Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
632 PM EDT Tue Apr 14 2020
Valid 12Z Sat Apr 18 2020 - 12Z Wed Apr 22 2020
...Overview and Guidance Evaluation...
Models and ensemble means agree rather well that an upper-level
ridge will remain stationary across Alaska through the
medium-range period. In contrast, the most uncertain area in the
forecast period continues to be from the Aleutians southward for
early to the middle of next week where a cyclone should be in the
vicinity. First of all, the spread of the cyclone center location
between the GFS and ECMWF has increased in recent runs, with the
GFS placing it over the central Aleutians but the ECMWF much
farther east by next Wednesday. The CMC also shows a stronger low
farther west comparable to the GFS solutions. On the other hand,
the GEFS' cyclone center locations in recent runs exhibit a
gradual eastward trend toward the 00Z EC mean center located
farther to the east. This appears to indicate that the 00Z EC mean
solution is more credible for the longer range. With the faster EC
solutions, the ridge over Alaska becomes weaker in the longer
range while the arctic air farther north is forecast to edge
closer toward Alaska. Therefore, the WPC pressure fields were
derived using a consensus of the 12Z ECMWF/12Z GFS/12Z GEFS
trending increasingly toward the 00Z EC mean for the longer range
period.
...Weather/Threats Highlights...
Expect a broad area of precipitation to cross Alaska through the
weekend, due to an initially strong low level flow ahead of a
dissipating front moving into the western mainland and a weakening
low pressure system over Aleutians/Bering Sea. The wavy front
persisting across the northern mainland for most of the period
will also provide a precipitation focus. Thus far there has not
been a coherent signal for which areas should see highest totals
during the period, with a number of regions potentially seeing
significant enhancement at least on a localized basis. The large
scale pattern evolution should promote a drier trend over much of
the mainland early next week. Parts of the Aleutians/Alaska
Peninsula could see meaningful precipitation/gusty winds depending
on the precise surface evolution by the latter half of the period.
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. Multi-day trends
have been toward a later southward push of the northern mainland
front but it should eventually drift south next week as broadening
cyclonic flow aloft over the Arctic begins to have some influence
over the northern part of the state.
Kong/Rausch
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, Fri-Sun, Apr 17-Apr 19.
- High winds across portions of mainland Alaska and the Aleutians,
Fri, Apr 17.
- Much above normal temperatures across portions of mainland
Alaska, Fri-Mon, Apr 17-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