Gale Warning 368, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
438 PM AKDT Sun May 7 2023

.ANALYSIS AND UPPER LEVELS...
There are two lows of note over the region this afternoon. The
stronger low is centered in the western Bering Sea, just a little
north of Attu. Its occluded front is extended across much of the
Bering Sea and then crosses the eastern Aleutians near Unalaska.

The second low is approaching the eastern Kenai Peninsula and and
shows up well on satellite imagery. While this low is associated
with a cold 500 mb low that over the area, it does not have any
jet stream support and is mainly bringing showers to the Gulf
coast region. Some of these showers may move inland briefly as it
progresses to the northwest.

In between these lows there is a ridge that extends over Southwest
mainland Alaska. This ridge is cleared out much of the Kuskokwim
Delta, but the upper level low and weak easterly flow aloft have
conspired to bring areas of stratus to the Bristol Bay region and
increased cloud cover farther inland for the Kuskokwim Valley.

&&

.MODEL DISCUSSION...
Models are holding together well through mid-week in the synoptic
scale as the concerns mentioned on the previous discussion look
to have resolved in the more current model runs. The big issue
during the middle of the week will revolve around the complex low
that will have moved into the Gulf of Alaska at that time and how
the structure of the secondary lows around it develop.

&&

.AVIATION...
PANC...VFR conditions will persist. Southeast winds are likely to
develop over the terminal this afternoon through the evening, but
look like they will not be overly strong with expected maximum
gusts 15 kt or less. Monday will see southeast winds develop in
the afternoon again, but they should be stronger than today.

&&

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

A shortwave trough and attendant surface low currently south of
Seward will lift through Southcentral overnight, bringing showery
weather to most areas other than the Copper River Basin. Quick on
the heals of this system is a strong front moving into the
Western Gulf tomorrow morning. The front will bring elevated winds
and rain to Kodiak Island first before pushing into the eastern
Prince William Sound/Eastern Kenai Peninsula by tomorrow evening.
Cold air pushing north ahead of the front will likely bring snow
down to road level in Turnagain Pass before a slow rise in snow
levels over the coming days, which will raise and lower in a
diurnal trend. This front is expected to linger along the coast,
having periods of heavier precipitation and stronger winds a meso-
lows develop along the front underneath the broad upper level
trough. Most, if not all of the precipitation, should remain
coastal and over the Chugach and Kenai Mountains, with little
spillover due to downsloping.

The other side to this system will be the winds, with elevated
gusts developing through the easterly and southerly gaps starting
tomorrow afternoon. Expect the Turnagain Arm wind to bring
stronger gusts to West and South Anchorage through Monday evening
before tapering off. The Knik and Copper River Wind wind will
also bring gusty winds to the Mat Valley and Copper Basin
respectively. A similar diurnal trend in gap winds is likely
again on Tuesday, but aren't expected to be quite as strong as
Monday. Due to the low location in the Gulf, the Turnagain Arm
wind should stay down inlet on Tuesday, but will remain elevated
through the Arm and at higher elevations.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(Days 1 through 3: Tonight through Wednesday night)...

An active pattern is expected for much of the Aleutian Chain and
Southwest Alaska into midweek as a series of low pressure systems,
and associated frontal boundaries, move through the regions.
Currently, a low pressure system is in the Southwestern Bering
Sea, pushing a leading frontal system across the Eastern Aleutians
and drawing Southeasterly gales through the Pribilofs into the
central Bering. For the moment, an unsettled pattern rests over
Southwest Alaska, a system that provided favorable conditions for
areal fog in the Lower Kuskokwim Valley this morning, expected to
repeat late overnight tonight. Looking forward, the low will
advance steadily eastward across the Southern Bering, bringing
sub-gale northerlies along the backside of the system. The low is
expected to reach, and cross, the Alaska Peninsula by Tuesday
morning. However, ahead of the low the frontal boundary will
persist, pushing into Southwest Alaska by Monday morning. Some
gusty winds are expected overnight tonight near Cold Bay as a
favorable wind direction may channel some gusts toward the city.
Winds will become increasingly southeasterly in Bristol Bay as the
front approaches, spreading inland by Monday morning. The leading
edge of precipitation associated with this front as it approaches
Southwest Alaska may contain a brief period of mixed
precipitation, however a quick transition to rain will follow.
Rainfall expected to largely be contained within the Greater
Bristol Bay region Monday and Monday night, easing by Tuesday
morning as the remaining rainfall will be along the eastern edge
of the Alaska Peninsula and Kilbuck Mountains. The Eastern
Aleutians may see some showers persist following the passage of
the front and low pressure system as late as Wednesday morning as
flow over the top the rotation continues to bring potential for
precipitation.

Back out west, a new low pressure system looks to approach the
Western Aleutians by Tuesday morning. While the southerly shift in
winds is not currently anticipated to be as strong as this
current low system, another wave of precipitation will be moving
in Tuesday morning. Rainfall will be the predominant precipitation
type with this system, however it is too early to determine if any
mixed precipitation present. This wave is expected to push
eastward, making its way to Adak before the driving low pressure
system moves south, pulling the precipitation out of our area by
Wednesday afternoon.

&&

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

For Thursday, models strongly agree over a large surface low in
the central gulf and rain across Kodiak, the Kenai Peninsula, and
north gulf coast. There is less agreement on the timing and
extent of how it weakens on Saturday, when it sends a trough north
toward Southcentral Alaska, while continuing south along the
northern Pacific Coast. Poor agreement thus far over the strength
of a meridional ridge spanning the Bering, and when a Kamchatka
low approaches from the west. The GFS portrays the low most
strongly, and brings it most quickly into the Bering. The ECMWF
brings the warmest 850mb air from the North Pacific across the
central and eastern Aleutians on Saturday in advance of that low.

Over the eastern side of the state, the ECMWF, and slightly later
the GFS, briefly bring above freezing 850 mb air across the ALCAN
border during the day Friday before it retreats north into the
Yukon Saturday morning.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CL
LONG TERM...ER