Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
130 PM akdt sun may 19 2013
Analysis and upper levels...the upper low which formed over the
Gulf on Saturday has now moved to the Yukon. A wave rotating around
the back side of the low center is just clipping the northeast
Copper River basin producing some snow showers along the Wrangell
Mountains. Otherwise sunny skies dominate the rest of southcentral
Alaska...the western Gulf...and much of southwest Alaska thanks to
a high amplitude ridge building in from the Bering Sea. Upstream of
the ridge a vertically stacked closed low south of the western
Aleutians is tracking to the east-northeast with the occluded front
spreading north and eastward into the Bering Sea. This is bringing
widespread rain and fog to the Aleutians and central Bering.
Model discussion...there are minor differences in how quickly the
upper ridge moves through southwest Alaska which results in timing
in the eastward progression of precipitation. Prefer the NAM which
is a middle ground between the faster European model (ecmwf) and slower GFS. Other
than that models are in good agreement with major features over the
next few days.
Short term forecast...
Southcentral Alaska...the upper ridge will build over southcentral
tonight and Monday...but will then quickly weaken as a piece splits
off and heads to northwest Canada Tuesday. Until then expect dry
and clear conditions. There will be one more night of widespread
sub-freezing temperatures before temperatures return to near normal
Tuesday and Tuesday night. As the ridge weakens on Tuesday the
remnants of the occluded front crossing the Bering will move to
the western Gulf Tuesday and Wednesday. Most of the dynamics with
this system will head to the northern Bering...so expect the main
impact to be clouds moving into western portions of southcentral...
with just a chance of rain. Otherwise...temperatures will continue
to moderate as we head through the week.
Southwest Alaska...the upper ridge will slide past southwest Alaska
relatively quick with clouds and precipitation arriving along the coast by
late Monday and then spreading inland Tuesday and Wednesday. With
much of the energy being pulled northward up the west side of the
ridge the occluded front will stretch apart over southwest Alaska.
Strong southeast flow will also produce downslope drying for many
inland locations. Thus...expect the bulk of rain to fall along the
coast with just a chance inland. There may be a bit of snow as
precipitation first arrive in the Kuskokwim Delta. Otherwise temperatures
will moderate quickly across the southwest Alaska so that any
precipitation that does fall will be in the form of rain.
Bering Sea/Aleutians...the low south of the Aleutians will track
right across The Heart of the Bering Sea advecting lots of warm
air and moisture northward resulting in widespread rain and fog.
The system will exit to the north middle week...although conditions
will remain favorable for fog and stratus.
Long term forecast...models show poor run-to-run consistency
in the day 4 through 7 time period and solutions vary significantly
among the various medium range models. Indications are that another
large Pacific system will affect the Aleutians and Bering...but
exactly where this system tracks is highly uncertain. The rest of
the forecast area will likely remain under the influence of weaker
features. Forecast confidence is below normal.
Aer/alu...watch/warning summary
public...none.
Marine...Gale Warning...155 160 165 170 171 172 179 180.
Fire weather...none.
Seb may 13
