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Prognostic Meteorological Discussion (PMD)

Issued by National Weather Service (NWS)

                            
000
FXAK02 KWNH 191848
PMDAK 

Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
247 PM EDT Wed Jun 19 2019

Valid 12Z Sun Jun 23 2019 - 12Z Thu Jun 27 2019

An upper level low just west of the Panhandle to start the medium
range period (Sunday) will shift south and remain off the
Northwest U.S. coast for the remainder of the period while upper
level ridging builds across Alaska and holds strong through day 6.
There is some indication in the models that troughing may start to
break down the ridge across the northern mainland by day 7, with
the GFS a bit more aggressive on this than the ECMWF or the
ensemble means. Meanwhile, multiple shortwave perturbations will
rotate around a broad upper level low anchored from the Kamchatka
Peninsula of Russia to the far western Aleutian islands. Ensemble
means continue to hint at a developing omega block across the
Alaska region which would indicate this overall pattern being slow
to change through the entire day 4-8 period. This sends a surface
low into the Bering Sea and a cold front across the central
Aleutians early next week with indications of a second system
developing south of the Aleutians late in the period.

Days 4 and 5 show good enough agreement to warrant a majority
deterministic model blend (between the 12z GFS and 00z ECMWF),
with smaller contributions from the ensemble means (GEFS/ECENS).
After this time, increasing weighting of the ensemble means was
used to mitigate the smaller and less predictable timing and
detail differences with individual systems rotating around the
western Aleutians trough. This results in a forecast fairly close
to yesterdays continuity.

In terms of the sensible weather, most places across the Mainland
should be fairly warm and dry, with the best chance for showers
across the elevated terrain of southern Alaska. Increased rain
chances will be possible across parts of the central and western
Aleutians as southerly flow ahead of the broad upper level trough
advects moisture into the region and a series of surface lows move
nearby.

Santorelli


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

No significant hazards are expected over Alaska during this
forecast period.


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

$$