Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 220127

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
527 PM AKDT Thu Mar 21 2019

The main feature on satellite continues to be the large occluded
low pressure spinning south of the Alaska Peninsula in the
Northern Pacific Ocean. The frontal boundary associated with the
system wraps from the low center northward through the central
Bering Sea, across the southern Mainland, then southward, stretching
nearly to the Hawaiian Islands. The front and disturbances aloft
will be the focus for active weather. A Blowing Snow Advisory has
been issued for the Pribilof Islands for this evening. The same
front extends into the Gulf of Alaska near Kodiak Island. The
other controlling features aloft is a ridge of high pressure over
western Canada. The combination of feature keeps the jet pointed
toward the North Gulf Coast, ensuring a parade of disturbances and
moisture in coming days.


In the very short term, guidance has honed in on frontal position
in the Bering and precipitation timing/amounts. No major
discrepancies. For the following frontal wave impacting the Gulf
Coast, timing and position is not well agreed upon, but the
existence of a feature is there in all models.


PANC...VFR conditions and light winds will persist. Strong
winds will persist down Turnagain Arm, but will bend south down
Cook Inlet. As the next front approaches early Friday the down
Inlet pressure gradients will weaken allowing increasing
southeasterly winds aloft to move closer to the terminal.
Thus, have added a period of low level wind shear.


through Saturday)...

A front lifting north across the central Gulf this afternoon will
be the primary weather maker for Southcentral right into Saturday.
While the front itself is slowly weakening, it is producing gale
force winds across a swath of the central Gulf from Kodiak north
through the Barren Islands and Shelikof Strait. As it moves
northeast into Prince William Sound tonight, it is expected to
stall out there and persist into the the day Saturday.
Southeasterly winds along the front means there will be a
continuous feed of onshore winds into the Kenai and Chugach
mountains. Thus, near steady valley rain and mountain snow is
expected through Saturday, particularly along the eastern Kenai
Peninsula. The front will continue slowly weakening through
Saturday, so those unfortunate enough to be along the front
through Saturday should see steadily improving conditions after
the worst weather impacts the area tonight.

With this weather setup in place, the winds through Turnagain Arm
are expected to increase tonight and remain persistent through
Saturday. The strongest winds will be tonight as that is when the
front will be the strongest. A low to mid level jet associated
with the front will be aligned from Prince William Sound westward
along Turnagain Arm. Thus, it appears likely that despite the
strong downsloping winds, some of the precipitation should impact
Anchorage, especially along the Hillside tonight into Friday
morning. The 00 UTC Anchorage sounding shows a very unstable layer
of atmosphere through the mid-levels, which will promote mixing
and help some of that rain make it to the Bowl. With that said,
however, any rain tonight will be light. While chances are slight,
they are still non-zero that snow may mix in, as the warming
effect of the Turnagain Arm wind is expected to remain south of
Anchorage, owing to the strong northerly down-Inlet winds. Thus,
lows should fall into the 30s for much of Southcentral tonight.
The Matanuska/Knik Valley winds are also expected to be ongoing
through at least Friday in the 15 to 25 mph range with higher
gusts, though which one of the two dominates is very uncertain.
Up through this point, it has been variable. A lack of any truly
cold air anywhere near Southcentral will help keep any winds from
becoming damaging. Temperature-wise, continued well above-average
readings are expected for the foreseeable future as highs for many
locations come very close to their daily records.

The parent low of the front, currently well south of Kodiak
Island, will track northwestward west of Chirikof Island Friday
morning. This will bring another round of gales to Kodiak Island
from late tonight through at least the first half of Friday. While
the front remains stalled over the northern Gulf on Friday, some
sunshine can be expected across Kodiak Island by Saturday along
with much-diminished winds as high pressure builds in.


A warm front currently located near Hooper Bay is bringing snow
and blowing snow to areas along the immediate coast. Snow is
expected to end over the coming hours, however blowing snow will
continue through Friday for this region in the wake of the front.
Elsewhere, south of the front over interior regions, strong warm
advection east of a low moving over the AKPEN will bring
unseasonably warm temperatures Thursday and Friday, with highs
approaching the mid- 50s in downsloped areas of the Alaska Range.
As the low dissipates over the Bristol Bay, advection will weaken
bringing cooler temperatures for Saturday. Isolated rain/snow
showers are possible, however they will be very light.


A warm front west of a low moving over the AKPEN is expected to
bring gale force winds and higher seas to the central Bering
southward to the Aleutians this evening through Friday. Snow and
blowing snow with reduced visibility is highly likely over the
Pribilofs. Most models have been indicating the front moving
faster to the west over the past 24 hours and conditions over
this region will gradually improve beginning later Friday
morning. The surface low will dissipate over Bristol Bay as it
becomes vertically stacked with an upper level low. Thus, winds
will diminish and seas subside across much of the Bering/Aleutians
from south to north Friday night into Saturday. An ~970mb low
moving south of the Kamchatka Peninsula will possibly bring gales
and higher seas to the western Aleutians through Saturday.


.MARINE (Days 3 through 5)...

Gulf of Alaska...Expect generally benign conditions, with winds
diminishing and seas subsiding as a low in the Gulf of Alaska

Bering Sea...Confidence is high that a gale force low will
approach the western Aleutians Sunday, bringing high seas and
widespread gales to the central Bering and Aleutians Monday. Some
model solutions depict a swath of storm force winds in the central
Aleutians/eastern Bering Monday...while we didn`t have the
confidence to go that high with this forecast package, the
potential for storms will need to be monitored. The low will
weaken and shift northward towards eastern Siberia by Tuesday
and winds will diminish.


.LONG TERM FORECAST (Days 3 through 7)...
Wet weather will continue over Southcentral as several waves
associated with a North Pacific low rotate into the area. However,
confidence is building that dry weather is in sight for
Southcentral. Models continue to develop a longwave ridge over
Southcentral early next week. Daytime conditions will trend even
warmer than observed this week, though valley locations will
likely see cold nights driven by clear skies. The main question is
when the ridge will degrade, and model agreement is poor on that
decision. Some solutions show the ridge breaking down as early as
midweek, with a return to wetter weather following.

Looking farther west, a series of lows will move through the western
and central Bering throughout the long term, starting with a
potent low expected to approach the western Aleutians late Sunday.
With a moisture fetch almost to the tropics, expect heavy
precipitation ahead of the low. As the low shifts northward into
the Bering Monday, the front and associated precipitation and
winds will progress eastward over the Aleutians and Bering, then
stall over Southwest Tuesday. A ridge in place over Southcentral
will likely diminish precipitation potential over the Southwest
mainland. Showers in cold air advection will persist behind the
front in the Bering. A series of smaller lows will bring periods
of unsettled weather to the Bering and Aleutians through next
week, while conditions over the mainland will depend on the
progression of the upper ridge.


PUBLIC...Winter Weather Advisory 195.
MARINE...Heavy Freezing Spray Warning 185.
         Gale Warning 119 120 130 131 132 136 137 138 139
                      150 170 171 172 173 174 175 176 178
   179 185.



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