to
bring more rain and high mountain snow mid to late next week.
&&
.DISCUSSION...Light spotty rain has been winding down through the
day today. Radar has been void of returns, however automated gauges
have been recording a few hundredths, mostly in the mountains and
in Del Norte county. The shallow light rain may persist into the
evening hours, but should it should dry out overnight as southerly
and southeasterly winds increase in advance of a warm front and
PWATs diminish. This warm front will likely bring another surge
of PWATS and an uptick in light rain for mostly the northern
portion of the forecast area, primarily during the afternoon and
evening hours. The greatest 12 hourly amounts will be in the
higher terrain of Del Norte county. Up to an inch will be
possible. Elsewhere, for the coastal plain and valleys, generally
no more than two tenths of an inch is forecast. In addition,
temperatures will be quite mild for latter December, with highs
generally ranging from the upper 50s to mid 60s inland and at the
coast. Overnight lows will also be near or slightly above normal
for latter Dec. The warm front will lift out on Sunday and allow
ridging and drying aloft to build. Precipitation chances will
dwindle to about 10% or less for much of the area, though a few
light showers may still occur over Del Norte county during the
morning hours.
By early next week, a leading shortwave trough is forecast
to break down an upper ridge over the PACNW region Sunday night
into Monday. An associated frontal boundary will aid in a focused
area of light rain across the Eureka forecast area during that
period. Model guidance also shows the westward trailing segment of
the front stalling, which will serve to anchor a second stronger
upper wave and associated surface cyclone developing Monday night
into Tuesday within the the exit region of a 140+ kt 250 mb
westerly jet. A rapidly tightening surface pressure gradient
combined with a 60+ kt southerly low-level coastal jet will aid in
gusts from 40 to 60 mph Monday evening-Tuesday morning, with the
highest gusts expected across exposed ridges and coastal headlands
in Humboldt and Del Norte Counties. An advisory for wind is most
probable with blended guidance and deterministic models indicating
gusts from 40 to 55 mph. High wind warning criteria appears less
probable with stable boundary layer conditions limiting mixing
and downward momentum transport.
Strong west-southwesterly 850 mb moisture flux and IVT values at
or above 500-750 kg/m/s will also impact NWRN CA Monday night/Tuesday
morning. Heavy rainfall rates will be probable as a result, with
the highest rates possibly trending toward areas over the King
Range south across Mendocino County. Debris flow on burn scars
will be possible if hourly rates reach or exceed 0.80-1.40in/hr.
Minor urban and small stream flooding will also increase Monday
night into Tuesday morning as the plume of high moisture or IVT
progresses southeastward. The heaviest rain looks to occur from
about Cape Mendocino and southward, though upslope southwesterly
flow will likely yield heavy rain for northern Trinity county.
The airmass on Tuesday will be warm through a deep layer, and
that will favor snow levels mainly at or above 4500 feet. Impacts
due to heavy snow will subsequently be confined to the high
terrain across the Trinity Alps in NRN Trinity County.
After Tuesday, deterministic and ensemble based forecast guidance
show a mean zonal flow regime occurring aloft with embedded waves
impacting the West Coast. The humid westerly flow regime and
augmented ascent with passing waves will support additional rain
chances well into the extended range forecast period.
&&
.AVIATION...Lingering light rain will gradually come to an end this
afternoon at KCEC. There will still be patches of fog along the
North Coast through the night as abundant low-level moisture remains
in place. Another front will approach the area on Saturday, with the
main impacts of low ceilings and visibilities in rain occurring from
KCEC northward. Some of the model guidance keeps the bulk of the
rain N of the OR border, so uncertainty is high regarding the KCEC
forecast late in the TAF period and beyond. There is the potential
of low-level wind shear once again at KCEC by Saturday afternoon.
At KUKI, low clouds persist this afternoon. Models indicate that
these clouds will gradually lower through the evening. Some breaks
in the overcast may become more pronounced overnight, but any
scattering of low clouds will lead to more the potential of a
developing lower cloud deck and/or fog. Winds at KUKI will remain
light. /SEC
&&
.MARINE...A series of fronts will approach the area through the
period, bringing several periods of increasing southerly winds to
the coastal waters. The strongest winds are expected Sunday night
and Monday morning, then again Monday night. During these periods,
gale are likely over the N waters, with the potential for a brief
period of storm force gusts over the N outer waters early Tuesday
morning. Due to the persistent storm track upstream from the area, a
persistent large W swell is forecast to develop this weekend and
persist through much of the coming week. W swell heights may reach
24 feet by Tuesday and Wednesday. Thunderstorms are possible over
the waters Tuesday and Wednesday. /SEC
&&
.HYDROLOGY...Another weak front will bring light rain to the
northern portion of the area on Saturday, primarily in the
afternoon and evening hours. The greatest 12 hourly amounts will
be in the higher terrain of Del Norte where an inch will be
possible. Elsewhere, generally a tenth or two is forecast. Heavy
rain with a moderate to strong atmospheric river is forecast to
impact the entire area Monday night through Tuesday night. 3 to 6
inches of rain is forecast Monday night into Tuesday night.
Heaviest rain rates of 0.30in/hr or more will most likely arrive
from Monday night through Tuesday morning. Integrated water vapor
transport values (IVT`s) will peak in excess of 750kg/m/s during
this period. The duration will be short, probably no more than 6-8
hours. Main stem rivers will experience rapid rises Monday night
into Tuesday. Monitor stages will be possible (30-40% chance) on
North Coast rivers, particularly the Mad River at Arcata and Eel
River at Fernbridge. Flood stages are not completely impossible,
however ensemble probabilities are no more than 15%. Likewise, for
the Russian River at Hopland and Navarro River at Navarro, probabilities
of flood stage exceedance remains no higher than 21%. The potential
for urban and small stream flooding will increase during this time
period of heavy rain and shortly after. There is an outside chance
for debris flow on burn scars late Monday night into Tuesday
morning, if deep convection or thunderstorms develop and rain
rates reach or exceed 0.80-1.40in/hr. This will need to be
monitored. The HRRR should shed more light on hourly rates once
within range of the convective allowing mesoscale models. Also,
snow levels will also begin to fall on Tuesday and precip rates
will generally start to wane as the plume of high IVT`s head
southeastward by Tuesday night. Locally heavy showers will still
be possible due to weak instability and steepening lapse rates.
Models remain consistent with another weak or moderate atmospheric
river (AR) arriving toward the end of the week. This AR probably
will not produce as much rain or long duration heavy rain rates.
It will need to watched as there are some ensemble members that
suggest a possible wetter outcome.
&&
.BEACH HAZARDS/COASTAL FLOODING...King tides will continue to
yield minor flooding across portions of Humboldt Bay during the
late morning hours through Sunday. As usual, King Salmon and
Fields Landing will be the most probable locations for minor
flooding. Otherwise, a large west-northwest swell will impact the
coast of Northwest California Tuesday through Wednesday. Breaking
waves from 25 to 28 feet will be possible, and will create very
hazardous conditions along area beaches, jetties, and rock
outcrops. /SEC
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
Coastal Flood Advisory from 10 AM to 2 PM PST Saturday for
CAZ103.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 9 PM PST Saturday for PZZ470.
Small Craft Advisory from 6 PM this evening to 9 PM PST Saturday
for PZZ475.
&&
$$
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For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png
Area Forecast Discussion
National Weather Service Spokane WA
327 PM PST Fri Dec 23 2022
.SYNOPSIS...
Very cold temperatures will begin to moderate as a warmer air mass
moves in from the Pacific. This transition will be slow as the
cold air near the ground will be difficult to mix out. This will
result in a gradual precipitation transition from snow to freezing
rain and then just valley rain. However this may not occur before
Tuesday for many valley locations. The warming will continue
through next week resulting in significant melting potential and
the possibility of some flooding especially over southeast
Washington.
&&
.DISCUSSION...
...Complex winter weather scenario tonight through Saturday night
with an increasing risk of freezing rain...
Tonight...We are seeing somewhat of a lull in the action late this
afternoon. The main activity revolves around a weak shortwave
currently producing light snow over extreme eastern Washington and
north Idaho. However we should see an uptick in the activity this
evening as a stronger disturbance...currently moving into the
Cascades tracks into eastern Washington and the Panhandle later
this evening. This promises to deliver another round of light snow
to much of the area with another 1-3 inches of snow expected and
locally heavier amounts over Shoshone County and the Blue
Mountains. While snow will be the primary threat, a warm nose will
be moving in from the southwest which should begin to introduce
freezing rain into the equation. Most of this is expected to
develop over the Palouse southward. Most of the short-range models
suggest this will occur around late evening, however we just saw
a webcam image of possible freezing rain near Uniontown and if
this remains consistent we will have to update the forecast and
grids accordingly. Winter weather advisories remain in effect for
this area through early Saturday morning. Meanwhile closer to the
Cascades, most of the precipitation is going to occur near the
Crest due to westerly winds and neutral to slight cold air
advection resulting in downslope flow for most of the area. Snow
accumulations here will range from 2 to 5 inches. There will also
be an increasing threat of freezing rain at Stevens Pass as the
warm nose which is bringing freezing rain to Snoqualmie Pass edges
a bit northward.
For Saturday and Saturday night, the next disturbance moves into
the region. This is a wetter and warmer system than the current
one. But is is also increasingly complex as the precipitation type
forecast gets dicey based on where the elevated warm layer sets
up and whether or not the cold air near the ground can mix out.
The models are a mixed bag in regards to how far north the warm
air aloft will go. The GFS is probably the most conservative with
the warm nose and generally brings it to areas south of the
Highway 2 corridor in WA and I-90 in Idaho. The EC is somewhat
similar albeit slightly warmer. The NAM and the HRRR are
considerably warmer and bring the warmer air all the way to the
Canadian border by Saturday afternoon. Meanwhile all the models
are likely too quick on mixing out the cold pool of air near the
ground. If we don’t see significant winds, which we likely won’t
the sub-freezing air is going to have a very difficult time mixing
out. Once again the NAM and the HRRR are very eager to do this
with above freezing temperature expected over most of eastern WA
and north Idaho by afternoon. This seems too aggressive and we
altered the temperatures accordingly. Meanwhile the one area the
models agree upon is in the lee of the Cascades where sub-freezing
air is likely to persist through the period due to cold-air
damming. So what becomes of this scenario? It looks like we should
see an increasing risk of freezing rain and some brief sleet/ice
pellets over the Columbia Basin, Wenatchee Area, Waterville
Plateau during the morning hours and gradually spreading eastward
through the day. We have issued a winter weather advisory for the
aforementioned areas for Saturday, but we may need to expand those
advisories eastward depending on whether or not temperatures can
rise above freezing for locations such as the Palouse, Spokane, LC
Valley. If they can, we would just see rain or snow with the next
round, if not, it looks like more advisories would be necessary
for freezing rain. Right now we have ice accumulations of anywhere
from 0.05” to nearly 0.20” for much of the Columbia Basin and
Wenatchee area. We will also see even heavier amounts of ice for
Stevens Pass, Plain, and the Leavenworth area with values nearing
a third of an inch. This is currently included in a winter storm
warning as the main threat shift from snow to significant freezing
rain. These amounts will certainly lead to travel difficulties
and possibly some minor tree damage if the ice and snow loads
become too heavy.
The weather will begin to quiet just a bit on Saturday night as
the aforementioned shortwave exits into Montana with rain or snow
showers persisting near the Cascade crest and over the ID
Panhandle. By the time all is said and done we are looking at snow
accumulations of 2 to 5 inches across most of the northern
valleys of Washington and north Idaho for Saturday into Saturday
night with much heavier amounts over the northern Cascades. Once
again it should be noted that this forecast has a great degree of
difficulty and a small change in temperatures at the surface or
aloft can result in a completely different forecast result. fx
Christmas Day: As this system remains in place, the threat of
freezing rain continues as well throughout Christmas Day. During the
morning hours the main threat is along I-90 from Moses Lake to
Spokane southward before shifting north to include Moses Lake,
Wenatchee, to just south of Omak. Make sure that if you are
traveling this holiday, to check your local forecast before you head
out. For current road conditions, call 511.
Monday through Thursday: As this system exits, a ridge builds for
Monday, warming temperatures above freezing. The next system move
through on Monday as well but with temperatures near or above
freezing, the lower elevations can expect rain with snow in the
mountains. Total liquid amounts will be an inch or more north of a
line from Omak to Pullman with areas south seeing closer to a half
inch. The mountains will see 1.5 to 2 inches of liquid but since
temperatures are cooler, near a foot of new snow above 3500 feet.
The highest peaks could see 1 to 2 feet of snow. The heaviest precip
will fall late Monday night/Tuesday morning, continuing through the
morning Tuesday.
Beginning Wednesday, shortwaves will pass over the area each day
bringing the chance of light showers over the region. Temperatures
during the day will stay above freezing for the lower elevations,
which would keep much of the precip as rain and snow in the
mountains. Temperatures in the lower elevations will be in the mid
to upper 30s with 40s possible in the LC Valley. /KM
&&
.AVIATION...
18Z TAFS: Widespread IFR/MVFR conditions are expected at almost
all the TAF sites through this period due to periods of
precipitation associated with an incoming warm front. The
precipitation from the warm front will largely impact the eastern
third of WA and the ID Panhandle through the remainder of the day,
however it will likely turn intermittent as slightly drier air
pushes over the Cascades. Another round of precipitations
currently moving into western WA will spread across the area this
evening, resulting in another round of widespread precipitation.
Most of this will be concentrated over the eastern third of WA and
N ID. Snow amounts for the TAF sites will generally be 1-2 inches
or less, but the next round will consist of wetter snow as
temperatures aloft rise substantially. In fact, they will warm
enough that we have placed a chance of freezing rain in the PUW
and LWS after 07z. Picking the precise time of a transition from
snow to freezing rain is tough, but we suspect it will certainly
occur before 18z Sat. Amounts should be less than 0.10" but
obviously any freezing rain can cause big issues for aviation
concerns.
&&
.PRELIMINARY POINT TEMPS/POPS...
Spokane 14 29 28 35 33 38 / 70 90 60 40 30 60
Coeur d`Alene 15 30 29 34 33 39 / 70 80 80 30 30 50
Pullman 20 35 34 39 37 41 / 70 50 70 40 10 40
Lewiston 25 36 35 43 39 43 / 60 40 60 30 10 30
Colville 10 24 23 30 29 35 / 30 100 30 30 30 60
Sandpoint 12 26 25 32 31 39 / 60 90 90 40 40 80
Kellogg 20 29 28 35 34 39 / 80 70 90 50 30 60
Moses Lake 11 24 23 31 30 34 / 30 90 20 50 20 50
Wenatchee 11 21 20 30 28 33 / 40 90 30 50 40 70
Omak 9 22 21 27 26 34 / 30 90 30 40 40 60
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 4 AM PST Saturday for Central
Panhandle Mountains-Coeur d`Alene Area-Idaho Palouse-
Northern Panhandle.
Winter Weather Advisory until 10 PM PST this evening for Lewis
and Southern Nez Perce Counties-Lewiston Area.
WA...Winter Weather Advisory until 4 AM PST Saturday for Northeast
Blue Mountains-Northeast Mountains-Spokane Area-Washington
Palouse.
Winter Weather Advisory until 10 PM PST this evening for Lower
Garfield and Asotin Counties.
Winter Weather Advisory from 4 AM to 7 PM PST Saturday for Moses
Lake Area-Upper Columbia Basin-Waterville Plateau-Wenatchee
Area.
Winter Storm Warning until midnight PST Saturday night for
Central Chelan County-Western Chelan County.
&&
$$