229
FXAK68 PAFC 200042
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
442 PM AKDT Wed Jun 19 2024

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

The upper level ridge continues to slide east with its axis over
the Alaska Panhandle this morning. This eastward progression of
the ridge will allow for the development of a more southerly flow
across the Gulf of Alaska that will advect a more stable airmass
over the southern half of Southcentral as well as drive a surface
front from the western gulf to the northern Gulf through Friday.

A diminishing marine stratus deck continues to hold over the
northern Gulf and immediate Prince William Sound coast. These
clouds should lift and become less expansive in coverage through
the day and into Thursday as influence from the aforementioned
ridge wanes.

Within the upper-level trough situated over the Gulf of Alaska,
embedded short-waves are swinging around the trough and into
Southcentral. One such shortwave allowed for the convection
observed across the Copper River Basin currently. A similar
feature is expected to push across Southcentral Thursday
afternoon, and with enough lingering instability, it may create
the potential for isolated thunderstorms and convective showers
across the northern Copper River Basin and Broad Pass regions.
Generally light southerly flow will keep storm initiation on the
Talkeetna mountains out of the Mat-Su valleys. Southerly gap winds
through places such as Seward also expected Thursday afternoon.

All-in-all little change is expected for places like Kodiak, with
persistent easterly winds, clouds, and periods of light rain.

-CL/TM

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS
(Days 1 through 3: This afternoon through Saturday afternoon)...

The big picture of the forecast remains largely unchanged.
Generally, expect rain showers across Southwest Alaska, with
overcast skies and areas of fog for the Bering Sea and Aleutian
Islands. With the stronger weather systems remaining mostly out of
the area, the weather continues to look relatively benign. As with
yesterday, forecast confidence remains lower for the details
(specifically, areas of thunderstorms and fog) as models struggle
to capture the weaker upper level shortwaves driving the weather
over the coming days.

Starting with the fog: locations such as Shemya, Adak, Saint
Paul, and Saint George saw low stratus and reduced visibilities
yesterday and into this morning as a ridge of high pressure
moves over the Western Bering Sea/Aleutian Islands. As the ridge
continues to transit eastward, it`s likely that fog will return
tonight for the Pribilof Islands and Central Aleutians (including
Adak and Atka). Though confidence is somewhat low, we`re expecting
fog to subside by Thursday afternoon as a weak North Pacific low
approaches the Western and Central Aleutians, breaking the hold of
high pressure over these areas.

As for thunderstorms, high-resolution and global models alike
continue to struggle with where showers and potential
thunderstorms will initiate. Steadily increasing afternoon highs
will help aid in thermal instability, but there remains a question
of whether this instability will be fully realized if cloud cover
remains in place. This, in combination with model differences as
they struggle to resolve weak upper level shortwaves, is leading
to continued low forecast confidence with thunderstorm locations
and rain amounts.

Here`s what we can say with decent confidence for Thursday and
Friday afternoons: Thursday afternoon looks to be the wetter of
the two days, with more widespread and likely heavier showers. The
steering flow will be approximately east to west, with the
Western Alaska Range, Middle Kuskokwim Valley, and Kuskokwim Delta
all seeing the potential for thunderstorms. For Friday, an
approximately north to south steering flow will keep thunderstorm
potential mostly over Middle Kuskokwim Valley and Western Alaska
Range, with the potential for storms to move south into interior
Bristol Bay. There could be localized areas of greater thermal
instability for Friday, which could result in more thunderstorms
than on Thursday. Thunderstorm potential continues through at
least Saturday afternoon, but confidence is too low to say much at
this point.

-KC

&&

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

Three main low centers on the upper air charts demonstrate the
most energy through the forecast period. A slowly retrograding low
over the Chukotsk Peninsula continues into Siberia. The second is
a Western Bering low, the next of a series that have moving
across the North Pacific, that will track across the Alaska
Peninsula by midweek. The last is a low center just South of the
Aleutians that will slide across the Southern Gulf of Alaska/
Eastern North Pacific for Wednesday. Most of Mainland Alaska is
under a weak ridge which supports surface thermal troughs and
areas of convection across the Interior for the entire forecast
period. Showers are expected across Southcentral. A series of
surface low and fronts bring mostly showery conditions along the
Aleutians, Bering and AKPEN, spreading into Southwest Alaska
through Wednesday. The next surface low from the North Pacific and
its front enters the Aleutians and Bering Tuesday, and move over
the Central portions by Wednesday. locally heavier precipitation
and gusty winds up to gale force spread into the Central
Aleutians.

-Kutz

&&

.AVIATION...

PANC...A change in the pattern, with low pressure moving into the
Gulf and a coastal ridge setting up out ahead of it will lead to
a return of Turnagain Arm winds. For later today, the southwesterly
up Inlet flow will still be the dominant wind. Thus, as the Turnagain
Arm jet forms this evening with the establishment of an E-W oriented
sfc ridge, it will meet up with the southwesterly flow and result
in a more southerly component to the winds coming into PANC.
Winds will likely start out with more of a SW component and back
toward the SSE overnight as the Turnagain jet strengthens. As is
typical, winds will die down late tonight/early Thursday with
weakening of the diurnally induced pressure gradients. However,
the Turnagain jet will be much stronger on Thursday and will come
into the terminal earlier. As always, there is some uncertainty
in the exact timing of arrival and dissipation of the gusty
winds.

Meanwhile, VFR conditions will prevail. With increasing easterly
flow aloft ahead of a short-wave lifting northward into the Gulf,
do NOT expect any chance of low clouds coming in as has occurred
the last two mornings. There will be increasing mid to high clouds
Thursday with just a slight chance of a passing shower - but
ceilings will stay safely in the VFR category.

&&


$$