936 
FXUS66 KPQR 132117
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR 
216 PM PDT Sat Oct 13 2018

.SYNOPSIS...Classic dry autumn weather for a while, with mild days
and cool nights, perfect for pumpkin patching. Will also see breezy
easterly winds ramping up tonight and continuing into early next
week. Dry weather will continue well into next week, perhaps longer.

&&

.SHORT TERM...Tonight through Tuesday...Visible satellite imagery
shows that all the low clouds from this morning have cleared, with
sunny skies in place throughout the forecast area. Temperatures are
generally running a couple degrees warmer than 24 hours ago, with the
Eugene area the main exception due to persistent morning fog and low
clouds. Suspect Eugene will catch up with the rest of the forecast
area within the next hour or two, and afternoon highs will generally
be within a few degrees of 70 for the lowlands today.

The temperature forecast for tonight will be a tricky one, largely
dependent on how persistent NE winds are through the night. Surface
high pressure will build into the Columbia Basin tonight and Sunday
behind a system departing the northern Rockies region. With the 18z
NAM showing the Columbia Basin high reaching 1034 mb by Sunday
morning, large-scale KOTH-KGEG pressure gradients may reach -13 mb or
possibly stronger. Based on the 18z NAM, synoptic-scale pressure
gradients remain N-NE through this evening, then become increasingly
easterly as the surface high settles in east of the Cascades.
However, pressures will remain rather high west of the Cascades as
well, so model gradients from KTTD-KDLS do not look all that
impressive at only -3.5 to -4.5 mb Sunday morning. On the other hand,
northerly gradients stay up through tonight, which may keep the
coastal valleys and the Willamette Valley too well-mixed to really
allow temperatures to bottom out overnight. Thus, we continue to
hedge temps above MOS values tonight for most areas, but we did nudge
them a little closer to MOS values with this forecast package.
Wind-sheltered valleys such as those in the Coast Range and Cascade
valleys have a better chance of reaching the 30s tonight, and if wind
goes calm enough to allow decoupling, there is no reason why other
valleys wouldn't be able to dip into the 30s as well.

The synoptic-scale offshore pressure gradients mentioned above really
come into play Sunday, with synoptic-scale offshore flow possibly
enough to deter afternoon seabreezes along the coast. With winds
downsloping off the Cascades and also the Coast Range, coastal areas
have a decent chance at being the warmest Sunday, with highs pushing
well into the 70s and possibly flirting with 80 degrees a mile or two
inland from the Central Coast of Oregon. It'll be warm inland as
well, with sunny skies and highs in the lower to mid 70s. Hood River
will be a little cooler due to their proximity to the cool Columbia
Basin high pressure system.

This will be the general pattern all the way through Tuesday, though
offshore flow will gradually ease and become increasingly confined to
areas near the west end of the Columbia Gorge. This will allow an
increasing number of valley locations away from the Gorge to dip into
the 30s and lower 40s overnight, with some cooler valley locations
possibly seeing some morning fog and/or frost. This will also be the
case for valleys north of the PDX metro area, while the PDX metro
area itself will remain a little warmer due to mixing from the
persistent east winds. Afternoon highs will likely remain in the
lower to mid 70s for the inland valleys, while the coast cools off a
bit due as offshore flow eases and allows the seabreeze to return. 
Weagle

.LONG TERM...Tuesday night through Saturday...Strong high pressure,
both at the surface and aloft, will only slowly weaken during middle
to latter portion of next week, per latest model consensus. Thus,
expect the stretch of mild days and cool nights to continue well into
next week. As offshore flow comes to an end, the chance of valley
inversions will increase, gradually bringing valley high temperatures
more in line with normal. The lighter winds may also lead to rather
chilly nights over the interior lowlands and mountain valleys. Very
well may see our first freezes for lowlands next week, especially
inland. This is not too far off from the average first freeze, which
typically is between Oct 15th and 25th.  Weagle/Rockey		  

&& 

.AVIATION...Last of the stratus around KEUG finally eroded around
19Z. VFR clear across the area early this afternoon. Thermally-
induced surface trough resides along the coast at 20Z, resulting
in low-level NE to E flow. However, offshore gradient yet to
develop through the Columbia River Gorge at 20Z. The KOTH-KSEA
gradient was -8.1 mb while the larger scale KOTH-KGEG gradient
was -5.6 mb. East surface wind expected to ramp up through the 
west end of the Columbia River Gorge late this afternoon or early
evening, with gusts up to 45 kt likely. Breezy conditions
elsewhere this afternoon and will continue through Sunday 
morning, especially along the coast and through east-to- west 
oriented coastal drainages and saddles and passes through the 
Cascades. 

KPDX AND APPROACHES...VFR clear at 20Z with no change through Sun
afternoon. Increasing east surface wind to develop near KTTD late
this afternoon and strengthen tonight. Pre-dominant NW wind
direction at the terminal through the afternoon, followed by a
shift to NE. Wind likely to go light and variable overnight.  
Weishaar

&&

.MARINE...High pressure will prevail through much of next week. 
Surface thermal low pressure to remain along the coast through
Sunday. Extended the small craft advisory for wind over the 
outer waters through 18Z Sun. 20Z buoy wind speeds a little less
than expected, but still have high confidence 25 to 30 kt gusts
will occur. Local gusts to 25 kt still appear possible over the 
inner waters in the vicinity of the coastal gaps through Sun
morning. Not enough support in the latest guidance, however, to 
warrant an advisory for the inner zones at this time. An advisory
may be needed if these gusts surface over a larger portion of 
the waters. The offshore pattern weakens early next week, with 
gusts returning to the 15-20 kt range by Monday. Wind speeds the
rest of the week will be generally 10 kt or less.  

Seas a little higher than expected, with the offshore buoys in 
the 6 to 7 ft range at 20Z. Expect wave heights today and 
tonight to remain constant, with the largest seas coincident with
the strongest winds. Conditions will be rather choppy through 
the weekend with a dominant period around 8 seconds due to the 
wind-wave contribution, as well as a pair of smaller swells. The 
largest seas will be over the outer waters, and may approach 
steepness criteria to warrant an advisory for hazardous seas. For
now, forecast periods appear to be long enough, around 9 
seconds, to avoid square-sea conditions, but this will need to be
closely monitored. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 11 AM PDT Sunday for 
     Waters from Cape Shoalwater WA to Florence 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.