Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
553 PM EDT Mon May 25 2020
Valid 12Z Fri May 29 2020 - 12Z Tue Jun 02 2020
...Guidance/Predictability Assessment...
Alaskan medium range forecast predictability remains generally
above average due to a relatively stable and blocky larger scale
flow regime, but quite a bit of uncertainty still builds over time
with offshore lows and with small scale weather features embedded
within the larger scale flow.
Accordingly, the WPC Alaskan medium range product suite was
primarily derived from a composite blend of well clustered
guidance of the 12 UTC GFS/ECMWF, GEFS/ECMWF ensemble means and
the 19 UTC National Blend of Models Friday into Sunday. Quickly
transitioned blend weightings away from the deterministic models
amid growing uncertainty next week, but applied manual adjustments
to ensure offshore low strengths consistent with upper support.
This maintains decent WPC continuity.
...Overview and Weather Hazards/Threats...
An amplified upper-level ridge lingers from the Arctic Ocean to
eastern Alaska and northwest Canada. This will support above
average temperatures with anomalies upwards of 15 deg F over the
Brooks Range and vicinity. This will enhance snow/ice melt, so
please refer to your local office for any seasonal river ice flow
issues.
A deepened east Pacific low will lift northward into the eastern
Gulf of Alaska mid-late week. Maritime wind/rain impacts may
modestly affect Southeast Alaska. The system should slowly weaken
and meander over the northern Gulf of Alaska next weekend, blocked
underneath the upper ridge.
Meanwhile, a surface system will continue to weaken and lift
northward on the northwestern periphery of the upper ridge to the
Arctic Ocean by Friday. Another low in the wake of this system is
expected to meanwhile dissipate over the far southwest Bering Sea.
A slow moving and deepened north Pacific low is then slated to
bring wrapping winds/rains to the Aleutians this weekend then
onward to the Alaska Peninsula and southern Alaska early next
week. The low would also present an organized maritime hazard.
Triple point low re-development and some system energy phasing
may spread activity downstream across the Gulf of Alaska early
next week.
Schichtel
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 southern mainland Alaska and the
Aleutians, Mon, Jun 1.
- Much above normal temperatures for parts of northern mainland
Alaska, Thu-Mon, May 28-Jun 1.
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