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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1809Z May 23, 2018)
 
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Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
209 PM EDT Wed May 23 2018

Valid 12Z Sun May 27 2018 - 12Z Thu May 31 2018

...Guidance/Predictability Assessment...

Guidance clustering has improved in the day 4/5 timeframe over the
mainland where forecast confidence is now above average. A blend
of the well clustered 12 UTC GFS and 00 UTC ECMWF/ECMWF ensemble
mean seems to provide a good starting point for the forecast.
Model variance still offers some timing/emphasis challenges over
time, especially with Pacific systems entering the Bering Sea, so
transitioned to mainly ECMWF ensembles days 5-7 amid growing
forecast spread to best maintain WPC continuity.

...Weather/Threats Highlights...

Overall, it still seems reasonably likely that two main deep lows
will highlight the weather forecast in the vicinity of Alaska days
4-8. A lead low roams over the Gulf of Alaska this weekend, to
weaken early next week. Wrapping moisture will fuel high
winds/waves and widespread precipitation over the north-central
and eastern Gulf of Alaska that should increasingly spread onshore
into southern and southeastern Alaska with gradual low approach
into early next week. Less defined vort centers lingering overtop
the interior offer less predictability but overall suggest periods
of precipitation underneath an arctic ridge bridging just to the
north of the state. Meanwhile, a second main low also has marginal
guidance support, but whose potential approach into the Aleutians
and southern Bering Sea from the northern Pacific early to mid
next week would threaten the region with high winds/waves and
sweeping precipitation.

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

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html

Schichtel