Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 240151
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
451 PM AKST Mon Jan 23 2017
.ANALYSIS AND UPPER LEVELS...
There is a large upper low centered near the eastern Aleutians
which covers most of the Bering Sea and southern Alaska.
There is a surface low centered just to the south of the upper
low. The main front associated with this low stretches from the
southeast Gulf of Alaska to the Kenai Peninsula, then westward
into southwest Alaska. Plenty of precipitation is associated with
this front, mainly along the Gulf coast. Precipitation is much
reduced inland due to down-sloping off the coastal mountain
ranges. This entire system is bringing in much warmer air, with
locations from the eastern Aleutians through Kodiak already
changed over to rain.
The numerical models are in reasonable agreement for the short
term portion of the forecast (through Wednesday afternoon). There
are some differences in how the models are handling the
development of a low south of Kodiak Island late Wednesday
morning into the early afternoon. The GFS and Canadian Gem are
developing a more robust surface low, while the ECMWF and Nam are
PANC...VFR conditions will return early this evening as the snow
ends. Some wind shear is expected tonight as the mid to upper
level front moves across the area.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A warm front tracking into the Northern Gulf coast and Cook Inlet
region will continue to produce widespread snow and some localized
areas of gusty winds over these areas, with temperatures gradually
warming both aloft and at the surface through tonight. However,
snowfall over the Anchorage area and Western Kenai will begin to
lighten up late this afternoon as cross-barrier winds become more
favorable for downsloping. Higher snow totals are expected along
the areas surrounding Prince William Sound and the Eastern Kenai
Peninsula through tonight.
The main uncertainty for this forecast package remains the
potential and timing of if/when Snow over the areas surrounding
Prince William Sound and the Eastern Kenai will change over to a
mix or rain. While this system is filtering in ample amounts of
warm air northward, cold air remains in place from Seward to
Valdez. Cold drainage flows are expected to persist through
tonight as the front pushes further northward. We are expecting
areas along the Northern Gulf coast to begin to mix with rain by
Tuesday morning, as the warmer airmass overtakes the colder air
already in place.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Snow and gusty northerly winds will continue to produce areas of
blowing snow across western portions of Bristol Bay through late
tonight as the front pushes inland. Conditions will then begin to
improve as winds diminish with the passage of the front. Showers
will continue across the southwest mainland through the middle of
the week in broad cyclonic flow on the periphery of upper trough
over the eastern Bering. Southerly flow will also bring gradually
warming temperatures, including during the overnight hours tonight
as warmer air moves northward behind the front.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The Bering will be characterized by generally benign showery
conditions in the wake of the strong front which has now mostly
pushed inland. Allowed the Blizzard Warning to expire for the
Pribilof Islands, but replaced it with a Blowing Snow Advisory
through the early evening hours to account for lingering
visibility reductions before snow diminishes in intensity and
winds subside slightly this evening. Otherwise, the upper trough
will remain over the eastern Bering through Wednesday as the first
North Pacific low weakens and another low moves south of the
Akpen. This will keep a mix of rain and snow showers over the
southeast Bering and scattered snow showers over the remainder of
the region in cold northerly flow.
.LONG TERM FORECAST (Days 3 through 7)...
The main challenge for Wednesday night into Thursday will be the re-
enforcing warm front which moves from the Gulf to the coast.
There is uncertainty on the track of the surface low that pulls
the front into the mainland. At this time, the low is expected to
cross from the Pacific to the eastern Bering. Precipitation along
the front over the Gulf will be rain which is expected to spread
inland creating a mix of rain and snow or changing over to rain by
Thursday afternoon. The other big challenge will be wind with this
front. A tight pressure gradient along the front will bring gusty
conditions across the gulf and for much of the southern mainland
as the front moves inland. East to West oriented gaps will see the
strongest winds with this system.
The weather trend through the end of the week continues above
normal for temperatures and precipitation for the southern
mainland with a cooler trend remaining across the Bering as the
long wave trough remains centered over the Bering. The upper level
pattern should shift east this weekend and bring cooler temperatures
back to Southcentral as strong shortwaves move off of the Kamchatka
Peninsula forcing the upper low center closer to the west coast.
The weather pattern continues in an active regime into the beginning
of next week. Details in the extended forecast will need to be monitored
as models have multiple strong waves to handle.
PUBLIC...WSW 161 and 195.
MARINE...Storm 119. Gale 125 131 174-176 179 185 351 412-414.
SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB