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000
FXAK69 PAFG 272246
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
246 PM AKDT Sat May 27 2017

.DISCUSSION...
Synoptic scale features continue to perform pretty much as
earlier advertised. The old trough aloft from about Wrangel
Island to Cape Newenham to the vertically stacked 1005 mb low
southeast of Cold Bay will continue to weaken without filling
entirely. The aforementioned low will move northeast toward
Kodiak Island tonight then turn north on Sunday, moving over
our Western Interior on Monday. The weak (thermal) trough that
has developed over Interior Alaska will gradually strengthen,
likely becoming particularly enhanced as it gets better support
aloft on Monday, though the models remain unenthusiastic about a
corresponding increase in the gap winds through Alaska Range
passes.

High pressure will continue to build over the Beaufort Sea. As
often happens this time of year, much of the pressure gradient
between the developing ridge and the thermal low will be
found over our Arctic Coast, and will be strongest in the east.
Expect brisk winds to develop east of Kaktovik Sunday morning,
with winds as far west as Cape Halkett trending up through Monday.

The area of moderate convective instability that appeared over
our Western Interior on Friday is in about the same place today
and a bit stronger. Expect the best action from just west of 160W
to about 100 miles east of 160W from the Brooks Range south.
Little potential in areas with strong maritime influence. There
is also some potential over the Brooks range as far east as
Arctic Village. The best convective potential will likely be
in the Upper Noatak Valley and western Brooks Range on Sunday,
with maybe some late bloomers in our Lower Yukon Valley.

The models diverge fairly early in the mid-range. One discrepancy
of interest in our southeast Interior: the GFS would have 850 mb
temperatures around +11 C Thursday afternoon (implying surface
temperatures a tad too warm for those of us who are adapted to
sub-arctic conditions), while the ECMF and Canadian GEM models
are about 6 degrees C cooler at that time, though they have
comparable temperatures in the Canadian Yukon. Don`t bet the
farm on the GFS, though it is showing pretty good run to run
continuity.

&&

.FIRE WEATHER...
Wind and RH near flag criteria in portions of zones 223 and 226
this evening, but likely falling a bit short.

&&

.HYDROLOGY...
No issues.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Brisk Wind Advisory for PZK245 Sunday.


&&

$$

DJH MAY 17


000
FXAK68 PAFC 280111
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
436 PM AKDT Sat May 27 2017

.ANALYSIS AND UPPER LEVELS...
Water Vapor and IR satellite imagery shows a deep stream of
moisture advecting north across the Gulf of Alaska between an
upper low center southwest of Kodiak Island and high pressure
along the northeast Pacific. Clouds overspread the southern
mainland this morning with a few isolated showers across the
region as weak disturbances moved ahead of the upper low. This
system is currently stacked with a 1006 mb surface center pushing
a front into the southern gulf this afternoon. Marine winds are
primarily southeast in the small craft range along the gulf, with
lighter east flow along the Kenai Peninsula and Inlet. Inland,
winds are generally out of the south this afternoon with a few
gusts along the Knik Arm and across the Copper river.

To the west...scattered showers are developing across the
southwest this afternoon as a short wave moves inland from the
Bering. A ridge parked over the central Bering is trapping low
clouds over the central and eastern waters with a front pushing
along its western periphery.

&&

.MODEL DISCUSSION...
The main challenge in the forecast through Monday is the timing
of the front moving up from Kodiak Island. Models are in good
agreement with the general synoptic pattern through the short
term, however there are some minor differences on how the low
pressure system near Kodiak lifts north on Sunday and Monday. Only
minor changes were made as trends continue to bring the main
frontal passage across Southcentral late Sunday night into Monday
morning. The most noticeable changes in the inherited forecast
were wind adjustments for Southcentral as the ridge building along
the northeast gulf progressed slower than anticipated today.

A few changes were also made along the western Bering for winds
as all models came into agreement on a surface low center tracking
along the western waters to the central Aleutians Sunday into
Monday.

&&

.AVIATION...
Mid level clouds will continue to stream in from the gulf as the
next front moves up from Kodiak Island. A few showers are expected
to develop in the vicinity, however VFR conditions are expected to
prevail through the next TAF package as southeasterly flow
downslopes rain chances over the terminal. Winds are going to be
light until the front begins to push north. There is still
uncertainty of the timing of the front, however all models are
currently showing the frontal passage late Sunday night.

&&

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

An upper trough is digging into the NPAC southwest of Kodiak
Island this evening. A plume of warm air advection and a leading
surface warm front are moving into the North Gulf, and this will
increase moisture and precipitation rates along the coast. Cross-
barrier flow will be rather efficient at downsloping most regions
downwind of the coastal mountains and the Chugach/Kenai Mountains,
but some light showers will be possible given the mostly southerly
flow aloft and deep layer warm air advection through early
tomorrow morning. Heavy precipitation in excess of 2-4" will
pummel the coast through Sunday night before tapering off Monday
morning as the upper trough lifts north.

Monday will be more of a challenge as the shortwave trough lifts
north into Southcentral. The main feed of deep layer moisture will
cutoff, but so will downsloping. Forcing for mass ascent along
the trough axis will help support some inland rain/showers for a
brief period Monday, but timing of the upper low is still slightly
uncertain at this time.

Winds with this system will help accelerate increasing southeast
gap winds, especially through favored areas like Turnagain Arm and
gaps in the Chugach/Kenai Mountains. Winds will also increase to
25 to 30 knots through Prince William Sound, so small craft
boaters should prepare wisely. The gradient will weaken late
Sunday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
A stationary trough extending south through southwest Alaska will
keep an unstable environment over the area allowing for showers to
continue through the weekend. With this setup there is also a
chance for thunderstorms to develop around the Kilbuck Mountains
this afternoon/evening. As an upper level low south of the Alaska
Peninsula tracks north over southwest Alaska more thunderstorms
are possible in the corridor from Bristol Bay to the Lower
Kuskokwim Valley Sunday afternoon/evening and Monday
afternoon/evening. As the low diminishes and continues north,
showers will diminish around southwest Alaska Tuesday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
Ridging over the Central Bering will slowly track east through
Monday keeping low clouds over the area and also keeping precip
off to the west. The ridging will block a low over the western
Bering from pushing east which will cause it to stall near the
Western Aleutians into Monday night bringing rain to the area.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The unsettled period of weather that appears rather fall-like in
appearance will likely continue through next week into next weekend.
Although models are having a hard time pinpointing individual
features, the trend of the models continues to keep much of Alaska
under some form of cyclonic flow whether it be a trough or an upper
level low. There is some encouraging news in the extended as 850 mb
temperatures are expected to warm through Wednesday which will help
stabilize the atmosphere and likely cause a break of a day or two
without too much widespread shower activity. However, by Thursday
models prog another cold air surge advected back into southern
Alaska as a low in the Bering Sea dives south into the Gulf of
Alaska. This will likely increase shower coverage and intensity
Friday and through the weekend. The ECMWF is by far the most
optimistic model by trying to bring longwave ridging into Alaska
next weekend but unfortunately the trends of the models have
continued to be wetter so persistence seems like the right way to go
until the models start agreeing on a synoptic pattern change.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...MMC


128
FXAK67 PAJK 272249
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
249 PM AKDT Sat May 27 2017

.SHORT TERM...Mid and upper level flow remains S-SW onshore
through the short term period with the large scale ridge axis over
B.C.. This is evident looking at satellite imagery, showing high
clouds streaming in from the gulf. At the surface however, the
pressure pattern shows a high centered over the NE gulf with a
weak northerly gradient. Since this will be countering the upper
level flow, think that predominant winds will be sea breeze driven
in the afternoons then become light and variable (mostly north)
tonight. Sunday night into Monday the surface high pressure
weakens due to a weak disturbance passing by to the west, then a
high pressure ridge re-orients along the panhandle forcing a
predominantly southerly flow through the inner channels (although
remaining relatively light).

Overall the high pressure will keep the panhandle dry, but the weak
disturbance/front over the central gulf, mentioned above could
introduce some light rain to the Yakutat area late tonight into
Sunday morning, so have left in the slight chance POPs for that.
Otherwise think that it will just make for some more clouds. Cloud
cover was increased some on Monday as well, which resulted in
slightly cooler temperatures (low to mid 60s) compared to those
for Sunday (mid 60s to around 70).

Preferred the ECMWF and GFS for updates to pressure and resulting
wind field. Made local adjustments to wind for sea breezes etc as
mentioned above. This was the biggest change to the forecast, both
to lower speeds and adjust some directions through Monday.
Forecast confidence is average.

.LONG TERM.../Sunday night through Saturday/ Upper ridge just E of
the area will shift slowly E through the end of the week. Upper
trof/low will shift gradually E into the EPAC through the end of
the week as well. This should increase threat for precip over the
area with time, but models differ in individual shortwave features
which makes timing them difficult at this point. Left in previous
forecast which has a gradual eastward shift of systems toward the
area. Forecast confidence is on low side day to day though due to
the differences mentioned. That being said, does not look like any
strong systems will affect the area through the end of the week,
so impacts will not be significant except for possible SCA level
winds from time to time.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Frost Advisory from 9 PM this evening to 6 AM AKDT Sunday for
AKZ020-025.
Frost Advisory from 10 PM this evening to 7 AM AKDT Sunday for
AKZ019.
MARINE...Small Craft Advisory for PKZ052.

&&

$$

Ferrin/RWT

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