Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
418 PM EDT Tue Mar 12 2019

Valid 12Z Sat Mar 16 2019 - 12Z Wed Mar 20 2019

The latest guidance maintains confidence that the ridging over
western Canada and southeast Alaska will remain in place along
with persistent troughiness near the Aleutian Chain. A series of
lows will rotate northward through the Gulf toward the Mainland
and quickly weaken onshore. The forecast during days 4-5 (Sat-Sun)
was based heavily on a blend of the ECMWF/GFS solutions, which
showed relatively good consensus during this early portion of the
extended period. While spread is a bit higher given the time
frame, models show general agreement that another low pressure
system should follow a similar track north across the Gulf on Mon,
with yet another following quickly on its heels just beyond the
forecast period.

Despite increased spread on the timing, intensity, and structure
of these systems later in the extended period, ensemble scatter
plots reveal some semblance of clustering even through the end of
the period. The forecast was shifted gradually toward heavier
weighting of ECENS and GEFS ensemble means starting on day 6 (Mon).

The continuous track of storm systems across the Gulf into
southern Alaska, and the persistent deep southerly flow will make
for a period of widespread and occasionally heavy precipitation
for many areas from southern mainland Alaska to Southeast Alaska.
The air mass will quickly lose its moisture content farther
inland, however, with relatively dry conditions expected to
persist across the Interior and the North Slope. Additionally, the
weekend system may bring the potential for high wind gusts to
southern mainland Alaska, particularly for coastal areas.


Campbell/Ryan


Bullet points from the WPC Days 3-7 Hazards chart:
<a href="https://www.wpc.ncep.noaa.gov/threats/threats.php"><u>https://www.wpc.ncep.noaa.gov/threats/threats.php</u></a>

- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Fri-Tue, Mar 15-Mar 19.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Fri-Mon, Mar 15-Mar 18.


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

<a href="https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif"><u>https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif</u></a>
<a href="https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml"><u>https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml</u></a>
<a href="https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html"><u>https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html</u></a>