Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
652 PM EDT Wed Jul 15 2020
Valid 12Z Sun Jul 19 2020 - 12Z Thu Jul 23 2020
The flow pattern across the North Pacific is forecast to become
gradually more amplified over the weekend and into early next
week, with an upper trough strengthening from the Bering Sea south
across the Aleutians, and an eastern Pacific ridge approaching the
Gulf region. The amplifying flow will allow for increasing
potential for arctic upper-level energy to move southward, with an
arctic upper low expected to affect the North Slope and portions
of the Interior this weekend, and another upper low forecast to
drop south across the western Bering Sea and then gradually
eastward across the Aleutians through the middle of the week.
The overall model and ensemble mean consensus has continued to
show some improvement with the synoptic scale pattern. Similar to
yesterday, the 12Z ECMWF is relatively well-clustered within the
overall consensus through much of the extended forecast period.
The CMC becomes more progressive with the first shortwave over the
Gulf of Alaska by Day 5 (Monday) and thus becomes slightly out of
phase thereafter, so it was not part of the model blend.
Therefore, the ECMWF was given slightly more weighting in the
model blend through Tuesday, along with some of the GFS. By the
middle to end of next week, a gradual trend toward more of the
GEFS and EC ensemble means was incorporated into the forecast to
account for increasing uncertainty in the deterministic guidance.
The primary impact of the system affecting the North Slope will be
on temperatures, with readings expected to be about 10 to 20
degrees below average through Tuesday before a moderating trend
commences. Portions of the Interior may also be slightly cooler
than normal for this time of year. Across southern Alaska, a low
pressure system will be approaching the southeastern Panhandle
region and the resulting onshore flow is expected to produce
enhanced rainfall from near Anchorage to the greater Juneau area,
with much of this rainfall being orographically enhanced. This
mainly holds true for Sunday and Monday, with less in the way of
organized rainfall for later in the week.
Hamrick
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 the Alaska Panhandle and
southern mainland Alaska, Sat-Mon, July 18-20.
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