Red Flag Warning 6, NWS Anchorage, AK

692 
WWAK61 PAFC 202240
RFWAER

URGENT - FIRE WEATHER MESSAGE
National Weather Service Anchorage AK
240 PM AKDT Thu Aug 20 2020

AKZ145-210300-
/O.CON.PAFC.FW.W.0006.000000T0000Z-200821T0300Z/
240 PM AKDT Thu Aug 20 2020

...RED FLAG WARNING REMAINS IN EFFECT UNTIL 7 PM AKDT THIS
EVENING FOR HOT DRY AND WINDY CONDITIONS FOR THE SUSITNA 
VALLEY...

* Winds...North 10 to 20 mph with gusts up to 30 mph.

* Relative Humidity...As low as 25 percent.

* Temperatures...Mid-to-upper 70s.

* Impacts...Rapid ignition, growth and spread of fires will be 
  possible.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A red flag warning means that critical fire weather conditions
are imminent or occurring now, or will shortly. It is directed
toward fire agencies, and through them to the public.

&&

$$

903 
WWAK61 PAFC 210304
RFWAER

URGENT - FIRE WEATHER MESSAGE
National Weather Service Anchorage AK
704 PM AKDT Thu Aug 20 2020

AKZ145-210415-
/O.EXP.PAFC.FW.W.0006.000000T0000Z-200821T0300Z/
704 PM AKDT Thu Aug 20 2020

...RED FLAG WARNING HAS EXPIRED FOR HOT DRY AND WINDY CONDITIONS
FOR THE SUSITNA VALLEY...

Warm, dry, and breezy conditions will persist for a few more 
hours in the Susitna Valley, but will not reach Red Flag warning 
criteria. Winds are expected to further diminish later this 
evening with decent RH recovery overnight.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
518 AM AKDT Wed Aug 19 2020

.ANALYSIS AND UPPER LEVELS...

The upper levels feature a low over the eastern Gulf, with an
associated disturbance tracking southwestward around the low
across Southcentral. Associated shower activity has moved away
from the southern Kenai Peninsula towards Shelikof Strait. Another
area of associated shower activity is also moving across the
Bristol Bay region from New Stuyahok southward. Elsewhere,
extensive cloud cover persists over much of Southcentral and
Bristol Bay regions, and along the coast of the Kuskokwim Delta
where Bering fog has moved into some coastal communities such as
Kipnuk. Extensive Bering Sea fog and stratus are over much of the
Aleutians and the Bering from the Pribilofs westward. Most
temperatures remain in the 50s this morning, but some cooler spots
have dropped into the 40s.

An upper level trough, the last vestiges of an upper level low
over the Bering, is over the Eastern Aleutians. The trough is
being absorbed into the upper level low over the Gulf. Meanwhile,
upper level ridging is building into the Bering. The ridge extends
northeastward into interior Alaska.

&&

.MODEL DISCUSSION...

The models remain in excellent agreement over the next few days,
as the weather pattern remains slow-changing, and thus remains
easy for all the models to track the disturbances. As usual, the
forecast challenges this morning remain at the local scale. In the
coming days, the most impactful threat will be another chance of
Red Flag conditions across portions of Southcentral. Thus, the
temperature, wind, and relative humidity forecast received extra
attention with this forecast package. The summer-like weather
will continue into Friday. Forecast confidence is very high.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Shower
activity today should be less active than yesterday.

&&

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

The pattern will become warmer and drier over the next 3 days.
Easterly waves associated with an area of low pressure in the
eastern Gulf of Alaska will continue to bring clouds today and may
produce showers at times, especially in coastal areas.

Upper ridging will build into the central Alaskan interior on
Thursday and will enhance the pressure gradient between the high
pressure ridging across the central Alaskan interior and low
pressure over the Gulf of Alaska. This will cause an offshore
northerly flow pattern across Southcentral Alaska and bring warmer
temperatures and breezy conditions. Temperatures will be
significantly warmer on Thursday and Friday due to ample sunshine.
Breezy conditions on Thursday will make for a deeper coupled
boundary layer and promote vertical mixing to help keep
temperatures warmer. Winds will be much lighter on Friday, however
with ample sunshine there is a good chance of a super-adiabatic
layer near the surface to make for very warm temperatures. The
warmest temperatures are expected in the lower elevations of the
Susitna Valley. Stability indices show the best chance for
convection to be confined to the Talkeetna Mountains. Relative
humidity will significantly decrease across the region on Thursday
due to the ample sunshine and stronger winds. The lowest relative
humidity will be located in the Susitna Valley Thursday and Friday
afternoon.

Temperatures will be cooler towards the Copper Basin on Thursday
as another easterly wave moves in from the east bringing more clouds
to the area with a chance for showers. A NAM/ECMWF blend was the
favored solution for resolving this easterly wave as both models
showed very similar solutions. The GFS was by far the outlier as
the GFS developed a closed 500mb vorticity maximum (maximum "spin"
in the atmosphere which is favorable for clouds and precipitation
development) while the NAM/ECMWF did not show any closed feature
in the 500mb vorticity fields. The GEM had a similar solution to
the structure of the vorticity associated with this easterly wave
as the NAM and ECMWF but had differences in the placement of this
wave.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 2)...

An upper level high is hovering over the Yukon Delta National
Wildlife Refuge and the Brooks Range. A few weak shortwaves are
pushing over Lime Village and King Salmon/AKPEN this morning.
These impulses are being kicked out from an upper low over in the
east Pacific/south of the Gulf of Alaska. This feature resulted
in isolated thunderstorm activity last evening over portions of SW
AK including a cell that went directly over Sparrevohn. More
showers and isolated thunderstorms anticipated today. However,
with the ridge over Hooper Bay and Bethel the extent of the
convection will be limited. Overnight and into Thursday the ridge
will build. Areas of fog are anticipated again for SW AK in the
morning. The warmer than normal temperatures will continue.
Yesterday, Bethel reached 75 degrees Fahrenheit which set a daily
record high. The previous record for that day was 74F which
occurred in 2004.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 2)...

On the latest ASCAT (Advanced Scatterometer) imagery a broad area
of high pressure was discernible between Attu Island and
Kamchatka. With GOES satellite imagery (specifically AVHRR/
Advanced Very High Resolution Radiometer) fog and low stratus has
been detected over portions of the Bering and Aleutians. Later
this evening/tonight a jet core of 125 kts pushes across Kamchatka
and starts to nose its way into the western Bering. The front
that is associated with this jet is currently over the Sea of
Okhotsk, but it will be in the western Bering early Thursday and
the dome of high pressure will move over the central Bering. The
longwave trough will become more amplified on Friday and the ridge
will be over the eastern Bering.

&&

.MARINE (Days 3 through 5/ Friday through Sunday)...

A front moves across the Bering through Sun. Confidence is good
for showers and southerly small craft winds and waves ahead of
the front into the eastern Bering, diminishing on Saturday.

An eastern North Pacific low over the southern Gulf moves into
the Canadian Maritimes on Sunday. A trough brings showers and
local northwest small craft winds and waves around the Barren
Islands on Friday, which will dissipate on Saturday. A weak low
forms near Kodiak Island through Sunday.

&&

.LONG TERM FORECAST (Days 4 through 7/Saturday through Tuesday)...

The forecast challenge for the extended will be temperatures and
precipitation potential, which is normally hard enough to pin down
at that time range. Add into the mix one forecast model not
playing well with the other two, and the picture gets even more
murky. In short, the ECMWF (a European model) and the Canadian
Global are in very good agreement with one another, as they
portray a trough digging slowly southeast from Siberia towards the
eastern Bering. The GFS (a long range American model), forecasts
a faster movement of said trough with a higher amplitude in its
development. This in turn places southwest and southcentral Alaska
is more of a moisture-laden southwesterly flow aloft, whereas the
ECMWF/Canadian is more of a hybrid zonal to slightly southwest
flow.

Although this too would bring precipitation to both areas, it
would be lighter in coverage and amounts, with less of an
accompanying cold pool aloft moving from the Bering into coastal
southwest Alaska. This in turn allows for less warming over
Southcentral (due to a flatter ridge amplification, but also
warmer temps for southwestern portions of the state (especially
the coast), given less cold advection aloft.

In any event, the model scenario above is good through the end of
the weekend, before even the Euro/Canadian diverge more. As a
result, after coordination with surrounding offices and WPC (our
Weather Prediction Center), we agree a slower approach with a
blend towards the ensembles seems a good "middle ground"
approach, especially for days 6 through 8 (Sunday and beyond).

In general, a cooler, cloudier, and wetter pattern will develop
across all of the southern mainland. The question is just how much
and to what degree.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...EJD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...MK/PD

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1013 AM AKDT Wed Aug 19 2020

AKZ141-210100-
Copper River Basin-
Including the cities of Glennallen, Eureka, McCarthy, Paxson,
and Slana
1013 AM AKDT Wed Aug 19 2020

...TAZLINA GLACIER DAMMED LAKE (GDL) RELEASING...

Tazlina Glacier Dammed Lake (GDL) is releasing causing water
level rises on Tazlina Lake and the Tazlina River (TAZA2).

Debris such as large trees may move down the Tazlina and Copper
Rivers. Individuals on or near the river should beware of
possible debris mobilized at and downstream of Tazlina confluence
with the Copper River.

Expected Impacts:
Rapid rises in water levels are possible on the Tazlina River
below Tazlina Lake including the area around the Richardson
Highway Bridge. All persons with interests near the river should
monitor the water levels and debris flows on the Tazlina and Copper
Rivers over the next several days and watch for information
updates.

Comments:
Pilot reports water level drop at Tazlina GDL while Nelchina GDL
remains full.

This statement may be updated if more information becomes
available.

www.weather.gov/aprfc