Graphical Hydro Meteorological Discussion

000
FXAK68 PAFC 240206
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
506 PM AKST Thu Jan 23 2020

.ANALYSIS AND UPPER LEVELS...

The upper level pattern with a trough over the mainland part of
the state and ridge over the Bering persists. The surface low
track remains south of the Aleutians out west. In the GUlf a low
can be seen near Middleton Island as the cold advection off the
Aleutian range gets wrapped up in it and keeps it nearly
stationary. That cold advection can be seen best of visible
satellite out of the gaps and channeled terrain from Resurrection
Bay southwestward to the Alaska Peninsula.

&&

.MODEL DISCUSSION...

Models remain in good agreement into Saturday around the region
and the Bering Sea area remains under good agreement into next
week. The issue in in the Gulf of Alaska by Saturday night when a
complex low starts to give the models fits as to how it will
develop and where the main low centers in it will be.

&&

.AVIATION...
PANC...VFR conditions and light (mostly) north winds are expected
to persist into Friday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Colder temperatures are expected to settle across the region
tonight as cold air advects from the interior to the Gulf of
Alaska. Gusty conditions develop through channeled terrain this
evening with gusts already established across the western gulf.
The strongest gusts are expected through typical areas such as Seward,
Thompson Pass, Whittier, Matanuska Valley, Broad Pass and Copper
River Delta. Mostly dry conditions are expected for inland
location and the western Gulf, with isolated to scattered snow
showers across the northeastern Gulf. The next front to monitor
develops across the eastern Gulf late Saturday, taking a slow
northwest track through Sunday. Increased snow chances along the
northeast Gulf coast on Sunday as models all show the boundary
pushing to Cordova in the morning. .

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Tonight
through Sunday)...
A blocking ridge over the eastern Bering Sea will lead to cold,
windy, and dry conditions across Southwest Alaska over the next
few days. Northerly flow will continue to advect clouds across the
Kuskokwim Valley and Kuskokwim Delta tonight, but expect at least
partial clearing by Friday as colder and drier air advects
southward from the Arctic. The magnitude of cold air advection
across Southwest Alaska will be weak through Friday night, though
both the ridge to the west and a low in the Gulf of Alaska will
strengthen with time, leading to tighter pressure gradients and
stronger winds. The presence of clouds and wind will initially
limit temperature drops, but generally expect a steady downward
trend in temperatures over the next couple days. For those areas
exposed to the winds, this will also lead to falling wind chill
temperatures. Have made some adjustments to existing wind chill
advisories for the Kuskokwim Delta and Bristol Bay to delay the
onset of the coldest wind chills (-40 degrees or colder). Further
adjustments will likely be needed as we fine-tune the temperature
and wind forecasts.

The strongest winds will be along the south side of the Alaska
Peninsula, as cold air funnels through the bays and mountain
passes. As we head through the weekend the a digging trough over
the Gulf will push the Bering ridge westward and the low level
flow will shift to a north to northeast direction. A reinforcing
shot of cold air advection will cross Southwest Alaska Saturday
night through Sunday and head toward the southern Alaska Peninsula.
This change in flow will shift the strongest winds south and
westward along the Alaska Peninsula. The persistent winds and cold
air advection of the next few days will also lead to widespread
areas of Heavy Freezing Spray across the Southwest Alaska coastal
waters. With the significant surge of cold air over open waters of
the eastern Bering Sea on Sunday, would also expect development
of snow showers.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through
3/Tonight through Sunday)...
A compact, but potent low south of the western Aleutians will
become vertically stacked tonight, slowing the westward
progression of the low. It will then weaken as it continues to
the far western Bering Sea Friday through Friday night. Meanwhile,
an occluded front strung out along the western to central
Aleutians will lift slowly northward tonight, then stall on
Friday. A core of storm force winds ahead of the front will shift
from the western to central Aleutians northward into the Bering
Sea offshore zones tonight, then gradually diminish through
Saturday. Expect periods of rain and snow, with surface
temperatures along the Aleutians remaining largely above freezing.
Another Pacific low will approach the Aleutians Saturday night
through Sunday, leading to restrengthening of winds. The
prevailing wind will remain easterly over the next three days
across the western half of the Bering Sea and along the Aleutian
chain.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska:

An occluded low and a surface low will persist over the Gulf of
Alaska Saturday, Sunday and Monday bringing moisture to the region.
Strong high pressure over the mainland coupled with the low
pressure in the Gulf will produce strong offshore flow winds,
especially near the Barren Islands and Kamishak Bay. Gale force
winds and heavy freezing spray possible.

Bering Sea and Aleutians:

A strong low south of the western Aleutians will keep widespread
gales with the possibility of isolated storms across the central
and western Bering Saturday and Sunday. Freezing spray will
continue to impact portions of the Bering. Winds will decrease by
Monday.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Looking at the synoptic pattern, expect low pressure over the
Gulf of Alaska and south of the Aleutians with a dense cold
airmass building up over the mainland. Below normal temperatures
will continue for western Alaska and southcentral Alaska. This
setup will result in enhanced gap winds through the coastal
mountains with precipitation mainly along the coastal regions of
the Gulf.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind chill advisory 155 161.
MARINE...Gale 119-121 127 129-132 138 150 155 170 172-174 178 185
Storm 175 176 177
Heavy Freezing Spray 126 127 129 130 132 138 139 141 150-165 179
180 185
FIRE WEATHER...NONE.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...BB
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SEB
MARINE/LONG TERM...PJS

000
FXAK69 PAFG 232323
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
223 PM AKST Thu Jan 23 2020

.SYNOPSIS...
Snow chances continue through Friday for much of the eastern
Interior, with snow tapering off Saturday as a low in the northern
Gulf of Alaska pushes waves of moisture north and west across the
eastern Interior. Highest snow accumulations will be along the
AlCan border where an additional two to two and a half inches will
be possible through Saturday. A very cold airmass will continue
to dive south and east out of Siberia, dropping temperatures
through the remainder of the week and into next week. As high
pressure builds east across the Chukchi, the pressure gradient
tightens, leading to increasing winds along the West Coast and
summits in the Interior. The combination of the winds and dropping
temperatures will result in wind chill values of 40 to 50 below
tonight and into the weekend in some locations and Wind Chill
Advisories have been issued.

&&

.DISCUSSION...
Aloft, at 500 mb, an Omega Block continues to set up over the
eastern Bering Sea. A trough extends south across the middle of
the state and into the northern Gulf of Alaska, while a strong
ridge builds north over the eastern Bering Sea through the
weekend. A very cold air mass will dive south and east out of
Siberia and across Alaska, with temps dropping through the
weekend. 850 mb temps are expected to range between -25C and -35C
for much of the Interior and North Slope by Sunday. Models
continue to show significant cloud cover across much of the
central and eastern Interior, which will limit the temperatures
realized at the surface. Surface temperatures are expected to fall
into the 30s and 40s below across much of the Interior and North
Slope this weekend.

Surface... Weak high pressure persists across most of the state.
Ridging will continue to build east north across the Arctic Plain,
as a 1028 mb high over Siberia strengthens and builds eastward
across the Chukchi. By Friday afternoon a 1035 mb center of high
pressure is centered over the Chukotsk Peninsula. This will
continue to push northeast a trough that stretches from a 1008 mb
low 300 nm N of Wrangel Island southeast to Cape Bathurst. The low
will weaken to 1013 mb as it moves into the high Arctic Friday
afternoon with the trough stretching southeast to Banks Island. An
area of low pressure stretches along the Gulf of Alaska coast
this afternoon from Sitka to Yakutat to Valdez with with a 992 mb
low 70 nm south of Cordova. The low will deepen Friday to be a 985
mb low 100 nm south of Cordova by Friday afternoon and persist in
the northern Gulf of Alaska through Saturday.

Models...
12Z model suite initialized well against the 12Z surface obs and
the 12Z RAOBS. Models continue to show a Omega Block over the Bering
Sea and Western Alaska and continue to exhibit good run to run
continuity. By Sunday, model spread increases with the placement
surface lows south of the Aleutians. Temperatures remain the
biggest challenge for the forecast period. Most model solutions,
with the exception of the 12Z and 18Z NAM, maintain mostly cloudy
to overcast skies across the eastern Interior through the weekend,
while the NAM clears skies out on Sunday. If clouds remain over
the area then temperatures will trend warmer but it the clouds
clear out, especially for an extending amount of time at any
location, then colder temperatures realized.

North Slope and Brooks Range: West to southwest winds will
persist through the weekend along the coast and range from 5 to 15
mph, with the exception for those areas east of Prudhoe Bay,
where winds will increase to around 25 mph tonight. In the Brooks
Range passes, winds will be from the north at 5 to 15 mph. Areas
of stratus, patchy fog, and flurries continue this afternoon along
the coast, with pockets of light snow over the eastern Brooks
Range. There will be a brief period tonight and Friday, when there
is weak high pressure aloft and at the surface, and skies may
partially clear from Utqiagvik west. Cloud cover will return by
Friday night for this area. Temperatures will be on a downward
trend through the weekend and highly dependent upon cloud cover.
Coldest temperatures will be across the Arctic Plain.

West Coast and Western Interior: Satellite imagery shows a mix of
clouds and clear skies across the region this afternoon. Flurries
and areas of light snow will likely persist where there are clouds
this afternoon and evening. As high pressure builds in from the
west, skies will clear overnight and mostly clear skies will
persist through the weekend. Temperatures will drop through the
weekend, with the coldest temperatures occurring from Ambler south
to Galena to McGrath, where low temperatures will fall to around
40 below zero. North winds of 5 to 15 mph expected along the coast
tonight. Winds increase Friday to 10 to 20 mph along the coast,
with areas along the Bering Strait Coast and northern Seward
Peninsula increasing to 15 to 25 mph Friday night. Inland north
winds up to 10 mph can be expected. Winds combined with colder
temperatures will result in wind chill values as cold as 45 below
tonight into this weekend. Wind Chill Advisories have been issued
for zones 207, 208, 210, and 217. Additional Wind Chill Advisories
may be needed over the weekend.

Central and Eastern Interior: Latest satellite imagery show a
large area of clouds across much of the area with pockets of clear
skies west of the Dalton Highway. Surface obs show areas of light
snow and flurries. Snow chances continue through Friday for much
of the eastern Interior, with snow tapering off Saturday, as a low
in the northern Gulf of Alaska spins several waves of moisture
north and west. Highest snow accumulations are expected along the
AlCan border, where an additional two to two and a half inches
are possible through Saturday. Temperatures around the Interior
will fall into the 30s to 40s below this weekend. In areas where
skies have cleared, temperatures have already fallen into the 35
below range. Temperatures in the Upper Koyukuk Valley will drop as
low as 45 below, while temperatures in the Middle Tanana Valley
will fall into the 20s to 30s below Sunday through Tuesday. Wind
increase along the higher terrain tonight and Friday. In the
Alaska Range passes, northerly gap winds of 15 to 30 mph are
expected to continue through Friday. This will cause some blowing
snow in the passes. Wind Chill Advisory have been issued for
zones 218, 225, and 226 for wind chills of 40 to 50 below.

Coastal Hazard Potential Days 3 and 4...None.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory for AKZ207-AKZ208-AKZ210-AKZ217-AKZ218-
AKZ225-AKZ226.
&&

$$

JAN 20

173
FXAK67 PAJK 240611
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
911 PM AKST Thu Jan 23 2020

.UPDATE...New guidance and monitoring of trends this evening have
caused us to lower snow totals for Juneau and much of the northern
Panhandle through Friday. As a low in the gulf moved onshore,
mixing increased through the north-central Inner Channels. This
raised temperatures not only near sea level, but aloft as well.
MDCRS aircraft soundings indicated a warm layer (temperature >
0C) of around 2800 feet this afternoon. This matched better with
GFS indicated temperature profiles which backed off on colder air
advancement to a later time on Friday. Thus, we have all but
removed snowfall accumulations for Juneau Thursday night. Yet we
have kept 1 to 4 inches for the capital city Friday. The bulk of
precipitation from training indicated below should arrive in the
morning. We cannot rule out heavy rates lowering snow levels to
the surface locally, potentially in the Mendenhall Valley tomorrow
morning and higher elevation neighborhoods like Mountainside and
higher streets on Douglas. If this happens, it will be wet and
very heavy slop. Precipitation becomes more consistently snow by
the afternoon as cooler and drier air filters in. Therefore,
melted numbers should be lower. But we compensated afternoon snow
amounts a little with greater snow ratios in the afternoon.
Finally, we expect temperatures to remain at least marginally
above freezing for most areas. This all resulted in lower numbers
that fell below advisory criteria; therefore, we cancelled. This
forecast has been difficult, as is the snow forecast for the
current late January weather pattern: small deviations of
meteorological parameters can make large impacts. The warning for
Haines looks solid even while there is lower confidence for
Skagway numbers.

&&

.PREV DISCUSSION......ISSUED AT ...249 PM AKST THU JAN 23 2020

SHORT TERM...Currently, an upper trof is amplifying over the
western gulf this evening, and is expected drift into the central
gulf tonight into Fri night. A series of shortwave trofs are
expected to move out of the southern stream into the far eastern
gulf and SE panhandle. At the sfc, a low located in the far
eastern gulf has come onshore and will move across the northern
panhandle before weakening tonight. Another low will move N into
the area late tonight and Fri followed by a sharp cold front
swinging in from the east.

Ended up issuing a Winter Weather Advisory starting at midnight
tonight for the Juneau area, mainly for the Mendenhall Valley
with 3 to 5 inches possible. The Winter Storm Warnings for zones
18 and 19 were kept as is. For this evening, as the band of precip
moves across the panhandle into areas of favorable frontogenesis
and ample lift, precip rates will begin to increase. With this,
snowmelt cooling should help to change from rain to snow. The
forecast track of the approaching low was not changed significantly
with this update. Based on this, areas including Sitka to
Gustavus will also see snow accumulations but under advisory
criteria. One area of concern is that any change in track of this
system will effect snowfall amounts. Also, there are still some
timing differences on the lifting strength associated with the
cold side of the system, which would affect QPF/snowfall forecast.
As of now, advisory criteria only for Juneau with snow amounts
widely varying, but as timing issues align, an update may be
warranted as confidence is moderate.

After frontal passage and colder air begins to take over, precip
will become convective causing more snow showers. For the far SE
panhandle, the precip is expected to remain mixed as the deeper
cold airmass will be further N. The snow showers will be most
frequent/heavy across the NW half of the area, especially along
the NE gulf coast. By Saturday, our next weather maker approaches
from the south.

LONG TERM.../Saturday through Thursday/As of 10 PM Wednesday/Complex
and quite stormy pattern will dominate the weather over the
Panhandle through the long term.

Upper ridging will be in place over the Bering Sea this weekend
and will slowly migrate westward through mid week. The downstream
result will be deep troughing over mainland AK and the Gulf of
Alaska. Very cold airmass will be in place over much of the state
but will generally be centered to the north and west of the
Panhandle through the period. To the south, shortwave energy
riding an active Pacific jet will periodically interact with the
deep northern stream trough and arctic airmass to generate several
potent storms. These storms will track towards the Panhandle in
the SW to S flow aloft. As usual with complex stream interactions,
operational guidance is in complete disarray in regards to tracks
of frontal waves along the tight baroclinic zone in the eastern
Gulf through mid next week. As stated yesterday, precip type may
be a huge issue as the pattern favors bouts of quite significant
precipitation along with shots of modified arctic air ejecting
across the Gulf and into SE Alaska. Will likely see precipitation
across the northern half of the Panhandle alternate between rain
and snow several times through the long term while the southern
Panhandle remains warm enough for mainly rain.

Given the strong baroclinic zone in place over the eastern
Gulf,periods of strong winds are also possible especially if
phasing between northern and southern streams can occur.

All in all, way too early to nail down details of any particular
system so left the forecast generally unchanged. The potential is
there for one or two significant winter storms with strong winds
and heavy precipitation (potentially heavy snow for the north)
from the weekend onward which is hard to reflect in a
deterministic forecast at this time.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Storm Warning until 6 PM AKST Friday for AKZ018-019.
MARINE...Small Craft Advisory for PKZ012-013-036-041>043-051-052.

&&

$$

JWA/CC/DEL

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