767
FXAK68 PAFC 181337
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
537 AM AKDT Thu Jul 18 2024

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

Discussion:

Overall, the forecast remains on track with continued cool and wet
conditions for the Mat-Su Valleys, Anchorage/Eagle River, Western
Prince William Sound, and Kenai Peninsula. Eastern Prince William
Sound, Cordova, and the Copper River Delta will see scattered
showers this morning taper off by early afternoon with drier weather
through Saturday morning. The Copper Basin may see a few showers
today but will trend warmer and drier heading into and continuing
through the weekend.

The upper level low that has been positioned over western Alaska the
past several days is finally started to drop southwards towards the
southern Cook Inlet today. It is trending a bit slower on its
southward trek, and as a result will likely see showers linger
through Friday morning for the Anchorage Bowl and into the early
afternoon for the eastern Kenai Peninsula. Light showers have also
been ongoing over the eastern Kenai and Western Prince William Sound
overnight as convergence increased over the Kenai Mountains and
eastern Kenai Peninsula in response to a deepening upper low to the
south and the aforementioned inland Alaska low to the north. Models
still in fairly good agreement with taking the northern low into the
southern Cook Inlet and across the Shelikof Strait/Kodiak Island
today. As such, Kodiak has a better chance of seeing slightly more
precipitation out of this system before it is absorbed into North
Pacific low. However, a slight shift in track either west or east
will result in lesser chances of precipitation. The North Pacific
low will move east today before getting blocked by broad ridging
over western Canada and setting up residence in the Gulf this
weekend. The setup will favor warmer, and drier air pushing into the
Copper Basin from the east, and moisture pooling along the northern
Gulf coast. Easterly waves look to rotate around the Gulf low and
with the CAPE axis pushing into the eastern Copper Basin...could see
increasing chances for thunderstorms this weekend. The northern Gulf
Coast will see their brief period of dry weather come to an end as
rain spreads east to west along the coast Saturday morning.

- PP

&&


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

A pattern change will be under way shortly as a ridge of high
pressure transits from the Bering Sea and Aleutian Islands towards
Southwest Alaska. Generally, expect a warming and drying trend
for Southwest Alaska under the ridge. For the Bering Sea and
Aleutian Islands, wetter and windier conditions are on tap as a
low moves in today and lingers through Saturday.

The biggest changes with the evening and overnight forecast
packages were to thunderstorm chances in Southwest Alaska, and to
fog across the Bering Sea and Aleutian Islands. Regarding
thunderstorm chances: with a robust upper level low moving from
the interior towards the Alaska Peninsula today, there may be
enough upper level support for isolated thunderstorms. The current
forecast keeps much of this activity near the Alaska Range, but
some model guidance is hinting at convective rain showers (with
perhaps enough thermal instability to support a thunderstorm or
two) further west in Greater Bristol Bay.

For fog, the influx of warm, moist air with today`s incoming low
provides a favorable environment for low stratus and fog to
develop across much of the Bering Sea and Aleutian Islands. As
such, have increased the coverage and severity of fog through late
Thursday night. The current forecast is for visibility down to
one statute mile, but visibility could be one-quarter mile or
less in some areas. Still, there`s uncertainty with whether there
will be a strong enough inversion for fog to be that dense;
surface pressure will be dropping as the low approaches and higher
pressure moves off to the east. In addition, warmer, summertime
sea surface temperatures mean that near-surface air temperatures
may not be cool enough for a strong inversion to develop. As such,
have kept forecast visibility to 1 mile or greater for now.

-KC

&&


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

An omega pattern will dominate the long-term period, with large
upper-level lows situated in the Bering Sea and the North Pacific
near the Gulf. Between these lows, a high pressure ridge will
situate itself over Southwest Alaska. This setup will keep the
Bering Sea, Aleutian Chain, and southern Alaska Peninsula active
due to numerous shortwaves rotating around the Bering low. The
ridge, initially over Southwest Alaska Saturday and early Sunday,
will shift eastward toward Southcentral Alaska while weakening. A
frontal system is expected to approach Southwest Alaska Sunday
night as this ridge shifts eastward, with locally heavy rainfall
possible. Confidence remains relatively low in the front`s ability
to bring precipitation inland, but the coast is most likely to
see rain. Showery and unsettled conditions are expected across
Southwest Alaska on Tuesday as more shortwaves pass through the
Bering.

For Southcentral Alaska, the North Pacific/Gulf low will pull
easterly waves from the Yukon into the region. This pattern will
be favorable for precipitation in the Copper River Basin and the
Susitna Valley. As the ridge nudges westward from the Yukon,
temperatures across Southcentral are expected to rise to near to
above normal values. Afternoon thunderstorms are possible from
Saturday through Tuesday, although confidence in timing regarding
these easterly waves are very low at this time.

&&

.AVIATION...

PANC...Rain showers expected to last much of the day and into
Friday morning as a low drops southwards towards the southern Cook
Inlet today. MVFR ceilings may bounce between IFR and MVFR
throughout the day with VFR ceilings returning by Friday mid-
morning Friday. Visibility may also dip to MVFR periodically today
with light southerly winds becoming more southwesterly by 03Z.

&&


$$