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000
FXAK69 PAFG 242240
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
240 PM AKDT Mon Apr 24 2017

.DISCUSSION...
The current upper air pattern features a ridge that has persisted
over northern Alaska the past few days. Currently this ridge sits
along a Tanana to Northway axis. The ridge will begin to weaken
tonight in response to a shortwave moving up along the west side
of the ridge. This weakening will only be temporary as the ridge
will build back along the same general orientation late in the
workweek. A 510 dm low a 500 mb currently sits just east of Adak
and will remain quasi-stationary until Thursday. At the surface, a
low currently centered along 80 N north of Barter Island. A front
stretches southwest from the low to Point lay. This front will
move eastward tonight. A 1024 mb high sits in the Chukchi Sea
north of the Chukotsk Peninsula.

North Slope: The past few mornings we have seen dense fog all
along the Arctic Coast. With the aforementioned front moving east
current thinking is that any dense fog tonight and tomorrow
morning will be limited to areas from Deadhorse east. Suomi NPP
VIIRS shows a large area of stratus behind the front, so as the
front spreads eastward cloud cover will increase. There will also
be some flurries tonight and tomorrow for areas behind the front,
along with some areas of fog.

Central and Eastern Interior: It currently looks like today will
be the warmest day of the week for most of the Interior. A cooling
trend will begin tomorrow. A shortwave will move through the
Interior tonight and tomorrow morning bringing along with it some
scattered rain and/or snow showers. Any precipitation that does
fall will be relatively light and for most places will only fall
right as the shortwave is passing through. Cloud cover will also
increase tonight across most of the Interior, with mostly cloudy
skies persisting for much of the remainder of the workweek.
Southerly winds with gusts of 35 to 40 mph are expected from late
Tuesday morning into Tuesday evening in and near Alaska Range
passes.

West Coast and Western Interior: A tight pressures gradient is
bringing northeasterly winds with gusts of around 45 mph to St.
Lawrence Island. This will persist through early Wednesday.
Scattered rain and/or snow showers are expected Tuesday and
Wednesday for much of the west coast and western interior south of
the Bering Strait. Chances for showers will decrease on Thursday
for the western interior but will remain for the west coast.

&&

.FIRE WEATHER...
Cloud cover will increase tonight across the Interior with mostly
cloudy skies persisting for the remainder of the workweek for most
locations. Monday will likely be the warmest day of the week for
most Interior locations. Temperatures on Tuesday will be generally
cooler with higher minimum relative humidity values. Southerly
winds with gusts of 35 to 40 mph are expected from late Tuesday
morning into Tuesday evening in and near Alaska Range passes.


&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory for PKZ210.

Brisk Wind Advisory for PKZ220-PKZ225.
&&

$$

APR 17


612
FXAK68 PAFC 242352
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
352 PM AKDT Mon Apr 24 2017

.ANALYSIS AND UPPER LEVELS...
A persistent upper-level low controls the Bering Sea southward into
the North Pacific. This is bringing in broad southeasterly flow
over the Gulf of Alaska and most of the southern mainland.

Over Southcentral... Despite downslope, cross-mountain flow
today in the Cook Inlet region... light rain dampened the dust in
the lee of the mountains this morning with one trough travelling
west-northwest. A second wave looks to repeat the process again
tonight. Forecast challenges for Southcentral Alaska will be
timing and setup of any rainfall across the region, especially in
the lee of the Kenai and Chugach mountains.

Over Southwest Alaska and the Aleutians, the stacked low will
continue the widespread circulation of clouds and showers.
Larger forecast challenges may hold off until the end
of the week when models indicate a building ridge over the
Western Aleutians and a digging shortwave developing over the
North Pacific.

&&

.MODEL DISCUSSION...
Models initialized well this morning but diverge with solutions
over the Eastern Gulf of Alaska. The GFS resolves the surface
features into a singular low pressure center. Forecasters prefer
solutions keeping two circulations at this time. Therefore, the
NAM is the preferred model today.

&&

.AVIATION...
PANC...VFR conditions will persist with light isolated showers
continuing off and on through the night. Another wave of light
rain will develop overnight and persist until early Tuesday
morning. Challenges with timing and onset of any Turnagain Arm
winds will persist through the evening. Previous forecasts have
indicated arrival at the airport, however this is looking less
likely as the day goes on.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The overall forecast hasn`t changed too much with the new
forecast package but higher rain chances have been added to inland
locations this evening as a short-wave moves across the Gulf of
Alaska and Kenai Peninsula. Downsloping signatures have been quite
weak as observed on the 12Z and 00Z RAOBS from PANC. Models
really don`t develop much of a downslope signature until Tuesday
morning following the passage of the shortwave which will help
mitigate rain chances across interior portions of Southcentral
Alaska Monday and Tuesday. The gulf coast will continue to see
periods of light to moderate rainfall as the rainfall upslopes
along the coastal mountains. Gusty winds have developed along
Turnagain Arm and the Knik River Valley and will continue through
Wednesday before winds really begin to diminish. The gusty winds
through the Knik River Valley may decouple during the overnight
hours at time which may lead for a reprieve in gusty winds but
will quickly pick back up by the late morning hours on Tuesday.
Cloudy skies will continue to be the norm through much of the week
although some guidance is hinting at partially clearing skies
later in the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Broad low pressure across the Bering remains stationary through
Wednesday keeping flow generally out of the southeasterly
direction. Weak disturbances rotating around this low brings
continued chances for rain through mid week as moisture advects in
from the Gulf. Patchy fog development late night will be a
challenge across the Kuskokwim Valley and Delta as a weak boundary
stalls through Wednesday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A stacked low pressure system over the central Aleutians remains
nearly stationary through mid week bringing lighter flow with
higher chances for rain amongst the weak short waves rotating
through the upper level flow. Temperatures cooling in the low and
mid levels over the eastern Bering will create a steep
temperature inversion just off the surface tonight and persist
through early Wednesday. Areas of fog will develop across much of
the eastern Bering under the inversion and shift around under the
stagnant pattern.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Southwest flow will persist through the weekend and will keep
moderately unsettled weather across the region. Thursday and
Friday, a low pressure system will slide north and into SE Alaska.
In its wake will be an abundance of moisture and cloud cover
across Southcentral AK. Friday and Saturday a closed Bering low
becomes an open wave over the Southwest with a trough axis
swinging over Southcentral which will bring increased chances for
rain across the southern mainland.

Weak ridging will build in across the southern mainland into the
weekend. Come Sunday, SE Alaska is expected to see a similar
scenario pan out as what will be happening Weds/Thurs. Numerical
guidance begins to struggle in day 5 and later time frame with
run-to-run consistency issues and large ensemble spread across
the Bering. There are similarities in timing of an elongated
frontal/trough passage across the chain this weekend, but wildly
different solutions on how strong and where the attached low will
be.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...MC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...SS



000
FXAK67 PAJK 242304
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
304 PM AKDT Mon Apr 24 2017

.SYNOPSIS...A weather front across the northern gulf will lift
north across northern Southeast Alaska tonight. A ridge of high
pressure across the Panhandle will weaken and move east by Tuesday
morning. A gale force low will approach the eastern gulf Tuesday.

&&

.SHORT TERM...Weak lift in onshore flow has resulted in very light
shower activity or sprinkles across parts of Southeast Alaska
today, but rates and organization to rain bands appear to be
increasing as vorticity advects northward into tonight. Still the
main thrust of rain showers will be into the northeast and eastern
gulf coast with only a chance of measurable precipitation
spreading inland. Farther south, ridging behind the front will
begin to suppress clouds with possible clearing into Tuesday
morning. We have added some patchy fog mainly across the southern
and central Panhandle late tonight early Tuesday morning.
Confidence is higher for fog in the south.

Tuesday a developing system in the North Pacific will swing
northeastward into the eastern gulf by late Tuesday. While
agreement exists for a low, differences in track and position
emerge as early as Tuesday afternoon which lowers confidence in
some details of the forecast. A more easterly track toward Dixon
Entrance like the ECMWF will slow rain`s arrival into the southern
Panhandle. A westerly track would increase the rain`s efficiency
of driving northward across the Panhandle. Thus, the chance of
rain for the north may become bona fide light rain earlier.

We have kept the stronger winds across Prince of Wales Island but
reduced them for many areas across the northern Panhandle as
gradients will be small. Winds will increase along the coast, but
we do not anticipate gusts above 30 miles per hour from Sitka
northward late Tuesday.

From Wednesday into Wednesday night, model differences were
smaller as all agree the low will remain in the eastern gulf, thus
edits were more sparse during this time.

We used 12Z ECMWF/NAM for guidance especially from Monday night
into early Wednesday. Temperatures were warmed a few degrees over
the north Tuesday to account for ridging and sunnier skies ahead
of the system approaching from the south.

.LONG TERM.../Wednesday night through Sunday/ The low will slowly
lift north but will remain south of Sitka through Wednesday night
before weakening and lifting east into the inner channels. Rain
will remain a high threat south of the low but north it will be on
the drier side. After the low moves into Canada there will be a
period of onshore flow but towards the weekend it looks like the
northern half of the forecast area could be dry with a low moving
over Dixon Entrance. The southern areas will see a higher threat
for precip over the weekend being closer to the low and near an
area of deformation.

There is average forecaster confidence through the long term
period. The overall trend in the models is to have bits of energy
from the jet lift north into the gulf but overall most of the
weather systems will be south of the area. For any changes done to
the forecast the 00z nam, and 00z gfs was used through Thursday
and then WPC after that.

&&

.AVIATION...Predominately VFR conditions today with areas of lower
clouds along the southern panhandle, western Baranof island as
well as the northeast gulf into the Yakutat region of MVR for
ceilings...although Yakutat has lowered to 800 feet this
afternoon. Light winds up 15 kt for most of the areas...although a
few higher winds and gusts near the showers as they track
northward.


&&

.MARINE...The front moving north across the northeast gulf tonight
will briefly send winds to 25 kt in zone 52 tonight. We have kept
the gale force easterlies in the southeastern gulf coast for the
system approaching from the south late Tuesday as well as the
small craft for Clarence Strait. Winds to the north were lightened
through much of the period slightly.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind from Tuesday afternoon through Tuesday evening for
AKZ027.
MARINE...Gale Warning for PKZ041.
Small Craft Advisory for PKZ036-042-052.
Small Craft Advisory due to Seas for PKZ043.

&&

$$

JWA/ABJ

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