Small Craft Advisory 377, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKDT Mon May 4 2020

.ANALYSIS AND UPPER LEVELS...
Multiple weak upper level lows and fronts were evident this
morning with the most prominent upper level low being the one over
the southern Gulf of Alaska. This is corresponding to a 998 mb low
at the surface moving northwest towards Kodiak Island. This low is
responsible for the brief return of unsettled weather to
Southcentral Alaska. Radar imagery shows light rain showers
moving through Cordova and the Valdez region as the surface low
spins in Pacific moisture from the southeast. Due to a mainly
southeast flow across the Kenai Peninsula and the Anchorage Bowl,
mainly cloudy skies were observed as most of the area is being
downsloped. Only sprinkles or a brief light rain shower were
occurring. Across the Anchorage Bowl, especially at Ted Stevens
International Airport, the Turnagain Arm winds have made it into
the area with winds gusting between 20-30 kts at times.

Southwest Alaska quiet conditions were observed with partly cloudy
skies with increasing clouds across the Alaska Range as the
surface low over the Gulf continues northwestward.

Over the Pribilofs, a stratus deck was observed along with a tight
pressure gradient in place as a result of surface high pressure to
the north and a weak low near Kipnuk. Winds were sustained 15-25
kts with gusts occasionally to 30-35kts.

Lastly, a frontal system was observed moving quickly southeastward
through the western Aleutians and Bering causing rain showers,
patchy fog and sustained winds of 15-20kts.

&&

.MODEL DISCUSSION...
Models continue to remain in good synoptic agreement through
Thursday morning.

&&

.AVIATION...
PANC...VFR conditions will persist through the TAF period. Gusty
southeasterly winds are expected late Monday afternoon into the
evening.

&&

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

An easterly wave moved across Southcentral early this morning
bringing in some light rain to the region as it went through.
This wave tracked a bit farther north than expected from yesterday
which brought more rain from Anchorage through Talkeetna whereas
a day ago, it looked like the greatest lift would be over the
Kenai Peninsula. This wave will move west of the area this
morning which will increase winds again late this morning or early
afternoon before winds diminish again overnight.

A slow drying trend should begin Tuesday as weak high surface
pressure builds over Southcentral. This also will cause a more
unstable atmosphere during the afternoon and evenings over higher
terrain which could lead to some showers. The most unstable
airmass looks to be over the northeast Copper River Basin on
Tuesday which could produce some isolated thunderstorms in the
afternoon or evening.

&&

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

A bit more activity is expected today across Southwest Alaska
weatherwise. A weakening easterly wave circulating around an upper
level low over the Gulf will move into Bristol Bay this afternoon.
The added moisture, already reflected in the mostly cloudy skies
that have overspread the area, solar heating, and the added lift
ahead of the wave will lead to showers to develop this afternoon,
with the best chances over Bristol Bay north of Dillingham. There
remains some chance that isolated thunderstorms will develop among
the heavier showers, again with a focus north of Dillingham. Most
of the moisture and shower activity will stay hung up along the
Kuskokwim Mountains, with only a few showers possible across the
Kuskokwim Delta late Monday night.

For Tuesday and beyond, quiet weather will return as an upper
level high builds towards the area. This will also promote warming
temperatures, which on Tuesday may be tempered a bit by residual
cloud cover from today. By Wednesday, however, mostly sunny skies
and continued mid-level warming may allow for temperatures area-
wide to approach 60 degrees, with lower 60s possible by Thursday.
Thursday's temperatures will be highly dependent on how far north
a low south of Kodiak Island will extend, which there is a lot of
discrepancy in the models. Winds should remain generally light for
most of the area through the entire short-term forecast. Gap winds
late this afternoon into Tuesday may get into the 15 to 25 mph
range out of the southeast across Lake Iliamna.

&&

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

A front moving into the central Aleutians this morning will
quickly weaken as the frontal energy shifts southeastward into the
North Pacific by this evening. This will leave the Bering devoid
of synoptic features until Tuesday. A strong front will enter the
western Bering and Aleutians Tuesday afternoon. This next front
will also weaken as it tries to push out the extensive high
pressure over the eastern Bering and the Alaska mainland. While it
will have a bit more success than the current front, it too looks
to meet the same fate, fizzling out and dying just west of the
Pribilofs on Thursday.

A Gulf low may spread some wet weather across the Shumagin Islands
and southern Alaska on Tuesday, but the better threat of stronger
winds and rain holds off until Thursday, when a strong low well
south of Kodiak Island spreads some moisture north into the
Aleutian range mountains and the Alaska Peninsula. How much
moisture and wind with this feature remains to be seen, as there
is significant model discrepancy on how far north and how strong
the front will be by Thursday.

&&

.MARINE (Days 3-5: Wednesday through Friday)...

Gulf of Alaska:
Potential for small craft advisory level winds across the North
Gulf Coast on Wednesday afternoon increases in confidence with
better model agreement today before the next, stronger system
enters the Gulf on Thursday morning. The front associated with a
North Pacific low will spread across the Gulf through Thursday
afternoon, with the potential to bring sustained gale force winds
along with it. Models are hinting at a stronger solution today
than yesterday's model runs, which leads to higher confidence of
at least small craft advisory level winds persisting across the
Gulf and coastal waters through Friday.

Bering Sea:
By Wednesday afternoon, models are in good agreement that the
active pattern over the western Bering will start to wind down as
a front continues to weaken over the central Aleutians through
early Thursday morning. Models are less certain heading into
Friday morning with timing and strength of the next system that
will enter the western Bering and Aleutians. The GFS is once again
the most aggressive model trying to bring gale force winds to the
region, while others remain a small craft advisory level. This
next system will bring a round of widespread precipitation
starting early Friday.

&&

.LONG TERM FORECAST (Days 4-7: Thursday through Monday)...

As the North Pacific low continues to lift northward in the Gulf
through the end of the week, a chance for rain showers will stay
in the forecast through the weekend for areas along the North
Gulf Coast. Chances for rain increase Thursday into Friday for
Kodiak Island and the Kenai Peninsula, northern areas of
Southcentral will see dry conditions while they are positioned
under an upper level ridge. This will help to keep above average
temperatures in the forecast through the start of next week.

Models are having more difficulty over Southwest Alaska as this
front moves towards the region. For now, kept a chance of rain
showers across interior Bristol Bay and the Alaska Peninsula from
Thursday afternoon through Friday to account for this
uncertainty. However, there is much better model agreement with
the next front approaching from the western Bering. This front is
on track to reach the Pribilofs late Saturday and the eastern
Aleutians by Sunday afternoon, which will bring the next round of
rain to these areas.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Warning 152 155 (Kuskokwim River)
 Flood Watch 155.
MARINE...Gale Warning 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MV
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...AH