Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 070331 AAA
Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
631 PM AKST Tue Dec 6 2016
.ANALYSIS AND UPPER LEVELS...
The upper level pattern is fairly stable with the ridge entrenched
over the Bering Sea with the trough digging southwestward out of
the Yukon and over Southcentral Alaska. As this trough digs over
the Copper River Basin it is enhancing some areas of light
snowfall to its south which stretches from around Glennallen to
Valdez. The jet stream is running south of these systems and
remains well south of the forecast area. At the surface, the ridge
is centered near the MacKenzie River Delta and extends over the
northern half of the state, through the Bering Strait and then
over the central Aleutians. A low in the western Gulf of Alaska
has tightened the pressure gradient over Southcentral Alaska and
is bringing snow showers to the Gulf coast. This low is weakening
but the general pattern of high surface pressure overt he interior
of the state and Bering Sea with low pressure over the Gulf of
Alaska will persist through the remainder of the week. The western
Aleutians, on the west side of the ridge, will be in the storm
The very stable weather pattern is contributing to good model
agreement over the state through the rest of the week. The only
place where there is expected to be less than ideal model
performance is with the low complex in the Gulf of Alaska and the
track of the smaller individual lows as the rotate around in the
Gulf. This will not be a big issue but could cause timing issues
for the snow showers around the Gulf coast.
PANC...VFR conditions and light winds will persist.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Low pressure has moved into the Gulf and will generally persist
through Thursday. Cold air aloft is helping to produce some
fairly vigorous shower activity out over the Gulf, which will
intermittently affect coastal areas of the eastern Kenai Peninsula
as well as the Cordova area. However, the associated Low center
should remain far enough south and east over the next few days that
snow showers will have a hard time spreading inland to affect the
population centers. At the same time, a gentle reinforcement of
the cold and dry airmass will move into the area from the
north...helping keep the lowest levels of the atmosphere dry and
lessen chances even more for anything more than flurries to reach
the ground around Cook Inlet. Meanwhile, a weak upper trough is
dropping southward through the Copper River Basin this evening,
producing some light snow around Glennallen and even all the way
down to Valdez. This should continue on and off through the night,
but will not amount to any significant accumulations.
Northerly/outflow winds will continue for the foreseeable future
in this pattern...especially around Prince William Sound, where
cold air and strong winds continue to produce very cold wind
chill values through Thompson Pass. The wind chill advisory for
this area remains in effect through noon Wednesday.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A series of weak upper level waves will move north to south across
the region through the next couple of days. With a sharp inversion
in place around 1000 feet above the surface, any change in the
flow at the inversion is allowing for overrunning stratus and
flurries to develop, squeezing out any available moisture in the
atmosphere. This makes predicting low-level cloud cover the
trickiest part of the forecast for the next several periods over
Southwest Alaska. For this forecast package, we have trended much
more pessimistic with the low-level cloud cover and possible
flurries through tonight, then with gradual clearing. However,
with little change in the pattern over the next couple of days,
low-level stratus could be persistent for (much) longer than
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Cold advection north to northwesterly flow will keep scattered
snow showers focused along the Bering side of the Alaska Peninsula
over the next fews days, with gusty Small Craft Advisory level
winds and freezing spray impacting the waters of the far southeast
Bering, and possibly the south side of the Akpen. Meanwhile,
benign conditions and perhaps even some sunny skies will be found
over the Pribilofs through the middle of the week beneath a stout
upper level ridge. A storm-force front will move over the far
western Aleutians tonight accompanied by possibly heavy rain, with
the front weakening as it moves into the southern Bering and
Central Aleutians Wednesday night into Thursday.
.LONG TERM FORECAST (Days 3 through 7...Fri through Tue)...
The big story in the long term will be continued dry conditions
through early next week for the Southern Mainland. On Friday, a
weak area of low pressure will drift from the Northern Gulf of AK
towards the Alaska Peninsula. This will bring an end to the last
vestiges of any light snow showers along the Gulf Coast. Into the
weekend, a dominant Arctic High will build in from Chukotka region
across mainland AK. This will make for clear and continued dry
conditions. Forecast confidence is high in this scenario. One
difference that will be noticeable will be slightly warmer
temperatures. Climatology puts Anchorage at 10F for a low and 23F
for a high. While things may not be quite this warm, they should
be warmer than last weekend. While the offshore gradient remains
in place, it will be markedly weaker than last weekend as well.
Thus, winds through the gaps such as Whittier and Thompson Pass
will be less gusty.
There is some uncertainty in how the ridge breaks down early next
week (12-13 Dec). All models indicate that some energy will make
it over or through the ridge and punch through Prince William
Sound. But there is uncertainty in what happens with said energy
thereafter. At this point, it looks like there will not be
sufficient moisture with that energy to produce any snow, but it
certainly could bring some gusty winds.
PUBLIC...Wind Chill Advisory for Thompson Pass.
MARINE...Storms 178. Gales 127 177 411. Heavy Freezing SPray 160
SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC