Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 271259
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 AM AKDT Thu Jul 27 2017

.ANALYSIS AND UPPER LEVELS...
The fronts that brought rain across the southern mainland over
the last 24 hours are rapidly diminishing as the potent upper low
over the southwest continues a southward dive to the North
Pacific. Energy rotating around the broad upper level trough over
the southern tier of the state and the gulf are bringing a few
showers early this morning. A ridge to west spans across the
Bering with the center residing just south of the central
Aleutians. The air mass over the southern mainland and surrounding
waters is saturated bringing low stratus and fog across the
forecast area under a weak flow regime. Across the Bering, winds
are northerly along the eastern Bering and west to southwest
across the central and western waters.

&&

.MODEL DISCUSSION...
Operational models are in good agreement with the synoptic
pattern through the end of the week. The main challenge in the
short range forecast is defining precipitation areas along the
weak disturbances that propagate toward southern Alaska from the
northern Bering and the low that tracks just south of the gulf.

 &&

.AVIATION...
PANC...MVFR ceilings are possible this morning with VFR conditions
expected this afternoon into Friday morning. Light winds shift to
the west late morning into the evening, however winds remain
under 10 kts as a weak surface pattern remains across Southcentral.

&&.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper low south of Kodiak Island will continue to move south
today, ending up in the far southwest Gulf by this afternoon. An
upper level ridge will build into south central Alaska. Conditions
will be drier over most of the area, though considerable cloud
cover will remain. The one area that will still see plenty of
precipitation today is the eastern Copper River basin, where
moisture is spilling in from Canada. There enough instability
inland that increases the risk for isolated thunderstorms from
the Susitna valley into the western Copper River basin this
afternoon and evening. Some of the moisture from the Copper River
basin will push west over the rest of south central Alaska tonight
and Friday, for an increase in shower activity.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Any remaining light shower activity across Bristol Bay will taper
off by later this morning as the upper low continues to move
south of the area and a weak transient ridge moves in from the
west. Temperatures will likely climb 5-10 degrees higher than in
previous days with a combination of rising heights and partial
clearing. This will also allow instability to build during the
afternoon across the Kuskokwim Valley and interior Bristol Bay,
potentially touching off a few thunderstorms late this afternoon
into the evening. Meanwhile, the next system will begin to push
into the Delta region from the west during the afternoon, bringing
a quick return of cooler and wetter conditions to the area as it
spreads eastward through Friday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The Bering will largely remain locked in a westerly flow pattern
atop the stout Pacific ridge to the south, keeping extensive fog
and stratus over the region into the weekend. A front pushing
southward through the region will bring another round of rain to
the Pribilofs this afternoon and then spread to the chain tonight,
with another disturbance dropping through the area from the
northwest on Friday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The extended period begins on Saturday afternoon with the current
low pressure over the Alaska Peninsula having migrated into the
eastern Gulf of Alaska. The low is part of a broad longwave trough
encompassing much of the Gulf. The other long-wave feature over
the Mainland is high pressure over the Interior, part of the
western North America ridge. Out west, the upper level pattern
will be controlled by a stout high pressure over the central
Northern Pacific and low pressure near the pole. The flow between
these two features will be pretty zonal with disturbances
propagating through the flow. Model guidance in this timeframe is
generally in the same camp. Uncertainty arises from energy from
the polar troughing digging southward and interacting with
whatever is left of the Gulf trough.

What does all this mean for the sensible weather forecast? Around
the southern Mainland, we look to be in a diurnal mountain
convection pattern. Afternoon showers and thunderstorms generating
on elevated terrain. Upper level forcing looks to be weak at this
point so mainly on and around higher terrain. Cloud cover will be
variable with moisture from the Gulf system in easterly flow,
anywhere from partly to mostly cloudy. Temperatures should be
right around normal for late summer. As troughing digs into the
southwest Mainland early to middle next week, widespread
precipitation will increase in that area. The digging low will
bring the Southcentral into a more stormy pattern with widespread
cloud cover and periodic rain from frontal systems.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...MTL



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