Small Craft Advisory 724, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
430 AM AKDT Mon Sep 24 2018

.ANALYSIS AND UPPER LEVELS...

An upper level low over Bristol Bay is still the driving force
for much of the weather throughout mainland Alaska. A surface
front stems from the low spreading across the Alaska Peninsula and
western Gulf of Alaska. This front, in combination with a jet max
skirting the eastern Aleutians, is creating a band of increased
vorticity and instability along the Alaska Peninsula. As the low
moves north and east, significant rainfall is occurring over
Bristol Bay and has arrived in Southcentral. Radar shows
significant stratiform rain throughout Southcentral and Bristol
Bay with some isolated areas of heavy rain near Dillingham and
Stuyahok. Heavy showers have also been popping up across the AKPEN
overnight, some of which have produced a few lightning strikes
east of King Salmon. Gusty winds have begun to pick back up
through Turnagain Arm as the front approaches the southern
coastline and the pressure gradient intensifies along the terrain.
Satellite imagery shows widespread cloud cover throughout the
Bering and Southcentral with a slight dry slot trailing behind the
front.

With calmer winds and clearer skies yesterday afternoon,
Anchorage was able to set yet another high temperature record. The
high temperature of 61 degrees tied the previous record set in
1965.

&&

.MODEL DISCUSSION...

Models are relatively consistent in regards to the placement of
the low over Bristol Bay as it moves farther inland through the
first 24 hours. Synoptically there is good agreement through the
period especially in regards to the front moving into the western
Bering and another front moving into the southern Gulf of Alaska
on Wednesday. One major discrepancy is in regards to the
development of a closed low in the southern Gulf of Alaska. The
GFS has the low developing Wednesday morning while the NAM and EC
have yet to come to a similar solution.

&&

.AVIATION...

PANC...LLWS is still likely this morning with a variable surface
wind under a strong low-level southeasterly jet aloft. These
gusty southeasterly winds may mix down to the surface at times
early this morning and impact the airport complex. LLWS is
expected to abate by midday as the front passes and surface winds
shift to the south. Following the frontal passage, southerly winds
will increase with gusts between 35 and 40 knots this afternoon
and evening. VFR conditions should also persist through the day;
however, there is the possibility of cloud heights dropping below
5,000ft with the frontal passage.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The forecast for today's storm, with widespread rain and wind
expected across Southcentral, is pretty much on track. Guidance
has backed off on the strength of winds behind the occluded front,
so have trended just a bit weaker with southerly winds this
afternoon and evening. The gusty winds will persist through
tonight, so despite the cold air advection, temperatures will
remain elevated overnight with a well mixed boundary layer.
Precipitation will linger along the mountains tonight, with snow
levels likely dropping to 4000 feet or lower. Both winds and
precipitation will then gradually come to an end on Tuesday.

Tuesday night still looks on track to be one of the coldest nights
of the season. While there may be a few lingering clouds over
interior Southcentral, it looks like most areas will be largely
cloud free. Thus, have trended downward with minimum temperatures,
with nearly all of Southcentral expected to bottom out in the 20s
to 30s Wednesday morning.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

A batch of unsettled weather has pushed into Southwest Alaska in
association with an occluded front. This system will continue to
steer moist air into the region and into the interior. This is a
fast moving system, so expect the precipitation to taper off
Tuesday and Wednesday will be relatively dry. In the wake of the
frontal passage, colder air will advect into the region.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

Cyclonic flow will continue to influence the Bering and the
Aleutians this forecast period. Embedded shortwave energy will
propagate around the upper low bringing intermittent showers. The
next organized front is anticipated late Tuesday which will push
eastward along the chain.
 &&

.LONG TERM FORECAST (Days 4 through 7: Wednesday Night through
Sunday)...

Wednesday night will start out with a front associated with a
North Pacific low moving northwestward, spreading rain across
Kodiak and the Alaska Peninsula. The models are trending a bit
further northeast with the northern edge of the precipitation
shield as compared with yesterday's runs. As such they're now
suggesting the rain spreads across much of Bristol Bay, and
eventually northwestward across the Kuskokwim Delta, though the EC
and GFS are about 18 hours apart as to when that rain makes it
into the Kuskokwim Delta. Thus, the differences between the models
still leave significant uncertainty as to the specifics of when
and how much rain falls in any one place in Southwest Alaska. On
Friday through Sunday, the trailing front behind the parent low
lingers along or off the coast, gradually drifting westward away
from mainland Alaska by Sunday. The presence of the front should
mean a sustained period of gusty southeast winds across Southwest
Alaska Friday and Saturday.

For Southcentral, the front and associated precipitation over
Kodiak will continue there into Friday, though the heaviest rain
should be winding down by Friday morning. During the day Thursday,
the rain will overspread the southern half of the Kenai Peninsula
and up the coast to about the Seward area before beginning to
diminish and retreat southwestward Thursday night. High pressure
over the interior will hold strong and keep Anchorage and points
north and east dry throughout the entire long-term forecast
period, though Thursday now looks to be a cloudier day than it
looked like in the models yesterday.

Temperature-wise, the entire long-term forecast will feature a
warming trend. Behind the front, much warmer air will move into
Southern Alaska Friday through Sunday, which will help support
well above average afternoon highs, though the longer nights and
mainly clear skies will still support some chilly nights for
lower elevation locations as inversions likely set up each night.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning...119 125 130 131 132 138 139 140 141 160
351 352.

&&

SYNOPSIS AND MODEL DISCUSSION...RA/TM
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
LONG TERM...JW