Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
525 am akdt Monday Mar 10th 2014
Analysis and upper levels...
an upper level ridge continues to build downstream of an upper low
south of the akpen. A strong North Pacific low south of the akpen is
stacked under the aforementioned upper low center and tracking
towards the northeast. The associated weather front over the
southwestern Gulf has brought a mix of rain and snow...along with
gusty winds to Kodiak Island this morning. Onshore flow continues to
strengthen over the northern Gulf Coast as the above mentioned
frontal system tracks closer to the coast. As a result...current
observations and radar imagery around Prince William Sound indicate
snow and rain beginning to fall over the area...as well as gusty
Out west...the tightened pressure gradient between the upper high
over eastern Russia and a long wave trough over the northern/western
Mainland continues to produce a broad and brisk northeast
flow across much of the Bering Sea and Aleutians. As the strong
surface low tracks closer to the akpen...a transition from offshore
flow to onshore flow has taken place over much of the southwest
Mainland. As seen with current observations and radar imagery...winds
and snow have begun to pick up along the akpen and over parts of the
southwest Mainland. Reports of gusty winds and snow have also been
reported over the Pribilof Islands...as well as the eastern and
central Aleutians on the back side of the strong low.
the models continue to initialize well...and remain in good agreement
with the overall synoptic pattern. Forecast trends remain fairly
close between the models...with very small differences in the timing
and strength of the strong low south of the akpen and the associated
frontal system moving through the Gulf today. The GFS solution
continues to be slightly faster and stronger than model consensus
with regards to the aforementioned systems...creating a slight
challenge for forecasting precipitation type along the northern Gulf.
Since the model solutions were in close proximity to each other...the
ec/GFS were utilized for their positioning and strength of the
initial frontal passage...where the NAM was utilized inland to
capture the winds in better detail.
Out west...the NAM was utilized throughout the short term to capture
more detailed winds associated with the aforementioned low south of
the akpen...and the low that tracks along the Pacific side of the
Aleutian chain Tuesday morning through Wednesday afternoon.
Short term forecast...
a weather front will track to the northern Gulf by late morning with
strong winds accompanied by a large swath of moisture/precipitation.
The eastern Kenai has a Winter Storm Warning for heavy snow and
blowing snow from Moose Pass northward until 10 PM this evening. The
snowfall amounts will range from 16 to 24 inches before the snowfall
slowly tapers off by late Monday evening. The pressure gradient
strengthens throughout today. Look for strong winds through Portage
Valley and Turnagain Arm region...which will enhance the possibility
of blowing snow in the area. There is a Winter Weather Advisory for
snow in the Matanuska Valley west of the Parks Highway for snowfall
amounts ranging from 5 to 10 inches from Monday afternoon through
early Tuesday morning. As the weather front moves to the northern
Gulf Coast by the early afternoon the winds will increase through
Thompson Pass. Therefore...with onshore flow and abundant moisture
coinciding with the gusty winds a blowing Snow Advisory for Thompson
Pass is in effect from this afternoon through the late evening. The
Anchorage bowl and majority of western Kenai the precipitation will
get downsloped out with only a slight chance of snow with the low
pressure system tracking through the region today.
precipitation will return to the southwest Mainland today as the
front associated with the low south of the akpen spreads snow
northward from the Bristol Bay coast. Strong northeasterly winds will
also accompany the front as it moves inland...leading to localized
areas of blowing snow before winds begin to subside and precipitation
diminishes in intensity with the passage of the front. Snow could
possibly mix in with rain at times today over coastal portions of
Bristol Bay as warmer air moves in behind the front. Snow showers
will persist through Tuesday as the low itself tracks through the
western Gulf of Alaska and into the Cook Inlet region.
the eastern Bering will begin to transition to a more showery regime
during the day today from the eastern Aleutians to the akpen as the
front passes to the north and winds back around to northwest in the
wake of the low. The Winter Weather Advisory for blowing snow over
the akpen has been cancelled as temperatures have climbed into the
low 30s and some rain may mix in at times. However...localized areas
of blowing snow will remain a possibility as snow showers could be
fairly intense at times and winds will remain strong and gusty with
cold advection on the backside of the low. Meanwhile...the rest of
the Bering will continue to see isolated snow showers in broad
northeasterly flow over the next few days as the next North Pacific
low begins to track south of the chain.
Long term forecast...
the transition to a more active pattern is underway as the strong
North Pacific low currently south of the akpen tracks into the Cook
Inlet region over the next 36 hours. This pattern will continue
through the remainder of the week as a series of lows follow closely
on the heels of the first system while taking a very similar track.
This will generally result in a much wetter period across the
southern Mainland...with strong winds at times as various associated
fronts arrive along the northern Gulf Coast. Precipitation type is
expected to remain mostly snow although rain could mix in at times as
temperatures trend upward...particularly along the coast.
public...Winter Storm Warning 125
Snow Advisory 145
blowing Snow Advisory 181
marine...Storm Warning 119 120 131 351
Gale Warning 125 130 132 138 139 141 160 165 170 171 172 177
179 180 181 185 352 413 414
heavy freezing spray warning 160 165 179 180 411 412 413 414
Tp/pld/cb Mar 14