Small Craft Advisory 489, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 PM AKDT Mon Jul 1 2019

.ANALYSIS AND UPPER LEVELS...
A weak trough is riding over top and dampening our record-
breaking ridge of high pressure that was in place over the
weekend. This has served to cool things down a few degrees today
and dry things out with a wind shift to the northwest. These
northwest winds have also helped to clear much out of the smoke
out of the population centers the the Mat-Su Valleys and the
Anchorage Bowl. However, satellite shows plenty of smoke over the
Swan Lake area drifting down the Seward Highway into Seward. There
is also still plenty of elevated smoke lingering in the higher
passes across Southcentral. Some minor cumulus fields have started
to form across part of the Copper River Basin. These should
continue to develop and a few thunderstorms are possible in that
area this afternoon.

For Southwest AK, riding over the ridge is a warm front stretching
towards the YK-Delta. Light rain is falling along the coastline
near Kipnuk through Hooper Bay. Plenty of low clouds and rain
dominate the rest of the Bering associated with this front and its
parent low over the Western Bering. A zonal upper-level (30,000')
parallels the Western Aleutians running west to east at 90 kts.
It then turns to the northeast at about 80 kts in support of the
warm front.

&&

.MODEL DISCUSSION...
The models are in excellent agreement resulting in very high
forecast confidence in the synoptic pattern. The ridge starts to
rebound from the North Pacific over Kodiak and into the Alaska
Range. This will yield another very hot and dry pattern across
most of Southern AK, especially in places with increasing offshore
flow (Seward). The only chances for rain across the mainland will
be near the YK-Delta as various fronts try to push over the
ridge. The biggest challenges will be exactly where the smoke goes
and how dense it gets. It will also be tough to nail down high
temperatures in a few local areas near the coast where sea
breezes may be overwhelmed by offshore flow. Record max
temperatures look likely again in many locations so long as the
smoke doesn't get too thick.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Smoke should
start to drift back in slowly overnight. Confidence is low in
whether or not it will restrict visibility at the terminal.

&&

.FIRE WEATHER...Swan Lake Fire...Western Kenai Peninsula:
Conditions will return to very hot and dry as the ridge rebounds
during the week. Temperatures will start to approach 90F by Thu
afternoon. Minimum RH values will start to trend drier as well
with low-mid 30 percent range expected by late week. While the
general steering flow will generally be north-northwest, the
surface winds will be mostly terrain and diurnally driven during
this pattern. As the ridge establishes, expect stronger overnight
inversions with increasing subsidence. This will only serve to cap
(picture a "lid") any existing smoke and allow it to spread it
slowly across the area.

&&

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

The ridge of high pressure maintains its hold over Southcentral,
and continues to rebuild northward over the next few days. This
will allow for another round of warm, dry conditions this week,
despite the brief reprieve we've seen today. Currently, weak
upper level waves traversing the north side of the ridge have
allowed for a few areas of convection over the northern parts of
the Copper River Basin. As the ridge builds northward on Tuesday,
offshore flow will strengthen, thus overpowering any potential for
sea breezes to develop along the northern Gulf coast. This will
allow for warmer daytime temperatures along the coast, especially
in Seward, Valdez, and Whittier for Tuesday and Wednesday. Inland
areas of Southcentral will see warmer daytime temperatures as
well.

A Dense Smoke Advisory is still in place for the Kenai Peninsula
through Wednesday 1PM as northwest flow will steer smoke from the
Swan Lake Fire toward the southeast. It is possible this advisory
will need to be extended through later in the week. Nighttime
inversions will likely keep the smoke trapped closer to the
surface, leading to the possibility of the smoke becoming more
widespread during the overnight hours.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (through Thursday)...
Currently a warm front is bringing rain to the Kuskokwim Delta,
but a brief break is in store tonight before a Bering Sea front
makes landfall tomorrow afternoon. The remainder of the mainland
will mostly see an increase in cloud cover and southerly winds,
with just a chance of precipitation. The front weakens in place
on Wednesday. Late Wednesday into Thursday, high pressure builds
back overhead from the southeast, bringing a very warm air mass
with it. Expect a return of hot temperatures and drier conditions
through the end of the week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (through Thursday)...
The current frontal boundary draped from south to north over the
Bering Sea will stall in the eastern Bering as it weakens Tuesday
into Wednesday. On Wednesday a disturbance will reinvigorate the
front as it moves it back to the west through Thursday.

&&

.MARINE (Days 3 through 5)...
Tuesday through Saturday will be characterized by high pressure
rebuilding over southern Alaska. There is high confidence in this
setup that will result in winds below gale force throughout the
marine areas.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Models are in good agreement that a strong ridge will rebuild over
southern Alaska mid this week and remain into the weekend. Hot
and dry conditions will persist across the southern mainland with
above average temperatures and light winds expected. By early next
week, there is a chance that an Arctic low over Canada will bring
a trough from the north through the state. However, the current
forecast shows that the ridge will remain strong enough that this
northerly trough may have little effect at the surface.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NPW 121 125, Flood warning 145(Yentna River).
MARINE...Gales 165 170 173-176 179 181 185 412-414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MO
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
MARINE/LONG TERM...LF