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Southcentral and southwest Alaska forecast discussion 
National Weather Service Anchorage Alaska
1255 PM akdt Friday Apr 18 2014

Analysis and upper levels...water vapor imagery shows an intense
low over the northeast Pacific about to occlude. It has just begun
a strong turn toward the north-northeast as ridge builds out ahead
of it. This system will be the focus of weather over the Gulf this
weekend. Meanwhile the large closed low which has been sitting
over the Bering and Aleutians has shifted eastward and is now
centered over the southern Alaska Peninsula. Colder air moving in
behind the low has changed precipitation to snow from the
pribilofs to the eastern Aleutians...but surface temperatures are
at or above freezing so don't expect any snow accumulation.
Multiple weak waves embedded within the flow around this low are
affecting most of the Alaska region. The most noteworthy short-
wave extends from Bristol Bay to the north Gulf Coast and is
moving northward. The air mass ahead of this trough is unstable as
indicated by 850-500 lapse rates of 7.4 to 8.2 c/km in 12z
soundings across the southern Mainland. This instability is
evident in the showery characteristic of radar returns this
morning. Even with instability the bulk of precipitation is falling along
the coast. A downslope hole is noted over southcentral in the Lee
of the coastal range...helping keep low levels pretty dry inland.


Model discussion...all models are pretty close with position and
strength of intense low over the northeast Pacific. However...the
European model (ecmwf) seems to be verifying closest to reality (based on satellite
imagery). Most is quicker to occlude the low this
morning and has generally shown the best run-to-run continuity
with this system the past few days. The one evident trend in the
latest run of the European model (ecmwf) run is to slow down the westward
progression of the triple point low which forms tonight. Slower
motion makes sense with the first low about to occlude and become
wrapped up...helping slow down the forward motion of the entire

There are some minor differences in track of low which develops
over the northwest Pacific and moves toward the Aleutians...but
nothing which fundamentally affects the forecast.


Short term forecast...

Southcentral Alaska...showers will quickly come to an end across
southcentral tonight as the short-wave exist to the north and
much stabler air moves in behind it. A building ridge along the
north Gulf Coast will produce gusty gap winds this afternoon and
evening...but the ridge will be quickly shunted northward by the
approaching northeast Pacific storm system and low level flow will
become northerly. This will aid in drying things out (and clearing
out any remaining low level clouds). As has been advertised the
initial impacts of the Pacific system will be confined to Kodiak
Island and the Gulf waters on Saturday while southcentral will
see sunny skies underneath a strengthening ridge. There has been
more uncertainty in the forecast for southcentral on Sunday as the
triple point low becomes dominant and curves westward across the
Gulf. A majority of models show the associated trough swinging far
enough north to bring clouds and a chance of rain to the north
Gulf Coast. Inland areas will see some residual middle to high
clouds...but it looks like conditions will remain dry. The upper
ridge will set up shop over the interior Monday with the ridge
axis extending southward over southcentral. Models indicate
potential for some showers with very weak waves embedded in the
upper flow...but with a stable air mass in place think the only
chance of showers will be on the mountains.

Southwest Alaska...mostly cloudy and showery conditions will
persist across coastal southwest through tonight due to proximity
to the low over the southern Alaska Peninsula. Models are more
aggressive in advecting moisture from northeast Pacific low
westward across the Alaska Peninsula into Bristol Bay on Saturday.
Thus...look fro continued cloudiness with areas of
rain...especially along the Alaska Peninsula. The rest of
southwest Alaska will dry out under the influence of the ridge
building over the Mainland. Even Bristol Bay should dry out Sunday
as the ridge builds over all of southwest Alaska. Monday is more
uncertain as a weak trough lifts northward up the west side of the
ridge. Right now it doesn't look strong to produce more than a few
clouds and perhaps some mountain showers.

Bering Sea/Aleutians...a brief break will ensue Saturday as the
upper low over the southern Alaska Peninsula is sheared apart and
ridge builds in ahead of a developing northwest Pacific low. This
storm system will be the focus for Sunday and Monday as it makes
its way into the Bering.


Long term forecast...general outlook for the day 4 through 7
period remains consistent...with a low in the Bering/Aleutians and
a high latitude block providing drier and warmer weather for much
of Mainland Alaska. One change from yesterday's model runs is that
the Bering low looks like it will impact the southwest coast
Tuesday into Wednesday. Forecast confidence is initially above
average...but falls by the end of next week with uncertainty in
whether the the Bering low will affect southcentral as it exits to
the northeast Pacific or whether the upper ridge will dominate and
keep out clouds and precipitation.


Afc watches/warnings/advisories...
Marine...Gale Warning 131 132 138 150 155.
Fire weather...none.



Seb Apr 14