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Southcentral and southwest Alaska forecast discussion 
National Weather Service Anchorage Alaska
137 PM akdt sun Sep 14 2014

Analysis and upper levels...
weather across virtually the entire alaskan domain remains
dominated by a huge vertically-stacked low in the far eastern
Bering. This low is now in the weakening phase...and a southward
elongation of the upper circulation is already evident on
satellite imagery. The original associated weather front is now
oriented north-south over the eastern Copper River basin and
portions of the north Gulf Coast. Rainfall rates have diminished
significantly over the Valdez and Cordova areas...though 48 hour
rainfall totals in excess of 9 inches continue to result in minor
flooding of area rivers. Back to the area of convective
showers moved through upper Cook Inlet overnight and dropped a
quick inch or so of rain over the western Susitna Valley...which
has led to quick river rises and the need for a Flood Advisory in
this area as well. Even though the low center is now weakening...a
secondary round of wind and rain associated with the low itself is
slowly grinding northward through Kodiak Island and into Bristol
Bay. Weak ridging behind this slow-moving storm is helping to
reinforce gusty northwest winds from the central Aleutians over to
the pribilofs and Alaska Peninsula.


Model discussion...
the models are in good overall agreement in the first few days of
the forecast...which is not surprising given the overall slow
movement of the major low currently dominating the area. As
such...will rely heavily on the higher resolution models today to
capture more detail in areas of channeled terrain. As the low
continues to weaken through early in the week the overall flow
will become a bit more progressive and allow multiple shortwaves
to move quickly through more zonal flow along the bottom of the
Aleutian island chain. The second of these shortwaves moves into
the western Aleutians Monday night and will be strong enough to
help pull the lingering circulation over the Bering southeastward
toward the far western Gulf toward midweek. The European model (ecmwf) is slower
than the other models bringing this wave through...and seems to be
playing catchup with the other models on a faster solution. Thus
will stick with the American models through the remainder of the
short term period for this feature as well.


Short term forecast...

Southcentral Alaska...
wet and windy weather associated with the low center itself is
currently impacting Kodiak Island. As the low weakens and
continues to move toward the southwest Mainland tonight this area
of rain and wind will spread up Cook Inlet. Precipitation rates should
not be nearly as impressive as with the original front...and as
per the norm most of the rain that does fall will be along the
Gulf Coast. The best chance for rain in the population corridor
from Kenai to Anchorage and the mat-su will be as the secondary
front passes through Monday morning. The possible fly-in-the-
ointment here is that lapse rates/instability will be quite
favorable tomorrow morning across much of the northern a
convective component to the precipitation may help precipitation rates to
exceed model outputs for both the coastal and inland portions of
the zone. By Monday evening...the upper low out west will be
almost indistinguishable from the overall longwave
which time the upper level flow over the region will once again
become southwesterly and lingering areas of steady rain (focused
along the Gulf coastlines) will diminish and instead be replaced
by more showery precipitation over virtually the entire area.

Southwest Alaska...
the weakening low will continue to move toward the Bristol Bay
coast this evening and move inland early tomorrow morning. The
area of steadier rain associated with a secondary front has pushed
into the far northern Bristol Bay zone and lower Kuskokwim valley
and continues to fall apart. All models forecast the remnants of the
low to push into interior Bristol Bay and then rotate
northwestward back toward Bethel by midday tomorrow and dissipate
shortly thereafter. In practical terms...this is going to lead to
showery precipitation and relatively light winds across much of the area
for the first half of the week. A few breaks of sun are
possible...but likely will not be too long-lived as southwest flow
at all levels will keep significant cloudiness around.

Bering Sea/Aleutians...
the longwave trough controlling big-picture weather across the
region will remain large and amplified enough that impacts from the
next few disturbances will remain mostly south of the Aleutian
chain. This will keep much of the region in a showery pattern with
relatively light winds for the next few days. By midweek...a
stronger low will start to take shape south of the Alaska
Peninsula...which will strengthen gradients across the eastern
half of the Bering and allow gusty northerly winds to usher in a
more seasonably cool surge of cold air from the Bering Strait.


Long term forecast...
the broad longwave trough centered over the eastern Bering will
begin to shift eastward during the middle of the week and then
remain over the western Gulf and slowly weaken through next
weekend. This will will result in a generally cloudy and showery
pattern over the Mainland as various disturbances rotate around
the eastern periphery of the trough...with steadier rain likely
along the northern Gulf Coast in closer proximity to an attendant
surface low. The eastern Bering will also remain showery as brisk
northerly flow becomes established over the region with the trough
departing to the east and high pressure building in over the
western Aleutians.


Afc watches/warnings/advisories...
public...Flood Advisory 131 135 145.
Marine...gale 130 155.
Fire weather...none.



Amend/cumulonimbus Sep 14

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