Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
400 PM akdt Wednesday Jun 19 2013
Analysis and upper levels...the pattern change is evident today as
the large blocking ridge has moved northward over northwest Alaska
and an upper level low sweeps from east to west from the northwest
Gulf into the Bristol Bay region late this afternoon. The cold air at
the core of this low has greatly increased the instability near it
and has touched off thunderstorms in the Gulf of Alaska and southern
Kenai Peninsula as it has passed through. A series of waves ahead of
this low brought showers and some thunderstorms to the Bristol Bay
area early this morning. This low in merging with another upper level
low that is south of Sand Point.
Most of the convective instability is west of the Alaska/Aleutian
ranges today with the greatest amounts from the Kilbuck Mountains
west in the middle of the evening. This is due to existing
instability in the Kuskokwim Delta meeting the cold upper level low
moving across the Bristol Bay region in the late afternoon and early
evening.
At the surface there is a ridge building in the eastern Gulf that
will move into the remainder of the Gulf and eastern Alaska by
tomorrow. This ridge will keep a low south of the Alaska Peninsula at
Bay and dissipate by Thursday night. A strong low I southwest of the
Aleutians islands which will move into the area tomorrow.
Model discussion...models are still doing reasonably well today.
They are all locked on the position and movement of the large high
but there is a little less certainty as to how the upper level waves
are all moving. However the largest model question revolves around
the large low approaching the western Aleutians tomorrow. This low is
extra-tropical and therefore bears watching due to model difficulty
in accurately depicting the moisture fields and movement. At this
time the European model (ecmwf) is a little faster than the GFS and NAM solution .
Short term forecast...south central Alaska will see skies clearing
and any residual showers exiting the area this evening as the ridge
in the eastern Gulf builds in. Southwest Alaska will see some showers
and thunderstorms through the evening...and possibly through the
night in the Kuskokwim Delta. There is a chance for dry thunderstorms
this evening in the southern Kuskokwim valley as this wave passes
though though the northern part of the valley will probably be to dry
for any convection at all.
Long term forecast...the forecast beyond Friday night remains low
confidence as models continue with inconsistency from run to run.
This is likely tied to the tropical origin of the large low that will
be near the Aleutian Islands. The latest model runs are leaning
toward a solution that will bring the low south of the Gulf which
would bring warm temperatures to southern Alaska...but not nearly as
warm as what has been seen over the past week. Due to the run to run
inconsistency in the models the next few runs should be followed to
see if they confirm this pattern or keep changing.
Aer/alu...watch/warning summary
public...Flood Advisory 111. Flood Watch 145.
Marine...gale 172 175 176.
Fire weather...red flag warning 141.
Jun 13
