Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 230401

Area Forecast Discussion
National Weather Service Medford OR
901 PM PDT Sat Apr 22 2017

.DISCUSSION...Previous forecast looks good and no changes are
needed for tonight. The latest radar shows isolated storms
developing in central Shasta County (south of our forecast area)
and are moving northeast. Models hint at some weak instability
northeast of the isolated storms, but probably not enough to
generate storms. The latest model runs are pretty consistent with
the previous runs with the timing and evolution of the next upper
trough which will bring increasing showers east of the Cascades
and the coast tonight into Sunday. More significant precipitation
along with gusty winds will impact the area Sunday night into
Monday. Details on this are outlined in the previous discussion
below. -Petrucelli


.AVIATION...23/00Z TAF CYCLE...Over the coastal waters...along the
coast...and in the Umpqua Basin...VFR with local MVFR cigs initially
with areas of higher terrain obscured.  Areas of MVFR cigs in
showers will develop later tonight and persist through Sunday.
Over the remainder of the area...VFR conditions will prevail through
Sunday with areas of higher terrain obscured.


.MARINE...Updated 150 PM PDT Saturday 22 April 2017...A weak front
will move onshore Sunday morning...followed by a stronger one Sunday
night into Monday morning.  The second front will bring hazardous
seas to nearly all of the coastal waters and near gale forced south
winds to the waters north of Cape Blanco. A weaker front will move
onshore Tuesday...followed by an even weaker front Thursday. There
is moderate to high confidence in high pressure building in across
the Eastern Pacific Friday through next weekend.


.PREV DISCUSSION... /Issued 244 PM PDT Sat Apr 22 2017/

DISCUSSION...Generally light showers continue to taper off this
evening ahead of a short wave that brings a trough onshore Early
Sunday morning with an upper level trough over the forecast area.
As is fitting to the tail end of this abundant rainy season, there
is very little in the way of a break between this short wave and
the next system that moves in Sunday afternoon. As has been the
case many times, the coast gets a short drink from the fire hose
as this system moves in on a strong +145 kt westerly jet, and with
strong 700 mb winds near 50 kt and an atmospheric river event
being indicated the south coast will see close to two inches of
rain, snow levels will be relatively low, near 5000 feet, and the
Cascades may see winter weather advisory snow amounts. The strong
jet axis moves down directly over the region by Monday morning,
and with the strong 700 mb winds, brief periods of white-out
conditions are also possible into Monday morning. However, since
this is tomorrow night, will wait until tonight`s model runs to
see if this still looks likely. The jet axis moves north and puts
the area in a less dynamically favorable right exit region, but
that just changes the fire hose to a big garden hose with showers
continuing through Tuesday night. Sven

LONG TERM...Wednesday through Saturday...The strong Pacific jet
will become oriented more/less northwest to southeast across the
area Wednesday and Thursday. This will keep SW Oregon and northern
California in a moist, onshore flow with plenty of showers, focused
along the coast, adjacent coast ranges and into
the Cascades/Siskiyous. While this pattern favors showers in those
areas, scattered showers are also expected in the valleys and
south/east of the mountains. Temperatures will likely remain below
average with highs in the upper 50s to low 60s over the west side
and in the low to mid 50s over the east side.

By Friday, the best forcing associated with an upper trough will
shift to the east and showers will diminish/end. Temperatures should
edge back closer to normal.

Models then indicate high pressure offshore building into the area
Friday night into Saturday. The ECMWF builds the ridge strongly,
which, if correct, temperatures could take a run at 80F here in
Medford. The GFS is more subdued and flatter with the ridge. Either
way though, temperatures should make it back above normal. -Spilde




Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Sunday for
     Small Craft Advisory for hazardous seas from 11 PM Sunday to 11
     PM PDT Monday for PZZ356.
     Hazardous Seas Warning from 11 PM Sunday to 11 PM PDT Monday for

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