Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
232 PM EST Wed Nov 07 2018

Valid 12Z Sun Nov 11 2018 - 12Z Thu Nov 15 2018

A slow moving upper-level low will plague the forecast through the
extended period, with downstream ridging initially in place across
western Canada/eastern Alaska. Model consensus is relatively good
with respect to the big picture, but solutions begin to differ
substantially from day 6 (Tue) onward with respect to the details
of individual disturbances rotating through the larger upper low,
as well as the degree to which the ridge across eastern Alaska
erodes/weakens. At least initially, the best clustered solutions
around an ensemble based consensus for the relatively strong low
pressure system near the Aleutians/Alaska Peninsula on day 4 (Sun)
appeared to be the ECMWF and CMC. Thus, these two solutions were
weighted heavily early in the extended period (days 4-5). The
ECMWF was slower to weaken the upper ridge from day 6 onward
relative to the CMC (and GFS), thus, the ECMWF was weighted a bit
more heavily relative to the CMC through much of the period.
Weakening of the ridge should allow the upper low to drift
relatively slowly eastward toward the Gulf of Alaska by the middle
of next week, with some potential evident among the guidance for
another strong surface low in the Gulf by that time. Given rather
poor clarity on the details, however, weighting of the ECENS and
GEFS ensemble means gradually boosted during the day 6-8 (Tue-Thu)
time frame.

The deep low pressure system near the eastern Aleutians/Alaska
Peninsula Sun-Mon will produce heavy precipitation across portions
southern mainland Alaska and Southeast Alaska, close to the coast.
Liquid equivalent precipitation amounts on the order of several
inches are likely, with heavy snow expected in mountainous areas.
This system may be accompanied by wind gusts in excess of 40 mph.
The next potentially significant system in the Gulf of Alaska
early next week could bring another round of heavy
precipitation/wind to some of the same areas, although as
mentioned above, details remain murky at this time. Relatively
warm and moist southerly flow will keep temperatures several
degrees above average across much of central/southern mainland
Alaska and Southeast Alaska through the period. The one exception
will be north of the Brooks Range where Arctic high pressure will
dominate through the period, keeping temperatures more than 10 deg
F below average for some areas, and also helping to keep
relatively dry conditions in place.


Ryan

WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html