Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
710 PM EDT Fri Apr 09 2021
Valid 12Z Tue Apr 13 2021 - 12Z Sat Apr 17 2021
...Locally heavy rain likely for parts of Southeastern Alaska next
week...
...Guidance/Uncertainty Assessment...
The upper pattern will be characterized by anomalous and blocky
flow next week with troughing along 160W and ridging over the
Bering and NW Canada/AK Panhandle. An upper low is forecast to
sink south-southeastward with multiple embedded vortices around
it, suggesting lower predictability on the smaller scale. Trend
has been toward a slower and more amplified pattern overall, and
this was supported by the 12Z ECMWF/UKMET/Canadian/Canadian
ensembles and 00Z ECMWF ensembles. The GFS and its ensembles were
just a bit quicker and weaker to start, especially with a deeper
system moving across the Aleutians Tue-Wed, and eventually were
completely out of phase with the larger consensus by the end of
the week and much quicker overall. Preferred the slower and more
amplified solution and used a majority deterministic weight
through next Friday to maintain system details and meridional
flow.
...Weather/Hazards Highlights...
Southerly flow early in the week will sustain well above normal
precipitable water values, perhaps nearing as high as they can
reach for this time of year, as a system moves into and through
the Gulf Tuesday with a stronger system early Wednesday. The
former may spread modest to locally heavier rain to parts of the
Panhandle while the latter may bring more widespread modest and
heavier rain (higher elevation snow) to Southcentral (southern
Kenai to Prince William Sound especially, in addition to the
western side of Cook Inlet). Several inches of rain will be
possible. Once that system lifts northeastward out of the region,
upper ridging will nose in from the southeast as the upper low
sinks southward through the northeastern Pacific. This should
introduce a drying trend for most of the state starting Thursday
into Saturday.
Temperatures will trend milder as southerly flow brigs warmer air
northward, especially over northern areas across the North Slope.
The Panhandle may see an extension of below normal temperatures
with high pressure nearby and the southerly flow mostly
west/offshore across the Gulf.
Fracasso
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon-Wed, Apr 12-Apr 14.
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