Scientific Forecaster Discussion
fxak68 pafc 191747 cca
Southcentral and southwest Alaska forecast discussion...corrected
National Weather Service Anchorage Alaska
947 am akdt Thu Sep 19 2019
Analysis and upper levels...
The active fall pattern continues. We have a shortwave trough
currently exiting our forecast area to the northeast, while a
deeper long wave trough is already working across the Aleutian
island chain and will move into southcentral Alaska later today.
Quickly moving zonal flow on the southern side of an upper level
low located over the northern part of Alaska will keep systems coming
at a rapid clip, with another low lining up in the western
Models are in good agreement for the short term. As a result,
forecast confidence remains high. They seem to be handling the
active fall pattern well, so there has been good continuity
between model runs and our forecasts.
Panc...VFR conditions and light winds will persist. Rain will
begin to fall at the airfield again this evening. It looks like
ceilings and visibility will mostly remain VFR, but there is a
chance we could see MVFR conditions with this next round of
Recent rains have released quite a bit of moisture over areas of
fire activity the past day or so. Rain has tapered off, but the
next round of precipitation will enter southcentral Alaska tonight
into tomorrow, providing more wetting rains for most areas.
Short term forecast southcentral Alaska (days 1 and 2)...
today is the break between weather systems as the low that brought
the widespread rainfall yesterday has moved into Canada. Some
lower clouds are packed up along the mountains in the low level
southwest flow up Cook Inlet and along the north Gulf Coast. The
clouds with the next system have already reached Kodiak Island as
they move in from the southwest and will quickly make sky
conditions cloudy again before rain spreads over the region from
southwest to northeast this evening through Friday.
The surface low with this next system is taking a bit of a
different track from the previous system. Whereas the previous
low moved generally from west-to-east over the region, this one
will enter the Gulf of Alaska from the south and bring a strong
weather front to the north Gulf Coast early Friday morning.
This front is now expected to bring gale force winds into Prince
William Sound late tonight and early Friday morning as well as
storm force winds in a barrier jet to the north Gulf Coast east of
Montague Island. This is an increase in winds from the previous
Short term forecast southwest Alaska (days 1-2: Thu-sat)...
A few showers remain along the Alaska Peninsula and southern
Bristol Bay this morning, while a weak upper level ridge begins
to build over the rest of southwest Alaska. Clearing conditions
across the Kuskokwim valley and Delta, including Bethel, could
lead to possible patchy fog. Areas in these interior locations
will see morning temperatures near the freezing mark, including
Aniak and Sleetmute, which have both already fallen slightly below
This afternoon will bring another chance of showers to Bristol
Bay and the Kuskokwim valley as a shortwave moves across the
region through the evening hours. Temperatures will once again be
cooler, but increases in cloud cover will keep it a bit warmer than
this morning's low temperatures. The showery pattern will persist
through Friday afternoon, with the next chance of widespread
precipitation returning on Saturday morning as a low in the
northern Bering moves inland over southwest Alaska.
Short term forecast Bering Sea/Aleutians (days 1-2: Thu-fri)...
Small craft winds over the western Aleutians this morning will
quickly diminish through the afternoon as the associated low
center drifts southeastward. High pressure will then build in
over the Aleutian chain on Friday and slowly move eastward
through Saturday. North-northwest flow on Friday afternoon through
Saturday over the eastern Bering and Bristol Bay will keep strong
winds flowing out of bays and passes south of the Alaska
In the northern Bering, a low moving from Kamchatka will bring
Small Craft Advisory winds across the region reaching the
pribilofs overnight Friday and continuing into Bristol Bay by
Marine (days 3 through 5)...
Beginning the extended period marine forecast on Saturday, a gale
force low will be stationary along the north Gulf Coast. Cold air
advection will be pushing high end gales through the Barren
Islands and Shelikof Strait, although the highest seas will be
through The Barrens where the longer fetch winds will produce
greater buildup. The low will move east toward the Panhandle on
Saturday. Attention turns to a powerful developing low over the
eastern Aleutians and eastern Bering Sea. Uncertainty is higher
with this low, but there is increasing likelihood that gales to
near storm force winds will impact these areas, focused from
Dutch Harbor eastwards, with the peak strength around Saturday
night through Sunday. The low will shift into the Gulf on Sunday
evening/overnight and last through Monday. By this juncture,
uncertainty with a developing triple point low in the Gulf is
high, but mariners should be expecting a potential high end gale
force to low end storm force low sometime on Monday across the
entire Gulf of Alaska. The next strong low moves into the western
Bering Sea Tuesday and Wednesday.
Long term forecast (days 3 through 7)...
Beginning the extended period forecast on Friday evening, there
will be a low bringing widespread rain to southcentral with a pair
of lows over the Bering Sea. The low over southcentral will be
driven in part by an Arctic trough to the northwest, so colder air
will be filtering in behind the rain through the remainder of the
weekend. Attention quickly turns to a rapidly developing low
along the Aleutian chain Saturday night. Currently, this looks to
rapidly deepen into a high end gale force to low end storm low as
it moves from eastern Bering Sea to the Gulf of Alaska Sunday and
Monday. Given the wrapped up nature of the low, the most rain is
likely to develop across parts of southwest Alaska, Kodiak, and
the north Gulf Coast with much drier conditions inland given the
downslope pattern. Unsettled weather will Switch Back to the
Bering Sea midweek as the storm track moves west again, giving a
break from the rain across most of southern Alaska.
Marine...Storm Warning 119.
Gale Warning 120 125.