Gale Warning 240, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
514 AM AKST Fri Mar 8 2019

.ANALYSIS AND UPPER LEVELS...

There are currently two upper level jets over the forecast area.
One is oriented north-south over the western mainland and the
other much stronger one of around 170 knots is tracking south of
the Aleutians. In the mid-levels, there is currently a weakening
upper level low over the central Bering with an amplified ridge
in place over eastern Alaska. A stronger upper level low located
in the left exit region of the aforementioned jet will intensify
and merge with the weaker low and will gradually break down the
ridge over the eastern mainland. At the surface, a ~970mb low over
the central Bering is weakening as it becomes vertically stacked
with the mid-level low. A stronger surface low is currently well
west of the Aleutians, but will quickly move into that region
today given the fast upper level steering winds and is also
expected to strengthen due to the upper level divergence and mid-
level PVA. It should be fully phased with the weaker low by this
evening.

&&

.MODEL DISCUSSION...

As has been true with preceding days, the models are still in
generally good agreement regarding the weakening of the central
Bering low and strengthening of the incoming western Bering low.
The two lows will merge over the central Bering and the associated
front will quickly track eastward, breaking down the ridge over
eastern Alaska and bringing unsettled weather to the entire
forecast region over the weekend. As all major models have shown
good run-to-run consistency over the past few days, confidence is
high regarding this overall upcoming pattern. Turnagain and Knik
Arm winds will likely increase Saturday afternoon and continue
through Sunday morning. One notable change from the previous
forecast is the earlier diminishing of these winds early Sunday
morning as latest models show the associated barrier jet departing
Prince William Sound slightly faster than previous runs.
Uncertainly remains on exactly when the localized stronger winds
will diminish.

&&

.AVIATION...

PANC...VFR conditions will persist through the day along with
light and variable winds. A front approaching the area is causing
strengthening southeasterly winds over the airport, leading to
wind shear conditions. Once the front moves into the area, there
may be some light rain tonight, along with strengthening Turnagain
Arm winds down to the surface. After the front passes, the mid-
level winds will diminish but the Turnagain Arm wind will persist.
Looking just beyond the TAF period, as another even stronger
front approaches during the day Saturday, even stronger winds at
2,000 feet are expected to produce more intense wind shear
conditions than those occurring presently. Thus, any break in the
wind shear Saturday morning will be brief.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Today and
Sunday)...

The active pattern will continue for Southcentral Alaska with two
fronts pushing through the area through Saturday. The first is
tracking into the Kenai Peninsula bringing a mix of rain and snow
to the region. Some areas along the coast have already
transitioned from snow to rain and as the front pushes north more
locations will see this transition. The heaviest precipitation
will fall over the eastern Kenai Peninsula but snow amounts will
be somewhat subdued due to the transition to rain for many low
lying areas. The front will diminish and track off to the
northeast tonight allowing temperatures to drop again.

The second front will move into the area Saturday bringing another
round of snow and rain to the area. This second system looks to be
stronger than the first with higher amounts of precipitation and
stronger winds. Areas around the Barren Islands and along the
north Gulf coast should see storm force winds as the front moves
through. Additionally, Turnagain Arm will see winds gusting in the
60 MPH range Saturday evening/night due to the front. Similarly
to the first front, the majority of the precipitation will be
along the north Gulf coast, with the heaviest amounts over the
eastern Kenai Peninsula. This system will also be warm enough for
many low lying areas to see a transition from snow to rain through
the day Saturday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

A dissipating front associated with a vertically stacked low in
the central Bering Sea continues to bring precipitation to the
southwest mainland. With temperatures hovering right around
freezing, expect mostly snow to continue, though expect a
changeover to rain along the AKPEN later today as temperatures
approach 40 in southerly flow. Expect conditions to temporarily
dry out from west to east later this morning, with another round
of precipitation over the Kuskokwim Delta coast this evening as
the vort max associated with the weakening low passes over the
area.

The next focus is a storm force low roughly 450 miles southwest of
Attu. This low will maintain a deep southerly fetch of moisture
and bring potential for moderate precipitation and a substantial
warming trend over southwest Alaska starting Saturday. Sustained
winds at the surface will likely crack 40 miles per hour, with
potential for gusts over 60 miles per hour at times. South facing
slopes will get the heaviest precipitation, with a foot of snow
possible in the Ahklun and Aleutian Mountains, while areas to the
lee will see considerably less. Visibility will likely be impacted
by blowing snow along the Kuskokwim Delta coast Saturday morning,
but with temperatures likely right around 30, but sustained
whiteout conditions are not expected at this time. As warm south
flow persists, cold air in place will erode and expect
precipitation to change over to rain by Saturday afternoon, save
for the higher peaks. Daytime highs Saturday will easily reach
into the 40s on the north side of the AKPEN, and likely hit upper
30s in the Kuskokwim Delta, lower Kuskokwim Valley, and Bristol
Bay areas. Warm conditions will persist in southwest Sunday, with
showers likely as the low moves overhead.

&&

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

Heavy swell from a weakening low in the central Bering continues
over much of the marine waters, though seas will subside slightly
this morning. The wet pattern will continue into Sunday. A storm
force low roughly 450 miles southwest of Attu will move
northeastward and bring gales with a swath of storm force winds
along the front later today. The low will shift into the eastern
Bering Sunday. Cold air advection around the west side of the low
will maintain a showery pattern over the Aleutians Sunday, with
precipitation types changing over to snow over the western
Aleutians.

&&

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

...Southern Coastal Waters along the Aleutians/AKPEN...

The main area of interest for the extended period is from Adak
eastward towards Kodiak Island on Sunday. For these locations,
sustained winds in the high-end gale range combined with good
fetch length will yield seas in the 30 to 36 feet range. Storm
force gusts are expected as well. After Sunday, winds will
decrease below gales and seas will subside as well.

...Bering sea and northern coastal waters of the Aleutians/AKPEN...

As an area of low pressure moves from the eastern Bering into
southwest Alaska, mid-range sustained gales are likely across the
western and southern portions of the sea southwards towards the
island chain. A few low-end storm force gusts aren't out of the
question as well, with seas generally in the 20 to 25 feet range.
Conditions will improve for Monday and Tuesday.

...Gulf of Alaska...

Following Sundays frontal passage/strong wind event, look for
small craft criteria winds and waves to persist across Shelikof
Straight and the Kodiak Island coastal waters northeastward
towards Prince William Sound on Monday, with improving conditions
expected on Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A strong eastern Bering low will move ashore across the coastal
Kuskokwim Delta on Sunday, with several disturbances crossing the
region in the cyclonic flow. Another low looks to move along the
Aleutian chain towards Bristol Bay for Monday into Tuesday, with a
third low rapidly deepening as it lifts towards Kodiak Island for
the Wednesday and beyond. All of this points to a showery pattern
continuing across most of southwest Alaska and the Aleutians.

Further east, some gusty winds are expected for the Turnagain arm
and Upper Hillside on Sunday, with the higher elevations near
Prince William Sound also getting in on the act. This will occur
in association with an occluded front crossing the region.
Precipitation will be a decent bet as well for most locations,
especially along coastal Prince William sound due to orographic
lift. The exception to this will be the Anchorage Bowl, where
down-sloping effect to the lee of the Chugach Mountains will
develop.

For Monday into Tuesday, the frontal system will weaken due to
frontolysis (the weakening of a front), as it outruns its upper
level support. This will lead to a decrease in the potential for
precipitation.

Our attention then turns towards the Kodiak low mentioned above.
The latest trend in the models is for a slower and stronger low to
develop as it enters the western Gulf mid-week. The European Model
(ECMWF) has trended towards the more persistent GFS solution, with
the Canadian in between. Should a stronger solution develop
verify, a pattern change may be in store for the region.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 119 120 136-139 141 155 165 170-173
 			   175 177 179 181 185 351 411-414.
		 Storms 130-132 150 160 174 176 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...JPW/AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...PD

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1237 PM AKST Fri Mar 8 2019

AKZ101-090945-
Anchorage-
Including the cities of Anchorage, Eagle River, Indian,
and Eklutna
1237 PM AKST Fri Mar 8 2019

...STRONG WINDS EXPECTED SATURDAY...

Gusty winds will return to the Anchorage Upper Hillside this
evening and again on Saturday.

Friday evening into late Friday night, winds will become gusty
for Upper Hillside residents. Gusts will be as strong as 50 mph.

Early Saturday morning, a lull in the winds will develop.

By late morning Saturday, a second surge of wind will move over
the Anchorage Upper Hillside with sustained winds of 50 to 65 mph
with gusts reaching up to 75 mph, but a few gusts may be
stronger, especially in exposed locations or in channeled terrain.
The strongest gusts will be near the Upper Hillside.

Lower elevation areas, including Anchorage and Eagle River, may
see gusts up to 35 to 45 mph.

Winds will subside by Saturday evening.

This period of wind is expected to significantly limit any rain
and snow and lower Anchorage elevations on Saturday even as a
weather system is passing through the area.

You can monitor local weather stations for wind gusts during these
periods at www.weather.gov/Anchorage/alaskaObs.

DS/PD