Small Craft Advisory 572, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
421 PM AKDT SUN JUL 17 2016

.ANALYSIS AND UPPER LEVELS...

A closed upper level high pressure system over the northern
Bering...and an amplified upper level ridge over the Gulf of
Alaska dominate the weather scene. Between these two main
features a col covers much of the Southcentral mainland Alaska.
Meanwhile...a fairly weak upper level wave, associated with a low
well to the north of Barrow, is progressing across the northern
fringes of Southcentral. Compared with the past several days, the
current atmosphere is a lot more stable today, and only a few
isolated showers have developed in the western mainland. In
addition...cloud cover associated with the upper level wave is
spilling into the Susitna Valley and Copper River Basin and
helping to limit diurnal heating. Meanwhile, high pressure
continues to build across the Southwest mainland which is helping
to support westerly winds especially through local gaps.

&&

.MODEL DISCUSSION...

Models remain in quite good agreement today with two major high
pressure systems dominating the region. As a result...a general
blend of models was used today. The greatest uncertainty remains
in the strength of westerly and northwesterly flow through local
gaps across both Southcentral and the Kuskokwim Valley as
pressure gradients increase tonight. As winds are already gusty in
many of these areas, it is likely winds will be stronger than
models have anticipated.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

High pressure will remain firmly entrenched across Southcentral
Alaska through Tuesday and keep max temperatures 10 to 15 degrees
above normal through the forecast period. Reaching critical fire
weather thresholds looks less of a concern on Monday and Tuesday
than previously thought as dewpoints continue to remain near 50
degrees. This moist air mass has been well sampled by RAOBs
statewide with precipitable water values right around
climatological normals (0.80" to 0.90"). These high precipitable
water values show that there is little dry air aloft that can mix
down and not too much dry air over the interior that can be
advected southward. Gusty winds will develop on Monday across the
Susitna Valley as winds downslope off the Alaska Range so some
modification of the moist air mass will be seen over the valley as
the air warms adiabatically as it descends. Gusty winds will be
seen along Turnagain Arm, through Portage Vally, Valdez, Whittier
and Seward with a nice outflow winds developing during the
overnight period.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Temperatures will moderate somewhat during the early part of the
work week but still generally remain above seasonal normal values as
the ridge axis over the Southwest mainland shifts westward into
the Bering, yielding increasing northwest flow aloft. Several weak
disturbances embedded in this flow will bring a chance of rain to
mainly northern portions of the Kuskokwim Valley beginning on
Monday and lasting through Tuesday. Increasing westerly winds will
lead to the potential for Bering fog to advect onshore over
portions of the Kuskokwim Delta and coastal areas of Bristol Bay
through Tuesday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Surface and upper level ridging will remain over the eastern half
of the Bering Sea through Tuesday, yielding persistent low stratus
and fog as well as patchy drizzle at times. A North Pacific low
will move into the Western Bering on Tuesday preceded by a front
on Monday night. This will bring a period of steadier rainfall to
the Western/Central Aleutians through Tuesday evening.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Tuesday evening, there will be a rather strong Arctic trough
centered over Beaufort Sea with another low over the western
Bering Sea. In between will be shortwave ridging over the eastern
Bering Sea. Offshore flow will keep Southcentral on the warmer
side while westerly flow over Southwest will keep that region more
moderated. Rain will be relegated to the Alaska Range and parts of
the Talkeetna Mountains/Wrangell Mountains. This pattern will
persist through Wednesday morning before a front associated with
the Bering low moves into Southern Alaska, spreading rain and
clouds eastward through Friday. This will be a moist and cooler
pattern after the hot and dry pattern most of southern Alaska has
seen the past week. By the weekend, uncertainty rises with just
how fast the low moves into the Gulf of Alaska and out of
Southcentral, but the weekend looks to improve as outflow winds
ensue behind the departing low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 130 131 177.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EN
SOUTHCENTRAL ALASKA...MC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...JA