Graphical Hydro Meteorological Discussion

000
FXAK68 PAFC 212330
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
330 PM AKDT Wed Aug 21 2019

.ANALYSIS AND UPPER LEVELS...
The upper level pattern shows the trough persisting along the
AlCan border. The low near the Central Aleutians is now beginning
to get entrained into that AlCan trough in the broad flow which
will help move it eastward. The jet stream continues to run south
of the Aleutian low and through then Central Gulf of Alaska
before curving southeast toward Washington State.

&&

.MODEL DISCUSSION...
Models remain in very good agreement through the weekend. They
also show remarkable run-to-run consistency with the development
of a series of triple-Point lows tracking south of the Aleutians
and into the southern Gulf of Alaska. Once again, the main issue
will be the small scale effects that will drive local winds around
the fires and the smoke.

&&

.AVIATION...
PANC...Smoke will continue to be around the airport through the
TAF period. Southeast winds through Turnagain Arm will increase
this evening but there is a bit of uncertainty as to whether they
will curve enough to move over the airport. At this time it looks
like the strongest of these winds will remain over the water and
could even cause periods of northwest winds due to an eddy effect
off the wind core. It remains to be seen whether these winds will
help or harm the smoke situation as they have to potential to
bring in more clear air from Prince William Sound or to increase
the smoke off the Swan Lake fire. Small differences in wind speed
and direction may cause very different results.

&&

.FIRE WEATHER...
For fire weather, the biggest question is how the strong the
southeast winds will be over the Swan Lake fire tonight through
tomorrow. Other fires in the region are not as susceptible to the
southeast direction as Swan Lake, including the ones in the
Bristol Bay region. Overall there will be a slow trend toward more
moist conditions into the weekend. Smoke is expected to remain an
issue across Southcentral and parts of Southwest Alaska for the
next few days.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Weak ridging is in place over Southcentral Alaska. There are
several wildfires in the state of Alaska and the particulate
matter from these fires has been trapped in the boundary layer.
Some of the local observation sites are reporting haze (HZ) while
other are reporting smoke (FU). A Dense Smoke Advisory is in
effect for the Interior Kenai Peninsula south to Seward. Light
winds and stable conditions will keep smoked from the Swan Lake
Fire trapped near the surface.

An organized front is on track to move into the Gulf Of Alaska
this forecast period. The lion`s share of the moisture will remain
over the Gulf Of Alaska. Kodiak and Prince William Sound can also
anticipate rain from this system but the mountains will prevent
the moisture from making any headway into Anchorage or the Mat-
Su Valleys. Friday the arctic trough will descend south of the
Brooks Range and later south of the Alaska Range. This trough will
usher cooler temperatures aloft into the region and increase the
chance of showers.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Southwest Alaska will continue to see quiet conditions and
relatively clear skies through this evening. The active weather
will remain on the southern portion of the AKPEN as a front
associated with the triple point low moves eastward towards the
Gulf. A chance for precipitation returns mainly along the Alaska
Range on Thursday as a trough pushes into the southwest, impacting
the mainland. As the trough and associated shortwave continue to
move southward on Friday, a chance for convective activity and wet
isolated thunderstorm make their return to the Southwest. The
best chance for these wet thunderstorms will be along the Alaska
Range, Kuskokwim Valley, and interior Bristol Bay.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Small craft advisory winds remain over the western Aleutians and
Bering through the evening hours. A front associated with a triple
point low will be the biggest impact to the southern side of the
eastern Aleutians and AKPEN over the next 24 hours. Winds will
continue to be small craft advisory level through Thursday
afternoon, but will likely increase to low end gale force winds
overnight tonight into the early morning hours. Once this system
moves out of the area, northerly flow will persist over much of
the Bering through the early weekend.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...
Westerly flow is expected across the Gulf through the long term
period. There is moderate confidence that a low will develop over
or just offshore of the Alaska Peninsula Sunday. However there is
low confidence regarding the exact track and strength of this low
as it moves eastward into the Gulf for Monday. Meanwhile over the
Bering, there has been consistent indication that a ridge of high
pressure will persist through early next week.

&&

.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...
Unfortunately there continues to be only muddled signals in the
long-term weather pattern for next week. We have high confidence
that a longwave trough will be in place over the state with a
ridge of high pressure over the western Bering. Model solutions
continue to vastly disagree in the timing and strength of several
shortwaves that move across Southcentral early next week. This
translates into an unsettled, cloudy, and showery weather pattern
that will likely persist through the middle of next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Dense Smoke Advisory 121 125.
Flood Advisory 121 125.
MARINE...Gale Warning 155.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...PJS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...KO

328
FXAK69 PAFG 212137
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
137 PM AKDT Wed Aug 21 2019

.DISCUSSION...
An area of low pressure centered near Eagle this afternoon will
continue east into the Yukon Territory tonight and into the
Northwest Territories of Canada by Thursday. Precipitation from
this system will diminish from west to east this evening and
overnight.

Behind this system, after a brief period of clearing across
portions of the Interior, a trough extending south from a low
pressure center entering the Beaufort Sea from the north will
bring showers into the North Slope and into portions of the
central Interior as early as tonight, spreading south and eastward
Thu into the Brooks Range and the eastern Interior. As with the
previous system, higher elevations along the Brooks Range could
see two to three inches of snow with this. Rainfall amounts are
expected to be light with just some isolated showers, mainly west
of Fairbanks, along the Alcan border, and near the Alaska Range.


A second system dropping into the Chukchi and Beaufort Seas
immediately after will bring precipitation and increased
northerly winds to the northwest Arctic coast and the West Coast
Thu afternoon. Expect northerly winds in the 20 to 25 kt range
along the West Coast and through the Bering Strait Thu afternoon
through Fri. Some beach erosion may be possible with some elevated
surf from Utqiagvik to Shishmaref to Savoonga. This system will
spread east Thu night through Friday, and the northerly winds
will diminish in intensity almost as soon as the system moves
inland. Precipitation will be more widespread from the Brooks
Range north, and more showery across the Interior. The most likely
chance for the eastern Interior receiving precipitation from this
will be during the day Friday as the trough axis moves over a
near surface low generally in the Yukon Flats to the Fortymile
County with a weak front extending through Fairbanks and into the
Alaska Range. Expect another 2 to 4 inches of snow will be
possible Fri night/Sat with this system. Isolated showers may be
possible Sat over the Interior as well as the surface low either
dissipates or moves off to the east, depending on which model
solution wins out. Expect just a little more precipitation with
this system, from around a quarter of an inch on the North Slope
and Brooks Range to one to two tenths of an inch from Fairbanks
south.

Precipitation will likely linger along the North Slope as several
shortwaves will move across from west to east this weekend. Model
solutions are not quite in line with the strength of the
shortwaves, but right now it looks like showers as well as
westerly winds of 15 to 25 kts, maybe stronger, are a good bet
across the North Slope from Saturday morning into at least early
next week.



Coastal Hazard Potential Days 3 and 4...
A 500-600 mile fetch of the Chukchi/Bering Seas with N winds
blowing 20-25 kt from late Thu into early Sat will cause elevated
surf at Shishmaref and the Bering Strait Thu PM into Sat AM. At
this time we do not expect high surf as high surf normally
requires winds 25kt or greater, but there normally is not a 500+
mile fetch length for several days, so this needs to be watched as
we get closer to Thu, Fri. From Utqiagvik West, expect NW winds
15-20 kt from late Fri through Sun. This would cause elevated surf
from Utqiagvik from Late Fri into Sun.


&&

.FIRE WEATHER...
Highs are expected to remain in the 50s to mid 60s across the
Interior and West Coast through the weekend. Expect RH to remain
near or above 40% through the weekend. Expect increasing winds on
Fri in the Western Interior but the winds will be accompanied by
moisture and cooler temperatures.

&&

.HYDROLOGY...
As river levels have decreased, we have been able to cancel all
remaining flood advisories. That being said, river levels will
remain high for the next few days across the Tanana and Chena
River basins. Ponding of water in low lying areas will still be
evident over the next few days as flooded or high water areas
slowly drain out. Even with the showers in the forecast, river
levels will continue to drop through the remainder of the week.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

AUG 19

000
FXAK67 PAJK 212242
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
242 PM AKDT Wed Aug 21 2019

.SHORT TERM...The gale force low took a more southerly course
across northern Haida Gwaii early this morning, thus avoiding the
worst possible wind impacts. The low is now weakening and pushing
off into Canada bringing most of the precipitation with it. All
eyes now turn to the next storm system expected to impact the
region Thursday and Friday. A gale force low will make its way
across the gulf on Thursday then slowly weaken Friday before
coming onshore around the central Panhandle.

For this evening and tonight, scattered showers will remain across
the central and southern panhandle and the Coast Mountains due to
onshore flow. Despite the presence of some showers, tonight should
be the driest part of the short term before heavier rainfall moves
back in on Thursday from the west.

Overall model consensus with this next storm system has been
fairly consistent, therefore did not make any major changes from
the previous forecast. The next gale force low entering the
central gulf Thursday will spread a swath of steady rainfall
across Southeast Alaska during the afternoon hours which will
persist through Friday. Total rainfall amounts in the 1-2" range
are expected by Friday night for much of the Panhandle with some
higher totals possible across the south and lesser amounts towards
the far north.

Winds are expected to pick up in the Gulf and through some of the
inner channels ahead of the low pressure system. SCA winds are
expected for the Coastal Waters Thursday morning with Gales in
the Central Gulf. Winds are expected to increase to Gales
Thursday afternoon for the Central and Southern Coastal Waters
from around Cape Fairweather to the Dixon Entrance. SCA winds
expected in the Southern Inner Channels Thursday afternoon as
well.

.LONG TERM.../Saturday through Wednesday night/As of 10 pm
Tuesday/Active zonal Pacific jet will continue just to the south
of the Panhandle through Saturday. In general this means the
continuation of a general onshore flow pattern and periods of
showery weather. As usual in zonal flow, forecast guidance is
having trouble nailing down individual shortwave features, but
overall a damp forecast through the long term period. There are
some indications early next week of upper ridging beginning to
develop over the eastern NPAC. This would tend to be a pattern
that would direct more subtropical moisture northward and into the
Gulf of Alaska but exactly when and where this sets up is still
in question. Very little in the way of change was made to the
forecast as the inherited forecast represented the above pattern
well. Temperatures were cooled slightly into the early part of the
weekend to account for more cloud cover and rainfall. Potential
for some warming early next week as the Pacific ridge begins to
assert itself. Forecast confidence is high in the general pattern
but as usual, low on the details.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ041>043.
Small Craft Advisory for PKZ022-035-036-051>053.

&&

$$

CM/DEL

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