Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
657 PM EDT Thu Apr 16 2020
Valid 12Z Mon Apr 20 2020 - 12Z Fri Apr 24 2020
...Overview and Guidance Evaluation...
Forecast uncertainty remains an issue from the Aleutians southward
for early to middle of next week as a double-barrel low pressure
system rotates in the vicinity. Nevertheless, the model spread
has decreased since yesterday as the ECMWF slows down considerably
while the GFS and the CMC speed up and weaken the system toward
the middle of next week. The ensemble means have also come into
much better agreement with each other, placing a cyclone center
south of the central Aleutians next Tuesday into Wednesday. The
WPC pressure fields were derived using a consensus of the 00Z EC
mean and the 12Z NAEFS together with the 12Z ECMWF and the 06Z and
12Z GFS. More of the ensemble means were used for the longer range
period, splitting between the 00Z EC mean and the 12Z NAEFS. This
results in a cyclone moving quite slowly eastward to a position
south of the Alaska Peninsula by next Friday.
Models are much more agreeable for other areas of Alaska. The
stationary ridge over Alaska should gradually weaken with time
while the arctic air farther north is forecast to edge closer
toward Alaska and then slide off to the east.
...Weather/Threats Highlights...
A good chance of precipitation should be across the southern to
central Alaska due to remnant moisture associated with a
dissipating front moving into the western mainland early next
week. The wavy front persisting across the northern mainland for
most of the period will also provide a precipitation focus. It
appears that the large scale pattern evolution should promote a
drier trend over much of the inland section while moisture will
tend to hover across the southern coasts as an occluded cyclone
approaches from south of the Aleutians. A lead wave on the
triple-point could bring a higher chance of precipitation into
southern and southeastern Alaska on Wednesday. Forecast
uncertainty continues to prelude more specific details for the
latter part of next week but lingering precipitation appears the
most probable scenario along the southern coastlines.
The temperature forecast looks consistent, with above normal
temperatures over most of the state during the period aside from
the Panhandle and major valleys over the southern mainland where
highs may be modestly below normal. Morning lows should tend to
be farther above normal than daytime highs and the northern
mainland will likely see the highest anomalies. As broad cyclonic
flow edges southward from the Arctic and then slides off to the
east, there is a general cooling trend for much of Alaska toward
the end of next week.
Kong
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 precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon-Wed, Apr 20-Apr 22.
- Heavy precipitation across portions of mainland Alaska, Sun, Apr
19.
- Much above normal temperatures across portions of mainland
Alaska, Sun-Mon, Apr 19-Apr 20.
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