National Weather Service United States Department of Commerce


136
FXAK68 PAFC 281234
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 AM AKDT Thu May 28 2020

.ANALYSIS AND UPPER LEVELS...

An upper level ridge from the Yukon border to the Alaska Peninsula
is pushing back against a semi-stationary stacked upper low in the
Northeast Pacific. Another upper ridge is building into the
eastern Aleutians from the North Pacific. An upper level low off
the Kamchatka Peninsula is pushing a front into the Central Bering
and Aleutians. The abundance of high pressure and weak pressure
gradients is keeping sensible weather in short supply this
morning. Some gusty southerly winds and rain in Adak and Atka
are the main topic of weather conversation.

&&

.MODEL DISCUSSION...

Models continue to agree on the Northeast Pacific low approaching
the Gulf of Alaska as high pressure recedes some. Thus, allowing a
series of easterly waves to propagate through the mean flow
between these two features. This will be the primary pattern for
the Thursday through Saturday time frame. Sunday things begin
shifting as an approaching low from the Aleutians begins to
interact with the Gulf low. There is some vague agreement between
models that this will continue the pattern of easterly shortwaves
impacting southern Alaska.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist at terminal
through the period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Saturday night)...
Offshore (northerly) flow will strengthen today across Southcentral
in response to a vertically stacked low moving into the Gulf of
Alaska. This will continue the warming and drying trend that began
on Wednesday. As inland areas warm up and become unstable expect
gusty winds and drier air to mix down to the surface, especially
over the northern Susitna Valley and northern Copper River Basin.
Offshore flow will also delay sea breezes along the coast which
will allow coastal communities to join in on the warm temperatures.
While the low levels will be quite dry, a leading upper wave
rounding the top of the Gulf low will combine with steep lapse
rates to initiate some isolated to scattered convection near the
mountains in the Copper River Basin. Storm motion will take these
showers (and possibly thunderstorms) westward across portions of
the Mat-Su.

The thermal trough will strengthen over interior Southcentral
on Friday while weak upper level waves continue to traverse
the region on the northern periphery of the Gulf low. Expect
a marginal increase in cloud cover and convection. The primary
corridor for showers and thunderstorms will remain the same,
from the Copper River Basin to the Mat-Su. However, will also
likely see a few showers for coastal areas as well.

Forecast confidence drops significantly for Friday night and
into the weekend due to a high level of uncertainty in the
amplitude and track of successive upper level short-waves.
The pattern favors cloudier and wetter conditions with a
likelihood of stronger "easterly waves" producing rounds of
steady rain. Stay tuned to forecast updates for the weekend
as we get closer and are able to better resolve where these
upper waves will track.

&&

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

An upper level ridge has built over southwest Alaska this morning.
A warming and drying trend associated with this feature will
continue for the forecast period. Expect weak instability
associated with a strengthening thermal trough following the
Alaska Range. This will increase the potential for thunderstorm
development this afternoon and into this evening for west of the
Alaska Range and into the Middle Kuskokwim Valley. The thermal
trough will continue to strengthen into Friday allowing for
increased instability across the region. This will lead to greater
chances for thunderstorms from west of the Alaska Range to the
lower Yukon Delta for Friday afternoon.

&&

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

A front associated with a low pressure system northwest of the
Bering Sea is bringing rain and increased winds to the western
Aleutians this morning. This feature will continue to propagate
eastward before it starts to dissipate Friday. Expect the front
to bring rain to the central Aleutians Friday and up into the
Pribilofs on Saturday before it completely dissipates. Another
low will move across the Aleutians to the south beginning
Saturday. This will bring increased winds, waves and chances for
precipitation to the Chain as it propagates to the east through
the end of the forecast period.

&&

.MARINE (Days 3 through 5)...
By Saturday, the low south of the Gulf will have weakened
significantly and then get absorbed by a new low late Monday.
There is a chance this new low could bring a barrier jet capable
of gale force winds to the north Gulf coast late Monday into
Monday night. This is uncertain as the low and front would have to
develop just right, but models are indicating this as a
possibility.

A front along the low on Sunday has the potential to bring an
area of gales along the eastern Aleutians on Sunday, but they
should be short-lived if they do occur.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The upper level low will have located itself along the Alaska
Arctic coast by Sunday. It will then remain there through Monday
and then move northward into the middle of next week. As this
happens, the upper level trough which will extend across Southwest
Alaska through the weekend will move south of the state setting
up easterly flow aloft for the weekend through the middle of next
week.

This pattern sets us up for easterly waves to move across
Southcentral and Southwest mainland Alaska. This will produce
more cloudiness with chances for showers over the region. Some
stronger upper level waves coupled with local areas of instability
and sunshine may spur isolated thunderstorms during the
afternoons, but details are too far out at this time to specify.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 174 175 176 413.
FIRE WEATHER...Red Flag Warning 145.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...LTB
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CK
MARINE/LONG TERM...EZ/MK



000
FXAK69 PAFG 282150 CCB
AFDAFG

Northern Alaska Forecast Discussion...CORRECTED
National Weather Service Fairbanks AK
150 PM AKDT Thu May 28 2020

.SYNOPSIS...A pleasant early summer day across the Interior and
West Coast with some isolated thunderstorms/showers devloping in
the Eastern Interior. Stratus will continue to hang on over the
Arctic with some patchy fog. Breakup continues in the Arctic with
flowing water in most channels. Temperatures warming. Winds
generally light this evening will become northeast and increase
on Friday and will continue into Saturday over the Interior and
the Arctic.

&&

.DISCUSSION...
The 12z model suite initialized well against the 12z surface
analysis and verified well against the 18z surface analysis.
Model spread on system location and strength is minimal in the
short range and remains reasonable in the mid range as well as the
extended range.

On the surface, a 1028 high pressure system north of Point Barrow
will continue to strengthen and move south over the eastern North
Slope into the weekend. This combined with a strengthening thermal
trough over the Copper River Basin and Southcentral Alaska will
produce gusty northeast winds over much of the interior,
especially over the Yukon Flats and Middle Tanana Valley. High
pressure continues to build over the West Coast and will set up
over the Arctic Coast tonight with a 1032 mb high drifting south
and east to be located just 200 nm northwest of Demarcation Point
Friday afternoon. Broad low pressure will persist south of the
Alaska Range with a 998 mb low 500 nm south of Yakutat. A decaying
weather front will merge with the Thermal trough as it slides
north into the Southern Interior Saturday night. This front will
be the focus for isolated thunderstorms on Friday and Saturday.

Arctic Coast and Brooks Range...Stratus and patchy fog continues
on and off with the northeast to east flow persisting across the
area. Winds 5 to 20 mph with the strongest winds southwest of
Point Lay. Temperatures warming with highs in the mid 30s to mid
40s, and lows in the upper 20s to mid 30s.

West Coast and Western Interior...The clearing this evening will
continue over night afternoon. Clouds will increase as well as
chances for showers and thunderstorms over the much of the Western
Interior Friday afternoon and over the southern portions of the
Western Interior on Saturday. Winds variable to 15 mph, but will
increase and become northeasterly over the Western Interior
Friday afternoon and again on Saturday afternoon and evening.
Temperatures will continue to warm with high temperatures in the
upper 60s and lower 70s on Friday and in lower to mid 70s on
Saturday.

Central and Eastern Interior...Pleasant early summer day with
isolated thunderstorms/showers in the Fortymile Country and Upper
Tanana Valley this evening. Highs tomorrow upper 60s to middle
70s warming to the 70s for most areas Saturday. Isolated
thunderstorms/showers along the north slopes of the Alaska Range
Friday and Saturday. Winds from the northeast will be picking up
Friday afternoon and evening and will pick up again on Saturday
afternoon and evening. with near Red Flag conditions developing in
the Middle Tanana Valley, the Yukon Flats as well as zone 221.

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

&&

.FIRE WEATHER...Warmer and drier over the next few days with a
slight chance/isolated thunderstorm activity. Red Flag Watch
continues for Friday and Saturday for zones 220, 221 and 222.
Northeast winds will be increasing Friday afternoon and continue
through Saturday with near Red Flag conditions during the
afternoon and evening hours mainly south of the Porcupine River
and south and east of the Yukon River.

&&

.HYDROLOGY...Breakup continues in the Arctic with water running
in most channels. A small ice jam was reported with minor flooding
of low lying areas, but no impact to assets at this time. Interior
and West Coast waterways continue to fall slowly. For the latest
river information go to www.weather.gov/aprfc.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch for AKZ220-AKZ221-AKZ222.

Small Craft Advisory for PKZ210.
&&

$$

CCC MAY 20


313
FXAK67 PAJK 281713
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
913 AM AKDT Thu May 28 2020

.UPDATE...Showers have been more aggressive on their way north
into the Wrangell/Petersburg area. We elected to expand the reach
of these showers and have added isolated to scattered light rain
showers across the central Inner Channels and Upper Lynn Canal
this afternoon. High temperatures still look reasonable, but we
did adjust starting points this morning, as cloud cover held back
temperature falls overnight across the north. We also increased
winds for Sitka a little this morning in accordance with the
spinning low to the southwest.

&&

.PREV DISCUSSION......ISSUED AT ...445 AM AKDT Thu May 28 2020

SHORT TERM...The mature vertically stacked low south of the Gulf
of Alaska will drift very slowly northeast and stall south of the
gulf by Thursday afternoon. An old occluded front will be moving
northward through the southern panhandle and is expected to
spread spotty showers over the panhandle Thursday and Friday. Any
rainfall accumulations are expected to be light. Showers to
impact the northern Lynn Canal area on Friday will be moving out
of north central BC as the remains of convection that is expected
to cross over the coast mountains late Friday afternoon and
evening. Not anticipating more than just light rainfall totals
from those showers either.

Before the northern panhandle clouds up with thicker clouds
cutting off daytime heating, the northern inner channels are
expected to have one more day of warmer temps into the mid 60s on
Thursday while the Friday highs are expected to be in the upper
50s to near 60. The southern panhandle will be a touch cooler with
temps in the mid to upper 50s.

Gulf of Alaska wind speeds about the low are 25 to 30 kt and they
have spread into the western coastal water zones. Inner channel
winds Thursday to Friday are expected to be primarily under 20 kt.


Only minor changes were made to the forecast that was in place.
Did use some GFS for a nudge in the PoP field and adjusted the
rainfall for the northern panhandle to a lower value of expected
total as those storms will have already rained out much of the
rain on the eastern upslope of the coastal range in British
Columbia.

LONG TERM.../Saturday through next Thursday night/ As of 10pm
Wednesday. The barotropic low that has been lingering in the Gulf
for several days will persist through Saturday. By Saturday night,
model guidance begins to weaken this feature, ultimately washing
it out into a trough on Sunday. This weakening should increase the
PoP chances to the north as the offshore flow breaks down. Winds
out in the Gulf can also be expected to slow down as the pressure
gradient around the low weakens. Flow turns onshore across the
panhandle and should prime the entire region for pretty decent
chances for rain Sunday afternoon and through the first part of
next week. Heaviest rain ATTM looks to occur on Tuesday as a front
associated with another low moves toward the region from the
southwest. While models seem in pretty good agreement regarding
the timing of this frontal band, the actual strength of it is
still a bit too early to determine with reasonable certainty. It
is of note though that the potential for some fairly significant
precip amounts and impactful winds does exist with this system.
Onshore flow continues for the duration of forecast period
continuing chances for precip across the panhandle. High temperatures
during the forecast period will be slightly below normal during
the forecast period, but with limited diurnal swing at night due
to persistent cloudy conditions.

Forecaster`s model of choice was a blend of GFS/ECMWF and then a
lean towards WPC guidance to maintain continuity. Forecast
confidence that the period will be wet is above average.
Confidence in the wind forecast is less the average, particularly
for the Tuesday front.

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ022-041>043-051-052.

&&

$$

JWA/Bezenek/JDR

Visit us at http://www.weather.gov/Juneau