Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
421 am akdt sun may 24 2015
Analysis and upper levels...
The zonal jet streak remains streaking off the Japan region
eastward with the exit region of the jet entering the western
Aleutians near Shemya. With a closed low at 500 mb and a gale
force low reflected at the surface is positioned just west of
Saint Paul Island this morning. On the backside of this low...the
western to central Aleutians/Bering Sea are being impacted with
westerly gale force winds accompanied by showery precipitation. An
associated trough extends southward from this system through the
eastern Aleutian chain. This is bringing gusty southerly winds
over the eastern Bering Sea and flowing into the southwest Alaska
region. The satellite imagery is showing a swath of moisture and
stratus with the frontal boundary moving through the southwest
region. In the Gulf...a ridge of high pressure is reflected at
the surface. This synoptic feature is positioned over the eastern
Gulf extending through the Kenai Peninsula...the lower Kuskokwim
valley and into the Kotzebue area. This is preventing any moisture
and precipitation from entering the Copper River basin eastward.
While the Gulf has marine layer stratus under the surface ridge
and the sport modus 24-hour microphysics rgb imagery is showing
the denser fog near the northern Gulf coastline near Icy Cape this
Model discussion (short term)...
the models are in good agreement with remnant of typhoon Dolphin
as in moves into the central Bering Sea and the new gale force low
dropping down form the Kamchatka peninsula. This low will track
into the western Bering Sea by Monday before moving back towards
the Kamchatka peninsula by Tuesday. The Gulf will have the ridge
of high pressure building back into the Gulf by Tuesday and
strengthen through rest of the week. The preferred models of
choice were the ECMWF/GFS. The forecast confidence remains above
average heading into the upcoming week.
Short term forecast southcentral Alaska (sunday and monday)...
Cooler and wetter conditions continue to slowly grind
inland across southern Alaska this morning. The band of
precipitation has now moved past Anchorage...but will stall over
the Matanuska Valley and western Copper River valley today and
slowly weaken in place. Most of the Cook Inlet region will be
drier than yesterday...but breaks of sunshine will still be hard
to come by as the broad longwave trough in the Bering Sea
continues to sling embedded shortwave troughs into southern
Alaska. For the start of the week...breaks in the cloud cover will
become increasingly prominent. With a shortwave trough lingering
over the area...any breaks of sun that do develop will likely lead
to the development of diurnal shower activity across most inland
areas. However...with deep-layer instability remaining quite
limited...no thunderstorms are expected.
Clouds spreading into the Copper River basin today will
bring an end to the string of record-breaking temperatures and
extreme fire weather conditions of recent days. However...with the
band of rain falling apart over the far western portions of the
basin much of the area will remain dry...and relative humidity values
will still remain quite low/dry today.
Short term forecast southwest Alaska (days 1 and 2)...
A low in the Bering Sea will continue to support periods of light
rain over most of southwest. Southeast winds will keep the lower
Kuskokwim valley and locations immediately downwind of the
Aleutian Range the driest...with the best chances for rain across
the Kuskokwim Delta and Bristol Bay region. More steady rain will
develop across Bristol Bay and the lower Kuskokwim valley Memorial
Day as a North Pacific low merges with the Bering Sea low as it
tracks inland. Rain will become more showery late Monday and again
Tuesday as diurnal heating enhances instability. Coastal locations
will dry out Monday and Tuesday as the low moves inland.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
The large but weakening low in the central Bering will move
eastward today...with showers over the central and eastern
Aleutians dissipating through tonight. High pressure will move
from the western Bering to the eastern Bering through
Tuesday...with a gale force warm front moving into the western
Bering...then spreading east toward the eastern Aleutians and the
Pribilof Islands on Tuesday...bringing periods of moderate to
Long term forecast (days 3 through 7)...
Models remain in agreement that a ridge of varying strength will
persist over much of the eastern Alaska Mainland through next week.
Southerly flow along the western flank of the high will bring
rain to the north Gulf Coast and some inland showers through Tuesday.
As the ridge increases in strength it will cut off the onshore
flow and precipitation Tuesday night through Thursday. A slight
weakening of the ridge will again allow onshore flow to bring rain
to the coast and showers to inland areas at the end of the week.
A broad area of low pressure will persist over the Bering. This
will keep rain and showers over the Aleutians and SW Alaska through
next week...enhanced at the end of the week as a low and
associated front move just south of the chain.
Marine...Gale Warning...173 175 176 1778
Synopsis and model discussion...pld
southwest Alaska/Bering Sea/Aleutians...ja