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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska
530 am akdt Tuesday Sep 23 2014

Short term...vigorous cyclone centered at 45.1n/140.6w is in the
process of occluding over the northestern Pacific this morning. As this
feature becomes vertically stacked...it is forecast to drift northward
toward haida gwaii through Wednesday. Meanwhile...progressive northern stream
will be located from interior Alaska into northwestern Canada. Embedded trough
within this flow regime will move from west-east during Tuesday
night...staying well north of the County Warning Area.

The passage of the northern stream wave will lead to strengthening
surface high pressure over eastern interior Alaska and the Yukon...which
when combined with low pressure approaching haida gwaii...will
yield a tightening gradient over much of southeastern Alaska. Gradient will be
strongest from Yakutat eastward to Skagway/northern Lynn Canal. As a
result...small craft winds are forecast to develop over northern Lynn
this evening...and possibly spread southward into southern Lynn by late
tonight. Elsewhere...north-northeasterly boundary layer winds will likely
strengthen to 25 knots from southern portions of marine zone 310 into 41
late this afternoon and persist through the night. Seas will
subsequently increase in response to the increasing winds...and a
S swell will spread north from the Pacific low into the southern outside
waters.

The strengthening pressure gradient in vicinity of Yakutat introduces
uncertainty regarding low temperatures Tuesday night. MOS guidance
indicates winds will become calm at Yakutat tonight...and if this
happens...then temperatures will likely fall into the low 30s
given the presence of a deep-layer of dry air/clear skies.
However...models may not be handling downslope winds
sufficiently...in which case...winds could stay up overnight
promoting boundary layer mixing and warmer low temperatures /mid
to upper 30s/. At this time...left lows for Yakutat in the middle 30s...and
also mentioned patchy frost given a killing freeze has not yet
been experienced.

Farther S...moisture will gradually spread northward from the northestern Pacific
low Tuesday afternoon and night. However...examination of forecast
soundings shows the boundary layer will be slow to
moisten...likely as a result of northerly-Ely boundary layer winds
emanating from the Coast Mountains. This...in addition to weak
synoptic/mesoscale forcing for ascent suggests that rainfall will
be light...and be confined to the southern Panhandle through tonight.

Long term...the vertically stacked low over the eastern Pacific
lifts slowly to about 300 nm south of haida gwaii and falls apart
by Friday afternoon. A weak off shore flow pattern from high
pressure over northwest Canada persists. While the low weakens and
moves to south of haida gwaii moisture will be pushing north into
the southern half of the Panhandle through he end of the week. Do
not expect large rainfall amounts from the associated trough
feature.

Meanwhile further west a low moves across the Aleutians spreading
front into the western Gulf of Alaska late Thursday and to nearly
the Panhandle by late Friday...bringing with it the next set of
rain. With this system the jet stream will start moving back into
the Gulf of Alaska rather than flow south it. Thus a more active
pattern back by the end of the month and into early October.

&&

Ajk watches/warnings/advisories...
public...none.
Marine...Small Craft Advisory for pkz012-013-041-042.

&&

$$

Garner/bezenek

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