Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
634 PM EDT Tue Jun 23 2020
Valid 12Z Sat Jun 27 2020 - 12Z Wed Jul 01 2020
...Overview and Weather/Hazard Highlights...
Two low pressure/frontal systems are expected to affect Alaska
early in the extended forecast period, one across the Aleutians,
and another across portions of western/northwestern mainland
Alaska. A relatively deep low pressure system forecast to cross
the central Aleutians Sat-Sun will bring showers and gusty winds,
which could extend along a front as far east as the Alaska
Peninsula. Rain (and high elevation snow) showers may persist into
early next week across mainland Alaska as this system pushes
inland and dissipates. Farther north, low pressure north of
Siberia will accompany a frontal boundary across the Bering Strait
and into western mainland Alaska Sat-Mon. This system is expected
to produce areas of heavy rain and some mountain snow across
portions of northwest mainland Alaska, with the potential for high
winds across areas close to the Bering coast over the weekend.
While widespread precipitation across mainland Alaska should
gradually subside toward the middle of next week, persistent broad
cyclonic flow will result in continued unsettled conditions, with
persistent clouds and precipitation especially across mountain
ranges. The widespread clouds and precipitation will also result
in below average temperatures for most of the state through much
of the extended period, with highs forecast to be 5 to 15 deg F
(even 20 deg for a few locations) below average.
...Guidance/Predictability Assessment...
The 12Z ECMWF was used heavily during days 4-5 (Sat-Sun), with a
shift to majority weight placed on ECENS/GEFS ensemble means
during days 6-8 (Mon-Wed). The ECMWF was representative of
consensus early on. Deterministic model differences began to grow
rather quickly from day 6 onward, with respect to the evolution of
the upper low and frontal system affecting western mainland
Alaska, and on the timing of an additional shortwave/low pressure
system crossing the North Pacific toward the middle of next week.
Differences among ensemble means with respect to these features
were smaller, with also some greater degree of consistency among
ensemble relative to the deterministic guidance - thus, supporting
the trend toward ensemble means from day 6 onward.
Ryan
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
Hazards:
- Heavy rain across portions of northwest mainland Alaska,
Sat-Sun, Jun 27-Jun 28.
- High winds across portions of northwest coastal Alaska, Sat-Sun,
Jun 27-Jun 28.
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html