Flood Watch 2, NWS Anchorage, AK

023 
WGAK68 PAFC 261218
FFAAFC

URGENT - IMMEDIATE BROADCAST REQUESTED
Flood Watch
National Weather Service Anchorage AK
418 AM AKDT Sat Oct 26 2019

AKZ125-270030-
/O.EXT.PAFC.FA.A.0002.191027T2000Z-191029T1400Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Western Prince William Sound-
Including the cities of Whittier, Seward, Girdwood, 
and Moose Pass
418 AM AKDT Sat Oct 26 2019

...FLOOD WATCH NOW IN EFFECT FROM SUNDAY AFTERNOON THROUGH LATE
MONDAY NIGHT FOR THE SEWARD AREA...

The Flood Watch is now in effect for

* A portion of Alaska...including the following area...Western 
  Prince William Sound. 

* From Sunday afternoon through late Monday night.

* Moderate to heavy rain will begin along the Gulf of Alaska side
  of the Kenai mountains early Sunday and continue through Monday.
  Additional rainfall is likely Monday night and Tuesday, though
  the rain intensity should not be as heavy. Strong southerly flow
  will focus the heaviest rain on upslope areas, including Seward.
  Storm total rainfall in Seward will likely be between 4 and 6 
  inches. 

* Expected Impacts: Rapid water level increases on streams and 
  rivers draining into Resurrection Bay Sunday. River and stream 
  levels could approach flood stage by Sunday evening. Creeks 
  draining from the mountains will likely be carrying lots of 
  sediment which will impede drainage. Low lying areas including 
  the Seward airport runway may see flooding. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A flood watch means there is a potential for flooding.

You are encouraged to closely monitor this weather situation.
Preparation for this potentially dangerous weather event should
begin now.

&&

$$

684 
WGAK68 PAFC 270023
FFAAFC

Flood Watch
National Weather Service Anchorage AK
423 PM AKDT Sat Oct 26 2019

AKZ125-270130-
/O.CAN.PAFC.FA.A.0002.191027T2000Z-191029T1400Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Western Prince William Sound-
Including the cities of Whittier, Seward, Girdwood, 
and Moose Pass
423 PM AKDT Sat Oct 26 2019

...FLOOD ADVISORY NOW IN EFFECT FROM SUNDAY AFTERNOON THROUGH 
MONDAY NIGHT FOR THE SEWARD AREA...

The Flood Watch for rapid water level increases on streams and
rivers draining into Resurrection Bay due to moderate to heavy
rain Sunday into Monday has been upgraded to a Flood Advisory.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 AM AKDT Fri Oct 25 2019

.ANALYSIS AND UPPER LEVELS...
A strong 960 mb low is tracking from west to east to the south of
the Aleutians early this morning. An associated frontal system
bringing storm force winds extends north across the western
Aleutians, east through the south central Bering and the south
through the central and eastern Aleutian into the north Pacific.
Upper level ridging extends over the eastern Bering and Alaska
Peninsula out ahead of the low, while a cold upper level trough
over the Chukchi Sea stretches south through the Bering Strait and
into the northern Bering. Skies have cleared across much of
Southwest Alaska overnight as a second upper level trough swept to
the east. Strong westerly flow has pushed over Shelikof Straits,
Kodiak Island, the Barren Islands and into the western Gulf.
Further to the north, showers persist over southcentral Alaska
supported by surface troughing running from north to south through
the Susitna Valley then turning to the east-southeast across the
Anchorage area, Chugach Mountains and Kenai Peninsula to extend
across the northern Gulf.

&&

.MODEL DISCUSSION...
Model agreement remains very good regarding the storm force low
south of the Aleutians and its large frontal system spreading
north and eastward. Models have come into better agreement with
the frontal wave developing south of the Alaska Peninsula Friday
night and lifting north into Southwest Alaska Saturday as well as
with a second front wave lifting north along the Southwest Alaska
coast and developing into a closed low on Sunday. Synoptic winds
were increased accordingly in both domains for the second frontal
wave.

&&

.AVIATION...
PANC...MVFR rain showers currently over the area may mix briefly
with snow this morning...possibly changing over all the way to
snow by 18Z before tapering off midday. VFR conditions are then
expected this afternoon through Saturday morning. Southeasterly
winds through Turnagain arm will start increasing Saturday morning
but should remain south of the Airport through the TAF period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2/Today
through Saturday night)...
A weak upper level short-wave trough tracking up Cook Inlet this
morning will quickly weaken through the day thanks to rapid height
rises upstream and increasing anticyclonic flow aloft. Cold air
advection with the trough will cause precipitation to transition
from rain to snow during the morning hours from Anchorage up to
the Mat-Su. Any snow that does fall at sea level will not last
long, so expect little to no snow accumulation. Gusty westerlies
over the Gulf and southern Cook Inlet (induced by the cold air
advection) will gradually weaken through the day.

The upper ridge will quickly build overhead of Southcentral this
afternoon through tonight, then shift eastward Sunday. With the
cold air advection, today will generally be unstable off the
surface which should allow most of the low level clouds to mix
out. There could be some patchy fog tonight, with high clouds
moving up the west side of the ridge arriving overnight and
helping to limit fog potential.

Attention will then shift to the high amplitude pattern with
accompanying atmospheric river. This will transport abundant
warm air and moisture northward to Southcentral Alaska as we
head through the weekend. As the pattern is in the process of
amplifying today, a weak low near 36N 157W will be picked up
in the flow and brought northward. This system will reach the
western Gulf and Bristol Bay early Saturday. With little in the
way of upper level forcing, precipitation will be focused in
upslope areas from Kodiak Island to the Kenai Peninsula and
on up to the northern and western Susitna Valley. The prevailing
low level flow will be southerly. The air mass will initially be
cold enough for all snow in the Susitna Valley and it will take
some time for the warm air to reach there. Have issued a Winter
Weather Advisory for Snow for north of Talkeetna where precipitation
will be heaviest. Expect snow to begin to mix with rain late
Saturday night or early Sunday.

The presence of a deep low along the Aleutians combined with the
passage of this first system will really tighten up pressure
gradients, leading to strengthening winds across the western
Gulf on Saturday as well as gap winds through all the usual
places. As energy rounds the base of the high amplitude trough
over the Pacific and begins to lift northward, a trailing cold
front will progress eastward toward the Gulf and Southcentral.
This will lead to even stronger winds Saturday night and Sunday.
Assuming nothing changes with the basic track of these features, a
High Wind Warning will likely be needed for Turnagain Arm and
higher elevations for Anchorage. Meanwhile, the warm air and heavy
rain associated with the atmospheric river will gradually shift
eastward to Southcentral as we head through the weekend. The
strong low level flow will limit rainfall in many of the typically
drier areas (western Kenai, Anchorage, Mat Valley), while Kodiak,
the Gulf coast, and portions of the Susitna Valley get the brunt
of the rainfall.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1-3: Fri-Sun)...

A shortwave moving over the northern Kuskokwim Delta coast this
morning could bring isolated snow showers to Hooper Bay before the
next big system moves over the Southwest coast by late morning. A
gale force front will move inland early this afternoon, along
with strong winds and abundant precipitation. As this front first
moves inland over the Kuskokwim Delta coast, precipitation is
likely to start off as snow, quickly transitioning over to rain as
southerly flow brings in warming temperatures. Any new
accumulations of snow will likely stay confined to the mountains.

Wet conditions will remain across the Southwest through the
weekend as the atmospheric river continues to bring a long fetch
of subtropical moisture to the region. Any new precipitation with
this system should fall as rain as above freezing temperatures
persist through Sunday. Strong winds also accompany this system
over the next few days, with some areas of interior Bristol Bay
likely to see wind gusts of 60 to 70 mph on Saturday through early
Sunday as southeasterly flow continues to impact the area.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1-2: Fri-Sat)...

The storm force low centered south of Adak this morning will
continue on its track eastward today. Its front will move into
the eastern Bering and reach the Southwest coast by this
afternoon bringing southeasterly gale force winds. Areas along
the AKPEN could see stronger gusts, especially out of gap areas.
Storm force northerly flow will remain stretched over much of the
western Bering and Aleutians through Saturday, as cold air
continues to be pulled down from the northern Bering.

&&

.LONG TERM FORECAST (Days 3 through 7: Sunday through Thursday)...

A busy long-term period is in the forecast this week. A nearly
stationary low over the Aleutians west of Dutch Harbor will have a
large equatorial extension on Sunday morning. This will pull large
amounts of rain in the form of atmospheric river northward into
southern mainland Alaska. The rain will be ongoing across most of
the region Sunday morning, through gusty winds and downsloping
will make the rain intermittent and light over Anchorage and the
Matanuska Valley. The firehose of rain will gradually move
eastward with time, but will linger longest along the coastal
Kenai Peninsula Sunday night and into Monday. More on the details
of that below in the hydrology section. The rain will move across
Prince William Sound on Monday, with the heaviest rain shifting
into the Panhandle by Tuesday. However, lingering light rain will
persist across all of Southern mainland Alaska into Tuesday, as
the low over the Bering keeps the onshore flow going.

In addition to all the rain, strong winds through Turnagain Arm
and higher elevations are likely Sunday into Sunday night. There
is some uncertainty as to how strong those winds will be, but
hurricane force gusts are at least possible once again. Plenty of
warm air with this system will keep any precipitation that falls
as rain for almost everyone, including those at high elevations,
as freezing levels rise as high as 9,000 feet. Upslope
precipitation is also expected along the Alaska Range for this
entire event through the day Monday. Since the predominant flow
will be southerly, cold air will be most persistent and hardest to
remove across Broad Pass north of Talkeetna. Shovellable snow is
likely Sunday into Sunday night into this area. Lingering showers
are likely into Tuesday for much of Southern mainland Alaska.

On Wednesday and into Thursday, the models rapidly diverge on the
track and timing of the next North Pacific low which will move
north into Southern Mainland Alaska. This too looks like it could
be a big wind-maker for much of the region, with additional rain,
heavy at times along the area mountains. Since the details of this
storm are highly uncertain, check back in future forecast packages
for updates.

&&

.HYDROLOGY...

There is high confidence that an atmospheric river event will
threaten portions of Southern Alaska Sunday into Monday. The
hardest hit areas are likely to be along the southern Kenai
Peninsula, including Seward. Rain will start Saturday afternoon
across the region and gradually increase in intensity through
Sunday morning. Heavy rain is expected from Sunday afternoon
through Monday morning. Four inches of rain in 24 hours starting
Sunday afternoon are likely in Seward, which does not include the
rain that will fall preceding this period, nor the fact that
shower activity is likely to persist behind the atmospheric river
into Tuesday. Additional hydrological concerns will be how much
rain impacts the Homer area, and with very high freezing levels
affecting the Talkeetna Mountains, if any rain falls on that snow,
there could be notable rises on eastern Susitna Valley rivers and
streams as well. Uncertainty with that is much higher than further
south along the coast, so it will continue to be monitored in
future updates.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 120 131 132 136 137 138 150 155 165 170 171
                      173 176 179 180 181 351 352 414.
         Storm Warning 130 160 172 174 177 178 185 411 412 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...JW

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
352 PM AKDT Fri Oct 25 2019

AKZ171-261300-
Kodiak Island-
Including the city of Kodiak City
352 PM AKDT Fri Oct 25 2019

...HEAVY RAIN EXPECTED FROM CHIGNIK TO KODIAK ISLAND TONIGHT
THROUGH SUNDAY...

An atmospheric river bringing copious Pacific moisture into the
area will cause heavy rain from Chignik to Kodiak Island tonight
through Sunday. The heavy rain will first impact the Chignik area,
where as much as 6 inches of rain is expected from late tonight
through Sunday morning. The heaviest rain in Chignik is expected
late tonight through Saturday.

The heavy rain will move east from Saturday afternoon through
Sunday afternoon, where heavy rain in the mountains south and west
of Kodiak City will increase the potential for mudslides and rapid
river and stream rises. Southeast winds of 40 to 50 mph with
higher gusts are also expected at the same time as the heavy rain.