Small Craft Advisory 483, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
417 PM AKDT SUN JUN 12 2016

.ANALYSIS AND UPPER LEVELS...
A large upper level low centered over the Gulf of Alaska dominates
the weather over the southern mainland of Alaska today. Satellite
imagery shows widespread clouds, but there is very little in the
way of precipitation. Weak instability combined with a series of
upper level waves rotating around the periphery of the upper low
will increase shower activity this afternoon, especially along
the mountains. The upper low is beginning to progress eastward.
This is the start of a pattern shift which will bring much warmer
and drier conditions to the southern mainland as we head through
the week.

Most of the Bering Sea is benign under the influence of high
pressure. A weak vertically stacked low south of the Western
Aleutians is drifting northward, blocked from any eastward
progression by an amplifying ridge.

&&

.MODEL DISCUSSION...
Models are in excellent agreement with the synoptic shift in
pattern over the next couple days and forecast confidence is
generally high. There are some minor differences with one final
trough dropping through Southcentral Tuesday before the upper
ridge shifts eastward. The ECMWF in particular is an outlier in
developing a closed low as the trough moves through. The character
of this feature will determine the details of how quickly we warm
up and dry out as well as the strength of the northerly winds. For
now will lean toward the majority of solutions and trend toward a
warmer, drier, and windier solution for Tuesday.

&&

.FIRE WEATHER...
There is a good possibility of reaching criteria for a Red Flag
Warning Tuesday and/or Wednesday over the Susitna Valley and
Copper River Basin. Northerly winds look strongest on Tuesday, but
as indicated in the model discussion, there is some uncertainty in
the passage of a trough axis which will affect how high
temperatures climb. Temperatures will certainly be warm enough for
Red Flag on Wednesday, but there may not be enough wind depending
on how quickly the ridge moves overhead.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
As the low in the Gulf moves off to the southeast, shower
activity will diminish across Southcentral Alaska through Monday.
This will also allow for less cloud cover and higher temperatures
on Monday. Over the Copper River Basin this could lead to isolated
thunderstorms in the afternoon and evening.

Forecast confidence is high that very warm and dry conditions
will develop this week as a ridge builds in from the west. A
period of strong northerly flow out ahead of the ridge Tuesday
into Wednesday will result in strong compressional warming off the
mountain ranges and likely prevent formation of sea breezes which
will lead to the hottest temperatures of the summer area-wide.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The showery regime over the Southwest Mainland will linger through
tonight, as the weakening shortwave over the Kuskokwim Delta
dives South into the North Pacific by Monday morning. Areas along
the alaska range and East of Dillingham will see evening showers
and isolated thunderstorms associated with the cold air aloft and
lingering instability over these areas. High Pressure with
northwesterly flow will build over the Southwestern Mainland
Monday into Tuesday, bringing a much drier and warmer air mass
over the area through mid-week. The persistent onshore flow will
also aide in pushing any fog developing over the Bering inland,
over the Kuskokwim delta and the Bristol Bay coast, during the
overnight hours through Tuesday. The only exception to this will
be Monday night into Tuesday, where a disturbance in the upper
level flow can help trigger some overnight showers along the
Alaska Range.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure will build over much of the Bering and the
Central/Eastern Aleutians this evening, with some areas of fog
developing under generally weak westerly flow. An east-west
frontal boundary will stretch across the North Pacific, and will
spread over the Western and Central Aleutians on Monday afternoon
while weakening. A triple point low will develop along this front
late Monday evening, affecting the Central and Eastern Aleutians
with steady moderate rainfall.

&&

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

Beginning the long term period Tuesday evening, there will be a
low across the western Bering Sea with a shortwave ridge axis
over the eastern Bering. An arctic trough will be centered North
of the North Slope with a piece of shortwave energy from that
trough digging into the Gulf of Alaska. Northerly offshore flow
will be in progress, with dry conditions across all of southern
Alaska. Temperatures will warm dramatically Wednesday and
Thursday, reaching the highest values of the year thus far across
most locations with widespread 70s and some localized inland 80s.
Even coastal locations on Wednesday will see rather high
temperatures as offshore flow inhibits sea breezes until late in
the afternoon. The front associated with the Bering low will
weaken and wash out across the eastern Bering Wednesday night with
the ridge building eastward into Southcentral. By Friday, a
secondary front will begin to make eastward progress with
gradually cooling temperatures as the ridge over Southcentral
weakens and moves into the Yukon. There is uncertainty with how
strong and fast this front will be with the ECMWF and Canadian
GDPS favoring slower solutions with the GFS about half a day
faster. For now, a WPC ensemble approach was favored to account
for that uncertainty. Either way, expect more precipitation
chances and cooling temperatures for the weekend and lasting into
early next week.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...JA