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FXAK67 PAJK 252205

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
205 PM AKDT Wed Apr 25 2018

.SHORT TERM...Large upper low continues to spin late this
afternoon over the Bering Sea while upper ridging is building
along the BC coast. Between these two systems is the remnants of
the front that brought 1.5 to 2 inches of rain to the Yakutat area
last night. This front is little more than a weak surface trough
but SW flow aloft continues to advect a narrow stream of moisture
over the northern/central Panhandle as evidenced by PW values
around 1 inch on GOES blended PW imagery. Southern areas have seen
partly to mostly sunny skies today with temperatures warming into
the mid 50s while the corridor from Sitka to Gustavus/Juneau as
seen chilly light rain with temperatures in the mid 40s.

Guidance indicates that the mid/upper ridge will continue to build
through Thursday. This will prevent the weak surface front from
advancing any further south. Instead, one or two weak waves will
run along the front through Thursday morning, keeping light
precipitation going through mid day Thursday in roughly the same
area as today. The front will eventually weaken and dissipate by
Thursday night as surface ridging begins to develop over the Gulf.
With continued weak onshore flow in the 925 to 850 mb layer
through Thursday, going to be hard to scour out the low level
moisture. Even Thursday night, as the flow turns NW`ly, while we
may dry out, clouds will likely hang around especially along the
coast and the northern/central Panhandle.

SW winds are currently gusting to 40 mph in the Skagway area with
25 kt southerly winds in N Lynn Canal. As the stronger SW flow
aloft diminishes this evening, expect these winds to diminish. By
Thursday morning, light winds are expected in most areas as the
gradient goes to almost nil. Kept 15 kt southerlies in Lynn Canal
Thursday afternoon due to thermal gradient but otherwise winds
should become more NW`ly by thursday night as surface ridging
builds over the Gulf.

Overall models are in good agreement and forecast confidence is
above average.

.LONG TERM.../Friday through Wednesday/...A large surface high
will be centered south of the Aleutians at the start of this long
range forecast period. Prominent ridge axis extends northeast
diagonally across the gulf. Farther north, a low near the Bering
Strait will be pushing a front east across the southern portion of
the state and along the northern periphery of the surface ridge.
Models are currently in significantly better agreement with this
set-up and changes were made in the extended forecast to reflect
this. Main change has been to increase the likelihood of rain from
Friday onward. The front referenced above will not make much
eastward progress beyond Cape Fairweather. However, a second
frontal feature will cross the central gulf beginning Saturday and
arrive along the central/southern outer coast by Sunday morning.
A third front will cross the gulf on Sunday and spread rain across
all of the panhandle Sunday night.

With the increases to PoP and based on model spectrum spreads,
decided to diminish daytime highs slightly. Overnight lows were
adjusted up even less. Net effect will be a diminished diurnal
range over the coming week.

Blended GFS, ECMWF, and the Canadian NH for pressure through
Sunday night. Used Canadian NH winds as a foundation through
Friday night, then primarily GFS. Preferred the SREF PoP field
early on, but then favored the upper level pattern depicted in GFS
for the second and third fronts and how they interact with the
surface ridge.

Forecast confidence in a continued wet pattern for the upcoming
week remains lower than average but is increasing.


.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 4 PM AKDT this afternoon for AKZ018.
     Strong Wind from 6 PM to 10 PM AKDT this evening for AKZ018.
MARINE...Small Craft Advisory for PKZ012.
     Small Craft Advisory due to Seas for PKZ022-041>043-051>053.




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