Gale Warning 381, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
549 PM AKDT Thu Aug 29 2019

.ANALYSIS AND UPPER LEVELS...
The afternoon Alaskan surface charts are dominated by a few
features. The first is a sprawling area of high pressure that
spans the Gulf of Alaska and stretches to the north/northwest and
well into the state. Out west is a vertically stacked, and
weakening, area of low pressure in the central Bering Sea. An
attendant front lay to the southeast of this system and is slowly
working to the east-northeast. Windy and rainy conditions
accompany the front along the Alaska Peninsula. South of Kodiak is
another area of low pressure moving to the north. Smoke from
various wildfires can be easily distinguished on GOES West,
spanning a fair area in the Southwest. The thickest smoke remains
across the Kenai Peninsula from the Swan Lake Fire. Persistent
high pressure has allowed smoke from this fire to slowly spread
across much of the Anchorage Bowl and Mat-Su.

&&

.MODEL DISCUSSION...
Models are in overall good agreement through the start of the next
work week. Differences begin to show with guidance moving low
pressure into Bristol Bay Sunday and Monday. While positional
differences exist, there is little difference in the sensible
weather expected.

&&

.AVIATION...
PANC...The primary forecast challenge remains density of smoke.
Winds continue to transport smoke from the sand Lake Fire, so
could see some marginal visibilities persists this evening.
Overnight, the low level winds will begin to shift, so may see
some slight improvement up to 6 nm or greater. If it does in fact
improve, would expect this to persist through the day Friday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Sunday)...

The most active weather Southcentral has seen in a month is on its
way. Here is the breakdown as it stands right now.

For tonight through the day on Friday, the weather will remain
much the same as it has been the entirety of August so far. South
of Kodiak, however, a pair of disturbances will be merging and
bringing an end (at least temporarily) to the quiet weather over
the area. Steady rain in Kodiak will begin early Friday morning
with the newly merged upper level disturbance. Kodiak should be
the primary beneficiary of rain from this disturbance, with around
an inch of rain expected by the time the steady rain ends Friday
afternoon. The rain will spread north Friday afternoon, with rain
starting in Homer and the southern Kenai Peninsula. In the late
afternoon to early evening, the rain will begin over
Kenai/Soldotna and over the Swan Lake fire. The best chance of
rain will be at the onset of the rain threat. Southeasterly cross-
barrier winds will limit rain Friday night over the western Kenai
Peninsula. Friday night will be the best chance of rain for
Anchorage. Due to the same cross-mountain southeasterly winds,
breezy conditions are expected along the Anchorage Hillside and
Turnagain Arm, but it will also limit rainfall amounts. Right now,
it looks like the rain will definitely be light, diminishing to
sprinkles or stopping at times, but the off-and-on rain may
persist into Saturday morning. Unlike areas further south, the
chances for rain have improved somewhat across the Susitna Valley,
with around a tenth of an inch possible up towards Talkeetna
Saturday morning.

By midday Saturday, lingering shower activity will move off to the
east, but mostly cloudy conditions will persist behind the end of
the steadier rain for the remainder of the day. On Saturday night,
the next round of rain and especially wind will approach the area.
The rain will begin in Kodiak first once again. Lingering rain
in western Prince William Sound may persist through the interim
between the two rainfall events. On Sunday morning, steady rain
will overspread all of coastal Southcentral. However, since the
rain is associated with a strong front, the winds will pick up
substantially as the day goes on, especially through the mountain
gaps, Turnagain Arm, and the Anchorage Hillside. The rain may be
heavy at times across Prince William Sound by Sunday afternoon.
For Anchorage and the western Kenai Peninsula, cross-barrier flow
and strong winds will once again greatly reduce the rainfall
threat. However, there is quite a bit of moisture that is expected
to be converted to rain, so there is some potential for some of
the rainfall to make it to Anchorage, the Mat Valley, and the
western Kenai Peninsula. Besides being stronger, the associated
sustained winds are likely to contain frequent higher gusts, which
are likely to impact the fires. Coastal rain and strong winds will
persist into Sunday night. Regardless of the rainfall amounts,
which remain uncertain, overcast skies, rain-cooled conditions,
and drastically increased relative humidity values should make for
improved, much more seasonable weather across all of Southcentral.

&&

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

The ridge pattern over Southwest Alaska is coming to an end as a
front approaches the coast by tomorrow morning. This will bring
an increase of cloud cover and rain to the area as the front
continues to move inland through Friday afternoon. The Bristol
Bay region will see an even higher chance of rain as a low in the
Gulf moves northward through Friday night. There will be a brief
period in the rain following this system before a second round of
rain approaches the coast on Saturday afternoon. A strong low in
the Bering will bring widespread rain across all of Southwest
Alaska beginning on Saturday evening. Strong southeasterly winds
will accompany this feature as it moves inland, especially along
the coastal areas.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Small craft advisory winds begin to weaken this afternoon through
the evening as a front in the central and eastern Bering continues
eastward. The larger feature of concern is the gale force low that
will move over the western and central Bering starting Friday
afternoon. As this low intensifies while moving over the Aleutian
Chain, heavy rain and storm force winds on the western side of
the low are likely. This low will continue to move to the eastern
Bering by Sunday afternoon, with gale force winds still expected
across the area.

&&

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

The most significant weather feature continues to be the broad
gale force low in the Bering Sea. Little change in the forecast
with this low, as models have been consistent with this system.
This low is still expected to travel northeast through the Bering
Sea, dropping below gale force level Monday evening as it passes
by the Y-K Delta.

A frontal system associated with this low will create small craft
to gale force winds in Shelikof Strait and the Barren Islands
Saturday into Sunday. We did have to increase the wind speeds in
this region as the models were underdoing the winds, but they are
consistent enough that we are confident in the forecast. A barrier
jet will also form in coastal waters near Prince William Sound Monday
as this front impacts the coast, producing some weak gales there.

&&

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

Models, while quite sloppy after Monday, are in agreement enough
to still show that we will have a transition to weather more
typical of this time of year. All are showing a more active
weather pattern with at least a couple low pressure systems
entering the Gulf of Alaska, which stem from long wave troughing
that will be in place in the Bering Sea.

Until then, the week will start with a frontal system approaching
the southcentral coast with our first real chance at significant
rain in months. It will also be windy, with a barrier jet setup
along the coast and increased winds down turnagain arm and the
Anchorage Hillside. It should be noted that while many areas
should see rain, it is likely that Anchorage Bowl and the leeside
of the Kenai Mountains (Swan Lake) should see blocking and
downsloping from the mountains. Out in the Bering, the broad slow
will be impacting much of the Aleutian Islands and southwest
Alaska with gale force winds and rain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Dense Smoke Advisory 121.
MARINE...Storm Warning 177. Gale Warning 173 174 175 176 178.
FIRE WEATHER...NONE.

&&

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