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.

SHORT TERM...Today through Sunday

Lingering moisture on the southern flank of the weakening atmospheric river continues to bring rain across southwest Washington and the north Oregon coast and Coast Range. Lingering rainfall rates up to 0.10" per hour will continue over these areas through 5-7 PM this evening. Elsewhere, most locations remain overcast and dry. Shower activity will decrease tonight as an upper level ridge builds over the Pacific Northwest. Will see some cloud breaks late this evening, which will support radiational cooling and thus higher chances for fog and low stratus development overnight. Winds will also be calm tonight, so little mixing will be present and very favorable for fog. HREF and REFS guidance suggests a 50-70% chance for visibility dropping below 0.50 mi across the Willamette Valley Friday morning between 4-11 AM. If you will be commuting in fog, make sure to slow down, use your low beam headlights, and leave plenty of distance ahead of you.

Fog should dissipate and visibility should improve by late Friday morning and early afternoon. Conditions will remain dry across the area as high pressure continues to build. There is moderate confidence (40-60% chance) for another round of fog and low stratus Friday night into Saturday morning. If conditions remain overcast on Friday with minimal cloud breaks, then fog will have difficulty forming. Low stratus development will be favored in this case, especially since the low level atmosphere remains moist. Guidance suggests fog and low stratus should dissipate by early Saturday afternoon as the upper level ridge moves overhead, making way for some brief sunshine.

Saturday night into Sunday, the next frontal system will move into the Pacific Northwest, returning clouds and chances for rain. Snow levels briefly fall to 6000-7000 feet, so it's still looking like rain will be falling at pass-level with this system. This upcoming front doesn't look too impactful and ensemble guidance keeps rain amounts generally light. NBM chances for 0.25" or rain or more in 24 hours ending 10 PM Sunday are 40-60% along the coast, Coast Range, and most of southwest Washington, 20-30% around the Portland/Vancouver Metro and north Oregon Cascades, and 5-15% across the central and southern Willamette Valley. -10

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 stalled frontal boundary remains oriented west to east over southern Washington. Flow remains westerly with most of the moisture remaining north of the boundary. However, there is still some moisture in the area, supporting light scattered showers along the coast and in the higher terrain. Conditions are a mix of VFR and MVFR as the cloud deck slowly lifts. Clouds continue to break up over the Willamette Valley which has allowed conditions from KEUG to KUAO to improve to VFR. Expecting cloud dissipation to continue this northward trend.

High pressure develops this evening, bringing calm winds and some clearing overnight. This will set the stage for widespread fog and low stratus developing across inland valleys, including all inland TAF sites. There is a 40-70% chance for VIS to drop below 1 SM for the sites within the Willamette valley.

KPDX AND APPROACHES...MVFR CIGs will improve to low end VFR later this evening. This will set the stage for fog and/or low clouds to develop by 11-12z Friday. There is a high probability, 60-80%, that fog 1 SM or lower develops around the metro late tonight into Friday morning. -19

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

BEACH HAZARDS

A Coastal Flood Advisory for minor tidal overflow has been issued for the north Oregon coast including Clatsop and Tillamook Counties until 10 PM Thursday. Minor flooding up to one foot above ground level during high tides is expected in the low lying areas near bays, sloughs, roads, and the lower reaches of the coastal rivers. Even though the Tongue Point tidal gauge is expected to rise near 7.2 ft Thursday evening and the Garibaldi tidal gauge is expected to rise near 6.9 ft Thursday evening, rivers are at least 80% of flood flow. In addition, lingering rainfall rates up to 0.10 inch per hour continue through 5 to 7 PM Thursday, which will contribute to further river rises.

There also remains an elevated threat for sneaker waves through this evening along the entire coast. The swell period increases to around 14-15 seconds with swell heights around 9-11 ft, with swell heights and swell periods decreasing late tonight into Friday. This will create energetic waves that will present a moderate to high risk for sneaker waves, which are waves that can run significantly farther up a beach than normal, including over rocks and jetties. Sneaker waves can suddenly knock beachgoers off of their feet and quickly pull them into the frigid ocean which may lead to serious injury or drowning. Caution should be used when in or near the water. Always keep an eye on the waves, and be especially watchful of children. -10/19

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.