Scientific Forecaster Discussion

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Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska
538 am akdt Friday Apr 18 2014

Short term...satellite imagery this morning showing an open
wave trough moving into the Yukon that is the remnants of the low
pressure system from Thursday. Shower activity over the Panhandle
is diminishing from south to north this morning, still have a
500 mb vorticity maximum crossing the central and northern Panhandle early
this afternoon which will keep scattered showers into the
evening. Skies will start to see some clear breaks developing
through the day, however not expecting completely clear skies due
to middle level disturbances today and cirrus shield from the
advancing low tonight. High pressure ridge currently building
over the Panhandle with southerly push increasing winds over the
central and northern Inner Channels. These southerly winds will
drop down through the day as the ridge moves eastward into
British Columbia as a gale force low in the North Pacific moves
towards the southeast Gulf. As the low moves in winds over the Alaska
Gulf will increase to easterly 35 to 40 kts for the southern
portions and 25 to 30 kts to the north. Inner channel winds for
pints south of Frederic sound will remain southerly but increase
through the night with gales developing over Clarence Strait.
Points north of Frederick Sound will shift to the north as the
pressure gradient develops. The advancing low and front will move
rain into the far southern Panhandle again late Friday night
while the off shore flow for the central and northern Panhandle
will create a drying trend. Temperatures will be seasonably
normal in the upper 40s to low 50s today and in the low to upper
30s tonight.

Good model agreement this morning with European model (ecmwf)/NAM having the best
continuity and initialization. Used some WRF for winds over the
Inner Channels, especially Friday night with the stronger winds
developing for the southern regions. European model (ecmwf) kept in higher probability of precipitation
bit too long so used more NAM/GFS. Forecast confidence is above
average.

.Long term...Gale force low mentioned in the short-term will
enter the eastern Gulf Saturday afternoon with gale force
easterlies/southeasterlies ahead and to the east of its path. The
low will then start to pull away westward. A trough or associated
frontal feature will push into the southern Panhandle Saturday
evening. 850 winds should provide fairly good jet support for
strong surface winds in zone 27. Best times for this Saturday
afternoon/evening and again on Sunday morning. Again, the
gradient not great for Clarence Strait, but decided to use the
70 percent rule of 850 winds...and this translated as gale down
to the surface. Right now left out strong winds for zone 28.
Think it will be a better set up for stronger winds at Metlakatla
than Ketchikan. Winds across the northern Panhandle will be at
most northerly 20 knots.

The low itself will spread rain into the southern zones Saturday
and this will advance northward with the trough Saturday night.
The best chance for the rain arriving in Juneau will be Sunday
morning, but left it as chance in the wording for now. Saturday
should be a fairly nice day in the north. Folks should see some
sunny breaks through the mostly cloudy skies. Haines/Skagway will
be even sunnier. Anything that falls will likely be light...as
midlevel winds will be more southeasterly than south or
southwest. This is a much drier direction of rain for the
northern Panhandle. Then once again...rain chances will diminish
Sunday afternoon as the low pulls the rain back toward the Gulf.

Looking further out...more model divergence increases next
week...but overall general troughiness with periods of onshore
flow should mean chances of rain and mainly cloudy skies for the
period. Temperatures will generally be fairly seasonable for this
time of year.

Model of choice was European model (ecmwf) with some help from Gem regarding pop
advancement northward.

Ajk watches/warnings/advisories...
public...none.
Marine...Gale Warning for pkz036-041>043.
Small Craft Advisory for pkz012-013-021-022-033>035-051-052.

&&

$$

Prb/jwa