Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
322 PM EDT Sat Jul 27 2019
Valid 12Z Wed Jul 31 2019 - 12Z Sun Aug 04 2019
It remains the case that the overall flow pattern across Alaska
should be fairly progressive during the medium range period
(Wed-Sun). This features an upper level low skirting the northern
coast Wed-Thurs before lifting north into the Arctic, which should
push a cold front through northern and central interior Alaska.
Meanwhile, one shortwave crosses the Aleutians Wednesday into
Thursday next week, while another trough builds into the Bering
Sea later in the week and next weekend. This type of pattern would
support increasing rain chances (with snow in the higher
elevations) from north to south through the week across mainland
Alaska, with more enhanced precipitation possible along the
favorable terrain. A couple of rounds of showery activity is also
likely across the Aleutians into the Peninsula as shortwave energy
passes through and the more amplified trough takes shape across
the Bering Sea late next week. Mean troughing over much of Alaska
would support temperatures near or below normal for most of the
period.
In general, the guidance shows fairly good agreement days 4-5
(albeit some minor timing and amplitude differences) to warrant a
majority deterministic blend for the first part of the period.
After this, detail differences in the deterministic runs increase
significantly, especially with respect to the deep low across
northern Alaska/the Arctic and the evolution and amplification of
shortwave energy entering the Gulf/north Pacific Thursday into
Friday. The ensemble means show very good agreement through the
entire period so increasing weightings of the means was used after
day 5. This approach fits well with yesterday's forecast, as well
as with continuity downstream across the CONUS.
Santorelli
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
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