textproduct: Portland

SYNOPSIS

Conditions remain cool and wet through tomorrow as an upper level low and surface fronts move over the region. A warming and drying trend is expected Thursday and through the start of next week as high pressure builds over the eastern Pacific.

DISCUSSION...Now through Monday Night

Conditions continue to trend cooler and drier as the upper level low continues to move inland. Bands of light rain will continue streaming in from the south/southeast through tonight. As the upper level low moves eastward, a second upper level low will slide southward from western Canada and push a cold front across the CWA tonight and into tomorrow. This second system will bring about a more west/northwest wind pattern as well as a second round of rain and clouds to the region through mid-day Wednesday. Cloud cover and rain will keep overnight temperatures in the upper 30s to upper 40s, but expect skies to slowly clear through the early afternoon on Wednesday. Clearing skies will enable daytime temperatures to warm into the upper 30s to mid 40s for the Cascades and mid 40s to upper 50s along the coast and inland locations. Rain will be light, with precipitation totals from this evening through mid-day Wednesday ranging from 0.05 to 0.50 inches for lower elevations. Better forcing along the Cascades will result in precipitation totals above 0.30 to 1.40 inches for the Cascades through the same time period. There is a 10% chance or less for thunderstorms confined to the southeastern portion of Lane county. If any storms or more convective precipitation develops, this could lead to locally higher rainfall totals.

As we move into the latter part of the week, conditions trend dry and warm, though light showers may linger over the Cascades early Thursday morning. High pressure looks to build over the eastern Pacific, which places the Pacific NW on the east/northeast flank of the ridge. This will result in skies clearing along with daytime highs warming into the upper 60s to low 70s on Friday with similar daytime highs expected through at least the start of next week. Overnight lows in the 40s expected during this time frame. Given that the region looks to be on the eastern flank of the Pacific ridge, we will be squished between this ridge and a broad area of low pressure that will be anchored over the far northern Planes and southern Saskatchewan. This is leading to some uncertainty as we move into the weekend. As the Saskatchewan low meanders into place, it will send a series of shortwave troughs that will ride the eastern flank of the ridge. Given that the shortwaves, originate from a continental system, they will lack moisture. This is generally supported in the NBM, GFS and ECMWF as well as the majority their ensembles. /42

AVIATION

At 20:30Z Tuesday, a slow-moving occluded front was lifting northward across northwest OR and southwest WA with widespread light rain showers. Ceilings were mainly MVFR with pockets of IFR, except VFR from KONP to KEUG as these two terminals are behind the frontal boundary. KSLE and KUAO were also starting to see ceilings lift to VFR as these terminals were near the backside of the front. However, KUAO and KSLE may see occasional drops back to MVFR thresholds with passing showers through 00Z Wednesday. For the remaining terminals, expect little improvement through 00-03Z Wednesday with rain showers continuing. Rain showers will taper off thereafter with ceilings likely improving to VFR at all inland terminals.

The break in precipitation after 00-03Z Wednesday will be short- lived as moisture on the backside of a low shifting into central/eastern OR rotates counter-clockwise into southwest WA and far northwest OR. This will result in light to moderate stratiform rain spreading southward into the area from the north, likely impacting KAST, KPDX, KTTD, and KHIO by 15Z Wednesday. Expect ceilings to lower back to MVFR thresholds with the arrival of stratiform rain. Rain will begin last at KUAO, KONP, and KEUG, most likely around 18Z Wednesday at KUAO and around 00Z Thursday at KONP and KEUG. Breezy southwest winds are also expected to develop Wednesday morning at all terminals, with occasional wind gusts up to around 20 kt.

KPDX AND APPROACHES...MVFR ceilings continue at the KPDX terminal Tuesday afternoon with light rain showers and light winds. Expect this trend to continue through at least 00Z Wednesday, before conditions trend towards VFR by 02Z Wednesday. This is also when a break in precipitation is expected to begin. This break will be short-lived, as stratiform rain is expected to move in from the north towards 15Z Wednesday. This will also bring the return of MVFR ceilings along with breezy southwesterly winds with gusts up to around 20 kt. -23

MARINE

Winds and seas will increase over the coastal waters tonight into Wednesday ahead of an approaching cold front. By early to mid Wednesday morning, a northwest swell will push seas up to 7 to 8 ft with westerly winds around 15 to 20 kt with gusts up to 25 kt over the central and northern waters. The southern waters will see winds and seas increase a bit later in time, beginning Wednesday afternoon. Seas peak between 9-13 ft Wednesday evening into Wednesday night at 10 to 12 seconds, bringing steep and hazardous seas. The highest seas are expected over the northern outer waters beyond 20-30 nm. Winds decrease Wednesday night behind the frontal passage, however seas will remain elevated until significant wave heights fall below 10 ft by late Thursday afternoon.

Therefore, a Hazardous Seas Warning has been issued for PZZ271 from 2 PM PDT Wednesday through 5 AM PDT Thursday, following a Small Craft Advisory that begins at 5 AM PDT Wednesday. The remaining marine zones have Small Craft Advisories in effect from 5 AM Wednesday until 5 PM PDT Thursday, except 5 PM Wednesday until 5 PM PDT Thursday for the southern waters as winds and seas take longer to increase south of Cape Foulweather. Note there is a 10-25% chance seas will peak near 14-15 ft over the northern outer waters, which represents a reasonable worst case scenario.

A strong ebb current will occur over the Columbia River Bar Wednesday morning, pushing seas up to 7 to 8 ft with steep ebb chop over the main channel. Seas then increase to around 9 to 10 ft over the main channel late Wednesday and remain elevated Wednesday night into Thursday. In addition, westerly winds will increase to 15 to 25 kt with gusts up to 25 kt. Winds will become southwest around 10 kt with gusts up to 15 kt Thursday morning. A Small Craft Advisory has been issued from 5 AM Wednesday PDT to 5 PM PDT Thursday for the Columbia River Bar to cover these hazards. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 AM Wednesday to 5 PM PDT Thursday for PZZ210-251-252-272.

Small Craft Advisory from 5 PM Wednesday to 5 PM PDT Thursday for PZZ253-273.

Small Craft Advisory from 5 AM to 2 PM PDT Wednesday for PZZ271.

Hazardous Seas Warning from 2 PM Wednesday to 5 AM PDT Thursday for PZZ271.