Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Sun Mar 17 2019
Valid 12Z Thu Mar 21 2019 - 12Z Mon Mar 25 2019
...Weather Highlights/Hazards...
Latest models and ensembles continue to highlight a pattern quite
favorable for multiple periods of terrain and coastal convergence
enhanced precipitation especially into the southern coast of the
Mainland as well into Southwest and northern Southeast Alaska
through this medium range period. Moist inflow will continue to
wrap around an active series of deepened Gulf of Alaska surface
lows that re-develop as energies work under influence of an
amplified mid-upper level mean trough/closed low. Systems will tap
atmospheric rivers to produce daily totals averaging several
inches with some additional and locally favored 5-day totals of
10+ inches. The airmass quickly loses moisture content farther
inland, but continue to expect modest snows inland from southwest
Alaska to the western/central Interior to northern Alaska as
energy lifts in a channel between a Bering Sea mean mid-upper
level trough/low and an Interior Alaska/western Canadian mid-upper
level ridge. Relatively dry conditions are expected to persist for
much of the east-central Interior under that ridge.
Meanwhile upstream, expect increasingly stormy conditions for the
southern Bering Sea/Aleutians mid-late next week then again next
weekend with deep surface low developments under a mean closed
upper low/trough position. Highly unsettled weather will
accordingly work steadily eastward with system progression toward
the Alaska Peninsula/southwest Alaska in advance of and with
triple point low transitions downstream of the deep parent lows.
...Guidance Assessment...
After consultation with local Alaskan WFOs, the WPC Alaskan Days
4-8 product suite was mainly derived from a blend of well
clustered guidance from the 00 UTC ECMWF ensemble mean and
deterministic ECMWF/Canadian models. This combination shows
detail/offshore storm intensities consistent with average
predictability, favorable dynamic support and pattern history, but
offer potential to be quite deep. We'll monitor this threat into
shorter time frames. Recent GFS/GEFS runs have been seemingly too
progressive with systems eminating across the north Pacific but
the latest 12 UTC versions have at least trended slower.
Schichtel
Bullet points from the WPC Days 3-7 Hazards chart can be found 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