Scientific Forecaster Discussion
fxak68 pafc 251243
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
443 am akdt sun Jun 25 2017
Analysis and upper levels...
the two main features on water vapor imagery are a pair of upper
low pressure systems. The stronger of the two is over the western
Bering Sea with a front extending through the Pribilof Islands
and the Alaska Peninsula. The weaker upper low pressure is west of
the Panhandle, generally weakening and moving eastward. The jet
stream is well to the south of the Aleutians, remaining active off
the Asian continent. The consequence of this is a stagnant
pattern poleward with the Bering system receiving infusions of
energy from the jet. The Mainland is left under ridging aloft and
generally weak flow, which has led to mountain convection in the
afternoon and evening, mainly over the Talkeetna Mountains and
Copper River basin. Winds are generally light over southcentral
Alaska while the southwest is under light onshore flow. The marine
layer over Bristol Bay completely mixed out during the day
yesterday so the chances of another low stratus/fog inundation are
due to the stagnant pattern with only two mature storm systems
over the area, models continue to be locked in synoptically. There
are no major differences in the pressure/height fields through the
next 3 to 4 days. Placement of afternoon/evening convection due to
resolution differences are really the only disagreement. All
guidance is picking up on a stronger shortwave entering the Gulf
on Tuesday as the Bering Sea system slides closer.
panc...VFR conditions and light winds will persist.
Short term forecast southcentral Alaska (days 1 and 2)...
today is the break between systems for southcentral Alaska. By
tonight the next front will be moving over Kodiak Island and then
over the rest of southcentral Alaska.
There is a good bit of pressure rises ahead of the front which
will cause decent southwesterly winds through Shelikof Strait and
into Cook Inlet through tonight.
Instability remains over the Susitna Valley eastward into the
Copper River basin again today and some more showers and
thunderstorms are expected again. There is also some increased
instability over the eastern Kenai Peninsula so there could be
showers/isolated thunderstorms there as well this afternoon and
evening but it does not look as likely as over the Talkeetna
Mountains and eastward. By tomorrow the only lingering instability
will be over the northeastern Copper River basin as the
approaching front will end the convective potential elsewhere.
Short term forecast southwest Alaska (days 1 and 2)...
a shortwave ridge moves in over the SW Mainland today ahead of a
potent low pressure system moving in from the Bering Sea. Ahead of
the system, temperatures will rise into the upper 60's to mid
70's for inland valley areas accompanied by breezy southerly
winds. By the evening, a warm front extending out from a low
pressure system centered over the Bering Sea moves ashore bringing
widespread rain and cooler temperatures to most of the area. The
front will also bring gusty winds along the coast through Monday
morning. The front stalls out over the SW Mainland on Monday
before upper level reinforcement moves in bringing more widespread
rain and showers to the area through at least Wednesday.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
A strong low pressure system in the western Bering will be the
major weather player for the region through at least the middle of
next week. The low is currently centered just north of Attu and
is being supported by a 110 kt upper level jet to the south. A
strong southerly low level jet out ahead of the low will bring
gale force winds to the central and eastern Aleutians today with
steady rain, heavy at times. The low center slowly moves east
along the Aleutian chain early next week before stalling out and
slightly retrograding back to the west by Wednesday.
Long term forecast (days 3 through 7)...
The extended forecast beginning next Wednesday brings increased
chances for rain across the southern Mainland and Gulf as energy
from the Pacific swings north over the Mainland. The main upper
level system centers over the Bering mid week and then a stronger
vort Max rotates through the flow off Kamchatka. This vort Max
develops a new progressive low center that takes an easterly track
across the central and eastern Aleutians during the end of next
week. The European model (ecmwf) and Canadian models are in better agreement with
continuous weak energy moving from the Gulf to southcentral ahead
of the newly developing low center. This supports increased cloud
cover and higher rain chances across the southern Mainland and
surrounding waters through the end of next week.
Marine...gale 155 170 172.