Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
225 PM akdt Wednesday may 22 2013
Short term...rather quiet along the Panhandle today as mostly
clear skies and dry weather remain the norm. The exceptions to
this rule today are Skagway and Haines where a middle level cloud
deck has given them overcast skies and cooler weather today. The
cloud cover there is the result of a middle level low that is moving
north just to their NE. The low is just far enough east that the
northerly middle level flow is dragging the clouds over Haines and
Skagway and has pushed the clouds as far south as berner's Bay
and Lena point. As this middle level low moves north this evening
the middle level flow should turn more northwest then west and eventually
clear the clouds out of the area. There already is evidence of
this starting to occur on recent satellite images.
Winds are becoming less of a concern as the inverted trough over
the Panhandle slowly weakens. Currently the only places with
small craft winds are Lynn Canal, Stephens Passage, and the southeast
Gulf. The former two are on a slow decreasing trend at the moment
and should drop below small craft by this evening.
For tonight and tomorrow, the clouds over the extreme north will
diminish this evening as the middle level low moves northward. Same
for the high level clouds that are scattered over the southern
Panhandle. These will be replaced along the outer coast and the
Gulf by the return of the marine layer clouds as the ridge that
is in the Gulf flattens tonight. Satellite images already show
some marine layer clouds starting to form in the eastern Gulf.
These clouds should spread across most of the Gulf tonight and
may encroach into Yakutat, Cross Sound, Sitka, and the extreme
western parts of Prince of Wales Island. These clouds will then
do their usual retreat out into the Gulf tomorrow with the day
time heating. Otherwise most areas will remain dry and mostly
clear.
Winds will not be much of a concern over the Panhandle for the
next 24 hours. Besides the usual sea breeze patterns most areas
will remain below 20 knots. The southeast Gulf is a different story, the
continued interaction between the Gulf high and the British
Columbia low will continue to cause 25 knots northwest winds in the southeast Gulf
through at least midday tomorrow as the high slowly weakens.
Fire weather. Cloud cover over the extreme northern Panhandle
has so far prevented any drastically low humidities from
occurring in Skagway today. Air temperatures at Skagway have only
risen into the middle 50s and with dew points having risen overnight
to around 30, the relative humidity has been holding around
40 percent. Winds have also been 15 miles per hour or less today so no red
flag warning was issued. We will continue to monitor fire weather
conditions in the area tomorrow as with clearer skies the daytime
temperatures are expected to rise again and fuel conditions
remain dry, but with increasing dew point temperatures and
continued lighter winds it is becoming less of a concern that red
flag conditions will be reached tomorrow. Fuel moisture levels
remain too moist in other areas of the Panhandle for extreme fire
weather conditions to develop.
Short range models were in good agreement today with few
differences noted. Decided on sticking with the NAM and a little
of the European model (ecmwf) for updates to get more of the details that those
models provide. Forecast confidence is above average.
&&
.Long term...High pressure ridge over the Alaska Gulf that has been
providing sunny dry weather will break down through the week. Low
pressure system over British Columbia will track northward with
potential for rain moving westward over the Coast Mountains.
Marine layer over the Alaska Gulf will move eastward but still
uncertain to its eastward extent over the Panhandle. Low pressure
system moving across the North Pacific will interact with a
Bering Sea low as it passes south of the Aleutian chain.
Interaction between these Tow systems along with the break down
of the ridge lead to high uncertainty in extended forecast. By
the weekend a series of resulting weak low pressure system will
move into the Alaska Gulf. Overall the stronger centers look to now
track southward so overall precipitation should be along the southern
Panhandle starting on Sunday and for areas along the Coast
Mountains from the British Columbia low. Keeping increasing cloud cover through
the weekend with the advancing marine layer and low pressure
systems. Not much in the way of pressure gradients or frontal
boundaries so winds through the long range should be less than
20 kts. Temperatures are also looking highly variable between
models. GFS is bringing in a warmer air mass with positive
temperature anomalies over the region while NAM/European model (ecmwf) are cooler
by 4 to 8 degrees f. Cloud cover will be one of the main issue
regarding day time highs with the tracking of middle level air
masses another.
Had fair agreement between models for pressure and winds over
the Gulf. More variation for the inverted trough over the
Panhandle. Blended in some NAM/GFS with inherited grid but
overall little change through day 4. New wpc was a blend of
ensembles as operational models are showing large discrepancies
while ensemble spread is fairly low. Updated grids through day
8 with new wpc, also with little overall change. Forecast
confidence is low at this time due to the large variations
between models in poor run to run consistency.
Ajk watches/warnings/advisories...
public...none.
Marine...Small Craft Advisory for pkz041-042.
Small Craft Advisory due to seas for pkz043.
&&
$$
Eal/prb
