Funnel Clouds in Oregon, April 28 to 29, 2018

Area Forecast Discussion
National Weather Service Portland OR
233 PM PDT Sat Apr 28 2018

.SYNOPSIS...A cool upper level low pressure will slowly move across
the region this weekend, maintain plenty of clouds and showers. This
low will push east of the region early next week, with warmer and dry
weather returning Wed.

&&

.SHORT TERM...Tonight through Tuesday...Cool upper low pressure area
now sits over the Pac NW, with cool onshore flow across the area.
Scattered showers will continue, through still think these will
decrease a bit later tonight over far north zones, such as those
along and north of Columbia River. Instability just enough that can
not rule out an isolated thunderstorm into early this evening, but
best chance of such will be south of a Tillamook to Portland line.

Main center of the upper low will track across western Oregon tonight
into Sun, then east of the Cascades later Sun afternoon. So, this
will maintain decent chances of showers later tonight through Sun
evening. Will begin to see increasing north to northwesterly flow
aloft Sun night, which will act to stabilize the air mass. Think
showers decrease quickly Sun night, but will keep higher chance over
the Cascades. Yet another weak disturbance in the flow will pass over
the region on Mon, though main energy will stay offshore. Still, will
be close enough to maintain a chance of showers on Mon, but likely to
stay more over the mountains.

Will not stray much from MOS guidance on temperatures, as cool air
mass will keep temperatures generally in the middle to upper 50s and
possibly the lower 60s.

Now appears that Tue will be the transition day, as high pressure
builds offshore. Under this pattern, would expect morning clouds with
partly sunny skies in the afternoon. Likely to be fairly typical
spring day, with highs in the lower 60s. While could see a stray
shower over the Cascades, not confident will see. So, will remove
shower threat from Tue. 		      Rockey.

.LONG TERM...Tue night through Friday...Models show the offshore
upper level ridge building into the region on Wed. This will result
in warmer and drier weather for the middle of next week, but there is
still some uncertainty regarding how warm it will get. For now, will
keep inland highs generally in the 70s, with warmest day likely on
Thu. The 12Z models still have a weak shortwave trough moving across
the forecast area on Fri, which could bring some scattered showers to
the region while the 12Z ECMWF maintains the upper level ridge.
Decided to keep the mention of showers in the forecast for Friday
morning, but would not be surprised to see it removed in the coming
days.

&&

.AVIATION...A showery and unstable lower atmosphere should
produce predominantly VFR conditions areawide with short lived
and difficult to predict MVFR conditions at a taf site or two
from time to time through 03-06z Sunday. A stabilizing lower
atmosphere and lingering moisture should lead to MVFR conditions
returning to many taf sites towards 06-12z Sunday. Would not be
surprised to see a site or two drop into IFR conditions at least
temporarily overnight, but confidence remains low enough to
exclude it from any specific taf site for now.

KPDX AND APPROACHES...A showery and unstable lower atmosphere
should produce predominantly VFR conditions through this evening.
A passing shower could temporarily produce MVFR conditions, but
this will be difficult to predict with much notice. Light winds
and lingering low level moisture should result in MVFR conditions
returning towards 06-12z Sunday. /Neuman

&&

.MARINE...A weak front will drop southeastward across the waters
late tonight and early Sunday. Expect gusty northwest winds to
follow behind the front on Sunday. Wind gusts will generally
remain 20 kt or less across the waters except across the northern
outer waters, generally beyond 30 NM where gusts to 25 kt appear
possible. Stronger winds off Vancouver Island will result in a
fresh swell moving into the waters Sunday and Sunday night as
well. This swell appears likely to be steep and hazardous across
at least the northern outer waters with combined seas in the 9
to 11 ft range with dominant periods around 10 seconds. Small
Craft Advisories were issued to cover both the wind and wave
height hazards across the northern outer waters, but held off on
expanding them into the central Oregon waters and the nearshore
northern waters.

Otherwise, high pressure will build back over the northeast
Pacific and thermal low pressure will return to northern
California. This will result in a more summer-like northerly wind
pattern early next week, albeit somewhat subdued. Seas will
likely fall to near 5 ft or below during the second half of next
week. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds from 8 AM to 9 PM PDT Sunday for
     Waters from Cape Shoalwater WA to Cascade Head OR from 10
     to 60 NM.

     Small Craft Advisory for hazardous seas from 8 AM Sunday to 3
     AM PDT Monday for Waters from Cape Shoalwater WA to
     Cascade Head OR from 10 to 60 NM.

&&

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the CWA or forecast area.