Flood in Alaska, August 2 to 8, 2019

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
315 PM AKDT Thu Aug 1 2019

.SYNOPSIS...
Northern Alaska is now entering a wet southwesterly flow pattern.
This will cause a series of moderate to strong weather systems
move from the Bering Sea northeast across northern Alaska for the
next week, and bring substantial amounts of rain to most of
Northern Alaska, along with substantial winds with each weather
system. One low, now along the Arctic Coast, is causing gales and
high surf over zone 202 that will continue through this evening.
A second low moving in the West Coast on Fri night and Sat will
bring elevated sea levels and potential for coastal flooding to
the West Coast of Alaska south of the Bering Strait Fri afternoon
through Sat night, and high surf to the area from the Bering
Strait to Point Hope from Sat through Sun. This elevated sea level
combined with heavy rain will cause flooding along the Snake and
Nome Rivers near Nome beginning Fri PM.

Aloft...
The long wave pattern consists of a ridge over the N Pacific and
SW Alaska and a lone wave trough over the Western Bering Sea. This
pattern is slightly progressive, and the ridge will build over
southern Alaska by 4pm Fri with the trough over the Western Bering
Sea. This will set up a southwest flow pattern Fri that will
continue into next week. A series of strong short wave troughs and
associated surface systems will move through this flow and bring
copious amounts of rain to most of Northern Alaska over the next
week.

One short wave trough over the Eastern Interior will move east of
the Alcan Border this evening. This will allow isolated
thunderstorms east of Delta Junction to Arctic Village this
evening.

A second short wave in the western Bering will move to the
Eastern Bering on Fri, along the West Coast Fri night, to the
Western Interior Sat, and to the Eastern Interior Sat night and
east of the Alcan Border on Sun. This will push a strong surface
system and plenty of rain across Northern Alaska over the weekend.

Brief ridging will build in west of the second trough before a
third trough approaches from the west on Mon.

Surface...
A 987 mb low 180 NM north of Nuiqsut will move to 300 NM northeast
of Barter Island as a 998 mb low by 4pm Fri. West winds 25-35kt
just south of this low will move east with the low. This is
bringing gales and scattered showers to the Arctic Coast from Pt
Barrow east that will decrease after midnight tonight.

A cold front stretching from this low to Inuvik to Delta Junction
will move to Mayo to Northway by 4am Fri and then weaken. Expect
rain along and west of the front, and west winds 15 kt. Winds and
weather will clear out west of the front, other than some
isolated showers this evening.

A 995 mb low in the central Bering Sea will move to 200 NM west
of Gambell as a 991 mb low by 4pm Fri, to 50 NM west of Kivalina
as a 996 mb low by 4pm Sat, and to near Deadhorse as a 1004 mb low
by 4am Sun, and to as a 1000 mb low over Banks Island by 4pm Sun.
Expect east to south winds 25-35 kts ahead of the low to spread to
the West Coast on Fri and Fri night, and then W-NW winds 30-40kt
West of the low to spread to the coast Sat and Sat night.
Uncertain yet is winds will be this strong over the Arctic Coast
Sat night and Sun. This has lead to the Coastal Flood Watches and
West Coast south of the Bering Strait starting on Fri, and to high
surf advisories for the Bering Strait north on Sat. There is
potential for High surf along the Arctic Coast Sat night and Sun,
but much uncertainty at this point in wind strength and duration.

A warm front extending east from this low will move to Norton
Sound by 4pm Fri, to The Bering Strait to Eagle by 4pm Fri, to
POint Hope to Circle by 4am Sat and to Point Hope to Arctic
Village by 4pm Sat. Expect Widespread heavy rain to spread
northeast with this front along with SW winds 15 kt.

A cold front trailing the low will move to the Seward Pen south
to the YK Delta by 4pm Fri, to Point Hope to the YK Delta by 4am
Sat, to Umiat to Anvik by 4pm Sat, to Inuvik to Fairbanks to
Mcgrath by 4am Sun, and to Northway to Mcgrath by 4pm Sun.
Expect SW winds 25-35kt with the cold front along the West Coast
decreasing to SW 15-25kt as the front moves over the Interior.
Rain will continue between the warm front and cold front, then
taper off west of the cold front.

&&

.DISCUSSION...
Models initialize well aloft at 12Z, and show similar solutions
through 4pm Sat. After that time, the ECMF lifts the short wave
moving NE across the North Slope more quickly than the NAM, GFS
and Canadian. The NAM, GFS and Canadian are consistent aloft
through 4pm Sun, then start to see divergence between models on
strength and speed of short waves next week. Given that the
feature along the West Coast on Sat is becoming fully occluded and
slowing in its movement, and that 3 models agree on this, favor
the slower movement of the NAM, GFS and Canadian from Sat into
Sun.

At the surface at 15Z, models all verify 3-5 mb too weak on the
surface low north of Utqiagvik. The GFS keeps this feature deeper
than other models through Fri, though the track of the GFS and NAM
is similar. Since the GFS is the deepest solution, prefer the GFS
track on solution on this feature, but we will add 3-5 kt to max
winds through tonight to reflect the deeper actual deeper low and
stronger winds.

The GFS,NAM and ECMF are fairly similar with strength and
location of low moving into the West Coast on Sat. The ECMF then
moves this low NE faster than the NAM and GFS Sat night and Sun.
We prefer a blend of the NAM and GFS at the surface for Sat night
and Sun given the preference for their solutions aloft during
that time frame.

With precipitation, the ECMF is faster than the NAM and GFS with
precip incoming on Fri. Favor a blend of the NAM and GFS for
precip areal coverage and precip amounts.

Coastal Hazard Potential Days 3 and 4...
One low, now along the Arctic Coast, is causing gales and
high surf over zone 202 that will continue through this evening.
A second low moving in the West Coast on Fri night and Sat will
bring storm surges of 4 to 8 ft to the West Coast of Alaska south
of the Bering Strait Fri night through Sat night, and high surf to
the area north of the Bering Strait from Sat through early Sun
where winds will not have a long enough fetch length for flooding
but will cause high surf.

&&

.FIRE WEATHER...
Wet and windy flow pattern now moving over Northern Alaska. RH
should remain above 40% most areas for next 3 days, and possibly
longer. Few is any thunderstorms expected through Sun.
Heavy rain expected West Coast and Western Interior Fri into Sat
with 1-3 inches expected. Heavy rain expected Eastern Interior NW
of Chicken Fri night through Sun with 1-2 inches expected in most
areas.

&&

.HYDROLOGY...
Heavy rain expected West Coast and Western Interior Fri into Sat
with 1-3 inches expected.
Heavy rain expected Eastern Interior NW of Chicken Fri night
through Sun with 1-2 inches expected in most areas.
Expect sharp rises on Interior and West Coast rivers NW of
Chicken over the weekend. Could hit near flood stage on Nome and
Snake rivers Sat as rain water moves downstream and combined with
elevated sea levels.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory for AKZ202-AKZ207-AKZ209-AKZ210-AKZ213.

Coastal Flood Watch for AKZ211-AKZ212-AKZ214.

Flood Watch for AKZ211.

Small Craft Advisory for PKZ215-PKZ220-PKZ225-PKZ230.

Gale Warning for PKZ200-PKZ210-PKZ235-PKZ240-PKZ245.
&&

JB AUG 19