Area forecast discussion
National Weather Service Portland or
246 am PDT Sat may 18 2013
Synopsis...a cold front will spread light rain across the region
today. Showers will decrease tonight but continue over the mountains
through Sunday morning. High pressure will result in drier and
gradually warmer temperatures Sunday and Monday. An upper level low
will bring a return of rain and much colder weather Tuesday with
light snow accumulations possible below the Cascade passes by
Wednesday morning. Cool and showery weather will continue through
Friday.
&&
Short term...today through Tuesday night...the next front is
approaching the coast. Ascat satellite derived winds showed the cold
front around 300 miles offshore at 11 PM last night. Radar imagery
shows rain ahead of the front just reaching the northern Oregon coast
at 2 am this morning. AMSU shows tropical precipitable water around
an inch with the front. An upper level jet pointed towards southern
Oregon will provide enough lift to tap into this moisture...resulting
in light rain over much of the region today. The front should move
across northwest Oregon this afternoon with isolated to scattered
Post-frontal showers tonight.
Showers over the higher terrain will likely persist through Sunday
morning...but otherwise dry weather can be expected Sunday as high
pressure builds over the area. Sunday morning will likely be cloudy
with partial clearing in the afternoon...leading to inland daytime
highs in the middle to upper 60s and coastal highs in the upper
50s...slightly below the seasonal normal.
High pressure maintain dry weather for Monday which will likely be
the warmest day of the week. Increased sunshine should warm interior
temperatures to slightly above normal...low 70s and coastal areas to
near normal...lower 60s.
An upper level low will approach Monday night and bring a return of
showers and much cooler weather to the region. Models have backed off
the timing of the onset of rain around 12 hours. The coldest air
associated with the low will begin moving over the area Tuesday night
and snow levels should lower to around 3500 to 4000 feet.
Long term...Wednesday through Friday...a cold closed low will
continue unsettled weather with unseasonal cold temperatures
Wednesday...with record low maximum temperatures possible. Wednesday
will be the coldest day of the work week. Temperatures will remain
below the seasonal normals Thursday and Friday as a couple of
shortwave troughs will continue showery and cool conditions.
&&
Aviation...a front will approach the area this morning with ceilings
gradually lowering...with MVFR and occasional rain increasing between
10z and 14z. Front is fast moving...so return to VFR likely
between 19z and 22z...first on coast and later inland as the front
sweeps east of the Cascades by middle afternoon.
Kpdx and approaches...VFR conditions for the next couple of hours.
Areas of MVFR ceilings down near 2500 feet increase between 12z and 15z.
Front will push across kpdx Ops area between 20z and 22z...with
return to VFR with scattered showers.
&&
Marine...a front will push across the coastal waters this
morning...then inland in the afternoon. Winds not all that
impressive but there seems so be enough gradient to pop gusts 20
to 25 knots this morning. So will maintain current Small Craft
Advisory. Otherwise...winds turn west to northwest behind the front in the
afternoon and begin to ease.
High pressure will build over the NE Pacific sun into early next week.
This will keep northwest winds 10 to 15 knots through much of the coming
week...though may briefly get 20 to 25 knots gusts Monday afternoon into
the evening.
Seas remain at 5 to 6 feet for into early next week. May see seas
build up and become choppy at times with the brisk northwest winds on the
central Oregon coastal waters next week.
&&
Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...Small Craft Advisory for winds from 6 am to noon
PDT today for all coastal waters.
&&
$$
More weather information online at...
http://weather.Gov/Portland
This discussion is for northwest Oregon and southwest Washington from
the Cascade crest to 60 nautical miles offshore. The area is commonly
referred to as the forecast area.
