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FXAK67 PAJK 202223
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
223 PM AKDT Wed Jun 20 2018

.SHORT TERM...Strong mid and upper level ridge remains in place
almost directly over SE Alaska as of early this afternoon. A few
pieces of weak shortwave energy are attempting to rotate NW`ward
out of BC towards the southern Panhandle while a negatively tilted
upper trough is pressing NE`ward from the SW Gulf.

A SE`ly marine push is making its way slowly northward through the
southern Panhandle this afternoon. A weak surface circulation off
the west coast of Prince of Wales Island marks the leading edge of
the marine air. To the north of this weak circulation, winds have
remained offshore much of the day, allowing temps to warm into the
upper 70s to low 80s across much of the northern Panhandle. To the
south, an extensive area of marine cloudiness lurks through Hecate
Strait/Dixon Entrance and the SE Gulf. Daytime heating has kept
the low clouds at bay today but as the weak surface low slides
north this evening, expect low clouds to impinge on the outer
coast and southern channels tonight. Obs around Haida Gwaii
indicated cloud bases around 200-400 ft with areas of fog so added
mention of fog to the southern marine and land areas as well as
the outer coast from Elfin Cove southward for tonight and early
Thursday.

Convection has fired today over BC ahead of a weak mid level
shortwave. Stewart was sitting at 79 with a surface dewpoint of 54
this afternoon. Steep mid level lapse rates were observed this
morning on the Annette sounding so think there may be an outside
chance at a storm making its way westward toward the Hyder area
late this afternoon and evening. To maintain forecast consistency
decided to keep mention of thunder out of the forecast for now but
the evening shift can monitor convective trends and update as
necessary.

Thursday and Friday should be cooler with more cloud cover and a
few isolated to scattered showers each day as the trough to the
west shears out and comes across the Panhandle, shifting the ridge
axis into BC. Winds will generally remain 15 kt or less with the
exception of southerly small craft winds developing in northern
Lynn Canal each afternoon due to the combination of a
strengthening southerly pressure and thermal gradient. Overall
models were in decent agreement on the overall pattern with the
GFS being preferred overall.

.LONG TERM.../Friday through Wednesday/...As of 10 PM Tuesday,
the long term forecast`s primary impact will be a surface low
pressure system that forms as an upper level low pushes northeast
over the northern Pacific. This low looks to arrive in the
southeastern Gulf early Sunday morning. Precipitation associated
with the low will begin over the southern Panhandle first and
spread northward through the day. The low tracks toward the Dixon
Entrance on Sunday and pushes east of the Panhandle by early
Monday; however, precipitation may persist through the early part
of the week.

Outside of the low this weekend, Friday and Saturday will carry
some showers over the Panhandle. Greatest shower activity is
expected along the coast mountain range Friday; however, some
enhancement could occur along the outer coast and southern
Panhandle Saturday as the low begins to approach and some upper
level shortwaves pass over the area. Winds as a whole remain below
small craft levels with the exception of northern Lynn Canal
Friday afternoon where a combination of a tighter pressure
gradient and thermal drive may push wind speeds up to 25 kts.
Temperatures moderate with highs between the upper 50s and low 60s
through the extended forecast.

Not many changes to the extended forecast were made tonight as the
surface low was well represented by the inherited forecast. PoPs
were increased along the outer coast and over the southern
Panhandle late Saturday and early Sunday as the low pushes
ashore. Over the northern Panhandle, there is still a fair amount
of discrepancy in how far north the precipitation associated with
the low will spread so a chance of rain has been carried forward.
The ECMWF was favored to adjust the track and timing of the low
on Sunday. Behind the low there is still large variation between
models on whether a ridge builds over the gulf or another trough
moves into the area early next week.

&&

.HYDROLOGY...Temperatures have soared into the low to mid 80s over
interior portions of the northern Panhandle this afternoon. This
has increased the runoff from snow melt and glacier fed streams.
As a result, rises have been noted on the Alsek, Taiya, and
Chilkat Rivers as well as Mendenhall Lake. The Chilkat River is
expected to briefly go above minor flood stage early Thursday
before falling back below flood stage early Friday. A Flood
Advisory has been issued for the Chilkat River. All other rivers
are expected to remain below flood stage at this time.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Areal Flood Advisory until 7 AM AKDT Friday for AKZ019.
MARINE...Small Craft Advisory for PKZ012.

&&

$$

DEL/JB

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