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FXAK67 PAJK 192331
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
231 PM AKST Mon Feb 19 2018

.SHORT TERM...Weather pattern in the short term will continue to
be dominated by amplified mid/upper ridging over the western Gulf
and interior of AK. Weak shortwave energy that brought 1 to 2
inches of snowfall to the central and southern coastal areas this
morning is currently continuing to push south towards the Pacific
NW of the US mainland this afternoon. As this trough amplifies
slightly, weak cold advection will set up tonight, and northerly
winds will respond accordingly. Not expecting any real marine
hazards with only 20 kt northerly flow in Lynn Canal.

A piece of mid level energy will break off from the strong system
over the Bering Sea and attempt to make a run over the mean ridge
by late Tuesday. This system will be moisture starved and rather
weak, tracking a bit further east than the system from this
morning. Some light snowfall is possible for a few hours over the
northern and interior Panhandle by Tuesday evening as this system
tracks overhead, with minimal if any accumulation expected.

Ridge will begin to flatten late on Wednesday night as a stronger
upper shortwave approaches from the Bering. Height falls over the
northern Gulf in response to the approaching upper trough will
induce a weak surface trough by late Wednesday night.
Additionally, strong W`ly flow aloft will allow surface pressures
to fall over the Yukon. This will set up a tightening southerly
surface pressure gradient by late Wednesday night with the
majority of the southerly push felt initially in the northern
Panhandle. Adjusted temps up on Wednesday night over the north
based on expected increasing cloud cover and increasing southerly
winds which may eventually have some bearing on precip type
concerns for Thursday. Still some model timing and strength
differences regarding this system so left Thursday alone for now.

Overall, good agreement with a low impact forecast through
Wednesday.

.LONG TERM... / Wednesday through Sunday as of 9 PM Sunday/ A
ridge of high pressure continues to remain in place over the Gulf.
A shortwave and its associated surface low will reach Alaska`s
mainland by early Thursday, pushing southeast over the panhandle
and dying by late Thursday night. The ridge looks to flatten later
this week and bring in another system Saturday and another
potential shortwave into the day 7/day 8 timeframe.

Changes to pressure were mostly the result of a GFS/ECMWF blend
early on and continuing with some WPC after Friday. Today`s WPC
discussion mentions not using the GFS in their own blend due to a
much faster track for Thursday`s system than previous model runs.
However, the GFS seems to line up quite nicely with the ECMWF for
the mid-week time range. Despite a tightening pressure gradient
over the northern panhandle, wind speeds were decreased locally
based on MOS Guidance. And as Thursday`s system ramps up, winds
over the Gulf were increased and will easily reach 35 kt.

Temperatures will be on an increasing trend, before dropping
steadily after Friday. To go along with this trend, the NBM was a
nice middle ground and matching well with both WPC and MOS
Guidance. Thus, maximum and minimum temperatures were raised
accordingly through mid-week.

The NAM/SREF was used early on for changes to POP, which
decreased POP`s for Wednesday`s system and confining any
precipitation/ flurries to the early morning hours. POP`s were
increased for Thursday with precip beginning in the late afternoon
and QPF increased slightly using a blend of the GFS/RFC. Snow
levels were once again raised, but with preliminary snow amounts
of up to 2-3" across the panhandle for Thursday.

Although confidence is still not great through the latter portion
of the period, we have seen a slight improvement compared to
yesterday.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...None.

&&

$$

DEL/SS

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