NWS Anchorage, AK wrote its last area forecast discussion before the first event at May 3, 3:55 PM AKST, 8 hours 5 minutes earlier.
Area forecast discussion, May 3, 3:55 PM AKST, 8 hours 5 minutes before
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
455 PM AKDT Mon May 3 2021
.ANALYSIS AND UPPER LEVELS...The upper levels continue to support
a broad trough stretching across the central Bering all the way
into the Eastern Gulf of AK. Further west, there is a shortwave
ridge passing over the Western Aleutians in front of a strong
front in the North Pacific. Within the trough, this a complex of
lows. From west to east, the first one is a beautiful low on
satellite driving from St Paul to Dutch Harbor. This low is
ferrying down a much colder airmass, between -10C and -15C at 850
mb (5,000') through much of the Bering. This is creating
widespread (and at times, heavy) snow showers for much of the
Eastern Aleutians. Farther to the east along the Alaska Peninsula,
a dissipating low continues to produce steady precipitation in
the form of a mix of rain and snow, with all snow reported at
Chignik. The final low in the series is very broad in nature
across the Central Gulf. This low continues to bring steady rain
to Kodiak Island. Its associated front is starting to work closer
towards the Gulf Coast and the Middleton Island radar is picking
up on more steady rain across the area.
The jet at 300 mb (30,000') is primarily flowing over the Bering
before turning to go south of the Gulf of AK. It moves into the
Western Aleutians at about 130 kt from the southwest. It then
climbs over the shortwave ridge before diving back sharply from NW
to SE near Dutch Harbor at 145 kt. The entire mainland features
light flow aloft, which usually results in relatively quiet
weather.
&&
.MODEL DISCUSSION...Models remain in good to great synoptic
agreement. The result is moderate to high forecast confidence. The
forecasters generally preferred the GFS model in handling the
forecast for the Aleutians and Western Alaska. We have elected to
hold the incoming front near the Western Aleutians at gale-force
(vs storms). Across the Gulf of AK into Southcentral, there is
little model disagreement through Wed. By Thu, models start to
diverge on handling the track of a surface low in the southeastern
Gulf. The GFS is a distinct outlier in tracking the low
significantly further west than any of the other models. We have
leaned away from that solution at this time, electing to keep most
of the precipitation further south and east.
&&
.AVIATION...
PANC...VFR conditions will persist. There is a good chance of the
winds bending off the Turnagain Arm over the terminal later this
afternoon. Much like Sun, the exact timing remains uncertain.
Regardless of start, it does not look to be very strong with gusts
just above 15 kt. Winds should return to light and variable after
midnight.
&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Wednesday night)...
A low will weaken over the central Gulf today, remaining just out
of reach of a trough south of the Alaska Peninsula lifting
northward toward Kodiak and the southwestern Gulf of Alaska.
Previous forecasts were based on the idea that this low would be
pulled westward toward Kodiak Island as the upper trough
approached. As a result, rainfall on Kodiak Island will initially
be quite light. However, expect a new surface low to form near
Kodiak Island in response to the upper level short-wave and
rainfall rates will increase this afternoon and persist through
tonight. The airmass accompanying the trough is quite cold for
May, with 1000-850 thicknesses as low as 1285 to 1290 meters. As
this airmass reaches Kodiak Island late tonight through Tuesday
morning, expect some snow in the mountains and perhaps even a mix
of rain and snow down to sea level. Surface temperatures at sea
level will remain above freezing, so do not expect any snow
accumulation. The low will exit southward on Tuesday, with
precipitation tapering off through the day.
For Southcentral, the remnants of the trough currently over the
Gulf along with a weak surface front will push onshore along the
north Gulf coast tonight through Tuesday, bringing areas of rain
(and mountain snow) to the eastern Kenai Peninsula and Prince
William Sound areas. Some of this moisture will spread inland in
the form of showers on Tuesday, aided by cold air advection aloft
and the resultant increased instability. While precipitation will
not be widespread, it is looking more favorable for showers to
track across Anchorage and the Mat-Su.
The entire region will dry out Tuesday night through Wednesday and
remain dry through Thursday. Very weak cyclonic flow aloft will
persist, so some clouds will likely remain in the region. Still,
would expect at least some breaks of sun each day along with a
gradual warm-up in temperatures.
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Pattern remains relatively the same across the Southwest Mainland,
with much of the activity confined to the southern AKPen.
Springtime temperatures will persist through the forecast period,
however, there will be a slight downward trend tomorrow and Wed as
a colder airmass moves into the region. Otherwise, expect
conditions to be showery across the Kuskokwim Valley and interior
Bristol Bay, with some scattered cloud cover across the Southwest
Mainland.
&&
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Periods of briefly heavy snowfall have been bombarding the
Eastern Aleutians and Southern AKPen as a polar low pushes south
across the Bering. Conditions should begin improving later this
afternoon as the polar low continues to weaken as it travels. Our
gale force front moving across the western Bering this afternoon
through Wed morning also weakens as it travels and briefly stalls
just west of the Pribilof Islands Wed afternoon. It then merges
with a secondary North Pacific low pushing towards the Central
Aleutians from the south. This will allow for the development of
gale force winds across the Eastern Aleutians and into the Bering
Sea beginning Wed afternoon. Additionally, this will bring another
round of showers the the Eastern Aleutians, however, with a
significantly warmer airmass, precip will likely fall as rain.
&&
.MARINE (Days 3 through 5: Thursday through Saturday)...
Bering: A low moves into the Central Aleutians through Saturday.
Expect high end small craft winds over the Eastern Aleutians and
Alaska Peninsula with areas of gale force winds near channeled
terrain as well as the southern Bering Sea on Thursday. Winds
should diminish on Friday.
Gulf of Alaska: A complex low near the southern Gulf Thu and
Friday is bringing a bit of uncertainty to the areas. Gales are
possible with a barrier jet along the north Gulf coast Friday
into Saturday. There is just a slight chance for gales farther
south in the Gulf with this low during the period.
Long Term Forecast (Days 4 through 7: Friday through Monday)...
Models are struggling with the long-term with forecast confidence
being low. Anticipate increased winds, waves and precipitation
along a front across the Bering and over the eastern Aleutians on
Friday. The backside of this elongated area of low pressure,
should be over the western Aleutians around this time, bringing an
increase in winds, waves and precipitation to this area. As the
front moves across the Gulf and the Barren Islands, winds should
meet gale force criteria through gaps and passes into Saturday.
The low is expected to remain nearly stationary through Sunday as
it dissipates. For Monday, models bring a low into the southern
Gulf and south across the central Aleutians. If this scenario is
to play out, expect an active pattern across both regions Sunday
into Monday.
&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Warning 145.
MARINE...Gale 132 150 174 176 177 178.
FIRE WEATHER...NONE.
&&
SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...MK/CK