Winter Storm Warning 11, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
343 PM AKST Tue Mar 7 2017

.SHORT TERM...Upper level trough remains over the eastern AK gulf
and panhandle. Surface low centered mainly over Dixon Entrance
will begin to weaken and slowly shift to the east through
Wednesday. Tight pressure gradient between cold arctic high
pressure over the Yukon and the low to the south will begin to
weaken slightly Wednesday afternoon along with the Dixon entrance
low.

Outflow winds will remain but expected to be slightly lower than
previous days. Storm force winds have dropped to max gales or even
small craft levels. Still have long fetch of winds for Lynn canal
down to Chatham strait keeping high seas. Taku wind gusts picked
up to 60 to 65 mph over night due to well formed critical level.
Have dropped the High Wind Warning for Downtown Juneau has getting
a less well defined critical level from model soundings but still
strong inversion and moderate cross barrier flow. So with the
inversion and cross barrier flow expect strong Taku gusts up to 55
mph to last through the week.

Once again expect another night of very cold temperatures with
lows in the teens to single digits. Southern locations will be a
bit warmer due to cloud cover in the low 20s. Due to the cold
temps and winds have extended the Wind Chill Advisory for White
Pass out to Friday morning. Wind chills near sea level will be
down to 10 below zero for some locations.

The low to the south moved in bands of snow showers over the far
southern panhandle resulting in highly variable snow amounts.
Reports over zone 27 and 28 varied from a dusting to 8 inches.
The highly unstable atmosphere was conducive to the variable
showers. With the low still in place, bands of showers moving
over the southern regions will last through the early morning
before the low weakens. Snow amounts should be less than today so
only expecting an additional 1 to 6 inches through the morning.
Once again models have wide spread (not only between each other
but also run to run) on tracking down exactly where these showers
will be so did a broad brush for pop and a slightly less broad
brush for QPF. Ended the Winter Storm Warning due to the lower
snow rates and amounts but continued with a Winter Weather
Advisory due to remaining showers for zone 27 and 28.

GFS/NAM/ECMWf were close in position of the low and wind fields
but highly variable for pop and QPF. Made little change to first
two fields and as stated above a super blend/broad brush for pop
and QPF. Forecast confidence is average.

.LONG TERM...The very large upper low situated over the panhandle
through the short term and at the beginning of the extended range
forecast period will morph early on into a sharply defined,
strongly positively tilted upper trough Thursday night. By Friday
morning, a separate upper low will pinch off well to the southwest
over the northern gulf. A smaller upper low will remain over the
panhandle and western Canada through Friday morning but becomes
heavily sheared by Friday night. Models are showing another upper
low forming over the panhandle again on Saturday but then
retrograding west over the northern gulf on Sunday.

Net effect on sensible weather will be a continuation of colder
than normal temps under mostly clear skies and very strong
northerly/northeasterly winds outflow winds through the remainder
of the week. Chance PoPs re-enter the forecast as the upper low
retrogrades into the northern gulf. At that time, a developing
wave or triple point feature will spin up a closed circulation
south of the eastern gulf and push a front over the southern
panhandle from the south. Model agreement on a feature this far
out in the future is not very good when it comes to the details,
but the Canadian, the GFS, and ECMWF are all indicating increasing
chance for precip late this weekend. With the upper low moving
west over the northern gulf, the door will be open for warmer low
level air to advect in with this front. however, it looks as if
this will begin as another snow event for the southern zones
before transitioning to rain on Monday.

Updated Friday night and Saturday morning with a blend of GFS,
Canadian NH, and ECMWF for pressure Saturday and Saturday night.
WPC thereafter. PoP no factor until Sunday, at which time, GFS and
ECMWF were blended to the latest WPC. Over water temps adjusted
down to reflect maximum temps over the gulf in the mid 30s.
Overall forecast confidence is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 9 AM AKST Wednesday for AKZ027-028.
     Strong Wind through Wednesday afternoon for AKZ018-025.
     Wind Chill Advisory until 9 AM AKST Friday for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ012.
     Heavy Freezing Spray Warning for PKZ013.
     Gale Warning for PKZ012-013-022-031-051.
     Small Craft Advisory for PKZ011-021-032>036-042-043-053.
&&

PRB/Fritsch

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