Marine Weather and Tide Forecast for Jeffers Gardens, OR

SHORT TERM
Now through Wednesday Night...The region remains beneath the storm track as repeated shortwave impulses bring rounds of rain and winds through the next two days. An initial wave approaching the coast was responsible for earlier rainfall, however showers continue, particularly over areas of terrain, where sufficient instability exists above the surface layer to support narrow bandlets of rainfall. These features should trend lower in intensity and coverage from north to south through this evening as the shortwave moves onshore. A strong low-level jet reaching 60-70 kt only a few thousand feet above the ground couped with this convective environment has allowed for strong wind gusts to reach the surface, particularly along the coast and in areas of terrain so far today. As the jet both weakens and moves inland, the risk for further strong wind gusts will decrease into this evening, but isolated occurrences may continue in exposed areas of high terrain. As such, the High Wind Warning along the coast has been allowed to expire, but the Wind Advisory in effect for the Oregon Coast Range and Willapa Hills will remain in place through 4 PM this afternoon.

The overnight period will offer a brief respite before another wave brings renewed rain and wind to the region Tuesday into Wednesday. This system is expected to be more potent than the first, with a deep surface low tracking inland near the north end of Vancouver Island and a strong trailing cold front extending southward to the Oregon coast. Another shorter- duration period of high vapor transport will be associated with this atmospheric river, resulting in a relatively brief period of rain across the region, but one that could nonetheless bring heavy enough rain rates to continue a risk of flooding in poor drainage areas, especially given continued high saturation levels in soils across the region. An additional risk from this next system will be further strong winds. Again, just ahead of the cold frontal boundary, a low-level jet reaching 60-70 kt at 925 hPa will move onshore through Tuesday night. As today, periods of strong wind gusts reaching down to the ground appear likely, and there is a 30-50% chance of wind gusts of 55 mph or higher along the immediate coast, and similar or slightly higher chances in higher terrain and particularly along the Cascade crest. Chances for gusts reaching 45 mph in valley areas remains around 10-25%, however an isolated gust over 50 mph also cannot be ruled out. Additional wind hazards may need if confidence in occurrence of these winds increases.

Wednesday will bring another relative lull in the pattern, with brief drying and a break from strong winds through much of the day. As the front sags southward, a cooler air mass will arrive in its wake with temperatures closer to seasonal norms but still about 5 degrees above normal. Snow levels falling to 3000 ft or even slightly lower will allow for some snow to accumulate as pass level through Wednesday and Wednesday night. This colder period is when precipitation amounts will be reduced between systems, so snow amounts remain unremarkable, with a 40-60% chance of 6" of more of accumulation at Cascade passes. There is a 10% chance of snow levels falling to 2000-2500 ft. -36


LONG TERM
Thursday through Monday...Another moderate to strong atmospheric river takes aim at the region Thursday into Friday, bringing additional rain on top of elevated rivers and saturated soils. Initially, heavy rain rates raise the risk for urban or small creek and stream flooding on Thursday, while the risk for river flooding increases late Thursday into Friday as the abundant runoff makes its way downstream. As is typical with ARs, the highest precipitation totals are likely to be over the coastal terrain and across the Cascades, and the warm dynamics will also favor increasing snow levels during the heaviest precipitation. Rainfall forecasts have tended to shift slightly between forecast updates, but guidance remains in good agreement that the AR will impinge on the northern OR coast before tracking southward toward the southern OR coast by Thursday night. Unlike recent ARs which have been directed moreso at the Washington coast, the highest rain totals are currently focused across the southern half of the region, generally south of US-26. Chances to exceed 2" of rainfall Thursday and Thursday night increase from 30% to 50% south along the I-5 corridor from Kelso/Longview to Eugene, and from 50% to 75% in the Coast Range and Cascades. Chances to exceed 4" of rainfall are 5-15% across inland valleys and 20-40% in areas of higher terrain.

This amount of precipitation over only 24 hours would support river flooding as saturated soils will allow most of the rain to make its way into area rivers as runoff. Chances for Minor to Moderate river flooding continue to increase, with the highest confidence in flooding for rivers draining the central OR Coast Range, both toward the coast and into the Willamette River.
Those who live near areas prone to river flooding should keep a close eye on the forecast moving forward, and additional information can be found in the Hydrology discussion below.

The veritable parade of weather systems does not look to let up this weekend and into next week. While confidence in forecast details is low at this lead time, the active pattern and persistent chances for rain will most likely continue. -36



AVIATION
Radar imagery as of early Monday afternoon depicts lingering showers as a system moved through the area. This is bringing a mix of MVFR and low-end VFR CIGs across all terminals, with some IFR/LIFR CIGs along the coast. Expect this trend to continue through 03z Tue, with CIGs briefly improving to predominately VFR this evening. High confidence (80% chance or greater) CIGs drop back down to IFR or lower along the coast after 12-15z Tue as the next system moves in.
During this same time frame, inland terminals also have a 20-40% chance of dropping back down to MVFR.

Southwesterly winds are gusting to 25-30 kt along the coast and 20-25 kt across the Willamette Valley as of early Monday afternoon. Winds around 2000 ft are around 40-50 kt, which will create a strong crosswind especially for E-W aligned runways and some low level speed shear resulting in turbulence. Winds across the area weaken overnight, and become breezy again after 12-15z Tue with the next system with gusts to 20-25 kt across the region.

KPDX AND APPROACHES...Mix of high-end MVFR and low-end VFR CIGs , with CIGs trending more VFR this evening. South-southwesterly winds gusting up to 25 kt through the afternoon. Low level speed shear is possible due to 40-50 kt winds around 2000 ft. Winds weaken below 10 kt after 00-03z Tue, with breezy southerly winds returning after 12-15z Tue. -10

MARINE
Observations at buoy 46029 and 46050 as of early Monday afternoon show southerly winds with gusts to 30-35 kt and seas hovering around 14-16 ft at 9-10 sec. Should be seeing seas peak around 16-18 ft this afternoon with seas unlikely rising above 20 ft (only a 1-2% chance of exceeding 20 ft). High confidence that winds will gradually weaken this afternoon, decreasing to 10-15 kt with gusts up to 20 kt late this evening.
Seas may remain steep and choppy during this brief lull; therefore, a Hazardous Seas Warning is in effect across all waters including the Columbia River Bar from 4 PM this afternoon to 4 AM Tuesday. Seas fall to 10-13 ft by late Tuesday morning.

The brief lull ends early Tuesday morning when another frontal system approaches the waters. This will return breezy south- southwesterly winds with widespread gusts ramping up to 25-30 kt between 4 AM-10 AM Tue, then 35-40 kt between 10 AM-4 PM Tue, and strong Gales with gusts up to 48 kt arriving after 4-7 PM Tue. For the inner waters out 10 NM including the Columbia River Bar, there is a 20-30% chance for isolated Storm force wind gusts up to 55 kt due to the potential for a coastal jet. It's a marginal set-up for a coastal jet since guidance isn't really showing much of an inversion in the low-level atmosphere to squeeze the strong winds toward the surface. Either way, it will still be very windy. Behind the front, winds turn westerly around 1-4 AM Wednesday. Seas will also re-build to 14-16 ft Tuesday evening, and peaking and holding around 18-20 ft at 10-11 sec between 1 AM-1 PM Wednesday. Another Gale Warning will likely be issued for this system this afternoon.

Going forward, an active weather pattern continues through the week bringing additional winds and wave hazards to the coastal waters. Seas are very likely to remain elevated above 10 ft (greater than 90% confidence) from Wednesday through Friday as additional weather systems move onshore. At least models are beginning to hint as some larger breaks between weather disturbances next weekend into the following week, but at this 7-8 day time-scale, the confidence in this slowdown materializing is only low to moderate at this time. -10/27

HYDROLOGY
Abundant rainfall is a relatively short period from Thursday through Thursday night atop saturated soils while area rivers remain high following well above normal rainfall thus far in December has resulted in an elevated risk for flooding late this week. As is typical in atmospheric rivers, the highest rainfall totals are likely to be over areas of terrain including the Coast Range and Cascades, while lesser totals can be expected across inland valleys. Nonetheless, rainfall is likely to be measured in inches across most of the region. Unlike recent other ARs, this system looks to favor a more southern placement along the central OR coast of these highest rainfall totals, which may allow some river basins to better handle these rainfall amounts without yielding flooding. Other areas to the north within the Coast Range in Lincoln, Tillamook, Benton, Polk, Yamhill, and Washington Counties may see more overlap between recently observed heavy rainfall and additional heavy rainfall with this upcoming system. Similarly, river basins covering the central OR Cascades in Lane and Linn Counties have a slightly more optimistic outlook than north into Marion and Clackamas Counties, but that does not mean flooding cannot happen in all of the aforementioned areas. Luckily, where rainfall has so far been the heaviest across southwestern Washington and far northwestern Oregon may see the lowest totals from this system, although even 1-2 inches of rain over 24 hours may be enough to cause additional flooding in these very saturated areas.

At this point, the rivers with the highest confidence of reaching flood stage are those which drain the central Oregon Coast Range, including the Wilson, Trask, Siletz, and Siuslaw draining toward the coast, and the Marys, Luckiamute, Yamhill, and Tualatin draining toward the Willamette. The chances for these rivers to reach at least Minor flood stage are 25-55% at this lead time. Rivers draining the Cascades, including the Mohawk, Santiam, Pudding, Molalla, Clackamas, and Sandy, have slightly lower but still significant chances of 15-45%. These rivers will begin to rise later on Thursday as heavy rain continues, not cresting until Friday in most cases. The Willamette River main stem itself also has a 5-10% chance of reaching flood stage above Willamette Falls, and slightly higher chances in tidally-influenced portions downstream of Oregon City, however runoff will take longer to reach the Willamette and flooding would be delayed later than in its tributaries. A Flood Watch has been issues across all of northwestern Oregon and southwestern Washington from 4 AM Thursday through 4 AM Saturday to highlight these risks.

These river forecasts remain very sensitive to rainfall forecasts, and interested parties should expect changes as the event nears. The latest river forecasts across the region can be found at www.water.noaa.gov/wfo/pqr. -36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Hazardous Seas Warning until 4 AM PST Tuesday for PZZ210-251>253- 271>273.

Small Craft Advisory from 4 AM to 4 PM PST Tuesday for PZZ210- 251>253-271>273.

Gale Warning from 4 PM Tuesday to 10 AM PST Wednesday for PZZ210- 251>253-271>273.