Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 242352
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
352 PM AKDT Mon Apr 24 2017
.ANALYSIS AND UPPER LEVELS...
A persistent upper-level low controls the Bering Sea southward into
the North Pacific. This is bringing in broad southeasterly flow
over the Gulf of Alaska and most of the southern mainland.
Over Southcentral... Despite downslope, cross-mountain flow
today in the Cook Inlet region... light rain dampened the dust in
the lee of the mountains this morning with one trough travelling
west-northwest. A second wave looks to repeat the process again
tonight. Forecast challenges for Southcentral Alaska will be
timing and setup of any rainfall across the region, especially in
the lee of the Kenai and Chugach mountains.
Over Southwest Alaska and the Aleutians, the stacked low will
continue the widespread circulation of clouds and showers.
Larger forecast challenges may hold off until the end
of the week when models indicate a building ridge over the
Western Aleutians and a digging shortwave developing over the
Models initialized well this morning but diverge with solutions
over the Eastern Gulf of Alaska. The GFS resolves the surface
features into a singular low pressure center. Forecasters prefer
solutions keeping two circulations at this time. Therefore, the
NAM is the preferred model today.
PANC...VFR conditions will persist with light isolated showers
continuing off and on through the night. Another wave of light
rain will develop overnight and persist until early Tuesday
morning. Challenges with timing and onset of any Turnagain Arm
winds will persist through the evening. Previous forecasts have
indicated arrival at the airport, however this is looking less
likely as the day goes on.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The overall forecast hasn`t changed too much with the new
forecast package but higher rain chances have been added to inland
locations this evening as a short-wave moves across the Gulf of
Alaska and Kenai Peninsula. Downsloping signatures have been quite
weak as observed on the 12Z and 00Z RAOBS from PANC. Models
really don`t develop much of a downslope signature until Tuesday
morning following the passage of the shortwave which will help
mitigate rain chances across interior portions of Southcentral
Alaska Monday and Tuesday. The gulf coast will continue to see
periods of light to moderate rainfall as the rainfall upslopes
along the coastal mountains. Gusty winds have developed along
Turnagain Arm and the Knik River Valley and will continue through
Wednesday before winds really begin to diminish. The gusty winds
through the Knik River Valley may decouple during the overnight
hours at time which may lead for a reprieve in gusty winds but
will quickly pick back up by the late morning hours on Tuesday.
Cloudy skies will continue to be the norm through much of the week
although some guidance is hinting at partially clearing skies
later in the week.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Broad low pressure across the Bering remains stationary through
Wednesday keeping flow generally out of the southeasterly
direction. Weak disturbances rotating around this low brings
continued chances for rain through mid week as moisture advects in
from the Gulf. Patchy fog development late night will be a
challenge across the Kuskokwim Valley and Delta as a weak boundary
stalls through Wednesday.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A stacked low pressure system over the central Aleutians remains
nearly stationary through mid week bringing lighter flow with
higher chances for rain amongst the weak short waves rotating
through the upper level flow. Temperatures cooling in the low and
mid levels over the eastern Bering will create a steep
temperature inversion just off the surface tonight and persist
through early Wednesday. Areas of fog will develop across much of
the eastern Bering under the inversion and shift around under the
.LONG TERM FORECAST (Days 3 through 7)...
Southwest flow will persist through the weekend and will keep
moderately unsettled weather across the region. Thursday and
Friday, a low pressure system will slide north and into SE Alaska.
In its wake will be an abundance of moisture and cloud cover
across Southcentral AK. Friday and Saturday a closed Bering low
becomes an open wave over the Southwest with a trough axis
swinging over Southcentral which will bring increased chances for
rain across the southern mainland.
Weak ridging will build in across the southern mainland into the
weekend. Come Sunday, SE Alaska is expected to see a similar
scenario pan out as what will be happening Weds/Thurs. Numerical
guidance begins to struggle in day 5 and later time frame with
run-to-run consistency issues and large ensemble spread across
the Bering. There are similarities in timing of an elongated
frontal/trough passage across the chain this weekend, but wildly
different solutions on how strong and where the attached low will
SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH