Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
537 am akdt Tuesday Jul 22 2014
Short term...an upper level ridge is building along 145w or so
this morning as the low pressure system has now moved well S of
the forecast area. Return flow from the east around the low is
bringing middle and high clouds over most of the Panhandle this
morning. The clouds plus more drying than previously thought
yesterday has repressed most of the fog. Yakutat had strong
radiation and light wind for fog there.
Still thinking that some showers will move over the Panhandle
from the east today and later tonight. Introduced the risk of
thunderstorms along the eastern mountains: mentioned upper taku
near the border and zone 29. Model positive buoyancy values are
strong and watched lighting in b.C. To think a little might at
least hit the border. Also mentioned fog again for early Wednesday
morning with light wind and trapped moisture.
All models agree that the upper ridge will move over the
Panhandle by 12z Wednesday which sets up another upper flow change in
this progressive pattern Summer. Confidence high in this movement.
Long term...ridge of surface high pressure will become situated
over the Panhandle by Wednesday afternoon. This will aid in tightening
the pressure gradient over northern Lynn Canal resulting in southerly small
craft winds. Southwesterly winds up to 25 miles per hour also appear likely in
Skagway. Meanwhile...an upper trough will enter the Gulf...with a
surface frontal boundary approaching the northern/central coast Wednesday
evening. Atmosphere will begin to moisten ahead of these features
over Southeast Alaska...resulting in increasing clouds and rain chances
spreading inland...becoming widespread by Thursday afternoon into Friday.
Temperatures will begin a downward trend as this takes
place...initially over northern/central areas...while still mild over
southern areas Wednesday afternoon /highs in the middle to upper 60s/...then
decreasing into the Lower/Middle 60s over the entire region Thursday into
the weekend. Model guidance agrees that a trough will persist over
the Gulf going into early next week...but show considerable spread
with the shortwave details. Regardless...the lingering trough will
continue to favor rain over the County Warning Area throughout the remainder of
the long term forecast.
Used a blend of the European model (ecmwf)/Gem to refresh pressure/winds through
12z Sat...with the GFS included in the updated pop/qpf/sky
forecast. No major changes were made to previous temperature
forecast. Confidence is generally at or above average during much
of the long term in overall trends...but below average in smaller
scale details beyond Sat morning.
Aviation...IFR fog conds at paya for a few more hours. Pawg and
on a few webcams have some patchy fog this morning. Otherwise VFR
until tomorrow morning.
Marine...westerly regime due to surface ridge offshore. Swells
down. Kept wind in 10 to 20 knots range. Expect some sea breeze
especially Lynn Canal and cross/icy. A little worried that area
12 may see 25 knots this afternoon and at Cape Spencer. Mentioned
fog in most areas early Wednesday morning as wind drops off.