Two Sundays ago, I proudly proclaimed that Juneuary would end on the 17th. But taking a look at the webcam from Timberline Lodge this morning, that appears to have been a premature call! Just another example of why you can’t give much weight to any forecasts more than 2 weeks in advance. And don’t even get me started about seasonal forecasts…
Snow is officially sticking at Timberline Lodge this morning (Mt. Hood, Oregon). I guess in 2020, it’s only fitting that we wrap up this final weekend in June with snow in the Cascades. #Juneuary #ORwx ❄️ pic.twitter.com/KEUff7XWSP
— Jeff Forgeron (@WeatherJefe) June 28, 2020
I don’t see any more snow occurring at Timberline this June, but what about next month? Will we have a “Julybruary,” or will we finally see the warmer and drier weather that long-range forecasts have been advertising for the past several months?
After looking at the models, here are my main takeaways:
- We’ll see an onshore flow pattern for the next two weeks, and this will result in near or slightly below-average temperatures most days.
- Tuesday/Wednesday this week should be the coolest days of the next two weeks, with highs near 70 for Portland. Onshore flow weakens slightly Thursday, and Friday-Sunday should feature mostly sunny skies with highs near 80. Onshore flow may strengthen again next week with highs dropping back to the mid 70s.
- West of the Cascades looks drier-than-average, with the only precipitation being occasional light morning drizzle. Inland areas could see more t-storms/afternoon convection, especially over terrain.
- Cool, strong NW flow is a high fire danger pattern for the Great Basin and Desert SW. Widespread Red Flag Warnings are currently in effect there, and I expect them to see more Red Flag Warnings over the next two weeks, particularly during periods of strong northwest flow (which, counterintuitively, is the pattern that gives Western WA/OR cool and cloudy weather).
Current Conditions
Despite it being the end of June, we currently have a textbook pattern for heavy mountain snow, with a big ridge in the North Pacific, a deep trough over the Pacific NW, and cool, unstable NW flow. If it was December, January, or February, this pattern could bring us several feet of snow to the Cascades in rather short notice.
Credit: David Ovens/University of Washington
But even though our storms are weaker and warmer in the summer, the added summer sun can increase instability by preferentially warming the surface, and this effect is most pronounced when you have a deep upper-level trough with cold air aloft moving over the area. The Northern Rockies are getting absolutely soaked today – fantastic news for wildfires and water managers alike.
Forecast:
This general pattern with onshore flow doesn’t look to be going away any time soon. However, we also don’t appear to have any particularly strong/wet troughs coming through. Compared to winter, cloud cover and precipitation (or lack thereof) play a much bigger role in temperatures than the origins of air masses – provided the flow is onshore. This is because the poles preferentially warm compared to the equator during the summer, leading to weaker temperature gradients in the midlatitudes. The exception is when we have offshore flow from the Intermountain West and/or see a thermal trough building northward from the Central Valley of California, as the Central Valley and areas east of the Cascade/Sierra Crest can become very hot during the summer.
Models show one trough coming through on Tuesday/Wednesday, which would bring us another period of stronger onshore flow with thick morning clouds burning off in the evening and highs 5-10 degrees below-average (average this time of year for Portland is 76).
Weak, transient ridging rebuilds inland to end the week, and Friday-Sunday should be nice with highs near 80 degrees. This southwesterly flow will also allow moist, subtropical air to move into the Desert SW/Intermountain West and will likely give them a few monsoonal afternoon t-storms Friday and the weekend, but nothing out of the ordinary.
As the spaghetti plot below shows, ensembles are in pretty good agreement that onshore flow with near or slightly below-average temperatures will continue next week. So while we won’t see any ‘Julybruary’ weather, I don’t see any bonafide heat waves occurring the next two weeks either.
Fire Danger:
When one thinks of fire weather, they usually think of strong, dry, hot offshore winds, like the winds that allowed the Eagle Creek fire to grow dramatically from late September 4th to early September 5th or the Santa Ana and Diablo winds that routinely bring extreme fire danger to Southern and North/Central California, respectively. And these are indeed the classic ‘high fire danger patterns’ for areas west of the Cascades and Sierra Nevada.
However, this cool, northwesterly flow regime that we are currently seeing is the classic fire pattern for the Intermountain West and Desert Southwest. Despite the flow having onshore origins, relative humidities inland remain low due to the Interior West being so hot during this time of the year and the cool temperatures of the Pacific Ocean, which keep dewpoints low. The National Weather Service currently has Red Flag Warnings throughout the Desert Southwest, Intermountain West, and even Northern California due to these strong winds and low relative humidities..
Fire danger should decrease for most of the West later tonight as onshore flow decreases, but it will increase again Tuesday/Wednesday as that second upper-level trough comes through and could remain high next week with continued moderate/strong onshore flow. Thankfully, there aren’t too many fires burning right now and there’s not a big thunder threat there through Wednesday, but models show some monsoonal thunderstorms Friday and the weekend over New Mexico, Colorado, and Eastern Arizona/Utah that could ignite blazes that would subsequently spread under critical fire weather conditions next week. It’s nothing that is out of the ordinary for this time of the year, but critical fire danger is always something to be cognizant of!
Thanks for reading and have a great week!
Charlie
Featured image: Looking west towards downtown Portland from Hawthorne Bridge. Image credit: Eric Baetscher
