Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 280010
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
410 PM AKDT Thu Apr 27 2017
.ANALYSIS AND UPPER LEVELS...
Water vapor imagery shows that a residual light southeast flow
aloft remains around Southcentral Alaska today. A weak surface
trough was lifting northward toward the Alaska Range. A weak high
pressure center is over Southwest Alaska and a weak low is over
the eastern Aleutians.
Without strong steering currents or local synoptic features aloft,
rain has been slow to move and slow to end. And as a reminder of
the season, snow was noted on the Glen Alps web cam and in the
mountains near Eagle River. Both locations are roughly 2,000 feet
In the West, an Aleutian Low is developing a weak ridge southwest
of Kodiak Island and a southwest flow is slowly breaking up the
heavier cloud cover in the Gulf of Alaska. Fog and low clouds
were a part of the Kuskokwim Delta`s morning. And where the sky
has cleared off in Southwest, cumulus were forming by midday.
Models initialized well this morning and appear to be in good
agreement through 00z Saturday when they diverge on the handling
of a Pacific Low moving into the Southeastern Gulf of Alaska
through the weekend.
In Southcentral, forecast challenges will be the extent and
intensity of precipitation, especially in an early-season
In Southwest, forecast challenges will be with aviation impacts
from localized visibility issues and the timing of the next
Pacific front moving through the Aleutians beginning this
afternoon and tonight.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
After some clearing and daytime heating earlier today, showers
will reform this evening throughout Southcentral ahead of a
shortwave approaching from the south. Due to the widespread rain
and cloudcover this morning, these showers will be significantly
weaker over the Anchorage Bowl and Matanuska Valley than those
that brought very small hail to areas of Southcentral on
Wednesday, with no hail expected this evening. The approaching
shortwave will then allow for showers to continue into Friday
morning, which may mix with light snow along higher elevations of
the Anchorage hillside, providing only light accumulations.
The cloudy and showery pattern will then continue into the weekend
as the upper level trough currently over the AK pen slowly
approaches from the west. This trough will bring widespread rain
primarily to the gulf coast and potentially Kodiak Island, though
a few showers may be possible over Southcentral as cold air aloft
begins to move in.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Low pressure remains dominant through the weekend bringing
continued chances for rain showers. Weak surface flow across
Southwest becomes southeasterly on Saturday and Sunday as a front
moves into the central Bering. Patchy fog is expected to re-
develop tonight along the Kuskokwim Delta coast spreading inland
during the early morning hours. Fog conditions will quickly
improve late morning with diurnal heating.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A North Pacific front moves into the western Aleutian Chain
tonight bringing moderate rain along the frontal boundary and
gusty gale winds. The front pushes quickly across the western
Bering and central Aleutians on Friday then slows as the surface
low fills on its track across the western Chain. On Sunday, the
low pressure system weakens further with scattered showers
lingering across the Bering and Aleutians as weak short waves
propagate around the associated upper low.
.LONG TERM FORECAST (Days 3 through 7)...
The weekend will be characterized by a low moving through the
southern Bering that will keep cloud cover over much of the
southern mainland and Aleutians with continued shower activity.
As the low tracks across the Aleutians and into the Pacific on
Monday it will push a front into Southcentral Alaska bringing more
steady rain to the north Gulf coast. After this point the models
vary greatly on what to do with the low and another low
approaching the area from the south. Ensemble guidance was used
for mid week which brought a more middle ground and consolidated
low position into the Gulf Wednesday, which is also slightly
weaker than some of the operational models.
MARINE...Gales 174 176-178 411.
SYNOPSIS AND MODEL DISCUSSION...SB/DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH