Gale Warning 328, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKDT Thu May 23 2019

.ANALYSIS AND UPPER LEVELS...

The upper air pattern is dominated by a closed/vertically stacked
upper low centered over Kodiak Island. The coastal front has
stalled along the North Gulf Coast with precipitation favoring the
coastal areas. This low remains very low end gale force with the
core of strongest winds over the southwest Gulf of Alaska. Ahead
of the low there is interior upper ridging extending into Alaska
from the Yukon. The next upper trough in line is developing south
of the Bering Sea from 48N to 30N, with satellite imagery already
showing a nicely defined subtropical moisture connection in the
form of a plume of warm air advection/cirrus.

&&

.MODEL DISCUSSION...

The numerical models are in excellent agreement with the general
pattern heading into the weekend. However, they are still
adjusting to the track and timing of a subtropical warm front
moving into Southern Alaska Saturday as a warm front/surface low
tracks into Bristol Bay. It seems the trend has been slower and
farther westward. For this forecast the onset of precipitation has
been slowed down for Saturday for Southcentral, as it now looks
like inland Southcentral will see a warm/dry day for most of
Saturday. Preferred a blend of models for this forecast.

&&

.AVIATION...
PANC...VFR conditions will persist through the TAF period. Gusty
southeast winds off Turnagain Arm will move back into the terminal
in the late afternoon and will persist through the late evening.
Vicinity showers are possible through the period.

&&

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

The occluded front over the northern Gulf will make landfall this
morning. The trailing low near Kodiak will continue to weaken and
will shift off to the east across the Gulf tonight and Friday.
Rain will generally be confined to the coasts with mainly a few
showers inland. The coastal ridge will not be as strong today and
the thermal trough will be weaker, so gusty afternoon and evening
gap winds across the Copper River Basin, out of the Knik Valley,
and along Turnagain Arm will not be as strong as Wednesday. The
retreating upper trough over the Gulf and and slowly building
ridge over the western Gulf will bring drier weather and cloud
breaks to the mainland Friday. A few showers will likely be
evident, but should be be confined the the mountains.

A weather front heading north toward the Gulf brings a return and
windy and wet conditions to Kodiak Island Friday night and
Saturday. This front is expected to be somewhat slower than
previous model runs, so rain should not move any further east than
the Kenai Peninsula/Western Prince William Sound by Saturday
evening.

&&

.FIRE WEATHER...

On Saturday, a strengthening thermal trough over the mainland
lowers interior pressures, while at the same time a north
advancing front across the Gulf builds the coastal ridge. The
resultant pinch in the pressure gradient will give rise to very
gusty southerly winds across the Copper River Basin Saturday
afternoon and evening. Windy conditions combined with afternoon
temperatures nearing the lower 70s and RH values in the 20s will
approach critical fire weather indices. That said, there is still
some uncertainly on the temperature piece of the puzzle as model
consensus is poor on the degree of warming which will take place.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A trough across the Southwest...combined with energy from an
upper level low tracking over the region today...brings scattered
to numerous showers with isolated thunderstorms possible for the
northern Kuskokwim Delta and Valley. Rain activity dissipates late
tonight with a dry day on tap for Friday. The next North Pacific
front pushes to Bristol Bay early Saturday morning spreading rain
and gusty southerly winds across the Kuskokwim late morning and
afternoon.

&&

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

The most active weather remains across the eastern Bering as a
ridge over the western waters persists. Low pressure over Kodiak
lifts today with small craft gusty west flow developing in its
wake around the Alaska Peninsula as a short wave ridge follows.
The next front is quick to follow with an occluded low pushing a
boundary over the central and eastern Aleutians late tonight.
North to east small craft winds are expected around the core of
this 1000 mb low and frontal boundary which pushes northward along
the eastern Bering Friday night and Saturday. Yet another front
moves to the western Aleutians Friday night bringing direction
wind changes for the western Chain and rain. The two low pressure
systems working against the ridge will allow the front along the
eastern waters to move its front across the central Bering on
Saturday.

&&

.MARINE (Days 3 through 5)...
Winds in the 30 to 35 kt range are likely with the frontal system
lifting north across the Alaska Peninsula and into the southwestern
Gulf Friday and Friday night. Additionally, gales are also
possible in association the deepening surface low that swings
through Bristol Bay on Saturday and with the portion of the front
over the western Gulf, supported by a strengthening triple point
low near Kodiak Island. As the front lifts further north Saturday
night and Sunday, easterly winds may also increase into the 30 to
35 kt range along the northern Gulf Coast and Prince William Sound
area.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Confidence continues to increase in a transition to a much wetter
pattern starting Friday night and Saturday. The upper level ridge
in the Gulf amplifies and shifts east to merges with the ridge
centered over Northwest Canada to form a substantial blocking
feature that by Saturday will stretch from around 30N, across the
eastern Gulf and Southeast Alaska Panhandle through northwest
Canada and into northern Alaska. To the west, a deep elongated
trough will form, extending south from an upper level low in the
southeastern Bering. A resulting long southerly fetch of tropical
moisture will feed the frontal system lifting north into southern
Alaska Friday night and Saturday bringing both heavy rain to the
coastal areas as well as widespread wetting rains further inland.

As we progress into the weekend, models are showing the areas of
heaviest rain which will initially push across the Alaska
Peninsula and Kodiak Island Friday night through Saturday morning,
shifting more to the north over the Kenai Peninsula Saturday
afternoon through Saturday night and over Prince William Sound
Sunday.

The upper levels will shift gradually to a more southeasterly
flow pattern through the first half of next week with the upper
low centered south of the Alaska Peninsula and the big ridge
further inland over western Canada but still tilting to the west
into northern Alaska. For southern Alaska the result will be a
less continuous stream of warm, high content moisture air but
still an active, wet pattern with numerous frontal systems
tracking through the Gulf and inland.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA/FIRE WEATHER...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
MARINE/LONG TERM...JR