Small Craft Advisory 486, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
453 AM AKDT Sun Jun 30 2019

.ANALYSIS AND UPPER LEVELS...

The upper level high/dome of hot air responsible for the hot,
dry, and indirectly smokey weather across much of southern Alaska
is finally beginning to make a brief departure from the area. The
center of the upper level high is currently centered near
Middleton Island. Thus, the Cook Inlet region north through
Anchorage and the Mat-Su Valleys are now under broad upper level
southwesterly flow. This flow is translating lower into the
atmosphere as well, with mid-level and even surface winds at Kenai
all out of the southwest. Thus, nearly full atmosphere
southwesterly winds are causing the Swan Lake fire smoke to advect
north and east into Anchorage and the Mat-Su Valleys, which are
experiencing diminishing visibilities and worsening air quality
this morning.

The upper level high is shifting south and east into the Gulf in
response to the approach of an upper level shortwave trough, which
also translates down towards the surface in the form of a cold
front. Rain associated with the front is limited, and is mostly
staying along the Kuskokwim Delta coast. Across the Bering, rain
associated with the next low is approaching the western and
central Aleutians, with southerly winds increasing across the same
area.

&&

.MODEL DISCUSSION...

With a very slow-changing weather pattern in place and likely to
continue for much of the next week over Southern Alaska, model
agreement also continues to remain excellent regarding the large-
scale weather pattern. As such, overall forecast confidence
remains very high. There is very high confidence that much of
Southern Alaska will remain with well-above average temperatures,
and most areas will remain dry. That said, local effects continue
to add some uncertainty into the forecast. These local effects
include the southerly extent of this afternoon's expected showers
and isolated thunderstorms across the Lower Kuskokwim Valley,
Susitna Valley, and Copper River Basin, and the extent and density
of Swan Lake fire smoke into Anchorage and the Mat-Su Valleys
through the day today and into tonight. The extent of marine
stratus across Southwest Alaska also remains a forecast challenge.

&&

.AVIATION...

PANC...Smoke from the Swan Lake fire remains the only factor
impacting the airport today into tonight. Deteriorating visibility
is expected through the early morning as south to southwest winds
transport occasionally dense smoke across the airport.
Visibilities could drop into the IFR category at times. By late
morning, the winds will turn more southwesterly, which is expected
to move the densest smoke more along the mountains and allow for
some improvement at the airport back to MVFR visibilities. A wind
shift to a northwesterly direction is expected this evening
after midnight. This is expected to continue improving the
visibilities to VFR overnight. VFR conditions will persist with
perhaps some lingering haze through Monday.

&&

.FIRE WEATHER...Swan Lake Fire...Western Kenai Peninsula:

Hot and precipitation-free conditions are expected to continue
across the area right through much of the upcoming workweek,
including the Fourth of July. After one more hot day with highs
well into the 80s today, temperatures will cool slightly back to
the upper 70s to around 80 for Monday and Tuesday, after which a
return back to the mid to upper 80s is expected by the Fourth.
Other than the smoke, skies will include some cloud cover late
tonight as a front crosses the area, and again for the day on
Tuesday as a dry upper level disturbance crosses through. From
Wednesday on, full sunshine is expected, allowing for the hot
temperatures to return.

Winds around the fire will generally be light out of the southwest
today in the mid-levels, with light and variable winds at the
ground. The winds will turn predominately northerly after the
front crosses through late tonight, and will persist out of the
north to northwest through Tuesday. At the ground once again winds
will be light and variable, subject to sea breezes and other local
gust fronts at times.

Minimum relative humidity values are expected to be in the 30 to
40 percent range once again this afternoon, with values a bit
higher for Monday and especially Tuesday. When the hot weather
returns midweek, relative humidity values should return back to
around 30 percent.

&&

.CLIMATE...

Multiple high temperature records were set once again yesterday
across Southcentral; here are some highlights:

Anchorage International's temperature climbed to 82 degrees for a
high yesterday. This easily surpassed the previous daily record
of 77 degrees set in 1990, 1989, and 1968. This was the warmest
high temperature in 3 years, since Anchorage got to 83 degrees on
June 16, 2016. The high of 82 tied several other days for the 6th
hottest high temperature on record. When average temperature (High
temp + Low temp)/2 is used, yesterday was the third hottest day
on record in Anchorage. The high temperature of 82 + a low
temperature of 60 made for an average temperature of 71. The only
two hotter days were on June 16, 2015, with an average temperature
of 72, and on July 8, 2003 with an average temperature of 71.5.

For the month of June, the average temperature is now at 60.4
degrees, which is now almost a full degree above the next warmest
June by average temperature (59.5 degrees in 2015). June also
remains the driest June on record with just 0.06 inches of rain
recorded for the month. No rain is forecast for today, the last
day of the month. The next driest June recorded 0.17 inches of
rain for the month, which occurred in 1993.

Other daily record highs yesterday included Cordova, which got to
79 degrees for the third consecutive day, beating the previous
daily record for June 29th at 76 degrees in 2002.
Gulkana reached 89 degrees yesterday, the warmest high
temperature in 6 years (since June 25, 2013). The previous daily
record was 81 degrees set in 1997 and 1946.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Tue night)...
While the hot and dry pattern will persist, we will come down a
bit from the lofty high temperatures of the past couple days. A
short-wave trough and surface cold front will lift overtop of the
dominant upper level ridge. While these features will largely
remain north of the Alaska Range, it will flatten the ridge over
Southcentral and allow 850 temperatures to cool. This will allow
some isolated to scattered convection to form inland and bring a
few clouds into the region. Lastly, with the ridge axis to our
east, strong southwest flow up Cook Inlet will also help moderate
temperatures.

This will all be temporary, as the ridge builds back upstream of
Southcentral Monday through Tuesday. Thus, we'll head right back
into a warming trend, with temperatures climbing back into the 80s
for most inland locations on Tuesday. The surface ridge will build
faster than the upper ridge. This will lead to a shift in winds
back to offshore flow tonight into Monday morning. This flow looks
stronger than when the ridge first built in last week. Have
strengthened offshore winds in Seward/Resurrection Bay and
Whittier/Passage Canal tonight through Tuesday night. In fact,
winds look strong enough to completely keep sea breezes at bay
which means temperatures in both Seward and Whittier will approach
80 degrees.

As for the smoke forecast, southwest winds will continue to advect
smoke from the Swan Lake fire northward to Anchorage, the Mat-Su,
and over to the western Copper River Basin until the low level
flow shifts overnight tonight. A dense smoke advisory is in effect
for Anchorage until 10 pm this evening. Expect conditions in
Anchorage to continue to deteriorate during the morning hours
underneath a shallow temperature inversion. Once the flow does
shift tonight, there should be some improvement but some smoke
will likely linger. The worst of the smoke will then head back
southward across the interior Kenai Peninsula, affecting the
Sterling and Seward Highways and Seward.

&&

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

On the Bethel radar, there is a band of precipitation from Hooper
Bay to Kipnuk. There is a reinforcing shortwave behind the frontal
boundary and that should help to advect the moisture inland. On
the latest satellite imagery there is stratus and fog over
Bristol Bay and its possible that it will be observed inland with
the onshore flow. With the frontal boundary and the reinforcing
shortwave the expectation is that the ridge will be suppressed and
that temperatures will cool a little bit. This is not a juicy
front but we are anticipating the possibility of showers for the
Kilbuck Mountains and portions of the Y-K Delta. This system is
fast moving and by Monday it will be dry again. A second system
will follow in its wake on Tuesday. With the ridge holding steady,
its looking like this will be another event for Kipnuk and Hooper
Bay.

&&

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

There is a frontal boundary east of the Pribilofs to Unalaska that
is going to move east and north. This is not a strong front but it
will bring some unsettled weather to the Central and Eastern
Bering. Ridging will briefly build back over the Bering. All the
while a second low will push into the western Bering. This system
will have gale force winds. Then it will steadily moved eastward
along the chain and push across the Pribilof Islands. It will
stall out midweek as the ridge amplifies over the North Pacific.

&&

.MARINE (Days 3 through 5; Tuesday through Friday)...

A nearly stationary gale force front will be over the central
Bering from west of Dutch Harbor through the Pribilofs to west of
Nunivak Island Tuesday morning. It will weaken below gale force
through the day except to the lee of the gaps in the Aleutians
around Unalaska Island. The front shifts west and restrengthens
back to gale force in the area around Atka Thursday morning. The
front weakens once again by Thursday evening.

Near gale-force westerly winds are possible east of the Barren
Islands early Tuesday morning, and again Wednesday morning.

&&

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

Models are in good agreement that a strong ridge will rebuild over
Alaska through next week. Hot and dry conditions will persist
across Southcentral with temperatures again approaching 80 in the
Anchorage area.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Dense Smoke Advisory: 101.
MARINE...Gale Warning: 175-177 412 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...AP