Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 231301
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKDT SAT JUL 23 2016
.ANALYSIS AND UPPER LEVELS...
IR satellite shows the low that was over Southcentral has now
moved out over the northern Gulf. At the surface radar indicates
that much of the precipitation has moved out of the Anchorage area
and is now mostly confined to the northern Gulf coast and Copper
River Basin. A shortwave ridge upstream of this feature is moving
through the Bristol Bay region where some locations have cleared
out as evident with surface observations exhibiting clear skies.
a mid level low spinning over the Kuskokwim Delta this afternoon
with a front stretching eastward to the Copper River Valley.
Across the southwest, IR satellite shows the next shortwave
moving down from the northwest and beginning to enter the
Kuskokwim Delta region. Further west, a surface ridge is keeping
low clouds an patchy fog across the Bering, with westerly flow as the
dominant wind direction.
Models are generally in good agreement with the synoptic pattern
bringing an active weather regime through the weekend. The main
forecast adjustments were made to local effects in regards to the
coastal ridge that will be developing and have gone with the NAM
as it captures this feature and local gap winds the best. QPF
amounts varied amongst the models, with the NAM being the outlier
and decided to go with a middle ground for now. The Southwest
mainland and Bering remain in good agreement and needed little to
While today certainly looks drier then Friday did, a wet pattern
will continue through at least the first half of the upcoming
week. The upper level trough and surface low that brought
widespread wetting rains to southern Alaska on Friday continues to
shift eastward this morning and is helping to bring an end to
rainfall across Southcentral Alaska. This reprieve from rain will
be short-lived as a developing shortwave trough over the Bering
Strait shifts to the southeast. This trough will bring rainfall
to Southwest Alaska by mid to late afternoon and spread toward
Southcentral Alaska around midnight tonight. Gusty winds will
continue across Southwest Alaska until rainfall begins to move
inland while Kodiak Island should remain fairly gusty through
Sunday with a broad surface low anchored nearby.
This cooler and wetter period is expected to hang around through
at least the middle of this upcoming week with no large changes to
the synoptic pattern expected. If anything, the developing
shortwave trough near the Bering Strait should only act to
reinforce the current pattern we have shifted into. Rain showers
are expected to continue across much of southern Alaska through
the middle of the upcoming week with an expansive vertically
stacked low remaining well entrenched across the state
..SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level low that brought widespread rainfall to much of
Southcentral continues to spin into the Gulf of Alaska. Conditions
will continue to dry from west to east through this afternoon as
the low continues to progress eastward. However, due to the
relatively slow progression of this low, widespread showers will
be supported in the Copper River Basin through this evening.
On late Saturday night into Sunday morning, a weaker upper level
system will again push towards Southcentral, but will be partly blocked
by a ridge pushing westward. However, the combination of cooler
temperatures aloft and vorticity will be enough to support
widespread showers across Southcentral, especially over the
mountains. In addition, there will be sufficient pressure
gradients to support local gap winds from the building coastal
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
A frontal system and trailing upper level trough digging down from
the north will swing over Southwest Alaska today. Rain currently
pushing onshore across the Yukon and Kuskokwim Delta coast this
morning will spread southeast and inland through the day. Behind
the front steady rain will change over to showers with showers
remaining widespread tonight through Sunday. Shower coverage will
taper off to scattered Sunday Night then increase again to
numerous Monday afternoon and evening as weak trough rotates in
from the east.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Flat ridging and west to northwesterly flow over the Bering will
persist through the week. Upper level ridging will begin to
sharpen over the far western Bering around Monday while the upper
low over Southwest Alaska drops south-southwest to become centered
over the Alaska Peninsula.
.LONG TERM FORECAST (Days 3 through 7)...
There is a northerly 80 knot jet streak over the Bering Strait,
and northerly 90 knot jet stream over the Kamchatka Peninsula that
transitions to a westerly flow over the Western ALeutians by
Sunday. These synoptic features merge into one jet streak as they
dig into the base of the longwave trough located south of the
Central Aleutians. By Tuesday evening through Wednesday this jet
streak transitions to a 110 knot southwesterly jet streak south of
the Eastern ALeutians extending into the Gulf of Alaska. Meanwhile,
an upper level closed low over the Lower Kuskokwim Valley becomes
elongated as it tracks south of Eastern Aleutians by Tuesday
afternoon. This will result in a deep southwesterly flow in the
North Pacific ocean as the jet stream moves into the Gulf, and
extends into the Southeast Panhandle by Thursday. Therefore, look
for a wetter pattern as shortwaves track through the Southwest
Alaska region, and swings around the base of the longwave trough
before moving through the Southcentral region. This synoptic
scenario will bring abundant moisture, and precipitation to the
Southwest/Southcentral regions through Thursday.
SYNOPSIS AND MODEL DISCUSSION...LIW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR