textproduct: Portland

SYNOPSIS

Valley rain and mountain snow has returned today thanks for a warm-frontal boundary passing overhead. Lingering cold air will promote Advisory level snowfall across portions of the Cascades and in the upper Hood-River Valley. The pattern remains active into early next week with a weak atmospheric river keeping moisture streaming overhead late Sunday through Tuesday. Breezy easterly winds near the mouth of the Gorge and through other Cascade gaps continue into Sunday coupled with Storm and Gale Force southerly winds over the waters as well. Chances (40-60%) for showers persist on Wednesday through the remainder of the week as conditions stay close to climatological norms.

LONG TERM...Monday through Friday

As we move into early next week the upper-level pattern sees added complexity over the PNW. Ensemble and deterministic models continue to suggest another round of rain on Monday into Tuesday associated with a atmospheric river. Still on the weaker side, there will be the potential for more widespread and sustained precipitation. The challenge is that the precipitation will fall within a fairly narrow band (as is common with atmospheric rivers) and where that band ends up setting up is still to-be-determined. Models continue to fluctuate between impactful rainfall, to our typical rainfall totals based on the location of the atmospheric river. Currently it is trending further south, but it easily could shift northward over the next day or two as we get closer to the event. Exploring the EPS members, 24-hour rainfall totals in Newport for example range from 0.9 inches to 3 inches on Monday into Tuesday, and for Portland Airport span from 0.75-2.5 inch in 24-hours. For inland areas, we typically begin to see localized small stream and urban flooding impacts once we break about 2 inches in 24 hours. Given the duration of the atmospheric river, the previous days of rain, and the snowfall from the last several days above ~1000-2000ft, we cannot rule out isolated flooding/river flooding. Confidence is incredibly low as there is less than a 10% chance of our most prone rivers reaching action or minor flood stage on Tuesday. However, if the axis of heaviest moisture shifts northward or the accompanying frontal boundary on Tuesday stalls, then those probabilities may rise as we will see more rainfall accumulation. We will continue to monitor, but if you see a widely fluctuating rainfall forecast, the location of the atmospheric river is to blame.

Showers persist through Wednesday then the flow becomes zonal as a weak longwave high pressure forms Wednesday night. Some rain potential remains through Friday but overall it resembles that of our typical forecast for late February. -99/27

AVIATION

Expect mostly VFR conditions at all terminals as a warm-frontal boundary spreads light rain across the airspace. Potential for MVFR conditions remains limited with light rain and offshore winds at the surface (20-40% chance of MVFR CIGs). Expect rainfall inland to decrease through late this morning, ending around 19-23Z Saturday. Coastal sites will hold onto rain a bit longer, with rain in KAST through most of the TAF period and rain diminishing around 04Z Sunday for KONP. Expect easterly winds with gusts up to 30 kt in the western end of the Columbia River Gorge (KTTD eastward) this afternoon and evening.

KPDX AND APPROACHES...Expect VFR conditions through the TAF period. Expect east-southeasterly winds with gusts around 25-30 knots possible at the eastern end of the airport through most of the TAF period, ending around 12Z Sunday. Otherwise, rain will mostly diminish by 23Z Saturday, then rain returns by 14Z Sunday. ~12

MARINE

Seas have begun to build early this morning as a robust weather disturbance moving into the region kicks off a period of strong winds and elevated seas for this weekend. Winds have already increased across the outer waters with gusts between 40-45 knots observed at buoy 89, and as the main body of the system finally arrives today Storm Force gusts up to 50-55 kt are expected for the outer waters south of Cape Falcon into Sunday morning. Zone PZZ271 could see isolated gusts up to 50 kt from today through very early Sunday morning as well but winds across the inner water will be comparatively lighter - gusts between 30-35 knots. Expect seas to be dominated to southerly wind waves and an accompanying fresh southerly swell, peaking Saturday night/Sunday morning in the upper teens for the inner waters and 20-24 ft for the outer waters. Confidence in these significant wave height coming to fruition is moderate to high. Headed through Sunday, winds and seas will start to slowly subside with wind gusts below 20-25 kt and sub 12-14 ft seas anticipated by Monday. Conditions expected to continue to moderate by the middle of the week (wave heights 5-7 ft) before the arrival of a WSW swell pushes seas around and/or above 10ft towards the end of the week. -99

PQR WATCHES/WARNINGS/ADVISORIES

OR...Winter Weather Advisory until 10 PM PST this evening for ORZ121- 126.

WA...Winter Weather Advisory until 10 PM PST this evening for WAZ211.

PZ...Hazardous Seas Warning until 4 PM PST Sunday for PZZ210-251>253.

Gale Warning until 10 AM PST Sunday for PZZ271.

Gale Warning until 10 AM PST this morning for PZZ272-273.

Storm Warning until 10 AM PST Sunday for PZZ272-273.