Scientific Forecaster Discussion

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Southcentral and southwest Alaska forecast discussion 
National Weather Service Anchorage Alaska
1248 PM akdt Sat Apr 19 2014

Analysis and upper levels...a high amplitude trough extends from
the Bering Sea to the northeast Pacific with an intense low moving
up the east side of the trough just south of the Gulf of Alaska.
Central pressure bottomed out over night with the occlusion
wrapping itself around the low center. The low has become
elongated east-west with the original center on the west side and
a secondary low on the east side beginning to dominate. A trough
extends northwestward from the low south of Kodiak Island to the
Alaska Peninsula with a solid band of rain from Kodiak into
Bristol Bay. As the surface low rotates back toward the main
trough axis a short-wave ridge is building from Southeast Alaska
and across the southern Mainland. This is gradually pushing the
low level trough and precipitation shield southwestward toward the
eastern Bering and southern Alaska Peninsula. Skies have cleared
out over most of southcentral with this ridge building in. Another
short-wave trough over the eastern Bering is also pushing westward
with a band of precipitation from near the Pribilof Islands down to the
eastern Aleutians. Lastly...a ridge is building into the western
Bering ahead of an intensifying low over the northwest Pacific.


Model discussion...models continue to differ on the exact track
of the northeast Pacific low as it curves westward across the
southern Gulf and then back southward. There has been a trend
toward a more southerly track with good agreement between the
European model (ecmwf)/gemglb/gemreg will follow this trend. One higher
impact difference in the models is handling of the low level
trough which rotates across the Gulf north of the low center. NAM
seems too aggressive with easterly winds as this reaches western
Prince William Sound. Based on the position of parent low and
orientation of isobars expect enough of a northerly component to
winds to prevent strong easterlies from pushing inland. Gemreg
seems like it has a more realistic depiction of this. If winds
were to come up then there is a good possibility red flag
conditions would be met in the Palmer area Sunday afternoon.

Models are otherwise in good agreement and forecast confidence
is above average.


Short term forecast...

Southcentral Alaska...the bulk of impacts with the northeast
Pacific low will remain over the Gulf and Kodiak Island. The low
level trough mentioned above will bring some showers to the
Prince William Sound region during the day Sunday along with some
clouds for the rest of southcentral. Air mass over southcentral
will remain quite don't expect any showers to trigger
with the approach of this trough and increase in middle/upper level
moisture. Meanwhile...the upper ridge will build over interior
Alaska and remain in place as we head into early next week. That
will provide for mostly dry conditions across southcentral. Low
level thickness look slow to the air mass will remain
relatively stable. Models hint at a weak wave along the periphery
of the ridge moving in from the Yukon which could produce some
clouds and a few showers...but don't yet have confidence in that

Southwest Alaska...the building upper ridge will push all precipitation
out of the Kuskokwim Delta and Bristol Bay by early Sunday. The
trough currently pushing westward across the eastern Bering will
shift gears and lift back northeastward Sunday night and Monday
just clipping part of the southwest coast...mainly along the
Kuskokwim Delta. This will provide some clouds and perhaps a few
showers. Elsewhere across southwest Alaska the ridge and some
sunshine will lead to warming temperatures. The next system moving
into the Bering will push a front toward the southwest coast
Tuesday...but there is some uncertainty in exact time of arrival
as the front begins to elongate and slow its eastward progression.

Bering Sea/Aleutians...the approaching system over the northwest
Pacific and ridge out ahead of it will cause the eastern Bering
trough to stall this afternoon and head back the other direction
tonight. The ridge will provide a brief period of benign
conditions before the system makes its way into the Bering Sunday
and Monday. The surface low will bottom out just south of the
southern Aleutians so expect a strong front to push across the
Aleutians...but it will quickly lose steam as it spreads out
across the Bering Sea Monday and Tuesday.


Long term forecast...medium range models differ on the
details...but show the same general trends. The blocking ridge
over the Mainland will gradually retreat northward toward the
Arctic next week. The ridge will keep the system which moves into
the Bering away from the Mainland...forcing it to exit to the
northeast Pacific late next week. The biggest area of uncertainty
is over the southern Mainland between the ridge and exiting low.
Models are all over the pace with individual features embedded in
the it is hard to pinpoint any single feature. Barring
any significant short-wave would expect there will be quite a bit
of sun around next week over the southern Mainland and conditions
will be on the dry side (which is very typical for this time of


Afc watches/warnings/advisories...
Marine...Gale Warning...119 120 131 132 138 155 170 172 173 174
175 176 177 178.
Fire weather...none.



Seb Apr 14