Flood in Alaska, May 18 to 21, 2023

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
220 AM AKDT Thu May 18 2023

.SYNOPSIS...
Conditions continue to dry out south of the Brooks Range with
warming temperatures, low relative humidity levels and dry
northeast winds developing over much of the Central and Eastern
Interior. Fire Weather concerns will be in focus especially on
Friday for the Fortymile Country, the Yukon Flats, and the Middle
and Upper Tanana Valleys. Ice jam flooding remains a concern in
Buckland where a Flood Warning remains in effect. The potential
for Ice Jam flooding has prompted a Flood Watch for the Yukon
between Galena and Koyukuk. Snow melt flooding potential continues
along the Porcupine River where a Flood Watch has been issued for
the Porcupine River between the Canadian Border and Fort Yukon.

&&

.DISCUSSION...
Upper Levels and Analysis...
The upper level trough over the Bering Sea and Western Alaska
continue to be displaced by strong upper level ridging building
east out of Siberia and from strong upper level ridging building
west out of the Yukon over Northern Alaska. A weak shortwave
continues to move east over the Eastern Arctic with weak ridging
building in from the west over the North Slope. Chances for
precipitation are minimal over most of Northern Alaska for the
next several day with the high pressure ridge firmly entrenched
overhead. Some moisture with isolated showers and thunderstorms
will try to push into the area from the southeast late on Sunday
and into Monday with a easterly wave.

Models...
The 18/00z model suite initialized well against the 18/00z
surface analysis and upper air observations and verified well
against the 06z surface analysis. The model suite remains in tight
agreement on synoptic scale features and their track and strength
through the short and medium range. Models continue to show
reasonable agreement into early next week.

North Slope and Brooks Range...
Southwest winds will increase today and continue on Friday with
clouds decreasing inland and along the Brooks Range. Low clouds
and areas of fog will persist along the coast where the fog may be
dense at times. High temperatures will be in the 20s and 30 along
the coast while temperatures rise into the 30s and 40 inland and
along the foothills of the Brooks Range.

West Coast and Western Interior...
After several days of wintry precipitation, low clouds and strong
winds high pressure building in from the Bering Sea will bring
much warmer and drier conditions to the area. Clouds will continue
to diminish today and tomorrow with light winds expected. High
temperatures today will be in the 30s along the coast and in the
mid 60s in the Western Interior. Low clouds and fog will push in
along the coast this evening. Low temperatures tonight will be in
the 20s and 30s along the coast and in the 30s to lower 40s in the
Western Interior. Fire Weather concerns will increase over the
next several days and in particular on Friday as meteorological
near Red Flag conditions begin to encroach into the eastern
portions of the Western Interior with temperatures in the lower
70s, minimum relative humidity levels dropping into the 20s and
northeast winds increasing to 10 to 15 mph on Friday. See
hydrology section for discussion on ongoing and potential for Ice
Jam flooding.

Central and Eastern Interior...
Near Red Flag conditions for Thursday and Fire Weather Watches for
the Fortymile Country, the Middle and Upper Tanana Valley remain
in effect for Friday for Hot Dry and Windy conditions. Criteria
for Red Flag Warnings are looking more favorable for the Yukon
Flats on Friday as well. Temperatures are expected to clime into
the upper 60s and lower 70s today and into the mid 70s on Friday
for the above mentioned areas. Minimum relative humidities are
expected to drop into the 20s and 30s today and into the low to
mid 20s on Friday. Gusty and dry northeast winds are expected to
develop tonight and continue on Friday and into Saturday with many
of the above locations likely to meet all three criteria for Red
Flag Warnings on Friday. Precipitation chances are minimal over
the area today into the weekend.

Warming temperatures across the region later this week, combined
with a above normal snowpack over higher elevations, is/will
cause a significant increase in snowmelt. Runoff into rivers south
of the Brooks Range is keeping elevated water levels on many
Interior rivers and is causing water levels to rise on the
Porcupine River. A Flood Watch for snow melt flooding has been
issued for the Porcupine River from the Canadian border to Fort
Yukon. See hydrology section additional details.

Coastal Hazard Potential Days 3 and 4...None.

&&

.FIRE WEATHER...
Hot, dry and breezy conditions over the Central and Eastern
Interior and along and near the northern foothills of the Alaska
Range Thursday and Friday will be the main concern. A ridge
building in aloft from the Bering Sea and from the Yukon will
limit precipitation and will drive minimum relative humidity
levels down into the 30s and 20s between the Alaska Range and the
Brooks Range. The driest locations will be in the Yukon Flats, the
Fortymile Country, the Middle and Upper Tanana Valley's and along
the northern foothills of the Alaska Range on Thursday afternoon
and evening. Relative humidity levels will drop to similar levels
on Friday afternoon and evening in the same locations.
Temperatures will rise into the upper 60s to the lower 70s over
the same areas on Thursday and will nudge a few degrees warmer on
Friday with many locations in the Middle and Upper Tanana Valley
and Fortymile country rising into the mid to upper 70s. Winds will
be the key factor with most locations reaching Red Flag Criteria
for Temperatures and Low Relative Humidities by falling just short
of Red Flag Criteria for winds. Gusty northeast winds will develop
over these areas on Friday with the wind criteria likely being
met in the above locations in addition to temperature and low
relative humidity levels. Fire Weather Watches have been issued
for Friday for these areas. Near Red Flag conditions will likely
occur in the areas mentioned above on Saturday. Increased clouds
and moisture will lower the threat on Sunday.

Western Interior fire weather concerns will increase over the
next several days and in particular on Friday as meteorological
near Red Flag conditions begin to encroach into the eastern
portions of the Western Interior with temperatures in the lower
70s, minimum relative humidity levels dropping into the 20s and
northeast winds increasing to 10 to 15 mph on Friday.

&&

.HYDROLOGY...
A flood warning for ice jam flooding remains in effect for
Buckland along the Buckland River, which is based off of latest
spotter reports. A Flood Watch has been issued for the Porcupine
River and other lo-lying and flood-prone locations along the
Porcupine river from the Canadian border to Fort Yukon for
snowmelt flooding. A second Flood Watch has been issued for the
Yukon River between for ice jam flooding between Galena and
Koyukuk.

Warming temperatures across the region later this week, combined
with a much above normal snowpack over higher elevations, is/will
cause a significant increase in snowmelt. Runoff into rivers south
of the Brooks Range is causing water levels to rise and breakup
to begin on some rivers. Local ice jams may form and result in
elevated water levels. The increased runoff may also cause smaller
rivers and streams to rise to bankfull levels or overbank in low
lying areas.

People along rivers and streams should prepare for the
possibility of high water levels this week due to ice breakup and
snowmelt runoff. River access points and gravel bars will likely
be covered with water along with increased debris in rivers.

The latest breakup information is available at
www.weather.gov/aprfc/breakupMap.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...Flood Watch for AKZ220.
PK...None.
&&