NWS Anchorage, AK wrote its last area forecast discussion before the first event at Apr 8, 6:18 AM AKST, 7 hours 37 minutes earlier.
Area forecast discussion, Apr 8, 6:18 AM AKST, 7 hours 37 minutes before
Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
718 AM AKDT Thu Apr 8 2021
.ANALYSIS AND UPPER LEVELS...
Two upper level shortwave troughs exist over Alaska this morning,
both of which will be responsible for the active weather over the
mainland the next two days. The southern of the two lows, which
brought blizzard conditions and widespread snow to Southwest
Alaska yesterday, has shifted southeast over the AKPEN this
morning. This shortwave will help to pull an unseasonably cold
airmass and polar low over northern Alaska to the south, thus
amplifying the pattern over our Area of Responsibility (AOR). The
cold airmass can be seen well on infrared satellite with cold
brightness temperatures measured at the surface and cloud streets
streaming south of the Bering Sea ice. Meanwhile, the next frontal
system is rapidly approaching the western Aleutians.
Widespread snow has been observed on radar and surface
observations across Southcentral with the northerly extent
reaching as far as Talkeetna and Glennallen. Northerly winds have
been picking up throughout Southcentral as the low shifts into the
Gulf.
&&
.MODEL DISCUSSION...
Overall, models are in excellent agreement in synoptic scale
features in the short term. Thus, forecast confidence in the short
term is high. Minor discrepancies exist in the strength and
southern extent of the polar trough as it moves over the Copper
River Basin on Friday. The NAM is the most aggressive and coldest
of the models over this area. However, the differences are minor
and have little impact on forecast confidence.
&&
.AVIATION...
PANC...VFR conditions at 12z this morning are expected to lower to
MVFR as light snow redevelops over the airport complex by 14z.
IFR conditions are then expected between 14z and 18z as bands of
snow move from west to east across the terminal. By 18z, snow is
expected to be east of the terminal, falling over the Anchorage
Hillside. By this afternoon, gusty northerly winds will develop
over the airfield. These winds will increase in intensity through
the evening and overnight hours, with gusts approaching 50 mph.
The northerly winds will slowly diminish Friday but are expected
to remain gusty.
&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 3: Thursday
through Saturday)...
Model guidance is very much on track with a late-season storm
event that is making an impact on our area since late last night.
A potent shortwave trough has moved over the southern AKPEN, with
an associated triple point low developing along a frontal
boundary northeast of Kodiak Island. An initial push of moist,
southwesterly flow aloft allowed snow to fall over the western
Kenai Peninsula, Anchorage Bowl, and Mat-Su Valleys.
As the low moves over the central Gulf this morning, the easterly
flow along the north Gulf will allow snow to fall along the
immediate coast. A deformation band along the back side of the low
will also allow a band of snow to move across Cook Inlet and the
Anchorage Bowl this morning. This band of snow is expected to
linger across the Anchorage Hillside and upslope regions of the
Chugach and Kenai Mountains through most the day, with a couple of
inches of snow possible. Moist, cyclonic flow will keep the
chances of scattered snow showers going over the Copper River
Basin as well as north and west facing mountain slopes through
Friday afternoon as the low exits to the eastern Gulf.
Thereafter, a polar shortwave trough will move south from the
northern half of the state on the heels of the aforementioned Gulf
low late Thursday night and into Friday. Very cold, arctic air
will spread across the southern mainland and create gusty,
northwesterly winds funneling through the usual gaps and passes,
with Anchorage Bowl potentially reaching up to 50 mph or more by
Thursday night. A High Wind Warning has been issued for Thompson
Pass, Seward, and Kodiak Island to account for this significant
wind event. Additionally, northwesterly storm to hurricane force
winds with heavy freezing spray concerns will blow across the
usual gaps and passes, including Resurrection Bay, Kamishak Bay,
Shelikof Strait, and Lower Cook Inlet, from Thursday afternoon
into Friday morning (please see Marine Weather Statement for
details).
Wind chills will be another area of concern associated with the
strong winds and colder temperatures for Thursday night and into
Friday night in the low-lying and surrounding high elevations. The
gusty, northerly winds are expected to diminish by Friday night
into Saturday morning, allowing overnight lows to plummet anywhere
from the single digits to sub-zero. Some of these overnight lows
will have the potential to approach or break daily cold
temperature records for early to mid April. A low-level amplitude
ridge of high pressure will bring fair, mild weather over the
southern mainland by Saturday. Looking ahead, a storm system with
a deep fetch of tropical moisture is expected to arrive late
Saturday and into Sunday. Some uncertainty exists with
precipitation timing and duration with subsequent model runs
needed to iron out specific details. Suffice it to say that
unsettled weather will return late this weekend, so stay tuned for
the latest updates!
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA (Today through Saturday)...
Blizzard conditions will persist across the Kuskokwim Delta coast
early this morning on the backside of a low. Conditions will
improve through the day as winds diminish. The pressure gradient
will tighten over interior Bristol Bay into this afternoon,
leading to blowing snow in the Iliamna area. Otherwise, mostly
sunny skies are expected. An extremely cold airmass will drop
temperatures well below zero overnight across much of the region.
Conditions will remain quiet through the day Friday. A front will
move onshore Saturday morning, bringing more accumulating snow to
Southwest Alaska.
&&
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Today through Saturday)...
Strong, cold northwesterly flow on the backside of a low centered
in the Gulf is expected to bring hurricane force gusts out of bays
and passes south of the Alaska Peninsula through today along with
heavy freezing spray. A front tracking west to east across the
Bering will lead to blizzard conditions for the Pribilofs Friday
morning. Precipitation will quickly change to rain by mid-morning
and persist through the afternoon. Brief snow is possible across
the central and eastern Aleutians ahead of the front, changing to
rain in southwesterly flow behind it. Colder air wrapping around
the associated low will bring widespread snow showers through
Saturday.
&&
.MARINE (Days 3 through 5: Saturday through Monday)...
An active pattern is expected to continue for the forecast period
with a large gale force low anticipated to slowly traverse the
Bering Sea. Differences arise after the Saturday night time
period in regards to exact strength and placement of the low. The
one thing that looks to be fairly certain is that gale force winds
are expected on the northwest to southwest side of this low the
duration of the forecast period subsiding Monday.
More uncertainty arises for what happens on the eastern side of
this low as another piece of energy is expected to move northward
from the North Pacific and towards the Gulf of Alaska. The low in
the Bering may transfer some of its energy to this other system.
The less energy transferred the weaker this other system will be,
keeping the system in the Bering stronger for a longer time frame.
The strength of this other system that will move into the Gulf is
uncertain at this time ranging from small crafts to potentially
gale force. One thing that is certain is the track that this
feature will take moving from the southwest part of the Gulf
towards Southeast Alaska Sunday through Monday.
&&
.Long Term Forecast (Days 4 through 7: Sunday through Wednesday)...
Model guidance is in fairly good agreement on the upper level
features early on in the forecast time period before diverging for
Tuesday and Wednesday. All guidance agrees that there will be an
upper level trough present across the Bering and western Alaska.
This will extend southward from another upper level low present
over the Arctic for Sunday into Monday with some slight placement
differences. Model guidance agrees on an upper level ridge
nudging up into eastern Alaska and along the ALCAN border with
Southeast Alaska under the axis of this ridge early on before
pushing off to the east. Beyond Monday night, model guidance
spreads widely on the strength of these features, though,
placement looks to be in fairly good agreement.
Basically, the main takeaway will be that a fairly active pattern
will return to southern Alaska. There is the potential for an
atmospheric river aimed somewhere in between the eastern Kenai
Peninsula and southeast Alaska as multiple systems will impact
the region over a couple days. Temperatures look to slowly warm
each day, possibly reaching the upper 40s maybe even 50 degrees
for some areas of Southcentral towards the end of the forecast
period, though, this will all be determined by the exact strength
and placement of upper level features Tuesday and Wednesday. There
is also the chance temperatures may not drop to or below freezing
which may impact the continuing running tally for consecutive
nights at or below freezing for Anchorage which by this time frame
will be in the top 5. Therefore, expect near average temperatures
to start the period, rising to above normal for the second half
of the period. As these systems come up, precipitation types may
be an issue across the area as warm air tries to overcome the very
cold air mass present out ahead of it. Also, potential exists for
some fairly high precipitation amounts in the four day period
mentioned, especially in the mountainous terrain. Lastly, with
this upcoming pattern next week, rapid snowmelt is anticipated
especially if temperatures get as warm as currently progged to do.
&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155 195.
Winter Weather Advisory 161.
High Wind Warning 125 131 171.
MARINE...Hurricane Force Wind Warning 130 131 138.
Storm Warning 120 121 127 128 150 155 352.
Gale Warning 119 125 126 129 136 137 139 140 160 165 173
177-181 185 351 411-414.
Heavy Freezing Spray 119-121 125 127-131 137-141 160 180
185
FIRE WEATHER...NONE.
&&
SYNOPSIS AND MODEL DISCUSSION...CJ
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...MV