Flood in Alaska, July 1 to 2, 2016

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
533 AM AKDT FRI JUL 1 2016

.SHORT TERM...The biggest story over the next 24 hours is the
ongoing glacial dam release from Suicide Basin into Mendenhall
Lake and River. This will be covered further in the hydrology
section below.

As for the weather, the main feature is a 1000 mb low pressure
system currently in the southeast gulf which will gradually weaken
while moving north to near Cape Fairweather by late tonight. A
secondary wave of low pressure will develop southwest of Haida
Gwaii late tonight but is expected to remain south of the area.

Stratiform rainfall is currently ongoing across the southern half
of the panhandle aided by warm air advection in association with
the advancing low. This will continue to spread northward through
the day reaching the Juneau area this morning and the far northern
panhandle this afternoon. Precipitation chances will remain high
throughout the next 24 hours across all of Southeast Alaska.
Expecting rainfall totals to generally range from one half of an
inch to an inch with heaviest amounts over the southern panhandle.

This system will enhance winds over the southern half of the area
but am only expecting 10 to 20 mph for the land areas and 20-25 kt
for the inner channels. Decreased winds across the far northern
panhandle as a parallel pressure gradient to Northern Lynn Canal
will lead to lighter winds.

Used the 06z NAM and Hi-Res model guidance for updates to the
short term period. Forecaster confidence is above average.

.LONG TERM...Through the weekend, generally a zonal flow pattern
in place across the north Pacific aloft. The closed low at 500 mb
over the Gulf of Alaska weakens and moves into western Canada
Monday while a broad weak ridge aloft forms over the western gulf.
Weak to null flow aloft over the northern panhandle will be in
place headed into early next week. Long range trend for Southeast
Alaska looks to be for a development around mid week to the end of
the week over the gulf.

A surface low near Cape Fairweather is weakening, while a low
moving across the southern gulf along 50N and then curving north
across Haida Gwaii on Saturday. This will spread rain into the
southern half of the panhandle. Saturday evening the low will move
into British Columbia while the low off of Cross Sound dissipates.
The surface pattern across the gulf Friday into Saturday becomes
west to northwest. The potential for low probability showers from
onshore flow will exist along the outer coast Sunday into Monday.
With the main flow pattern to the south of the forecast area not
expecting a significant weather system for the next few days.

&&

.HYDROLOGY...Suicide Basin has released and a flood warning is in
effect for Mendenhall River and Lake until Saturday morning. The
current forecast crest of 11.6 feet is close to the previous
record value of 11.85 feet set in 2014. As of early this morning,
Mendenhall Lake had risen to a stage of 8.5 feet and the rate of
rise is steadily increasing as expected. The level in Suicide
Basin continues to fall rapidly. Residents near the lake or the
river should remain alert and keep track of updates to this event
as they are issued by NWS Juneau.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ033>036-041>043.
&&

TPS/Bezenek

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