Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
442 PM akdt Thursday Oct 30 2014
Analysis and upper levels...
cloud breaks developed over the Copper River basin on the
backside of an westerly moving upper wave overnight and allowed
temperatures to drop below zero in places. The cloud shield in advance of
a westerly moving frontal trough over the Yukon is moving into the
central Copper River basin this afternoon. The remainder of
southcentral has some scattered to broken middle clouds associated
with a weak deformation zone. There also were a few lower clouds
associated with cold advection over the southern inlet. Pressure
gradients increased across the north and west Gulf this
morning/afternoon with lowering pressures over the Gulf and high
pressure over the Mainland. The resultant gradient produced strong
westerly/North Gap flows through gaps in the Aleutians range over
the western Gulf...Barren Islands...eastern Kenai/western Prince
Out west...stratus blanketed the Delta as well as eastern
Bristol Bay/Kuskokwim valley. Otherwise fair skies prevailed over
the SW Mainland. The leading edge of the cloud shield associated
with a developing storm center near the western Aleutians spread
North/East to over the eastern Bering Sea and western Alaska Peninsula.
Rain with strong southerly winds was reported near Adak with
brisk northwest winds in Shemya. Rain reached both Dutch Harbor
or Saint Paul early this afternoon.
the main challenge of the day will be the evolution of the
developing storm center near the western Aleutians. The models
continue to struggle with the eastward progression of the center
once it crosses into the Bering Sea. The European model (ecmwf) consistently is
the further west...though the 12z run has shifted the forecast
center east. The NAM/GFS appear to be moving the center too
quickly east...so for now will lean more toward the inherited grid
solution of a 00z European model (ecmwf)/Gem global blend. As the upper trough
elongates east toward the Gulf...broad westerly flow sets up over
the North Pacific. It is likely then that the surface front will
stretch eastward as a triple point develops over the western Gulf
Friday. Models in general are in very good agreement with this
feature. Timing of the front as it moves across the Aleutians and
into the Gulf are also in fairly good agreement.
Short term forecast...
gap winds across the north Gulf will diminish tonight as pressure
gradients weaken. Light snow will likely move into the central
Copper River basin tonight with a wave moving out of the Yukon.
Weak low pressure over the Gulf will likely keep showers along
the coast through Sat. A frontal system will enter the southern
Gulf on Friday morning and will move to the north Gulf Coast/Kenai
Peninsula Sat. Precipitation will briefly start as snow Friday morning near
Kodiak then should rapidly shift to rain. Rain and snow will be
likely along the coasts before becoming rain. Strong cross
barrier flow across the chugach will mitigate snow/rain chances to
the Lee side initially with the approach of the front Friday. Cross
barrier flow weakens Sat which should allow some spill over of
rain and snow inland.
clouds will increase across the SW Mainland Friday with the approach
of the occluded front. The Bristol Bay zone will see the greatest impact
precipitation wise. Warm air slowly creeps north to the northern
Bristol Bay coast on Friday evening. Rain is expected south of this
line. Snow will be likely to the north with chances of pockets of
light freezing rain. Conditions will slowly start clearing on Sat
with the return of northerly flow.
the low developing south of western Aleutians will cross the
chain west of Adak this afternoon...then progress slowly eastward
to Bristol Bay late Friday night. The associated front will move to
the western Alaska Peninsula/pribilof's tonight then to Bristol Bay on Friday.
Easterly storm force winds are expected in advance of the front
and north of the low over the eastern Bering Sea. Westerly storms
are expected along the Aleutians to the south of the low center.
Storm force conditions will slowly diminish Friday.
Long term forecast (mon through thu)...the middle-long range models
continue to struggle with this pattern as we remain in the fall
transition season. The details are quite messy from start to
finish...though the general idea remains almost a "rinse and
repeat" pattern compared with the end of this week.
Remnant low pressure near Bristol slides into the western Gulf of
Alaska early in the week. This low looks to slowly weaken and broaden
across the Gulf through Wednesday. Meanwhile out west...a Sharp Ridge of
high pressure will move quickly across the Bering to start the
week. This will spell dry conditions for a brief period...but
could also make for some tighter gradients leading to gustier
winds. Another low tracks off the Kamchatka peninsula by mid-week.
As of now...the general consensus is that this feature should be
filling and elongating by that time and thus...have limited winds
to gale- force.
The rinse and repeat portion occurs towards the end of the long-
term. Sprawling low pressure across the Bering begins to interact
with weak low pressure in the Gulf. The details remain very
hazy...but there looks to be signs of another triple point low
forming very near where the one for tomorrow is prognosticated to form.
marine...Storm Warning 155 170 172 173 174 175 176 179
Gale Warning 119 130 131 132 150 160 165 171 177 178 180 181 185
Rmc/MO Oct 14