Flood Watch 1, NWS Anchorage, AK

103 
WGAK68 PAFC 200036
FFAAFC

FLOOD WATCH
NATIONAL WEATHER SERVICE ANCHORAGE AK
436 PM AKDT MON SEP 19 2016

...HEAVY RAINFALL NEAR SEWARD MAY CAUSE FLOODING TUESDAY NIGHT
INTO THURSDAY...

.THE STRONG STORM SYSTEM THAT WILL BRING HIGH WINDS TO PORTIONS
OF SOUTHCENTRAL ALASKA WILL ALSO BRING VERY HEAVY RAINFALL TO THE
EASTERN KENAI PENINSULA TUESDAY EVENING INTO WEDNESDAY MORNING.
RAINFALL WILL BEGIN TUESDAY MORNING BUT THE HEAVIEST INTENSITIES
WILL BE OVERNIGHT TUESDAY NIGHT. ACTUAL RAINFALL AMOUNTS ARE
STILL UNCERTAIN BUT LOOK TO BE IN THE 5 TO 7 INCH RANGE IN A
12 TO 18 HOUR PERIOD. RAIN SHOULD TAPER OFF WEDNESDAY MORNING BUT
STREAM AND RIVERS WILL REMAIN HIGH WELL BEYOND THAT TIME.

AKZ125-201900-
/O.CON.PAFC.FA.A.0001.160921T0500Z-160922T2000Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
WESTERN PRINCE WILLIAM SOUND-
INCLUDING THE CITIES OF...WHITTIER...SEWARD...GIRDWOOD...
MOOSE PASS
436 PM AKDT MON SEP 19 2016

...FLOOD WATCH REMAINS IN EFFECT FROM TUESDAY EVENING THROUGH
THURSDAY MORNING THROUGH THURSDAY MORNING NEAR SEWARD...

THE FLOOD WATCH CONTINUES FOR

* THE SEWARD AREA

* FROM TUESDAY EVENING THROUGH THURSDAY MORNING

* HEAVY RAIN MAY PRODUCE 5 TO 7 INCHES OF RAINFALL IN THE SEWARD
  AREA IN A 12 TO 18 HOUR PERIOD.

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.

&&

$$

318 
WGAK68 PAFC 200036 CCA
FFAAFC

FLOOD WATCH...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
436 PM AKDT MON SEP 19 2016

...HEAVY RAINFALL NEAR SEWARD MAY CAUSE FLOODING TUESDAY NIGHT
INTO THURSDAY...

.THE STRONG STORM SYSTEM THAT WILL BRING HIGH WINDS TO PORTIONS
OF SOUTHCENTRAL ALASKA WILL ALSO BRING VERY HEAVY RAINFALL TO THE
EASTERN KENAI PENINSULA TUESDAY EVENING INTO WEDNESDAY MORNING.
RAINFALL WILL BEGIN TUESDAY MORNING BUT THE HEAVIEST INTENSITIES
WILL BE OVERNIGHT TUESDAY NIGHT. ACTUAL RAINFALL AMOUNTS ARE
STILL UNCERTAIN BUT LOOK TO BE IN THE 5 TO 7 INCH RANGE IN A
12 TO 18 HOUR PERIOD. RAIN SHOULD TAPER OFF WEDNESDAY MORNING BUT
STREAM AND RIVERS WILL REMAIN HIGH WELL BEYOND THAT TIME.

AKZ125-201245-
/O.COR.PAFC.FA.A.0001.160921T0500Z-160922T2000Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
WESTERN PRINCE WILLIAM SOUND-
INCLUDING THE CITIES OF...WHITTIER...SEWARD...GIRDWOOD...
MOOSE PASS
436 PM AKDT MON SEP 19 2016

...FLOOD WATCH REMAINS IN EFFECT FROM TUESDAY EVENING THROUGH
THURSDAY MORNING NEAR SEWARD...

THE FLOOD WATCH CONTINUES FOR

* THE SEWARD AREA

* FROM TUESDAY EVENING THROUGH THURSDAY MORNING

* HEAVY RAIN MAY PRODUCE 5 TO 7 INCHES OF RAINFALL IN THE SEWARD
  AREA IN A 12 TO 18 HOUR PERIOD.

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.

&&

$$

625 
WGAK68 PAFC 202150
FFAAFC

FLOOD WATCH
NATIONAL WEATHER SERVICE ANCHORAGE AK
150 PM AKDT TUE SEP 20 2016

AKZ125-202300-
/O.CAN.PAFC.FA.A.0001.160921T0500Z-160922T2000Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
WESTERN PRINCE WILLIAM SOUND-
INCLUDING THE CITIES OF...WHITTIER...SEWARD...GIRDWOOD...
MOOSE PASS
150 PM AKDT TUE SEP 20 2016

...FLOOD WATCH IS CANCELLED THROUGH THURSDAY MORNING NEAR
SEWARD...

THE FLOOD WATCH HAS BEEN CANCELLED. THE FLOOD WATCH HAS BEEN
UPGRADED TO A FLOOD ADVISORY.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKDT SUN SEP 18 2016

.ANALYSIS AND UPPER LEVELS...
An upper level low is currently centered just east of Kamchatka
Peninsula while an impressive upper level ridge encompasses much
of mainland Alaska and is maintaining relatively dry conditions
across Southcentral. At the surface a gale force front is draped
across the Aleutians and curves towards the Kamchatka low while a
broad ridge is across the Western mainland. A low in the eastern
Gulf continues to dissipate and push eastward. The pressure
gradient between the ridge across western mainland Alaska and
the Gulf has supported light northwest downslope flow across
Southcentral, which has helped to erode much of the stratus that
was sitting beneath the ridge this morning. The Kamchatka low and
Mainland ridge are expected to support much more inclement weather
towards the end of the short term, as the ridge stalls and amplifies,
supporting a stronger jet and surging moisture northwards into the
mainland.

&&

.MODEL DISCUSSION...
While models are generally showing similar synoptic conditions,
with the Kamchatka low moving into the Central Bering and the
ridge stalling, there is still uncertainty in the timing and
intensity of the front as it pushes across the Gulf of Alaska
toward Anchorage Tuesday afternoon into Wednesday. Models
currently disagree on the location and intensity of a triple point
low that forms along the front. The spread in low track
differences covers about 300 miles, from Shelikof Strait to Cook
Inlet. This will strongly influence the extent of downsloping
across Southcentral as well as whether strong winds are felt at
sea level. As a result, certainty is below average for this
forecast.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A surface ridge transverses west to east across Southcentral
clearing skies through the evening. This will allow for cool
temperatures as radiational cooling maximizes overnight. A
relatively quiet start to the work week is in store for Monday
as the ridge axis shifts toward the eastern Gulf of Alaska.

The main challenge for this week is a stacked low pressure system
tracking east across the Bering which is expected to bring gusty
winds and rain back into the region Monday night into Tuesday. The
storm system will be fast moving toward the Southwest coast. With
a slower moving ridge across the gulf, the pressure gradient
tightens between the two systems increasing winds late Monday
night across the western Gulf, Cook Inlet and Turnagain arm. The
surface front pushes into Kodiak Island early Tuesday morning with
west flow changing direction to the east. Winds will noticeably
increase through the day as they shift to the southeast across the
rest of Southcentral. However, rain will not make much advancement
until Tuesday evening when the storm system sends a strong wave of
energy around the base of the low. This strong wave further tightens
the pressure gradient as ridging holds along the northeast Gulf. A
High Wind Watch has been issued with the afternoon package for
Portage Valley, Turnagain arm and Higher Elevations. Despite
model differences, all solutions point toward high winds in these
areas. Confidence is low for many of rainfall amounts and wind
for other areas because of the high dependence on the track of the
surface front and triple point low.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
An upper level ridge is positioned over the Southwest Alaska
region resulting in drier conditions Tonight, before the onset of
a strong fall storm tracking into the region by Monday. Meanwhile,
upstream a 120 knot southwesterly jet steak enters the eastern
Bering by Monday afternoon. This synoptic feature will drive a
Gale force weather front from the Bering into the Southwest
Alaska coastline during the early Monday afternoon time-frame.
Have continued the High Surf Advisory from Kuskokwim Bay through
the Hooper Bay region starting Monday afternoon as these Gale
Force winds move in around the time of high tide. Look for these
conditions to diminish as the fast moving weather front moves
onshore by late Monday evening.

This quick moving front will bring widespread rain with moderate
to heavy rainfall at times before this system exits the Southwest
Alaska region. By Tuesday afternoon a triple-point low forms near
the southern end of Kodiak Island. This system looks to move into
the Bristol Bay interior while the frontal system pushes north and
east right into a ridge sitting over portions of Southcentral.
This will strengthen the pressure gradients and produce strong
gusty southeasterly to easterly gap winds along the Aleutian
Range and into portions of the Bristol Bay zone.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
The sprawling occluded low east of Kamchatka Peninsula continues
its slow eastward track across the Bering Sea through Wednesday.
This system continues to push a Gale force front through the
Bering/Aleutians through Monday afternoon, before the front pushes
inland over the Southwest Alaska and the Alaska Peninsula region.
Southerly gap winds along this front will be strongest from the
Central Aleutians to the western Alaska Peninsula Tonight through
Monday. In addition to winds along the front, southerly moisture
advection will support rain and marine stratus/fog as the front
moves through the Bering and Aleutian Islands. As a stout
downstream ridge builds over mainland Alaska midweek and the low
becomes removed from the subtropical jet support to the south, the
system will stall and weaken over the eastern Bering Sea through
Wednesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The models continue to struggle with the rapidly developing triple
point low near Kodiak Island late Tue-Wed, and as a result forecast
confidence hasn't change significantly over the Cook Inlet region.
In particular for the waters of south Cook Inlet, guidance is
indicating anything from northerly to southwesterly Gale force
winds depending on the low position, so forecast confidence in
this area is very low on Wednesday. Further to the east, there is
much better agreement however with the associated front moving
into Prince William Sound, so expect widespread storm force winds
across that area through Wednesday. For Turnagain Arm and higher
elevations of the Anchorage Bowl, confidence has improved enough
for a High Wind Watch to be issued with the afternoon forecast
package as all guidance now indicates a significant pressure
gradient setting up on Tuesday evening.

Another concern from this system surrounds the potential for
persistent heavy rain and flooding along the Gulf Coast. In
particular for the Seward area, there remains some uncertainty as
to how long the heavy rain will last, however even the quickest
solutions are bringing at least 4-5" of rain in 12 hours, so
appears likely that this will be a significant rain event,
possibly heavier than the system from last Sunday. Its still a
little too far out at this point to determine exactly what
response this heavy rain will have on area rivers and streams,
but this should become more clear in the coming days.

Looking into later this week, the models have all trended
significantly weaker with next low that will rapidly develop and
intensify in the Gulf on Thursday. As a result it now appears
that this system will not become as significant as initially
thought a few days ago, but it will still bring active weather
to the Gulf and southern Mainland into Friday. This low will
likely bring a prolonged period of gusty winds and rain to the
Gulf Coast, and in particular Prince William Sound, that looks
to last into late this week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 101 125. High Surf Advisory 155.
MARINE...Gale Warning 150 155 160 165 170 171 172 173 174 175 176
178 179 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...EN
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD/RD
LONG TERM...DEK