Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
614 PM EDT Sat Apr 10 2021
Valid 12Z Wed Apr 14 2021 - 12Z Sun Apr 18 2021
...Locally heavy rain possible for parts of Southcentral
Wednesday...
...Guidance/Uncertainty Assessment...
The upper pattern will feature anomalous and blocky flow next week
with troughing along 160W and ridging over the Bering and NW
Canada/AK Panhandle by Friday. An upper low is forecast to sink
south-southeastward with multiple embedded vortices around it,
suggesting lower predictability on the smaller to medium scale.
The trend over the past day or so has been toward a bit quicker
progression of the trailing shortwave that tugs the upper trough
southward late next week into the weekend, which allows folded
over ridging to connect along 55N late in the period. This would
open up the flow to the north from the northern Bering across the
North Slope and Beaufort Sea to more zonal flow. Though the GFS
and Canadian were a bit removed from the better clustering (and
better consensus) of the 12Z ECMWF/UKMET/Canadian ensembles and
00Z ECMWF ensembles, they were not too far from consensus around
the edges of the domain. Therefore, a small minority weighting of
the GFS/Canadian rounded out the larger consensus weighted mostly
toward the ECMWF/UKMET and Canadian/ECMWF ensembles. This did
nudge the systems around here and there as smaller timing
differences at the onset grew with time, but overall the pattern
evolution remained much in line with continuity.
...Weather/Hazards Highlights...
Southerly flow Wednesday coincident with the system through the
Gulf will sustain well above normal precipitable water values,
perhaps nearing as high as they can reach for this time of year,
as low pressure moves across Kodiak. Widespread modest to heavier
rain (and elevation snow) are possible for parts of Southcentral
(southern Kenai to Prince William Sound) where 1-2 inches of rain
will be possible with locally higher amounts on south-facing
terrain. 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. A system will skirt through the North Slope with
little precipitation.
Temperatures will be milder than average for especially northern
areas of Alaska as southerly flow brigs warmer air northward. The
Panhandle and parts of Southcentral/southeastern Alaska may see an
extension of below normal temperatures with high pressure nearby.
Fracasso
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