Graphical Hydro Meteorological Discussion

000
FXAK68 PAFC 020042
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
442 PM AKDT Wed Jul 1 2020

.ANALYSIS AND UPPER LEVELS...

In the upper levels, a ridge extends north from the Alaska
Peninsula to over the Chukchi Sea. To the east, an upper low was
over the eastern Brooks Range and to the west a low over the
Central Bering Sea. A 50-70 kt jet stream to the east of the
Bering Sea low supported a surface front extending across the
eastern Bering sea to the central Aleutians. Satellite imagery
showed fairly extensive cirrus flowing down the eastern side of
the ridge across Southcentral and lower clouds under the ridge
axis over Southwest Alaska. Evidence of strong subsidence under
the ridge was evident by strong temperature inversions on morning
soundings and surface observations of low stratus and fog across
the Southwest Mainland. Rain and strong southerly winds were
observed along the frontal band over the eastern Bering/Aleutians.
Gusty outflow winds were evident across the eastern Kenai
Peninsula and portions of Prince William Sound.

&&

.MODEL DISCUSSION...
Models are in good agreement on the placement of synoptic
features through the short term. The main adjustments will be with
mesoscale winds with outflow conditions along the north Gulf Coast
and the eastern Kenai Peninsula.

&&

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

&&

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

A warming and drying trend will be the theme as we head into the
holiday weekend. A ridge of high pressure will build across the
mainland during this time, with 850 mb temperatures climbing from
+3 C this morning, to +11 by Saturday afternoon. This warming
aloft will translate to afternoon highs increasing each day
through the 4th of July, with highs in the 70s being fairly widespread.
How much into the 70s remains the question though, as several
disturbances in the westerly flow aloft across the region will
bring bursts of increased moisture and resultant cloud cover.
There could even be a few light showers for portions of the Alaska
Range and Talkeetna Mountains as this moisture is augmented by
orographic lift and diurnal heating.

The tricky part to the high temperature forecast is timing of
these shortwaves, as the current model runs indicate morning
sunny skies and then increased cloud cover by evening scenario,
or vice versa. This can be seen somewhat on Thursday but more so
Friday and Saturday. This leads to a high "bust" potential, as if
the clouds clear earlier than currently projected or arrive later
than anticipated, we could see highs in the upper 70s to near 80
degrees by the start of the weekend area-wide, as an offshore flow
pattern develops.

That said, the latest numerical guidance trended the temperatures
down for the afternoon by a good 5 degrees or more compared to
what we had in the forecast. Given the forecast uncertainties
described above, took a middle ground approach and lowered them a
few degrees for now, and we`ll see how later runs play out.

&&

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

A front associated with a large Bering Sea low is pushing toward
the Bering Sea coast tonight. The weak ridging ahead of this low
will flatten, and moisture from the front will push over the
southwest mainland tonight, bringing with it ample cloud cover,
cooler conditions and increased rain potential. Following the
front, the ridge builds back over southwest Alaska, however, the
upper level southwest flow will continue to allow for clouds to
spread over the top of this ridge.

Thursday night another upper level trough will move across
the top of the ridge over southwest Alaska bringing more clouds
and an increased chance of rain. The ridge builds back Friday over
southwest Alaska, and warmer air aloft moves over the southwest
mainland. This will bring warmer temperatures to the area Friday.
A strong front is pushing across the Bering Sea and will be along
the Bering Sea coast by Saturday morning, thus returning the
region to the cool cloudy conditions.

&&

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

A near gale force low is currently over the western Bering Sea
pushing and front to the Bering Sea coast. This low will rapidly
move north northwest into Siberia as a ridge briefly builds in
behind it through Thursday evening. A north Pacific low will move
to the western Aleutian as a low moves into the western Bering Sea
Friday morning. These lows merge Friday night and will produce
near gale force wind in advance of the associated front across
the Central Aleutians and central Bering Sea. The overall theme
for the next several days will be unsettled wet and windy weather
for much of the Aleutians, Alaska Peninsula and Bering Sea.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska: Easterly winds along the North Gulf Coast are
expected to switch to Westerly winds across the Gulf by Mon.
Confidence is good the winds remain below small craft levels.

Aleutians and Bering: An elongated Western Bering low slips
towards Northern Kamchatka. Confidence is good for widespread
small craft winds and waves spreading from the Aleutians into the
Bering through Mon with pockets of Gale force winds with higher
waves across the Central Aleutians dissipating through Sun.

&&

LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

The strong upper level ridge over western Alaska Sunday weakens
through Wednesday. This allows short waves spinning off of the
Bering Sea trough to progress eastward across the Mainland. This
pattern change will bring intrusions of moisture from the west
resulting in cloudier conditions, increased chances of
rain/showers, and a lowering of daytime high temperatures across
the southern Mainland. Although the model trends are similar with
the weakening of the upper ridge, differences in solutions will
pose a problem in timing systems. So confidence is low on exact
timing but fair to good on a trend toward more clouds, cooler
temperatures, and chances of rain.

With the main upper low center and trough holding over the Bering
Sea, expect generally mostly cloudy conditions with periods of
rain/showers and gusty winds.

&&

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

&&
$$

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SA
MARINE/LONG TERM...MK/BC

000
FXAK69 PAFG 012252
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
252 PM AKDT Wed Jul 1 2020

.DISCUSSION...

.SYNOPSIS...Showers on the West Coast will be pushing east this
evening, but will remain generally west of Fairbanks as the front
decays and is pulled back to the northwest Thursday night. High
pressure will be building in over the Interior Thursday with
clearing skies and warming temperatures.

&&

.DISCUSSION...

Models...The 01/12Z solutions are in good agreement short term,
but diverge on the location of the lows over the Bering Sea and
Arctic by Saturday, but not surprising. ECMWF has been jumping
around midrange and extended, so will lean more to the GFS, then
the Ensembles later in the forecast. Surface solutions
initialized well against the analysis. Convective indicies are
poor. Will use a blend for the winds with the only concern some
of the solutions may be a bit light out west. Temperature
solutions are a bit challenging, so will not be making too many
changes unless necessary.

Aloft...At 500 hpa...Ridging is building north over the West Coast
and Western Interior, while a 556 dam low has parked itself over
the Eastern Brooks Range. Troughing to the West is moving toward
the coast with a 535 dam low near the Gulf of Anadyr Thursday
morning. Ridging is also pushing south over the Central Arctic for
a 576 dam high near the Pole. By Friday morning ridging will move
over the Central part of the state merging with the ridging over
the Arctic, while the low over the Brooks Range moves over the
Northern Yukon Territory at 549 dam. The low near the Gulf of
Anadyr will move northwest over Yakutia. At 850 hpa...The 0C
isotherm is north of the Brooks Range and will be northeast of
the state by Thursday evening as warm air is pulled north and the
+10C isotherm moves over the Upper Tanana Valley. Temperatures
will be pretty steady over the West Coast, but will be warming in
the Central and Eastern Interior. The +10C isotherm will be over
the Eastern Interior and Eastern Alaska Range.

Surface...A weather front has moved to the West Coast and will
push inland tonight into Thursday, then is dragged to the
northwest as it decays. A 1025 mp high is over the Upper Yukon
Flats and a weak thermal trough is in the Tanana Valley. High
pressure over the Central Arctic extends south over the Central
and Eastern Arctic Coast. Weak trough of low pressure over the
Arctic Plain and Brooks Range continues to bring clouds to the
area, but will slowly dissipate tonight. By Thursday afternoon
high pressure will extend from Bristol Bay over the Central and
Eastern Interior, the Eastern Brooks Range, and Northwest to a
1032 mb high near 80N. The weather front over the West Coast will
be pulling back to the northwest as the low moves Northwest into
Yakutia. Weak thermal troughing will lie in the Tanana Valley and
the Upper Yukon Flats.

North Slope and Brooks Range...Decaying front remains in the area
with cloudy conditions prevailing for most of the area with a few
showers. Showers ending along the coast. Some clearing in the
Brooks Range. A front moving to the West Coast is spreading
clouds to the Northwest Coast. Winds northeast to east 5 to 20
mph tonight then increasing winds Thursday, especially east of
Prudhoe Bay where winds will increase to 20 to 30 mph and gusty.

West Coast and Western Interior...Cloudy with showers over most of
the area. Rainfall amounts up to 1 inch in the upslope areas
tonight, then and additional amount up to a quarter inch tomorrow.
Winds inland variable 5 to 10 mph, but approaching the coast winds
will increase to 10 to 25 mph with the strongest winds on the
Capes. Temperatures will remain on the cool side with highs in
the coastal areas only making it into the 50s and the inland areas
only seeing 60s through Friday.

Central and Eastern Interior...Isolated showers and thunderstorms
in the Northeast Interior this evening. The high clouds will stick
around, but expect some breaks. A front moving over the West Coast
will move into the Central Interior as it falls apart Thursday
night and Friday with a few showers generally to the west of
Fairbanks. Temperatures warming. Winds will be variable to 10
mph.

Coastal Hazard Potential Days 3 and 4...A strong low will spin up
in the Southern Beaufort Sea/MacKenzie Bay Friday night creating a
strong onshore push on the Eastern Arctic Coast. This may produce
a strong push of ice to the coast east of Prudhoe Bay impacting
vessel traffic as well as the coast.

&&

.Fire Weather...Showers in the west will keep things pretty quiet.
Drying condition in the Central and Eastern Interior through the
weekend. Some isolated thunderstorm activity this evening in the
Northeast Interior, otherwise it will be quiet through the
weekend. Relative Humidity values remain high, with excellent
overnight recovery, but they will dry to the 20 to 30 percent
range in the Central and Eastern Interior this weekend. No
significant winds expected through the weekend.

&&

.HYDROLOGY...River levels are running at elevated levels on the
Yukon River as the high water from the Tanana and the Upper Yukon
move downstream. No flooding is expected but sloughs and boggy
areas along the river may see some water move into them. No
significant rainfall expected through the weekend. For the latest
river conditions go to www.weather.gov/aprfc.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

Small Craft Advisory for PKZ200-PKZ210-PKZ220-PKZ225-PKZ230.

&&

$$

SDB JUL 20

000
FXAK67 PAJK 020323 AAA
AFDAJK

Southeast Alaska Forecast Discussion...UPDATED
National Weather Service Juneau AK
723 PM AKDT Wed Jul 1 2020

.UPDATE...After mid-afternoon temperatures did more than inch
higher than forecast for today, in line with still strong offshore
winds Thursday, we went ahead and pushed highs tomorrow up to the
low 80s for Juneau and Upper Lynn Canal. Considering we are
squarely under the influence of a very warm air mass, despite any
potential channel breezes developing Thursday afternoon, we feel
like these temperatures will not be difficult to reach. Mid 80s
are not out of the question away from the water in Upper Lynn
Canal. AMDAR Soundings out of Juneau Airport around 0230Z Thursday
(around one hour ago) reveal that 850 mb temperatures are merely
up to 8.9 C. Coupled with the strong offshore winds, we rose to
78 F this afternoon. Given some models are going up to 13 C at 850
tomorrow, albeit with slight weakening of offshore flow in the
afternoon, we feel strongly that the northern Panhandle will be
even warmer Thursday. Other than this, we went more optimistic on
sky cover this evening for Wrangell, Petersburg, and Sitka before
allowing clouds to re-enter from the east.


&&

.PREV DISCUSSION......ISSUED AT ...314 PM AKDT Wed Jul 1 2020

SHORT TERM...Afternoon satellite imagery shows continued clearing
across the bulk of the panhandle which has contributed to the
balmy temperatures much of SE Alaska is enjoying. The main weather
story continues to be the impacts of the developing inverted
trough over the Panhandle. A more northerly wind regime has taken
hold, and has helped scour the cloud cover from much of SE, as
well as contributed to downsloping winds in locations like Haines
and Skagway, helping to drive temperatures back into the 70s in
these locations. Another consequence of this inverted trough will
be generally dry weather for the panhandle through the short term
forecast period. Exceptions do exist, particularly for the
southern inner channels including places like Misty Fjords,
Ketchikan, Klawock, and possibly Petersburg and Wrangell. These
areas will see easterly wave shower activity increase through the
next 48 hours, though do not expect any substantial precipitation
accumulation at this time. The clear skies throughout the rest of
SE will allow daytime high temperatures to warm well into the 70s
at the surface across much of the central and northern panhandle
on Thursday, with 850mb temperatures approaching 13 C. Low 80s
cannot be ruled out yet, but would be dependent on local effects.

Apart from the dry weather, relative humidity values are falling,
particularly over the far northern inner channels. We are not in
a situation that warrants a Red Flag Warning, but conditions will
definitely becoming more conducive for fire weather. Fortunately,
any lightning associated with thunderstorm activity is expected to
remain on the Canadian side of the Coast mountains.

Winds have reached SCA in Lynn Canal, and look set to remain
blustery through Thursday night as a pressure gradient builds over
the northern Panhandle. Winds will also reach between 15 and 20
kt throughout most of the other inner channels, though it does
look like winds will begin to calm down on Friday.

Models remain in fairly good agreement. Overall forecast
confidence is average.

LONG TERM.../Friday through Wednesday/An omega block consisting
of two lows--one over the Bering Sea and the other the west coast
of North America--and a ridge sandwiched over the western Gulf of
Alaska will keep Southeast Alaska in more or less a static
weather pattern this weekend into next week.

The pattern favors drier northwesterly flow aloft and potential
lower pressure over Southeast and the eastern gulf. Thus, we can
also expect warmer than normal temperatures given weaker flow
through the Inner Channels and a tendency towards mean offshore
flow. Forecast challenges will periodically arise from poorly
discernible waves that support convection in Canada. While models
are bullish for showers across northern BC in largely upslope
flow, they continue to tone down threat of any reaching the Inner
Channels. We lowered rain chances for most of the weekend and
warmed temperatures slightly for the north where highs should
fall mainly in the mid to upper 60s. With thermal troughing
induced across the northern and central Inner Channels, the south
looks likely to find itself in a slightly cooler regime with
largely southerly flow opening up the marine atmosphere of Dixon
Entrance/Hecate Strait. Thus we limited temperatures across the
south to the lower to mid 60s with presumed cooler temperatures
along the immediate coast like Sitka.

As ensembles continue to indicate an overall upper atmospheric
pattern of northwest flow, we kept slightly above normal
temperatures into next week. This is in line with the CPC`s
expectation of above normal temperatures next week, which is quite
a change from June as we draw deeper into July. Those with
outdoor plans on the Fourth of July should be in luck, as only a
slight chance of showers exist for the southern and central
Panhandle.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ012-013-022-041>043-053.

&&

$$

JWA/GFS/JWA

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