Area Forecast Discussion
Issued by NWS Anchorage, AK

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

000
FXAK68 PAFC 260025
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
425 PM AKDT Tue Jun 25 2019

.ANALYSIS AND UPPER LEVELS...
The pattern remains very much the same as the last 24 hours. Fog
and stratus continue to plague much of the Bering and marine
locations across Southcentral. A weak trough of lower pressure
is sandwiched between the ridge of high pressure over the Copper
River Basin and the building ridge over the Alaska Peninsula. This
trough ushered in stronger southwest flow which helped to bring
smoke from the Swan Lake fire up through many of the population
centers overnight into this morning. Much of the smoke is
lifting/breaking up this afternoon as the June sun helps to
provide some mixing to the atmosphere. Some thunderstorms have
fired over the Copper River Basin, but they are expected to be
more limited in strength and coverage today as stability
increases.

The only real upper level (30,000`) jet activity to speak of is
supporting the broad trough over the Bering. A piece of the jet
cuts under the base of the trough over the North Pacific at 115
kts. A weak finger at 80 kts is helping to ferry some of the
moisture up along the West Coast of the mainland. Light rain is
falling across the Central Aleutians up through Nunivak Island.

&&

.MODEL DISCUSSION...
Models remain nearly in lock step, so forecast confidence is very
high in the synoptic pattern. The couple of areas that could
prove challenging will be the marine stratus across the Cook Inlet
and Gulf of AK, the smoke density and movement, and the high
temperatures as they relate to sea breezes. In general, the NAM
Nest was preferred for details, but most updates were made with
hand edits.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Smoke should
continue to dissipate through the evening.

&&

.FIRE WEATHER...Swan Lake Fire...Western Kenai Peninsula: The 2
main stories over the fire area will be the shift in wind
direction and the hot temperatures/low minimum RH that will
develop for the end of the week. As the trough exits to the east
tonight, a strong ridge of high pressure will build in. Flow
around the fire is already starting to respond and turn back to a
more northerly direction. As the ridge sets up over Kodiak Island
over the next couple of days, the general steering flow will
become northerly. However, surface winds will remain susceptible
to local and diurnal influences. Temperatures will rise through
the end of the week pushing into at least the low to mid 80s.
Minimum RH values will also be on the decline reaching the low to
mid 30s by Thu. The high pressure will also put a cap on any
convective potential.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Tonight
through Friday)...
A weak upper level short-wave combined with thermal trough over
interior Southcentral will once again lead to some showers and
thunderstorms across the Susitna Valley and Copper River Basin
this evening. An upper level ridge will then build in from the
west and strengthen through Friday. The combination of subsidence
underneath the ridge and offshore flow will lead to hot and dry
conditions across the region. This includes coastal communities
such as Seward, Whittier, Valdez, and Cordova where locally gusty
offshore winds will delay the onset of sea breezes each day.

The smoke in Anchorage and the Mat-Su should improve tonight
through Friday as winds shift from southwest to northwest. Under
this new flow regime, which will dominate the next few days, the
bulk of smoke from the Swan Lake Fire (on the western Kenai
Peninsula) will move across the eastern Kenai Peninsula and out
into the Gulf of Alaska and western Prince William Sound.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Tonight through Friday
night)...

A warmer weather pattern will continue to build through the
weekend. A weather front across the eastern Bering will slowly
stall out west of the mainland. Most areas will see plenty of
sunshine through the afternoon and evening hours, with the
exception of the coastal areas of Bristol Bay and most of the
Kuskokwim Delta. That same area is the only area that is set to
see any shower activity. Thunderstorm activity is not expected
across the region today, nor the Alaska Range, as instability
is marginal and a building ridge will inhibit any vertical
growth. As we move into the middle and end of the week, ridging
will dominate. Temperatures across the interior will continue
their upward trend, with widespread 80s expected by Thursday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Tonight through Friday
night)...

A front extending from low pressure across the western Bering is
bringing active weather across to the central and eastern
Aleutians. Rain, clouds and southerly winds will be a semi-
permanent fixture across this area through the end of the week as
high pressure to the east, stalls the eastward progression of this
front. High pressure will begin to nose in across the central
Aleutians and Bering on Friday, while a Kamchatka low will bring
rain to unsettled weather to the western Bering late into the
week.

&&

.MARINE (Days 3 through 5)...
(Friday through Sunday)

...Bering Sea and Aleutian Coastal Waters...

A front will slowly cross the western half of the Bering and
Aleutians during this time, while slowly weakening as it bumps
into a ridge of high pressure. Sustained winds along and ahead of
this front look to remain just below gale force, but the models
have been trending up slightly with this aspect of it, thus some
low-end Gales aren`t totally out of the question. Otherwise, look
for seas to peak near 10 feet. Further east, winds and waves
will remain below small craft conditions.

...Gulf of Alaska...

A ridge of high pressure will remain in control. Some offshore
flow will likely develop over the weekend, but, even near the
coast winds look to remain below small craft conditions.

&&

.LONG TERM FORECAST (Days 4 through 7)...
(Saturday through Tuesday)

Forecast uncertainty remains high for the beginning to middle of
next week, as the numerical guidance continues to struggle with
their overall placement of synoptic features. In general, they
agree that there will be several areas of low pressure located
across the western Bering and eastern Siberia, rotating around one
another in a Fujiwhara pattern, with a downstream ridge centered
over southcentral.

As it does so, a significant disturbance breaks off of the low
sometime Sunday night into Monday, and tracks across the North
Slope as it acts to flatten the ridge. How strong is this piece of
energy and where does it exactly track is the dilemma, as the
ECMWF is much quicker to flatten said ridge and displace it much
farther southwest, compared to the GFS and Canadian Global
models. This has significant effects on the overall height field
alignment and relates to how much of this warmth maintains over
southwest and southcentral Alaska, while also having important
effects on the central and eastern Bering and Aleutians.

A further southwest centering of the low, per the ECMWF which has
the mid level ridge repositioned to well of Shemya, compared to
the GFS/Canadian consensus of it repositioning to just south of
Cold Bay or Dutch Harbor, would have a cooler and wetter solution
for much of the mainland with decreased fog potential across the
Bering and Aleutians.

After coordinating with our national Weather Prediction Center and
internal discussions here at the forecast office, preference is
for a slower breaking down of the ridge, similar to the GFS and
Canadian solutions. This is typically what tends to happen as the
models all too often try to dislodge or breakdown these ridges,
and with limited surface and upper air observations across the
Bering and Aleutians, the models have a harder time trying to
initialize the overall pattern.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 145.
MARINE...Gale 172.
FIRE WEATHER...NONE.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SS
MARINE/LONG TERM...PD



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.