Significant rain coming, could be just what doctor ordered

Weather Blog

Atmospheric river is setting up -- and this one looks juicy

PORTLAND, Ore. (KOIN) – Finally the forecast is showing signs of relief from this crusty, dusty, drought-stricken, heat-battered, smoke-filled summer.

An atmospheric river is setting up over the Pacific by the end of the week, and this one looks juicy. The extended band of moisture just might be enough to make a dent in our drought conditions. Let me emphasize, there’s a difference between improving drought and ending drought. We would need multiple atmospheric river events to say, “OK folks, drought is over”. This is not a drought ending event.

Something to note before the rain arrives – expect a bigger shift to cooler temperatures. Nighttime will feel very much like a cold autumn night. Portland may experience a dip to the middle 40s Wednesday night into Thursday morning. Outlying areas of the Willamette Valley could drop into the 30’s as well. It’s time to start thinking about how to keep your little Buddy warm overnight. That goes for your plants too.

Keep this number in mind: 9.43 inches. That is our rainfall deficit from the beginning of our water year (Oct. 1, 2020) to date. Portland is below normal by 9.43 inches. That’s significant. However, not the worst we’ve ever seen.

If we were to remain rainless from now until the end of September, we would rank as the 5th driest water year on record for Portland. However, this weekend could bring up our totals by close to an inch, if all goes according to latest forecast model guidance.

Timeline for rain

So when is this rain going to get here? Timing will fluctuate a bit as we are still 4 days out, but the first rain should begin Friday and continue through Sunday. As it looks right now, it appears the heaviest rain will arrive between Friday and Saturday, followed by more intermittent, showery weather through Sunday.

Potential rain totals

  • Inland Valley: 0.50 inch – 1.5 inches
  • Coast: 1 – 2 inches
  • Coast Range to Cascade Western Slopes: 1.5 – 3 inches
  • Recently burned areas, i.e. Santiam Canyon, may experience debris flows

Take a look at the slider images below. You can slide between the two models and observe the difference in totals for the same time period. The rainfall total on the left is a Euro model output. The rainfall total on the right is the GFS model output. Both start Friday 6 a.m. and continue through Sunday 11:30 p.m.. These are 3-day totals and there is a notable difference between the two model outputs. We expect these rainfall totals to change.

The rainfall total on the left is a Euro model output. The rainfall total on the right is the GFS model output. Both start Friday 6AM and continue through Sunday 11:30PM. These are 3-day totals and there is a notable difference between the two model outputs. We expect these rainfall totals to change.

Rivers

Rivers are not expected to flood considering our current severe drought conditions. Many of our rivers are already operating below normal flow. For reference, here’s the Bureau of Reclamation’s Hydromet – Reservoir Storage “Teacup” Diagrams. You will also find the latest drought update for Oregon below.

Signs of a serious drought were evident back in June. Driest meteorological spring on record…

RECORD EVENT REPORT NATIONAL WEATHER SERVICE 424 AM PST TUE JUN 1 2021

PORTLAND AIRPORT OBLITERATES RECORD FOR DRIEST METEOROLOGICAL SPRING…MARCH THROUGH MAY… BETWEEN MARCH 1 AND MAY 31 2021…PORTLAND AIRPORT ONLY RECEIVED 2.52 INCHES OF RAIN. THIS BREAKS THE PREVIOUS RECORD DRY SPRING OF 1994 WHEN PORTLAND AIRPORT ONLY RECEIVED 4.31 INCHES OF RAIN. WHILE ASTRONOMICAL SPRING RUNS FROM LATE MARCH UNTIL LATE JUNE… METEOROLOGICAL SPRING IS DEFINED AS MARCH 1 TO MAY 31. PER THE NEW 1991-2020 CLIMATOLOGICAL RECORDS…PORTLAND AIRPORT AVERAGES 9.37 INCHES OF RAIN DURING THIS PERIOD.

https://forecast.weather.gov/product.php?site=PQR&issuedby=PQR&product=RER&format=CI&version=29&glossary=0
Drought Update as of Sep. 7, 2021. Credit: Drought.gov

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