textproduct: Portland

SYNOPSIS

Lingering rain across southwest Washington and the north Oregon coast and Coast Range continues through this evening. This is maintaining elevated rivers as runoff continues to drain downstream. Dry weather returns Friday to Saturday as high pressure builds. A weak frontal system arrives Saturday night into Sunday, followed by a stronger system Monday to Tuesday which may bring heavier rain and breezier winds. Flooding concerns continue into next week given the persistent wet pattern.

LONG TERM...Monday through Wednesday

Confidence is increasing that a stronger frontal system will arrive Monday to Tuesday following the weekend system, potentially bringing heavier rainfall and breezier winds. There is still uncertainty with exactly how much rain we'll get, but current guidance suggests the chances for 2" of rain or more in 48 hours from 4 AM Monday to 4 AM Wednesday are around 15-25% for most interior lowland valleys and 50-80% across the Coast Range, Willapa Hills, and Cascades, with the highest chances north of Lane County. Chances for maximum wind gusts of 45 mph or greater are also around 50-60% along the coast and 10-20% for interior lowland valleys. There is also a 10% chance that the coast experiences wind gusts up to 60 mph Monday and Tuesday. Considering how saturated our soils are, wind gusts of this magnitude along with additional rain would make trees more susceptible to falling. Concerns for river flooding will also continue next week given that the rivers are already high coming out of this last atmospheric river. It's too far in advance to determine hourly rainfall rates, but urban flooding would also be a concern if we get persistent rainfall rates of at least 0.10-0.25" per hour or greater. Beyond this system early next week, ensemble guidance suggests wet weather continues through the end of the week.

There may be some positive signs next week for snow and winter sport lovers. Snow levels drop behind the Monday-Tuesday system, potentially bringing snow back down to pass-level. NBM chances for a foot of snow or greater in 48 hours from 4 AM Tuesday to 4 AM Thursday are 50-60% through Highway 26, Santiam Pass, and Willamette Pass. Will note that if the system early next week shifts northward, then we'll end up on the warm side of that system and snow levels will rise significantly. -10

AVIATION

A ridge of high pressure continues to build overhead headed into Thursday morning leading to calmer prevailing conditions. However the calm winds, ample surface moisture, and at least partial clearing will facilitate the development of widespread fog and low stratus across the inland valleys. The latest high resolutions models project a 60-75% chance for VIS to drop below 1/2 mile at all inland terminals by 12-14z Friday. From there flight conditions will be slow to improve with a transition from fog to a stratus deck late morning into the afternoon. It'll be a tough for the Willamette Valley to completely clear out during the afternoon hours - slightly better odds for the Portland metro to clear by 22-23z Fri. Just keep in mind the pattern heavily favors yet another night of fog and low stratus again Friday evening into Saturday morning.

KPDX AND APPROACHES...Conditions late this evening continue to bounce between MVFR to VFR. That said, there is a high probability (60-80%) that fog and or IFR/LIFR CIGs develop in the 12-14z timeframe. Guidance favors a return back to MVFR then VFR late morning into the early afternoon hours on Thursday but time time of it has a tendency to improve conditions a touch too quickly - only moderate confidence in the timing of categorical improvements Friday at KPDX. Winds stay light, generally less than 5-8 knots. -99

MARINE

Winds and seas have subsided and are expected to remain benign through Saturday evening as high pressure moves into the region. Seas below 10 feet are expected to continue dropping to around 5 feet by Saturday morning. Southwest winds around 10 kt with gusts less than 15 kt expected.

A front dropping southward toward the PacNW will bring an end to the relatively quiet stretch. Winds and seas will increase Saturday night into Sunday morning. There is a 60-80% chance for wind gusts to reach or exceed 21 kt (Small Craft Advisory) and probabilities for Gales is less than 10% with this system. However, this will only be the first of several systems that are expected to impact the region through the week.

A much stronger front moves into the region late Sunday night into early Monday, bringing hazardous seas and increasing winds. There is high confidence for southerly gale force wind gusts by Monday afternoon with this front, as probabilities are near 90% for max wind gusts over 34 kt between 10 PM Sunday and 10 PM Monday. Hourly probabilities are also high, especially over the inner waters. Storm force wind gusts over 48 kt cannot be ruled out either, as probabilities range from around 20% over the outer waters and near 40% chance over the inner waters. Probabilities are highest over the inner waters due to the development of a potential coastal jet. Guidance suggests seas will most likely peak somewhere between 15-20 ft Monday afternoon and evening, however the outcome will be highly dependent on wind speeds and how high wind waves are able to build. While unlikely to occur, there is a 5% chance significant wave heights will peak anywhere between 21-25 ft, which represents the worst case scenario. Probabilities for waves greater than 20 feet have increased Tuesday evening into Wednesday with a 10-15% chance. -19/23

HYDROLOGY

Rivers across southwest Washington and the north Oregon Coast Range remain elevated this afternoon due to ongoing light rainfall and continued runoff from earlier precipitation. Flood Warnings remain in effect for the Grays River near Rosburg, the Cowlitz River at Kelso, the Pudding River near Aurora, and the Luckiamute River near Suver. Most rivers have crested, but all are expected to remain elevated into Friday. Another round of heavy rain will be possible early next week. With soils remaining saturated, the probabilities for rivers rising into action and flood stages is increasing for next week.

PQR WATCHES/WARNINGS/ADVISORIES

OR...Coastal Flood Advisory until 10 PM PST this evening for ORZ101- 102. WA...None. PZ...None.