Areal Flood Warning 1, NWS Anchorage, AK

873 
WGAK88 PAFC 211811
FLSAFC

Flood Statement
National Weather Service Anchorage AK
1003 AM AKDT Wed Apr 21 2021

AKZ121-230630-
/O.CON.PAFC.FA.W.0001.000000T0000Z-210423T0630Z/
/00000.0.IJ.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Western Kenai Peninsula-
1003 AM AKDT Wed Apr 21 2021

...A FLOOD WARNING FOR AN ICE JAM REMAINS IN EFFECT UNTIL 1030 PM
AKDT Thursday along the Anchor River downstream of the Old Sterling 
Highway bridge....

At 10am river gage readings along the Anchor River were reading 
above major flood stage due to an ice jam just downstream of the Old 
Sterling Highway.  As of Wednesday morning water was very high but 
was not yet over the Old Sterling Highway or flooding the Anchor 
River State Recreation Area.  

As spring melt and breakup continues over the next few days, be 
prepared for fluctuating water levels and flood conditions along the 
Anchor River.  There are numerous ice jams on the lower section of 
river and flooding is still possible as they release and rejam or as 
new jams form.  The most likely areas to experience flooding are the 
Old Sterling Highway and the Anchor River State Recreation Area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.

A Flood Warning means that flooding is imminent or occurring. All
interested parties should take necessary precautions immediately.

&&

LAT...LON 5979 15181 5976 15179 5975 15184 5978 15185

$$

Shea

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
537 PM AKDT Tue Apr 20 2021

.ANALYSIS AND UPPER LEVELS...
A vertically stacked low south of the Eastern Aleutians continues
to weaken as it sinks slowly southward into the North Pacific.
Areas of rain persist along the Alaska Peninsula and Eastern
Aleutians, especially on the Pacific side. A large area of high
end small craft winds extend from the Alaska Peninsula and across
the eastern to central Bering Sea. Other than the winds, high
pressure over the western Bering is leading to quiet conditions
across much of the Bering and Aleutian chain.

A broad upper level trough extends north and east from the
aforementioned low center across Southwest Alaska and into the
Gulf of Alaska, with embedded weak waves rotating westward into
the eastern Bering. The trough is blocked from making any
northward progression due to an Arctic trough digging
southeastward across the eastern Alaska interior. The south end
of this short-wave is crossing the Alaska Range and the northern
Copper River Basin. There is little precipitation with any of the
troughs. The primary impact is an increase in cloud cover across
southern Alaska and marginally cooler temperatures than recent
days.

&&

.MODEL DISCUSSION...
Models remain in excellent agreement with large scale features
through Thursday. Solutions diverge with a Pacific low tracking
south of the Aleutians on Thursday, with uncertainty in the depth
of the low as well as how close it gets to the chain. For now,
don't have a preferred solution. Will just get the general idea
of a low into the forecast and update as we get closer in time.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

Quiet and dry weather is expected for the forecast period with
loads of sunny weather as the upper level high rebuilds over the
region. Temperatures will be mainly in the 50s and 60s across
Southcentral for the next few days with each day slightly warmer
than the last. With the upper level high overhead, a decent
radiational cooling setup is expected each night with
temperatures falling mainly into the mid to upper 20s area-wide
with lows in the low 30s to near freezing for Anchorage. Areas of
patchy fog are also possible through the remainder of the
afternoon and into the evening hours around Valdez to Thompson
Pass before winds begin to pick up overnight to mix out any of the
fog. There are also some areas of fog around the Kodiak area this
afternoon which is expected to remain through Wednesday morning.
The Turnagain Arm wind is also expected to pick back up Wednesday
afternoon through Thursday, though, expect these winds to bend
down Cook Inlet and not move over any land areas.

The only other item to note will be a gale force frontal system
associated with a low pressure moving towards the Aleutian
Islands. This will send copious amounts of rain to the Kodiak
area beginning Wednesday morning. Rain is expected to fall fairly
continuously from Wednesday afternoon through Thursday evening
with anywhere from 2 to 3 inches expected, with locally 3+
inches possible. This front is expected to push up to about the
southern tip of the Kenai Peninsula Thursday before the upper
level high pushes this front back down to the south on Friday.

&&

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

With the exception of some low cloud cover, subsidence under a
ridge of high pressure aloft is keeping much of Kuskokwim Delta
and the middle Kuskokwim Valley relatively quite today with mostly
clear skies and Spring-like temperatures. Meanwhile, a North
Pacific low will track westward along the Aleutian Chain late
tonight into Wednesday. A deep fetch of tropical moisture
associated with this low will move northward, bringing a chance of
rain showers over parts Y-K Delta and Bristol Bay Coast through
late Thursday night. Areas south and east of Toksook Bay should
remain rain free during this time period. The main impact will be
gusty, easterly winds on the backside of the low through the gaps
and passes of the Alaska Range and across parts of Bristol Bay
through late Wednesday night before diminishing. Otherwise, the
aforementioned ridge will be anchored over the forecast area and
bring fair, mild conditions with increasing clouds at times
through the end of the week.

&&showers

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

Wrap around moisture associated with a weak low south of Dutch
Harbor will continue to bring isolated rain showers along the
Aleutian Chain before tapering off this evening. After a brief
lull, another frontal boundary associated with a North Pacific low
is expected to arrive late tonight into Wednesday. This storm
system will have a deep fetch of tropical moisture and will bring
widespread rain along the Eastern and Central Aleutians,
spreading northward over the Pribilofs. As the low deepens and
tracks westward early Wednesday morning, a low-level easterly
barrier jet will form along the coastline of the Eastern Aleutians
with the strongest winds and gusts expected over the offshore
islands especially near Sand Point. Elsewhere, expect gusty,
easterly winds across much of the forecast area through the usual
gaps and passes and the Bering Sea as well. Precipitation will
taper off along with diminishing winds by late Thursday night as
the low weakens.

&&

.MARINE (Days 3 through 5/Friday through Sunday)...
A North Pacific low will track in the vicinity of the Aleutians
Friday through Friday night. There is forecast uncertainty in the
exact track and depth of this storm. At this point in time it
looks like it will remain just south of the Aleutian Islands and
produce small craft winds. However, there is potential for gale
force winds if the low ends up being a bit stronger. In any case,
it will begin to weaken by Saturday as it heads into the southern
Bering Sea.

Elsewhere, expect winds less than 35 kts and seas less than 20 ft.

&&

.LONG TERM FORECAST (Days 4 through 7/Saturday through Tuesday)...
A blocking ridge will hold firmly over mainland Alaska through
the weekend, continuing the recent stretch of mostly sunny and
warm weather. The storm track will be focused from the North
Pacific up into the Bering Sea. At this point, it doesn't look
like any of these storms will be particularly strong, but do
expect occasional stronger winds and rain along the Aleutians and
Alaska Peninsula and across the Bering Sea.

Medium range models indicate the blocking ridge may weaken or
shift away from mainland Alaska early next week, but diverge on
how and when this might occur. All solutions show a strong Arctic
trough dropping down the east side of the ridge. Some of these
drive the trough southwestward across Alaska while others keep
most of the energy over western Canada. This would certainly
affect the temperature forecast, though conditions would likely
remain dry under either scenario. Meanwhile, models are in
agreement on increased ridging over the Bering Sea as the long-
wave trough shifts back southward into the North Pacific. Thus,
would generally expect quieter weather. Stay tuned as we try to
figure out when the blocking pattern will break and what the new
pattern will look like.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory Anchor River (121).
MARINE...Gale Warnings 150-170 172 180 414 130 131 132 138 352.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...MV
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
MARINE/LONG TERM...RC