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000
FXAK69 PAFG 201330
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
430 AM AKST Sat Jan 20 2018

.DISCUSSION...
The 00z model suite initialized well against the 00z surface
analysis and verified well against the 06z surface analysis.
Model spread remains minimal in the the short range and is
reasonable in the mid range. Significant differences on large
scale features continue to plague the long range models with
several hundred miles difference between long wave axis noted
between the ECMWF, Canadian and GFS. In general the models all
keep the trough axis just west of Fairbanks which would continue
the idea of clouds moderating temperatures over the central and
eastern interior while predominately clear skies allow for strong
radiational cooling and will produce much colder temperatures
over the western interior. Surface temperatures will likely drop
into the 30s and 40s below while temperatures in the central and
eastern interior will only drop into the 20s and 30s below.

Snow and blowing snow continues over the eastern North Slope and
will continue to diminish through the day. Temperatures continue
to drop and with brisk winds continuing the Blizzard Warning and
Winter Storm Warnings have been replaced with Wind Chill
Advisories with wind chill values dipping below 50 below. Wind
Chill Advisories continue and have been extended through Sunday
over the North Slope and Kotzebue Sound as cold temperatures
combined with brisk winds produce advisory or near advisory level
wind chills over the western North Slope and western Brooks
Range. Conditions will briefly improve this afternoon but as
temperatures drop again tonight Wind Chill values will reach
Advisory levels again.

Under clearing skies tonight temperatures are expected to drop
into the 30s and possibly 40 below over the western interior.
Lingering light snow and clouds will moderate temperatures
especially to the east of Manley Hot Springs.

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

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory for AKZ201-AKZ202-AKZ203-AKZ205-AKZ206-
AKZ208-AKZ209-AKZ210-AKZ217-AKZ218.

Winter Weather Advisory for AKZ204.

Brisk Wind Advisory for PKZ240-PKZ245.
&&

$$

CCC JAN 18


000
FXAK68 PAFC 201259
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
359 AM AKST Sat Jan 20 2018

.ANALYSIS AND UPPER LEVELS...
The longwave pattern features a building ridge over the Bering
Sea and a trough with an axis spanning from the north slope and
into the Gulf Of Alaska. A shortwave continues to round the top
of the ridge and into northwest Alaska. Anomalously cold air has
been observed and expect this Arctic outbreak to impact the
Bering Sea and mainland Alaska. Ahead of the ridge, there is a
quasi-stationary weak low over the Gulf of Alaska which continues
to produce showers that are detectable on the Middleton Island
radar. West of the strengthening upper level ridge, a gale force
low with an occluded front is approaching the western Aleutians
and is also advecting warmer air towards Attu and Shemya.

&&

.MODEL DISCUSSION...
Models are in good agreement with the synoptic features and they
continue to exhibit good run to run continuity. The biggest
forecast challenge continues to be the duration and the areal
coverage of the fog and stratus in Southcentral. Fog is commonly
handled poorly by the models. The fog and stratus coverage will
have an impact on the temperature forecast. Places where the skies
clear out will experience radiational cooling and possibly be
colder than anticipated. Other than the temperature and the
fog/stratus issues, this is a high confidence forecast package.

&&

.AVIATION...
PANC...Light winds expected. The latest satellite imagery still
has stratus and fog over portions of Cook Inlet and along Knik
Arm. Vicinity fog remains in the TAF for PANC. Amendments may be
needed.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: through
late Sunday)...

Little change in the overall forecast philosophy has changed.
Cold air over the interior continues to push through the gaps in
the Alaska Range. Strengthening thermal and pressure gradients
are giving rise to locally strong gap flows along the north Gulf
coast/eastern Kenai Peninsula, and some inland near channeled
terrain. Fairly pronounced wind gusts(gale strength) are also
flowing through gaps in the Aleutian range over the western Gulf
marine areas. Generally windy conditions in the aforementioned
areas are expected to continue into Sunday, but should diminish
some along the North Gulf Coast with increasingly unfavorable
upper level support and weakening pressure gradients. A low and
its associated fronts moves west across the Gulf Sunday/Sunday
night bringing increased changes of snow to the North Gulf coast
and eastern Kenai Peninsula.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Over the next couple of days the story remains the same for the
southwest Mainland, as arctic air pours into the region and causes
persistent offshore flow and declining temperatures. This will
continue to push both daytime highs and lows downward with
increasing threats for bitter wind chills approaching -40F. This
will be most likely where the winds are the strongest, so it is
likely the Kuskokwim Delta will realize the coldest wind chills.
The one change in this forecast is it seems more likely that a
weak low will move into the Kuskokwim Delta, bringing some light
snow to the coast this evening. Otherwise, cold and windy
conditions with clearing skies will resume on Sunday and carry
into early next week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure settling over the central part of the Bering Sea
will induce more of an easterly flow component as cold air pours
over the eastern Bering Sea and a gale force front moves into the
western Aleutians then stalls. This front looks like it will not
make further progress than the western Aleutians, so increasing
winds to gale force will be the biggest impact with this front.
With cold air pouring over the Bering Sea, expect freezing spray
to be a threat from the Pribilof Islands eastward.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Colder than normal temperatures continue through the next week as
a ridge pattern dominates the Bering. Low pressure systems wobble
on either side of the ridge, with one along the gulf and the
other just south of the western Aleutians. This pattern keeps a
drier pattern across the southern mainland with scattered showers
mainly along area waters. Confidence is higher than normal for
the extended forecast as models are trending toward similar
solutions. WPC solutions incorporated use of the operational
ensembles of the GFS and ECMWF which maintains consistency along
the active low centers.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 411 150 155 165 177 178 180 130 131.
Heavy Freezing Spray 160 180 181 130 138 139.
&&

$$

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...KH


000
FXAK67 PAJK 201356
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
456 AM AKST Sat Jan 20 2018

.SHORT TERM...A low to the south of Haida Gwaii will travel
northwest and dissipate by Saturday evening. Another low is
tracking across the Gulf along 50 N. Behind this system, a third
low begins to drop down from the mainland into the western Gulf
late tomorrow into early Monday. Overall, we are looking at a
very active pattern into next week.

Run-to-run model consistency has not changed much with regards to
the location and strength of the next two systems, in which minor
modifications to the pressure pattern were based on the current
NAM. With the tightening gradient over the northern panhandle,
winds will be gusty in Skagway throughout the day and Northern
Lynn increasing from small craft advisory to gale force status. As
a result, some light freezing spray may exist along the northern
inner channels into tonight. Light winds and partial clearing
overnight has allowed for some patchy fog to develop across the
central and N panhanlde this morning.

POP`s were adjusted using a blend of the NAM/GFS early on and some
SREF/NAM into the tonight and tomorrow periods, which increased
the POP coverage over the northern panhandle into tomorrow. POP`s
will decrease throughout the day today as the strengthening outflow
pattern will keep most precipitation farther south. As winds
switch over to more of an onshore pattern, this will increase rain
and snow showers over the southern panhandle tomorrow night. Snow
totals over the panhandle by tomorrow night range from 1-2", with
higher snowfall amounts into Monday.

Local edits were made to temperature, either increasing or
decreasing maximum temperatures in certain areas. Most maximum and
minimum temperatures were well within the model spectrum spreads
with a few exceptions. For one, temperatures in Skagway were
needing to be increased due to downsloping and temps over the
inner channels increased as well. Although it will be a colder
night, minimum temperatures for tomorrow night were increased due
to cloud cover. Forecast confidence remains average to above
average, although some uncertainty remains with the strength and
timing of the next system.

.LONG TERM.../Monday through Saturday as of 10 pm Friday/
Still some important model differences to resolve with handling of
energy in base of upper trof over the gulf and EPAC for next week.
Ended up using WPC for the most part as it was based on ensemble
means and operational model blend. This shifted some of the
systems a bit further S especially for around Thu. Does appear
that a couple of fronts will move NE across the area for Mon-Wed,
so kept in higher POPs for those days. POPs were nudged down a
bit for Wed-Thu especially N area due to southward shift of main
low S of the area. Another trof will dig into the W gulf for late
week and the weekend and this would help increase precip threat
again as flow aloft becomes more S-SW.

Used GFS/EC blend to handle the 24 hr pre-WPC period for system
moving NW through the E gulf during Mon. Still looks like mainly
snow over the N half of the area, but ptype will be trickier over
the S as some milder air may come in ahead of the system. Will
likely be rain over the far S and outer coast from PASI
southward for Mon. Once this system moves past, colder air
wrapping around the upper trof will move in, and much of the S area
will become cold enough for at least a rain/snow mix, with the N
still seeing snow. Still a decent amount of uncertainty on how
much snow would fall over the N as this will likely depend on how
much cold air is in place and the direction of the 850-700 mb
flow. Too much of an E wind component in that layer would
diminish precip on W side of Coast Mtns, but would enhance precip
along E side of Baranof and Chichagof Islands.

For Tue into late week, next front will likely bring more precip
to the area Tue, with mostly snow N and mix or snow S. Latest
models hint at a low moving into the far E gulf for Wed. This
system looks like it would try to warm things some especially over
the S so that precip there would trend more toward rain. After
Wed the model differences increase so forecast confidence
decreases.

Did not change temps for long range. Still some model differences
on how much cold air moves in from the N and from the SW. Some
operational model MOS guidance suggested temps might be a few
degrees warmer, but ensemble MOS spread remains on the high side
so felt staying with current forecast was best thing to do.

Still looks like some outflow winds will occur but not expecting
more than gale force winds due to lack of a strong high over the
Yukon. The various fronts/lows moving in will probably have 25-35
KT winds with them over the gulf as well.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 6 AM AKST for AKZ018.
MARINE...Gale Warning for PKZ012.
Small Craft Advisory for PKZ013-022-031-035-041>043.
Small Craft Advisory due to Seas for PKZ051-052.

&&

$$

SS/BC/RWT

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