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000
FXAK69 PAFG 261353
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
553 AM AKDT Thu Apr 26 2018

.DISCUSSION...
An unsettled pattern will continue through the weekend for the
west coast and western Interior. The models are in good agreement
with the overall synoptic pattern out through the Weekend.

Aloft, at 500 mb, a 513 dam low over the Bering Strait will move
northwest today over the Chukotsk Peninsula where it will remain
quasi-stationary into Saturday. Several shortwaves will move
around this low helping to bring unsettled weather to the west
coast and western interior. A closed low will move east through
Bering Sea on Friday and Friday night, reaching the Yukon Delta
early Saturday morning. On Saturday this system will push through
the west coast and western interior. Another low will move
eastward through the Bering Sea Saturday and Saturday night and
will push through the west coast on Sunday and the western
Interior Sunday night.

At the surface, a 992 mb low north of St. lawrence Island will
move to the northern Chukotsk Peninsula by this afternoon. This
broad area of low pressure will persist over the Chukotsk
Peninsula into Saturday before moving north and east into the
Chukchi Sea. A 988 mb low will move across the Bering Sea Friday
and Friday night reaching Nunivak Island by early Saturday morning
at 993 mb. This low will push northward along the west coast
Saturday and Saturday night, reaching Unalakleet by Saturday
evening and Ambler by early Sunday morning. Another low will push
east across the Bering Sea Saturday night and Sunday. This low
will reach the Yukon Delta by Sunday afternoon and will push
northeast to near Ambler by early Monday morning.

Central and Eastern Interior: Southerly gap winds are expected to
persist in Alaska Range passes into Saturday. The highest gusts
will be around 30 mph; however, winds will vary over time as the
pressure gradient fluctuates. On Sunday the gap winds in the
Alaska Range will increase, possibly reaching advisory levels
(especially in the eastern Alaska Range). Isolated to scattered
showers are expected this afternoon and evening and again Friday
afternoon and evening. More organized precipitation will push into
the central Interior on Sunday. The GFS actually brings the
precipitation into Fairbanks on Sunday with chances for
precipitation extending into the eastern Interior Sunday night;
however, at this point the models differ on the exact details of
this system pushing though.

West Coast and Western Interior: The unsettled pattern will
continue into the weekend. Showers are expected today and Friday
as several shortwaves pass over the area. Precipitation will
mainly be in the form of rain in the western Interior during the
day today. Closer to the coast the precipitation will start to mix
with snow. In the Nome area 1 to 3 inches of snowfall is possible
today. A more organized system will push through on Saturday into
Saturday night, with another system late Sunday. The system
Saturday night may bring 4 to 6 inches of snow in the upslope
areas north of Ambler in zone 217. Gusty winds will continue today
along the coast with gusts up to 30 mph possible.

North Slope and Brooks Range: Relatively quiet weather today
along the coast. Current satellite shows fog and low stratus over
the eastern Beaufort Sea coast. This should move to the later on
this morning. Snowfall is expected to develop early Sunday in the
Brooks Range with an inch or two of accumulation.

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

&&

.FIRE WEATHER...
Southerly gap winds will persist in the Alaska Range into the
weekend. Today gusts up to 30 mph are possible. Minimum RH values
today will mainly be in the upper 20 to lower 30 percent
southeast of a line from Fairbanks to Circle with a small drying
trend expected tomorrow for many areas.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory for PKZ200-PKZ210.

Heavy Freezing Spray Warning for PKZ210.

Brisk Wind Advisory for PKZ215-PKZ220.
&&

$$

APR 18


000
FXAK68 PAFC 261307
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 AM AKDT Thu Apr 26 2018

.ANALYSIS AND UPPER LEVELS...
An upper level low situated over the Bering Straight is leading to
a broad area of cyclonic flow across most of the state this
morning bringing continued cool and unsettled weather over most
of the region. Persistent moist southwesterly flow combined with
a pool of cold air aloft is leading to widespread showers over the
southern half of the mainland, with periods of heavy rain seen
over the Gulf coast, Bristol Bay coast, and over the Kuskokwim
Delta this morning. The strong southerly flow is organizing these
areas of showers into narrow bands, leading to high variability in
the precipitation coverage this morning. A shortwave ridge is
beginning to build in across the western half of the Bering Sea
and Aleutian Island chain bringing a brief lull in the weather,
though widespread stratus is developing underneath the ridge axis.

&&

.MODEL DISCUSSION...
The models remain in good overall agreement through the rest of
the week with the timing of a series of short waves that will
rotate around the upper low this week. There continue to be model
differences in the placement of individual precipitation bands
today, thus used scattered or widespread coverage to capture the
spatial uncertainty of precipitation. Looking into Friday, models
are in good agreement with a surface low dropping south from
NE Russia into the AK mainland, increasing confidence of
widespread snow over southwest and rain/snow over southcentral.

&&

.AVIATION...
PANC...The terminal will remain predominately VFR through the day
as showers moving north up the Cook Inlet this morning should
stay to the west and east of the Anchorage Bowl. Gusty SE winds
should slacken a touch this morning before the Turnagain Arm
winds kick up again later in the afternoon. As the surface warms
and instability increases this afternoon, showers will become more
widely scattered with convective bands forming over the Chugach
and possibly downstream of the terminal. As a shortwave trough
moves through this evening, mid-level winds will become more
southwesterly directing any showers forming over the Kenai towards
the terminal.

&&

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

The large upper long wave trough still anchored over the eastern
Bering Sea/western Alaska will send a fairly well defined short
wave over the Cook Inlet to MAT-SU corridor this afternoon. This
wave passes through tonight, however, another more prominent wave
replaces it Friday afternoon. Unstable conditions will prevail as
cold air moves over the region supports shower development. The
main focus of showers will be with the short wave which moves in
today and the next wave which moves in on Friday. Cold air moving
in aloft combined with mild daytime temperatures will make for a
challenging precipitation type forecast. Overall, lower
elevations will see rain showers with a transition toward snow
showers in the mountains and northern Susitna Valley. A mix of
rain and snow showers are still possible at lower elevations
especially during the overnight hours and in the vicinity of
heavier showers. Stability indices today over the western Kenai
Peninsula could support isolated thunderstorms or certainly
locally heavy shower activity.

Gusty gap flows are still expected across Turnagain arm, out of
Knik Valley, and along the Copper River today through Friday.
Additionally, brisk southerly winds will develop over the western
Gulf/Cook Inlet tonight with the approach of the trough from the
west. Winds will likely hold until after trough passage later
Friday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A low near the Bering Strait is bringing broad southwesterly flow
to southwest Alaska resulting in showers over the area that will
linger through the day. Tonight a shortwave will push across the
northern Bering and move through southwest Alaska bringing a
short, but heavier, round of snow. Weak ridging will then move
over the area before a front from the Bering makes its way to the
southwest coast by Friday evening. The front will pull up a lot of
warm air from the south which will transition much of the snow to
rain as it pushes inland Friday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Ridging over the western Bering will keep the Aleutians in
westerly flow with minimum precip today until a front from the
North Pacific tracks over the western Aleutians this afternoon.
The front is pulling up a significant amount of warm air and will
primarily bring rain as it tracks across the Aleutians through
Friday. By Friday evening it will have made it to the southern
mainland leaving the Bering and Aleutians in broad westerly flow.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A system over Southeast Alaska Friday evening will quickly move
east and dissipate Friday night. A fairly significant upper low
will be over the central/eastern Bering Friday night. The leading
front will push across southwest Alaska early Saturday morning
and then into the Gulf and Southcentral during the day on Saturday.
The upper low will move eastward across the Gulf Saturday night.
A fairly strong surface low will move into the Bering on Saturday.
After this, the model guidance begins to diverge. The models
agree on continued fast zonal flow aloft, along with the general
idea of an upper low in the Bering and upper ridging over the
northeast Pacific into eastern Alaska. However, the location and
timing of various systems has a large spread in the guidance.
Therefore the fairly active weather pattern will continue, with
the details not well defined. Thus the WPC guidance begins to lean
fairly heavily on the ensemble means after Monday.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales...155 165 170 172 173 174 175 176 177 178 179.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KVP
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...BL


000
FXAK67 PAJK 261402
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
602 AM AKDT Thu Apr 26 2018

.SHORT TERM.../through Friday night/ A weak occluded front over
the eastern gulf will drift E, and dissipate over the central
panhandle this evening. High pressure ridge will build NE across
the eastern gulf and SE AK tonight and Fri. This ridge will weaken
some as a trof moves across the northern gulf Fri night. Used a
blend of the 06z NAM and 00z GEM to handle the main features.

Main forecast concern is precip potential. The front over the
eastern gulf will have a couple of minor sfc low pressure waves
that ride NE along it today. Strongest upper level shortwave will
move NE across the gulf today, and be into the Yukon by this
evening. Rain will occur along and just ahead of the front, and
will be most concentrated near the weak low pressure waves and
upper shortwave. Have gone with highest POPs across the northern
panhandle today, then a gradual decrease in the precip will occur
tonight as front moves inland and dissipates. The tail end of the
precip could be more like drizzle as shallow low level moisture
remains even after the front dissipates. Then, later Fri into Fri
night, there could be some precip with the weak trof that moves
across the northern gulf. Models differ on how strong the
supporting upper shortwave will be, which will affect how far S
any precip from the trof gets. For now, keeping highest POPs
(chance to likely) over the NE gulf coast Fri afternoon and
night. Do have low POPs into the N panhandle during latter part of
Fri night however as trof and supporting shortwave reaches the
N-central outer coast.

Otherwise, will have plenty of clouds around today, even over the
S, as mid-level cloud band moves through them. Have lowered max
temps a few degrees area wide today, due to precip over the N and
clouds over the S. Do expect more breaks in the clouds to develop
across the far S later in the afternoon, but not enough to reach
the previously forecasted max temps today. Any fog going on early
this morning should dissipate by mid-morning due to thicker
mid-level clouds moving in. Left out fog tonight as lower level
NW flow will be increasing with the ridge building in, but if
enough breaks in the clouds develop where light winds are
occurring, then cannot rule out some fog. The NW flow will
increase further on Fri, with up to 25 KT winds expected over the
far eastern gulf.

.LONG TERM.../Saturday through Thursday/ Upper level pattern goes
through slight pattern change early next week. Relatively zonal
flow over the weekend transitions into a more trough/ridge pattern
by mid next week featuring a ridge over the panhandle and western
Canada with a trough over western Alaska and the Bering Sea.
Generally good agreement on the overall upper level pattern from
the models though confidence becomes average toward mid next week
as trough/ridge axis position varies between models and the
operational GFS is displaying a much sharper, and stronger ridge
axis over the panhandle then any other guidance.

At the surface, a ridge over the gulf and its resulting NW flow
over the panhandle will continue the dry spell for areas east of
Mt Fairweather into the early weekend despite the upper shortwave
moving through at that time (thought some areas of the northern
panhandle may see some showers out of it). West of Mt Fairweather,
enough of the shortwave will survive for at least damp conditions
for the norther gulf coast. Into Sunday and Monday, the surface
ridge becomes flatter as more shortwaves pound into the western
side of it through the weekend. Surface flow becomes more onshore
and overall forecast becomes noticeably wetter especially for the
north Monday into Tuesday as a result. Feature is rather weak
through so not expecting a lot of rain or wind with it.

Forecast confidence begins to falter into Wed and Thu as
differences in how strong the upper ridge building over the
panhandle will be comes into play. The GFS displays a noticeably
stronger ridge that deflects most of the gulf storms toward Cook
Inlet while most of the other guidance displays a weaker and
flatter upper ridge that allows more storm systems into the area.
Current ensemble guidance favors the wetter approach displayed by
the ECMWF and Canadian so the current mid week forecast reflects
this with a generally damp and cloudy forecast. Temperatures
remain near or just below normal for the period.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ042.
Small Craft Advisory due to Seas for PKZ022-041-043-051>053.

&&

$$

RWT/EAL

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