Gale Warning 134, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 AM AKST Sun Feb 3 2019

.ANALYSIS AND UPPER LEVELS...

Snow has developed from Cook Inlet north through the Susitna
Valley as a developing low west of Bristol Bay swings a warm front
north of Kodiak Island. Snow is also falling over much of
Southwest Alaska as both the warm front extending across the
northern AKPEN and an occluded front over the Lower Kuskokwim
Delta both lift northeast over the interior. Behind these fronts,
a strong southerly flow of warmer air has pushed temperatures into
the mid 30s to lower 40s and has changed the snow over the rain.
This low continues to have upper level support as the center of
circulation sits under a 140kt jet streak positioned over the
eastern Aleutians. Farther east, the cold dome of high pressure
that has been dominant over the Copper River Basin the past few
days is beginning to erode as clouds and warmer air works in. A
weak area of low pressure near Middleton Island is drifting north
and bringing a band of rain and snow showers closer to the coast
near Cordova. Farther west, rain and gusty southerly winds are
occurring over the far eastern Aleutians and AKPEN in advance of
a cold front. An area of gale-force winds have also been observed
near the center of a low northwest of Shemya via the latest ASCAT
pass. South of the Aleutians, a strengthening low is lifting
north ans spreading clouds over the over the central portion of
the chain.

&&

.MODEL DISCUSSION...

There is decent agreement between the models concerning the
evolution of the overall synoptic pattern, especially for the
first 48 hours. Beyond that, there is noticeable disagreement on
the timing and track of the system moving across Southcentral for
late Monday into Tuesday, with the NAM becoming the slower
solution and most bullish in terms of warm air advection and
precipitation. The biggest struggle between the models is in the
details when it comes to winds and precipitation type and
intensity across Southcentral. This has been the most challenging
part of the short term forecast, especially for the Anchorage Bowl
where precipitation type amd amount is very much contingent on
wind direction. Father west, guidance remains in decent agreement
regarding the next North Pacific low to cross the Aleutians on
Sunday. The GFS and Canadian continue to be the solutions with the
strongest and most compact low while the EC and NAM are slight
weaker and are displaced to the north and east, respectively.

&&

.AVIATION...

PANC...Predominant IFR with occasional improvement to MVFR conditions
with light snow and northerly winds will continue through the
morning hours. A gusty southeasterly Turnagain arm wind is
expected to develop after noon today and remain over the airport
complex into this evening. MVFR conditions should prevail during
this time with improved visibilities, but ceilings are expected to
stay below 5,000ft. The increase in southeasterly winds should
also limit precipitation during the afternoon and evening hours.
Low-level wind shear, predominantly speed shear, is a possibility
in conjunction with the Turnagain Arm winds, but this remains
marginal at best and was not included in the TAF. A return to IFR
conditions is expected later tonight as light snow redevelops over
Anchorage.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Tonight
through Monday)...

An upper, long wave trough over western Alaska has set up broad
moist southwesterly flow aloft and brought widespread snow over
the Cook Inlet to MAT-SU Valleys corridor. The heaviest snowfall
is still expected over the Susitna Valley and along the Talkeetna
Mountains including Hatcher Pass. Total snowfall values in these
areas tonight will range from 10 to 15 inches in the Susitna
Valley to up to 2 ft along the Talkeetna Mountains and Hatcher
Pass. Further South toward the lower elevations of the Matanuska
Valley and Anchorage Bowl total snowfall values should not exceed
the 2 to 4 inch mark except perhaps upslope areas of the adjacent
Chugach Range. The current high resolution models are starting to
point toward the Turnagain Arm wind bending into south and west
Anchorage later this afternoon bringing locally gusty southeast
winds. This will tend to reduce snowfall potential for the late
afternoon and evening hours. Gusty winds are also expected to
develop along the lower elevations of the Chugach Mountains and
will lead to some blowing snow. Temperatures should warm enough to
bring some mixed precipitation types across portions of the Kenai
Peninsula and North Gulf Coast. Precipitation should taper off
across much of Southcentral by early Monday morning.

Any clearing on Monday will be brief as a weather front heading
east will bring rain to Kodiak Monday morning. Temperatures aloft
will warm with this system, so as precipitation spreads into the
Southcentral Monday evening mixed precipitation types become a
concern.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
(Today through Tuesday)

An active pattern looks to continue over the next few days.
A very weak surface front stretched from near Port Heiden towards
Nunivak, accompanied by another weak low lifting northeast across
the eastern Bering. Meanwhile, aloft the 850-250 mb axis stretched
from just west of Kipnuk to Nikolski. Both of these features will
likely remain in place through the morning, before a weak ridge
axis moves across the area this afternoon through Monday morning.
As this occurs, look for precipitation to be on a downward trend.

By Monday afternoon, another area of surface low pressure will
have moved into the western Bering from the Pacific, sending
another front across the region. This front will bring a
reinforcing shot of warm air and moisture to the region, while
acting as a focus for precipitation redevelopment. This feature
not only has strong convergence at the surface, but also strong
bursts of ascent aloft as multiple lobes of vorticity cross the
region associated with the Bering low as it fills (becomes
vertically stacked). Strong moisture transport with a tropical
connection should yield some decent precipitation totals given
the dynamics involved, with Monday afternoon through Tuesday
morning being the favored time frame for this to occur. Then, as
the front clears the region during Tuesday afternoon, colder air
will advect back into Southwest Alaska

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
(Today through Tuesday)

Winds have decreased in the wake of yesterday's storm, but
troughing persists across the western Aleutians northward towards
Siberia, with another storm system ready to enter the Bering from
the western Pacific. This system looks to cross near Adak during
this evening, deepening as it does so. Southwest flow with a
tropical connection will continue across most of the region,
allowing for any precipitation to be fairly heavy at times. Winds
will also be on the increase along a warm front, increasing into
the small craft variety.

The real story will be on the backside of the storm though, due to
the system filling as it bottoms out in the western Bering in the
~970 to 975 mb range. As it fills, its associated cold front will
race east-northeastward and catch up with the warm front as the
occlusion process matures. Strong cyclonic flow and dry low-
level advection will be juxtaposed across the west central
Aleutians with both a mid and upper-level jet streak, helping to
enhance downward mixing potential. For now we have increased
sustained winds into high-end gales with storm force gusts.
However, if the timing of the features continue to look favorable
as they cross one another, we may need to hoist storm warnings
for this region on the southern to eastern flank of the storm.
With the increasing winds and long fetch length, wave heights will
obviously be on the increase, with current forecasts having them
topping 20 feet.

&&

.MARINE (Days 3 through 5)...
The Gales expected in the Eastern Aleutians and eastern Bering Sea
Monday look to be on track and the strongest winds should remain
just below storm force. A sizable area of 20+ ft seas should
accompany the strongest winds in the Bering Sea Monday but then
settle below 20 ft by Monday night.

A second low should also bring some Gales and near-Gale force
winds from the Central Aleutians through Alaska Peninsula and
Bristol Bay Tuesday night into Wednesday. While winds will not be
quite as high with this second low, the persistent southwesterly
fetch will likely bring in 20 to 30 ft seas along the Pacific side
of a large potion of the Aleutian Islands Tuesday into Wednesday.

Confidence in the winds and waves around this second low is above
average as models are in good agreement with the development and
movement of the low that is causing these Gales.

&&

.LONG TERM FORECAST (Days 3 through 7)...
There is not a lot of overall change in thinking for the long
term forecast from Tuesday through next Saturday. The storm track
remains over the Bering Sea to the western Gulf of Alaska which
will keep a warming southwest flow over southwest and
Southcentral Alaska. One notable change in the forecast is that
there is an indication that there will be warmer air moving into
Southcentral Alaska on Tuesday which will push the rain-snow line
farther north at that time before a slow and slight cooling trend
begins Wednesday through Saturday for Southcentral. At this time
the rain-snow looks to be over Anchorage and the Matanuska valley
with the Kenai Peninsula mainly rain and the Susitna Valley
remaining snow. This system will likely bring another another
round of significant snow to the Susitna Valley Tuesday and
Tuesday night. By Wednesday, Southcentral temperatures for areas
not along the immediate coast should remain at or below freezing
and keep precipitation type all snow after that.

Southwest Alaska will see warmer air than Southcentral with
widespread above freezing temperatures Wednesday through Friday
with Thursday likely being the warmest day.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 145 152.
MARINE...Gale Warning 170 172 173 174 175 176 177 179 411 413 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
MARINE/LONG TERM...EZ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1105 AM AKST SUN FEB 3 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0930 AM     SNOW             1 NW SOLDOTNA           60.50N 151.10W
02/03/2019  M2.5 INCH        KENAI PENINSULA    AK   PUBLIC

            TOTAL SNOWFALL AS OF THAT POINT. STARTED
            SATURDAY EVENING.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
1113 AM AKST SUN FEB 3 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1110 AM     SNOW             GIRDWOOD                60.97N 149.13W
02/03/2019  M4.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            HEAVIEST SNOW OCCURRED OVER NIGHT INTO THE
            EARLY MORNING.

0930 AM     SNOW             1 NW SOLDOTNA           60.50N 151.10W
02/03/2019  M2.5 INCH        KENAI PENINSULA    AK   PUBLIC

            TOTAL SNOWFALL AS OF THAT POINT. STARTED
            SATURDAY EVENING.

&&