textproduct: Portland

SYNOPSIS

Cloudy, with a few sprinkles today. High pressure nudges into the region later tonight with dry conditions expected on Wednesday. A series of fronts will bring a wet period of weather later this week into the weekend across southwest Washington and northwest Oregon with potentially more impactful rain next week.

DISCUSSION

Water vapor satellite imagery this morning shows an upper trough digging across the Pacific Northwest. A weak front is pushing across northwest Oregon and southwest Washington today, and will ultimately fall apart as it pushes farther south. This will maintain cloudy conditions with scattered sprinkles to light rain showers into this afternoon. Light north to northeasterly flow spreads across the region late this afternoon into tonight. This may result in just enough clearing to allow fog and low clouds to redevelop overnight across inland valleys. The flow will turn more northwesterly Wednesday and open us to weak shortwave troughs that could bring light precipitation to mainly our far northern zones and terrain late Wednesday into early Thursday.

Models and their ensembles are in good agreement that the upper level ridge remains over the northeast Pacific on Thursday. WPC cluster analysis does indicate there is a high probability of the ridge flattening out, allowing for more westerly flow into the Pacific NW Friday and into the weekend. This should allow for frontal systems and attendant weak atmospheric rivers to bring increased rainfall and more active weather to the area. Ensembles are in relatively good agreement, a weak to moderate strength atmospheric river will spread into the region Friday into early Saturday bringing with it mainly beneficial rains to the region. The EC EFI does suggest some notable rainfall amounts will occur across the Oregon Cascades and foothills Friday night into Saturday relative to model climatology, but raw ensemble rainfall amounts appear unlikely to produce impacts with this first round of rain. With that said, there are handful of the 100 global ensemble members that produce enough rain that our flashiest rivers would rise sharply and approach minor flood stage Friday into Saturday, but at this point, confidence remains low in this scenario panning out based on available ensemble guidance.

Additional rounds of rain will continue for the remainder of the weekend as ensembles are in general agreement we will remain under zonal flow in the vicinity of the baroclinic zone. Given the westerly flow there will likely be periods where the Willamette Valley rain-shadows out, but it may be raining, at least lightly, for a significant portion of the weekend across the terrain, particularly areas farther north in the CWA. Uncertainty in the forecast details grow significantly early next week and mainly revolve around whether or not a stronger atmospheric river with potential impacts to area rivers will impact the region or not. HEFS guidance does suggest a 10-15% chance for rivers like the Willapa, Naselle and Wilson Rivers to reach minor flood stage at some point in the next 10 days with that day 8-10 timeframe being the main driver of those probabilities.

AVIATION

Increasing northwest flow aloft today as an upper level trough pushes east of the Cascades. A weak front pushing over the area will bring light showers and lowering CIGs from north to south this morning. As of 09z, CIGs generally range between 2000 to 4000 ft. Expect predominately MVFR conditions by 12z at the coast and across northern portions of the area, and after 14-16z Tuesday across southern parts. There is also a 10-20% chance of IFR CIGs below 1000 ft this morning.

Expect predominately MVFR cigs to give way to a mix of high-end MVFR to low-end VFR CIGs toward 22z Tuesday to 00z Wednesday. Cloud cover will likely become more scattered this evening as skies attempt to clear out. This will set the stage for widespread fog and low stratus development tonight into Wednesday morning as high pressure builds over the region. Probabilities for surface visibilities below 1/2 SM increase to 40-70% at all inland terminals by 10-13z Wednesday. Fog is much less likely to occur at the coast where light offshore winds will help prevent fog development.

KPDX AND APPROACHES...CIGs around 3500 ft are expected to lower to around 2500 ft by 12z this morning as a weak cold front moves through the area. Scattered light rain showers will also be possible. CIGs should then trend toward high-end MVFR to low-end VFR thresholds around 23z this afternoon and attempt to scatter out this evening. Fog and low stratus become increasingly likely tonight into Wednesday morning. Probabilities for IFR conditions increase to around 40-60% by 12z Wednesday. Light southeast winds turn northwest later this afternoon. /02

MARINE

A weak front will push across the waters this morning with northwest winds increasing to around 15-20 kt. Strongest winds, with gusts up to 25 kt, are expected across the outer coastal waters north of Cape Foulweather. Winds gradually ease this afternoon through tonight. A long period westerly swell will also push into the waters, building seas to around 8 to 10 ft. High pressure rebuilds over the waters on Wednesday as winds turn more northerly around 10 kt or less, and seas gradually subside back to around 4 to 6 ft Wed night.

A more active pattern develops later in the week as a series of frontal systems is expected to move across the waters beginning Thursday. Winds turn southerly on Thursday but are not expected to exceed 20 kt. Expect this parade of fronts to continue through the weekend, with the strongest of the fronts potentially on Sunday. But, even then there is just a 20% chance or less of winds reaching gale force. Seas should steadily climb towards 10 ft through the weekend. /DH

BEACH HAZARDS

A long-period westerly swell is expected along the northwestern Oregon and southwestern Washington coasts from late Monday through Wednesday next week. Wave heights increasing to 8 to 10 ft on Tuesday may not appear to present a safety risk to those on area beaches, but these energetic waves will present a moderate to high risk for sneaker waves, waves which can run significantly farther up a beach than normal, including over rocks and jetties. In addition, a period of perigean spring or "king" tides means these waves will have an even easier time reaching high up onto beaches, limiting the areas which may be safe from wave action.

A Beach Hazards Statement has therefore been issued from 7 AM Tuesday to 10 PM Wednesday. Sneaker waves can create potentially life-threatening conditions in the surf zone when beachgoers can be unexpectedly knocked off their feet and pulled out into cold ocean waters. Caution should be used when in or near the water, and those with children should be especially watchful. Never turn your back on the ocean, and be sure to keep an eye on the waves. Those participating in razor clam digs should additionally exercise caution.

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from noon today to 4 PM PST this afternoon for PZZ210.

Small Craft Advisory until 10 PM PST this evening for PZZ271-272.