Graphical Hydro Meteorological Discussion

000
FXAK68 PAFC 181241
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 AM AKDT Tue Jun 18 2019

.ANALYSIS AND UPPER LEVELS...

A broad area of low pressure in the Gulf of Alaska continues to
be the prevailing feature. However, the jet stream on the south
side of the low looks to be a harbinger of change, as it is
starting to slide the low center to the east. Meanwhile, an
Arctic low is descending down the the west coast and should park
over the southwest part of the state later today. This could make
for interesting day for convection. Otherwise, another easterly
wave is well seen on satellite starting to make its way through
southcentral AK.

&&

.MODEL DISCUSSION...

Models continue to generally agree on the pattern through the
short term. The pattern of easterly waves propagating around the low
pressure in the Gulf should be ending after today as the low
moves southeastward out of the Gulf and weak high pressure is
shown building over southcentral Alaska on all models. This agreement
in the latest model runs leads to high forecast confidence.

&&

.AVIATION...
PANC...VFR conditions will persist. Turnagain winds are expected
to diminish early this morning and leave winds light and variable
for the remainder of the TAF period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The generally northeast flow aloft remains over the region today
due to the presence of an upper level low in the Gulf of Alaska.
An easterly wave is embedded in this flow over the Copper River
Basin bringing in some showers. This wave will make it into the
eastern Susitna Valley and bring some showers as far south as the
Kenai Peninsula. However, it will stop moving westward and weaken
today as the low in the Gulf pulls southeastward. This will cause
the flow aloft to become more northerly over the Copper River
Basin and become light over the rest of Southcentral. This area of
weak flow aloft will be the area where a ridge will begin to
build over the area on Tuesday night and persist through Thursday.

This ridge will be strong enough to bring some clearing, but not
strong enough to put a good cap on the instability over the
entire area. Therefore there will still be some showers over
mountains in the afternoons and evenings and the Copper River
Basin may see a few thunderstorms Wednesday and Thursday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
The low over southwest Alaska will slowly track southwest through
the evening before finally stalling near the Kuskokwim Delta
coast. This disturbance will bring another round of thunderstorms
to much of southwest Alaska through this afternoon with the
highest chances around the middle Kuskokwim Valley. The
thunderstorms and showers will diminish overnight tonight. The
low will then linger near the coast through Thursday bringing
light showers to the area, primarily in the mountains.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Ridging over the western Bering will work to stall a front
approaching the area from making it much farther east than the
western Aleutians. It will bring some rain to the islands this
afternoon before weakening and stalling from the ridge. The
benign pattern will hold through Wednesday before the ridge
finally pushes east on Thursday. This transition will allow for a
new system to approach the western Aleutians Thursday night.

&&

.MARINE (Days 3 through 5)...

No major low pressure systems expected in the short term until
late this week, as a weaker system approaches Kodiak, and a
potential gale-force front over the Western Aleutians toward the
weekend. Across the eastern Bering Sea, a long period of light,
long duration/fetch westerly winds could produce some larger seas
than the wind speed would suggest.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Beginning the extended period forecast Thursday evening, there
will be a ridge axis over the eastern portion of the mainland of
Alaska with a weak upper trough over the eastern Bering Sea. A
weak warm front/low will be moving into the Gulf of Alaska but
will then be shunted southward as it tries to drift north on
Friday and Friday night. All the numerical global models and
statistical MOS guidance paint a pretty picture if you like summer
weather in Southern Alaska. The first significant "warm-up" looks
to be on tap as Southern Alaska heads into the weekend and next
week as the storm track shifts to the western Bering Sea and some
form of upper ridging and/or northerly upper flow builds over the
region. What this means is temps will likely push up into the 70s
(maybe even some interior 80s) with afternoon thunderstorms. Real
summer looks to be finally coming to the Southern Mainland.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
MARINE/LONG TERM...JA

539
FXAK69 PAFG 181316
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
516 AM AKDT Tue Jun 18 2019

.DISCUSSION...

Synopsis...Isolated thunderstorms and showers will continue south
of a line from Eagle to Fox to Ruby in the Central and Eastern
Interior during the afternoon and evening hours. Isolated
thunderstorms and scattered showers for the Middle Yukon Valley
south of Galena, the Interior Seward Peninsula, and the lower
Yukon Delta the next couple days. Warmer and drier conditions over
much of the forecast area as ridging aloft builds over the state
from the northwest and the south. A weather front will move south
to the Central Arctic Coast early Wednesday morning bringing low
stratus ceilings to the Central and Eastern Arctic Coast by
Wednesday afternoon. The Arctic Plains will remain warm and dry
with partly cloudy conditions.

Models...18/00Z solutions are in good agreement through 48 hours,
then have some issues with the low over the Southwest Mainland
breaking down. Precipitation solutions are in good agreement, so
will use a blend leaning toward the NAM, with a nudge to the SREF
to increase probabilities. Maintaining continuity with the wind
forecast by only nudging the current database with the NAMDNG.
Convective indicies showing more instability than the last few
days, especially in the Lower Yukon Delta with the upper level low
in the area Lifted Indicies are 0 to -2 and CAPE values area as
much as 400 J/kg. The remainder of the areas south of a line from
Eagle to Livengood to Huslia to Shishmaref has marginally unstable
conditions that will produce isolated convective activity.

Aloft...At 500 hpa...The stacked 516 dam low that has been over
the Eastern Beaufort Sea is finally moving off to the northeast
over the Canadian Archipelago dragging the trough over the state
over the Yukon Territory. A 550 dam low that developed over the
Eastern Brooks Range has move over the Lower Yukon Delta this
morning at 548 dam and will move over Bethel this afternoon at 556
dam. Ridging is building in over the Northwest Arctic Coast,
Arctic Plains, and south over the Central Interior this morning as
a 567 dam high develops over the Southwest Arctic. By this
afternoon the high will move over the Northwest Arctic Coast with
a ridge axis extending southeast over Anaktuvuk Pass and Eagle. By
Wednesday morning the low over Bethel will weaken to 558 dam,
while the high will move southeast over the Central Brooks Range
at 569 dam with a 569 dam high over Glennallen and ridging
extending south over the Pacific. A wave spinning around the low
in the Canadian Archipelago will sweep south to lie along 75N. The
wave will continue southeast to be over the Eastern Arctic Coast
by Wednesday afternoon. As the wave continues to dig south,
ridging will build north over the Western Arctic Plains, and the
Northwest Arctic Coast, while ridging over the Central and Eastern
Interior builds to 574 dam. At 850 hpa...Temperatures over the
forecast area generally +5C to +10C and will be warming to +6C to
+13C by Wednesday afternoon and continue to warm through Thursday
to +8C to +15C over most of the area. The exception will be the
Lower Yukon Delta which will cool Thursday to around +3C. The
warmest temperatures will be over the Eastern Interior and the
Eastern Brooks Range Thursday.

Surface...A weather front will persist along the north slopes of
the Alaska Range with a 1008 mb low developing in the Upper Tanana
Valley, a 1007 mb low in Middle Tanana Valley, and a 1003 mb low
in the Lower Yukon Delta. High pressure over the Arctic will
weaken as another weather front moves south into the area, then
east. A 1020 mb high will develop over the Western Arctic and move
over the Arctic Coast Monday. A 995 mb low in the North Pacific
will move to the southwestern Gulf of Alaska Monday. Weak high
pressure will persist over the Southeast Panhandle.

Arctic Coast and Brooks Range...Some stratus and fog east of
Point Barrow along the Coast will slowly pull offshore this
morning. Mostly clear inland over the Plains with warm and dry
conditions. To the west of Umiat temperatures will rise into the
lower 70s today with Relative Humidity values falling to around 30
percent. Onshore flow will limit temperatures within 20 miles of
the coast east of Wainwright to the upper 30s and lower 40s for
highs today. Winds generally northeast to east at 5 to 15 mph with
slightly stronger winds on the northwest Arctic coast at 10 to 20
mph with some gusts to 25 mph. A weather front will move south to
the Arctic Coast

West Coast and Western Interior...Will be a fairly active day for
thunderstorms and showers in the inland Lower Yukon Delta, south
of Galena in the Middle Yukon, and the Inland Seward Peninsula.
Warmer and drier over the next few days in the Noatak and Kobuk
Basins and from Galena north in the Middle Yukon Valley. Near Red
Flag conditions in the Noatak and Kobuk Basins. Winds generally
less than 15 mph, but expect some gusty winds, and small hail with
thunderstorms.

Central and Eastern Interior...Warmer and drier over the Northern
Interior today will spread southeast tonight and Wednesday.
Isolated thunderstorms and showers mainly south of a line from
Eagle to Fox to Ruby today. Winds generally light and variable as
they swing around from northeast to west.

&&

Coastal Hazard Potential Days 3 and 4...None.

&&

.Fire Weather...Warmer and drier conditions will spread over the
forecast area over the next couple days as ridging aloft builds
over the state from the northwest and from the south. Increased
potential for wetting rains in the Lower Yukon Valley south of
Galena, and the Lower Yukon Delta with scattered showers and
isolated Thunderstorms. Also expect isolated thunderstorms and
showers mainly south of the Yukon River and on the Seward
Peninsula. Low Relative Humidity values are also expected in the
Arctic Plains with values falling into the 20s. Relative Humidity
recovery overnight will be good.

&&

.Hydrology...Walker Fork of the Fortymile River saw a jump of
about 1.5 feet Monday, but has leveled off and will be falling.
Smaller Creeks in the Goodpaster, Tanana, and Fortymile basins
rose quickly as well Monday, but there have been no reports of any
being out of banks. Rainfall has ended, and all will be falling
the next few days. Expecting some heavier rainfall with
thunderstorms and showers over the Middle Yukon Valley south of
Galena, and the Lower Yukon Delta, so expect some streams to run
high the next few days.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

None.

&&

$$

SDB JUN 19

175
FXAK67 PAJK 181430
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
630 AM AKDT Tue Jun 18 2019

.SHORT TERM...A weak low that passed through the southern
panhandle has pushed into Canada and has begun to dissipate.
Onshore flow behind this system will continue to mire the region
in highly variable ceilings and rain for much of Tuesday.
Beginning in the afternoon, precip chances shall begin to lessen
in a North to South fashion into Wednesday. Wednesday does look as
though it should dry out some with largely diminished precip
chances but still fairly cloudy. Some potential does exist for a
retrograding wave to come into the region from Canada during the
day which could kick off some showers in the East. Currently,
there does not appear to be enough chances for any sort of
clearing to potentially build up some instability in the
potentially affected areas, therefore, thunderstorms are not in
the forecast. Will need to continue monitoring the situation for
future forecast packages, but as of now it seems unlikely.
Overnight Wednesday, weak ridging will build into the region,
leading to a Thursday that looks like it will be the pick day of
the week.

Winds through the inner channels look to be of minimal issue for
the forecast period with many locations topping out at around 15
kt early Tuesday then diminishing. The lone exception will be in
Northern Lynn Canal where the pressure differences are supporting
small craft criteria. Through the coastal waters, a low well out
in the Gulf will push seas to small craft criteria in zones 41 and
43.

Not too many significant changes to the forecast expect to bump
the winds in Lynn Canal. Aside from that, any minor changes deemed
necessary, nudged toward GFS per the previous shift to keep with
consistency. Overall forecast confidence is above average.

.LONG TERM.../Thursday through Tuesday night/...An upper level
ridge at the start of the long range forecast period will give way
to a progressive upper low on Friday. This will open the door to
an extended period of unsettled weather beginning Friday night.
At this time, it looks as if a front will push inland over the
outer coast late Friday night. Chance PoPs or better for the
coming weekend - sorry about that.

Northwesterlies over the eastern Gulf on Thursday will give way
to pre-frontal southeasterlies on Friday, but remain at or below
20 kts. Temperatures will continue to be seasonable in spite of
the wetter than normal weather around the solstice.

Updated pressure and wind early on with a blend of Canadian,
ECMWF, and GFS then used WPC for Saturday onward. No changes to
temperatures. PoP adjusted using SREF and GFS through Saturday
night, then WPC. Overall confidence is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ012.
Small Craft Advisory due to Seas for PKZ041-043.

&&

$$

JDR/Fritsch

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