By Gordon McCraw, GAM Weather Consulting
So, just had a briefing with the Portland National Weather Service on the upcoming storm event. The concern is obviously the possible flooding of rivers, and the list was big, not just in Tillamook County and not just along the coast but all through their forecast area. To aggravate the situation, we are having a period of astronomically high tides which will both affect how fast the swollen rivers drain, but also increase the Tidal Overflow Flooding. We are looking at some winds with the event but nothing excessive.
What can we expect, well, the front has been stationary up over Washington all day today but it will begin to slowly drift south tonight and be down in Lincoln County towards Newport by around sunrise tomorrow. We will see a brief break tomorrow morning then another area of rain pushes through tomorrow evening that will give us a heavier shot of rain, but the good news is it will be moving faster so though the rainfall rate will be greater, it won’t last as long. Because of the rainfall rates possibly hit ¾” per hour, Urban and Small Stream flooding concerns also increase. Total rainfall amounts for the event, from today thru Wednesday could be 4-6” here, and up to 5-10” in some areas of the Coast Range.
How will the rivers do? Well, there are a lot of rivers forecasted to reach flood or Bankfull over the next 24-48 hours, including some in Tillamook County. For now, and this could change, but for now the Nehalem River is forecasted to reach Minor Flood Stage early Wednesday morning. The Wilson and Trask Rivers are forecasted to be in Action Stage, up close to Bankfull. The thoughts are that the break in the rain tomorrow morning will provide sufficient time for the rivers to subside enough to handle the next bout of rain tomorrow evening. Unfortunately, the Nehalem River is traditionally slower in cresting so it will likely just cross into Flood Stage. I should mention the river forecasts have been updated several times today and each time the crest has been raised so all the rivers will need top be monitored closely and the changes could happen quickly, and the odds are higher that they climb over lowering.
Winds tonight will become breezy and gusty. I would expect them to be gusting to 30-40 in town, 40-50 in the coastal towns, and 45-55 along the beaches. The NWS said there are some models showing stronger winds so they could be higher. They also suggest the higher winds may be south of Tillamook. Obviously, the threat from this is downed trees blocking roads and/or power outages. The landslide threat is there also.
Finally, the beaches, I would expect higher than normal surf conditions along with a higher sneaker wave threat, especially during the astronomically high tide that is around 11:30am tomorrow, which is the peak of the King Tides, and 12:20pm Wednesday. Having seen some of the video from the tides yesterday, I would classify the danger as extremely high. The Tidal Flooding will also affect all the usual areas like in Nehalem, west of Tillamook long the Tillamook River, and down in Pacific City along the Nestucca River. There are other areas along Hwy 101 that may be affected, like in Nehalem near H St, in the North Main area near Hadley Rd, even up in Seaside in their usual spots.
It will be a long 2-3 days and we should all monitor the weather and the roads situation for changes.
9 AM …
A look at the satellite picture clearly shows we have a front with an atmospheric river event evolving. There is a large moisture plume extending from the coast to our north, southwestward well into the central and western Pacific. The front is currently approaching the Washington coast with the associated rain shield having pushed into extreme northwest Oregon. The front will stall today and with disturbances riding along the front it will move back and forth along the coast to some degree for the next couple of days, finally ending and pushing away Wednesday morning. With the rain being heavy at times this has the potential to give us 4-8” of rain in the Coast Range, and in the Cascades, and depending on which watershed receives the higher rain amounts, those rivers could reach or exceed flood levels. For now, it appears the hose will be pointed at areas to our north and into the Cascades where additional snow melt will add to their water levels. This does not mean we are out of the woods as this event is just starting and subject to change anytime between now and Wednesday, January 13th.
As for our flooding concerns, we already have a Coastal Flood Advisory that started at 8am this morning and is valid thru 4pm Wednesday related to Tidal Overflow Flooding that is a result of the rain on top of the King Tides that peak tomorrow. The higher High Tide today is at around 10:40am, tomorrow at 11:30am, and on Wednesday at 12:20pm. We could experience overflow flooding in the usual spots from a couple hours before to a couple hours after high tide times. We will continue to see higher surf conditions and the Sneaker Wave threat is also a major concern, especially at high tide times as there is little to no beach during that period. Outside of the above, during heavy rain periods, there is always the chance of Urban and Small Stream Flooding in areas where the rain rates exceed the grounds ability to drain the water off.
Now we can talk about the winds. They will be breezy today and increase tonight, gusting to 30-35 in town and maybe 45 to 50 at the beaches. With the grounds being supersaturated now, this could push some trees over causing some isolated power outages.
I think I have hit all the hazards with this event, which appears to continue into Wednesday morning when a high pressure ridge moves in and just leaves us with a slight chance of showers until Thursday, January 14th when we see a weak front pushing in more clouds then rain by Thursday night extending into Friday morning when that starts to ease further.
It is looking likely that the weekend is looking dry and somewhat mild with another ridge building in with daytimes highs in the mid 50s, lows down around 40.