Winter Storm Warning 14, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
622 AM AKST Thu Nov 8 2018

.SHORT TERM...A low pressure system centered over the north
central gulf will continue to drive our weather through Thursday.
Rain has been occurring across the panhandle all night, with the
exception of Haines and Skagway where snow has been falling. The
light N-NWLY wind has been key in these places to keep the
temperature in the upper 20s for snow. Elsewhere, breezy E-SE
winds have caused temperatures to warm overnight into the low 40s,
and even 50 degrees in Sitka! Due to the proximity of the low,
Yakutat has seen the greatest rainfall rates overnight. This will
continue today, even as things become more showery post front.

The 00Z GFS and ECMWF both led the low across the northern gulf
through Thursday night and into the north-central Panhandle by
Friday, and we favored their consensus. The Canadian offered a bit
faster solution, whereas the NAM was the outlier, taking the low
into the Panhandle late Thursday night. The track of the ECMWF/GFS
required edits across the northern Panhandle and lowered
confidence in the strength of a post-frontal ridge and the
assumption of stronger southerlies through Lynn Canal. Given the
fact that most winds across the northern Panhandle have been
either very strong easterly or weaker northeasterly, we elected to
remove the southerly small craft previously posted for this
afternoon and hold everything 20 kt and below for Lynn Canal.
However, confidence in the strength has fallen, and actual winds
may arrive much weaker than even 20 kt. Unfortunately, these winds
have a direct effect on the Haines/Skagway temperature and
snowfall forecast. If the southerlies do not come in time, snow
may last longer than expected. Likewise, if they arrive too soon,
a changeover to rain will come sooner. In addition, we shifted
Lynn Canal to northerly late tonight and Friday as the low pushes
onshore south of the region. We also tacked on a morning gale
warning in Stephens Passage to account for the stiff winds around
Skull Island that have been blowing all night. We also have strong
winds with gusts to 40 mph in the Ketchikan and Prince of Wales
Island areas early this morning with frontal passage. Once the
low moves ashore, weak ridging develops with 15 to 20 kt
westerlies over the gulf and lighter winds across the rest of the
Panhandle.

Expect snow to continue through the mid morning in Haines and
Skagway, so have kept the advisories in place with only minor
adjustments for todays accumulation due to snow lasting slightly
longer. However, due to warming temperatures aloft, there is a
chance for some freezing rain to occur before the low level winds
shift briefly to the E-SE in the upper Lynn Canal region. Have
added a mention of this possibility in the forecast and in the
advisory statement.

The upper level jet can be seen with satellite imagery by the
clouds being directed at the southern panhandle. As the jet
shifts south through tonight, the surface low will follow it and
subsequently weaken. Slight ridging is expected to build over the
gulf through Friday. This will help to scatter out the showers
through the day with some breaks in the clouds Friday night.

.LONG TERM.../Saturday through Thursday/...The upper ridge
shifting eastward from the Gulf Saturday into western Canada
Sunday will set the stage for an active fall-like weather
pattern. But uncertainty exists as to where exactly the greater
amounts of precipitation will fall.

A relatively large low pressure system will be positioned near
the eastern Aleutians and Alaska Peninsula late Saturday through
Tuesday. The initial associated front is expected to lift north
through the Gulf Saturday, reaching the outer coast later Saturday
night. Model solutions differ somewhat to the location where the
moisture plume will be directed, but the ECMWF has been the most
consistent lately, which has led us to shift the system a bit
further west. This would mean the bulk of the rain will be focused
on the NE Gulf coast, and the southern panhandle only seeing
slight-to-chance of rain Sunday. Monday could actually bring more
dry weather along the inner channels with a more southeasterly
gradient. But the N Gulf coast is likely to remain in the stream
of moisture with possible heavy rains at time, including Yakutat.

Multiple disturbances are likely to rotate around the upper low
through mid-week, but models differ handling the individual
details. Rain becomes more likely across the majority of the
panhandle Tuesday and Wednesday as the flow shifts to more of a
southwesterly direction. Forecast confidence is average through
the extended time frame.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 6 AM AKST early this morning for AKZ027-028.
     Winter Weather Advisory until noon AKST today for AKZ019.
     Winter Weather Advisory until 6 PM AKST this evening for AKZ018.
MARINE...Gale Warning for PKZ031.
     Small Craft Advisory for PKZ022-035-036-041>043-051>053.

&&

Ferrin/DDH

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