Prognostic Meteorological Discussion
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867
FXAK02 KWNH 232012
PMDAK

Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
411 PM EDT Mon Apr 23 2018

Valid 12Z Fri Apr 27 2018 - 12Z Tue May 1 2018

***Guidance/Uncertainty Assessment***

The medium range period begins on Friday with a lower than average
level of model agreement that only increases in time through next
weekend and into early next week.  There is general agreement on
the rapid weakening of the Bering Sea low that will be in place
through much of this week.  The CMC is differing from the model
consensus as early as Saturday with a lead surface low crossing
the Bering Sea, whereas the ensemble means keep low pressure much
farther to the west.  Since these differences with the CMC
escalate with time, it was not used in the forecast process.  The
GFS and its ensemble mean are farther south with the surface high
over the north Pacific and is a change from WPC forecast
continuity.  However, it is closer to the consensus with the main
surface low over eastern Siberia.  Given that the ECMWF is more in
line with the ensemble means over most of the forecast domain, it
was preferred over the GFS for this portion of the forecast period.


***Weather/Threats Highlights***

For Friday into the weekend, mostly dry weather is expected for
most areas with high pressure governing the overall weather
pattern.  Strong winds may affect the central and western
Aleutians later in the period as the strong low over eastern
Siberia begins to exert its influence over the Bering Sea and
northern Pacific.  Precipitation chances also increase for the
western third of the state by Saturday as this system gets
gradually closer.  The coldest temperatures, as expected, should
be confined to north of the Brooks Range, and gradually moderating
readings across most of the Interior.


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

D. Hamrick


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