Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
545 PM EST Sun Feb 23 2020
Valid 12Z Thu Feb 27 2020 - 12Z Mon Mar 02 2020
After getting a better handle on the large scale flow pattern
across Alaska during the extended period, guidance continues to
struggle with some of the details of individual systems. An
upper-level high should gradually weaken across the northern
Bering Sea by late in the week. This setup will allow for
increasing influence from arctic shortwave energy across much of
mainland Alaska, with another round of very cold temperatures
likely. Farther south, a very active North Pacific storm track
will persist across the Aleutians, with the potential for a deep
surface low to move into the southern Bering Sea by next weekend.
By day 4 (Thu) a low pressure system is forecast to cross the Gulf
of Alaska, bringing potentially heavy precipitation to portions of
southern mainland Alaska and the Alaska Panhandle. Guidance shows
some consensus that a second wave of low pressure along the
trailing portion of this front could move across the far
southeastern Gulf of Alaska on Fri, bringing a continuation of
precipitation for Southeast Alaska north of the low track. Farther
west, models show the potential for a couple low pressure system
to affect the Aleutians later in the week, one Thu night-Fri
(models show a fairly large degree of spread with this one) and
another one (the stronger of the two) Fri night-Sat. Opted to lean
toward the UKMET/ensemble means with the leading low, which showed
an initially stronger system eventually becoming absorbed in the
broader frontal zone before the second low approaches. For the Fri
night-Sat system, model differences were a bit less, but solutions
did show a fair degree of variability on the timing and track of
the system. Ensemble means showed low pressure shifting east
toward southern mainland Alaska by early next week, and this was
reflected on the day 8 surface prog. In general, the UKMET was
weighted relatively heavily along with some use of ECENS/GEFS
ensemble means during days 4-5. During days 6-8 (Sat-Mon), due to
increasing variability and spread among deterministic guidance,
leaned much closer to ensemble means, along with some limited use
of the ECMWF, which was reasonably well-centered within the
ensemble spread later in the forecast period.
Ryan
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