Storm Warning 51, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
254 PM AKST Sat Dec 5 2020

.SHORT TERM.../Saturday evening through Monday/ An area of low
pressure riding up along the outer coast and into Glacier Bay
today has spread moderate to heavy rain over much of the Panhandle
Saturday afternoon. The track of the low has jogged a bit east of
what was previously expected keeping the pressure gradient solidly
out of the north in Upper Lynn Canal. Rainfall rates and amounts
have been higher than expected as well across the Southern
Panhandle (3" in 12 hours for Ketchikan) leading to minor
flooding for Ketchikan streams and lakes. The heaviest
precipitation will follow the main low center this evening towards
the Upper Lynn Canal area. With temperatures near freezing and a
northerly gradient keeping the cold air locked in place, expect
snow to persist along the Highways and around sea level for
Haines. A Winter Storm Warning remains in effect for the Haines
Highway through noon tomorrow with 6 to 10 inches likely near the
border and lower amounts of 3 to 6 inches expected near sea level.
Colder air will stick around longer for White Pass, so the Winter
Storm Warning was extended through 3 AM Monday for the Klondike
Highway.

The next system to affect the region moves in right on the heals
of the Saturday system with little breaks in between.
Precipitation rates are expected to diminish late Saturday evening
through the early morning hours of Sunday before the front pushes
in increasing rainfall coverage and rates once again. Latest
guidance turns the pressure gradient southerly a few hours earlier
leading to a non diurnal temperature curve, especially around
Upper Lynn Canal. Expect low temperatures to occur just after
midnight and then rise overnight as the front pushes near. Expect
winds to turn southerly for Haines and Skagway after 12z, allowing
temperatures to rise and snow to change over to rain at sea level.
Another 1 to 2 inches of rain is expected with this front Sunday
to Sunday night across the entire Panhandle.

The more impactful story for the Sunday system will be the High
Wind potential across the south. As the storm force front pushes
through, a 70 kt low level jet will slam into the southern
Panhandle. The potential is there for those strong winds just
above the surface to mix down to the ground. For this reason, a
High Wind Watch has been issued for southern Prince of Wales
Island and Ketchikan Sunday morning through Sunday afternoon for
gusts to 60 mph.

Once the front passes through, a SW flow pattern will set up with
small waves increasing showers and rainfall rates at times.
Temperatures are expected to be above average in the 40s with
small diurnal curves. This pattern sets up Monday and will last
through the first half of the week.

.LONG TERM.../Mon through Saturday as of 10 pm Thu/ The long range
period continues to show strong indications of the active weather
pattern holding the course. Through the first half of the week a
broad area of low pressure in the Western Gulf will continue to
encourage onshore flow across the panhandle, keeping rain and
cloud cover at the forefront of the forecast. Some shortwaves
within this flow could bring chances of stronger winds and more
organized precipitation throughout the area during this time
period. Through Tuesday and Wednesday the low will slowly
dissipate. Afterwards, model agreement rapidly falls apart on the
timing and placement of the systems moving in after it.

Temperatures will be on a downward trend through the week. After
surging up with the more recent systems that have impacted the
area, CAA behind the Sunday front will begin a gradual cooling
trend which will be accelerated by cooler air moving along the
southern and western flank of the broad low in the gulf through
Wednesday. Some areas could see a return to snowfall at sea level
during this time period. Also of note is the possibility of some
periods of sun for parts of the panhandle during the second half
of the week. Though sharp disagreement remains, there are some
indications that a system on Wednesday or Thursday could track
South, which would bring Northerly flow to SE. Confidence in this
outcome remains low, and will need to be monitored.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind until 6 PM AKST this evening for AKZ026.
     Strong Wind Sunday morning for AKZ026.
     Strong Wind Sunday morning for AKZ023-027.
     High Wind Watch from Sunday morning through Sunday afternoon for
     AKZ027-028.
     Strong Wind from late tonight through Sunday afternoon for
     AKZ025.
     Strong Wind until 6 PM AKST this evening for AKZ023.
     Areal Flood Advisory until 3 PM AKST this afternoon for AKZ020.
     Areal Flood Advisory until 9 PM AKST this evening for AKZ028.
     Strong Wind from Sunday morning through Sunday afternoon for
     AKZ028.
     Flash Flood Watch through Sunday evening for AKZ018-019.
     Winter Storm Warning until noon AKST Sunday for AKZ019.
     Winter Storm Warning until 3 AM AKST Monday for AKZ018.
MARINE...Storm Warning for PKZ036-042.
     Gale Warning for PKZ031-035-041-043-051-052.
     Small Craft Advisory for PKZ012-013-022-032>034-053.

&&

CM/GFS

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