Graphical Hydro Meteorological Discussion

000
FXAK68 PAFC 071245
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 AM AKDT Fri May 7 2021

.ANALYSIS AND UPPER LEVELS...

In the upper atmosphere there is a pronounced area of troughing
from Kodiak to SE Alaska, a ridge axis well south of the AK PEN
in the North Pacific and and another deep trough over the Western
and Central Bering that extends south of the chain. On satellite
imagery there is a mature frontal boundary with an occlusion in
the Bering and a widespread cloud shield over much of Southcentral
associated with the remnants of a different low. The radars at
Kenai (PAHG) and Middleton Island (PAIH) have detected light
showers but nothing organized.

Currently, there is a Flood Advisory for an ice jam in Aniak along
the Kuskokwim River. Additionally, a Flood Watch remains in effect
for a different section of the Kuskokwim River which includes the
villages of Upper Kalskag, Lower Kalskag, Tuluksak, Akiak,
Kwethluk and Akiachak.

&&

.MODEL DISCUSSION...

Models are doing decent with the placement of the major features.
However, when it comes to pinging into the showers detected by
PAHG and PAIH the NAM, the GFS and the ECMWF were barren in the
vicinity of PAIH and only the Canadian picked up on these showers
by Middleton Island. But the NAM and the GFS as well as the
Canadian did pretty well depicting showers by Denali and over
Southcentral. The models also were in sync with the precipitation
shield in the Bering and Aleutians.

&&

.AVIATION...
PANC...At the onset of the TAF period, expect VFR conditions and
light winds. Light rain showers have been detected by the radar
at Kenai near PANC and will continue to be monitored. Around 23z
the winds will increase at PANC.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A cold-core upper level low is just north of Seward early this
morning and moving northward. The surface front extends from the
northern Kenai Peninsula to the southeast. This is putting the
main area of lift over Prince William Sounds with some showers
making it across the Chugach and Talkeetna Mountains. This wave
will move over the Alaska Range and into the Interior late this
afternoon.

The front can be easily seen on satellite as there is a sharp
break in the clouds behind this front. This clearing will be
relatively short lived as a second system, very similar to the
first, moves into the area. This second system will bring rain
into Kodiak by late this morning and weaken as it moves into
Southcentral. This is a slow moving system with the cold-core
upper level low expected to track to near Seward Sunday afternoon.
By then, Kodiak will be back in the rain due to a third front
taking a similar track over the area.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

A quiet start to the forecast period is expected as upper level
high pressure extends across Southwest Alaska today. This upper
level high pressure will result in partly cloudy skies and light
winds. A front will approach Southwest Alaska late Friday night
and bring showers to Bristol Bay and the southern Kuskokwim Delta.
Shower activity will increase north and east throughout Saturday
as the front gradually lifts northward. The greatest chance of
showers will be around the coast and the lowest chance will be the
farthest inland locations in the Kuskokwim Valley. The unsettled
but benign weather will continue into Sunday as shower activity
continues.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

An unsettled but benign weather pattern is expected to continue
across the Bering/Aleutians over the next 3 days. A broad low
continues to weaken while remaining nearly stationary over the
central Bering/Aleutians. Winds will generally remain below Gale
force, with the exception of coastal marine zone 150 as pressure
gradients will be sharp enough in that location to produce Gale
force winds today. These Gale force winds in marine zone 150 will
weaken this evening. For the remainder of the period winds will
remain below Gale force with no high seas expected.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

A broad area of low pressure will maintain winds less than 35 kts
and seas less than 20 ft over the Bering and the Gulf of Alaska.

&&

Long Term Forecast (Days 3 through 7: Sun through Thu)...

Looking ahead into the extended forecast, model guidance are in
overall agreement with the latest synoptic features affecting the
entire forecast areas for late this weekend into Monday, but
diverge significantly in the early to the middle part of next
week. Starting with the Gulf, continued widespread rain over
Kodiak Island associated with a North Pacific low and front will
spread further northward across the Eastern Kenai Peninsula and
coastal areas of Prince William Sound. A few isolated showers are
possible further inland as well as near surrounding terrain, with
mostly dry conditions over Anchorage Bowl and the Mat-Su Valleys.
Thereafter, models seem struggle with the track of the next upper
level shortwave and associated surface low advertised late Monday
night and the extent of the precipitation, timing, and duration
in the aforementioned areas.

Further west, there is moderate confidence that an elongated
trough encompassing the entire Bering Sea will eject multiple
shortwaves with associated surface lows, thereby maintaining a wet
and showery pattern along the Aleutians and the Pribilofs through
Tuesday. The bulk of the rain showers seem to be concentrated
over the Eastern Aleutians with enhance rainfall along the AKPEN
attributed with a deep fetch of moisture and orographic lift.
Where models begin to diverge and therefore increase uncertainty
is determining whether or not an upper level shortwave from the
Kamchatka Peninsula will merge with aforementioned Bering trough
or be the main weather producer driving systems over the Bering
and along the Aleutian Chain. Future model runs will be needed to
resolve specific details including precipitation timing and the
potential of gusty winds blowing through the terrain gaps and
passes. Suffice to say that unsettled weather will be the theme
with a few showers possible over the Coastal Southwest.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Watch and Flood Advisory 155.
MARINE...Gale 138 and 150.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
MARINE/LONG TERM...MF

695
FXAK69 PAFG 071134
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
334 AM AKDT Fri May 7 2021

.SYNOPSIS...
More active weather pattern is developing for today as a low over
the Barren Islands and N Gulf of AK lifts north today, crossing
the AK Range into the Eastern Interior then lifting north to the
North Slope tonight and Saturday. This system will bring the
threat for showers and thunderstorms to the Interior today, and
then snow and blowing snow to the North Slope and Brooks Range.

&&

.DISCUSSION...

Upper Levels and Analysis...
There is a closed migratory low over the Barren Islands and N Gulf
of Alaska. There is a weak shortwave trough moving through the
Eastern Interior this morning, and another low over the Panhandle
of Alaska which is aiding in a broad southeast flow aloft over the
Interior. There remains a weak blocking high over the Chukchi Sea
with a departing trough over the far eastern Arctic.

Central and Eastern Interior...
Light showers continue this morning across the Tanana Valley and
White Mountains. These will continue through the late morning and
early afternoon. Thereafter, a low will track north from the AK
Range and with afternoon heating will spark off stronger showers
and some isolated thunderstorms from the AK Range north to the
White Mountains and Fortymile Uplands. Some showers may contain
small hail/graupel given the very low freezing levels and
sufficient instability.

The low will track north overnight and showers will end from south
to north. A possible mix of rain and snow will fall across the
higher elevations above 1500 feet overnight and Sat morning before
the low tracks north over the Brooks Range. Weak upper ridging
builds in behind the low through the remainder of the weekend,
allowing for a return to drier conditions and partial clearing.

West Coast and Western Interior...
Not much change in weather through the weekend as a general
northeast wind continues. Expect periodic stratus and fog over the
Capes and Saint Lawrence Island. Otherwise, a few showers today
over the Yukon Valley with a better chance of light rain moving
into the Lower Yukon Valley/Delta and Norton Sound on Saturday
night and Sunday.

North Slope and Brooks Range...
Low stratus over the Arctic coast continues this morning, and this
will give way to more blowing snow as easterly winds increase to
the 25-35 mph range late today through Saturday. A low will bring
light accumulating snow to the eastern Arctic and Brooks
Range/Atigun Pass this evening through Saturday before departing
Sat night. There will likely be reduced visibility at times,
possible below a half mile at times, over the eastern Arctic
including Prudhoe Bay with the snow and blowing snow.

Extended Forecast Days 4-7...
Ridging builds back in next week and will allow for a seasonal
late spring pattern to develop as a subtle thermal trough develops
over the southern Interior and near the AK Range. This will allow
for showers and afternoon thunderstorm chances for much of the
week. Temps will run near seasonal normals across most of the
Interior.

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

&&

.FIRE WEATHER...
Isolated thunderstorms will be possible from the Ak Range to the
White Mountains and east to the Fortymile Uplands today as a
disturbance aloft tracks north. These will be of the wet variety,
and will most likely favor the Eastern AK Range and Fortymile
Uplands as this is where the greatest instability axis will be.
The weekend is looking mostly dry over much of the Interior with
gradually warming temps as ridging aloft builds back in. Showers
and possibly thunderstorms creep back in over the southern
Interior early next week as a ridge builds aloft and a thermal
trough forms near the AK Range and Tanana Valley.

&&

.HYDROLOGY...
The ice in Dawson, Yukon went out yesterday and will be making
its way down the Yukon River. There is a possibility of flooding
as the jam makes its way down the Yukon, thus a flood watch
remains in effect for the Yukon River at Eagle through Sat
morning.

The Tanana River at Tanana went out recently and there is a long
stretch of open water on the Yukon near the mouth of the Tanana,
but ice is still firmly in place through Rampart Canyon. Ice on
the Yukon River has lifted at Ruby, but anchor ice is still in
place, and could go out this weekend. Ice remains solid and
lifted on the Porcupine with no signs of movement. The ice
continues to rot in place and has darkened significantly in most
areas over the past few days as the candling process accelerates.

As breakup continues things can change rapidly so go to
www.weather.gov/fairbanks or www.weather.gov/aprfc for the latest
Warnings, Advisories, and forecasts.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

Flood Watch for AKZ224.

Winter Weather Advisory for AKZ204.

Small Craft Advisory for PKZ210.

Brisk Wind Advisory for PKZ225-PKZ230-PKZ240-PKZ245.

&&

$$

AHSENMACHER MAY 21

000
FXAK67 PAJK 071356
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
556 AM AKDT Fri May 7 2021

.SHORT TERM...Friday through Sunday... Unsettled conditions will
continue across Southeast Alaska through the short term. the first
round of precipitation a low pressure system West of the Dixon
Entrance. This system quickly diminishes as it turns eastward and
crosses into the continent. Thankfully model consensus on this
recent change in the track of the low pressure system has raised
confidence with this solution which most operational runs have
adopted along with the ensemble consensus.

While the low is around today, it will have strong enough winds
to create small craft advisories along the outer coast and
Clarence strait today. Precipitation with this system will be
rather disorganized as unsettled conditions are stretched across
the panhandle due to a weak trough associated with the
aforementioned low.

The next trough bringing more uniform rain impact the area on
Saturday, with some potential for a brief break in precipitation
late.

Neither system looks to create too significant precipitation
totals, with amounts general ranging to about a half inch, with
some locations possibly seeing more.

The biggest impact from this system will be the continued cool
temperatures with this unstable flow, have leaned more towards
persistence with temperatures remaining slightly above model
guidance which continue to be overly aggressive in dropping
temperatures in this active weather pattern.

.LONG TERM...Sun through Fri as of 9 PM Thu...Model guidance
still supports an upper low over the Bering Sea persisting into
early next week before weakening, then restrengthening mid to late
next week. This will maintain an active pattern across gulf and
into SE AK through the extended forecast, but details are
difficult to identify as model solutions diverge in timing and
strength of perturbations ejecting out the parent low and across
the gulf. Current operational runs and ensembles remain in good
agreement regarding the upper pattern, but differ regarding
surface features in the timing and strength. Period is expected to
begin with one system dissipating and another approaching from
the SW. This approaching system will impact the region Mon into
Tue, but confidence in details regarding strength of the system
and precip amounts remains low. Strongest signals from all
guidance is for slightly below normal temps with afternoon highs
in the upper 40s to mid 50s through mid week. Given the
uncertainty in the extended, made little change to inherited
forecast with trends towards WPC guidance late next week.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ036-041.

&&

$$

Suk/Suk

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