In the Pacific Northwest, springtime is generally the time of year with the greatest day-to-day variability in our high temperatures.  While the daily normal high temps rise only gradually between April and early June, there is a wider range of temps possible on any given day. (In fall the reverse is true: average temps drop off rapidly, though there isn’t typically a huge deviation from the seasonal norm.)

The next few days we are going to see both sides of the spring weather coin.  Today was the first of two “nice” days; filtered sunshine and highs well into the 60s after a frosty start this morning. Vancouver and Portland Airports both topped out at 66; it was 65 in my neck of the woods.

Tomorrow should feature similar sky conditions, but much warmer temperatures! A brief “thermal trough” is going to form in Western Oregon, causing the airmass overhead to warm as east wind comes down the Cascade slopes. The 12z ECMWF (Euro) is showing 850mb temps near 16 degrees C tomorrow afternoon:

In July, this kind of airmass could easily push the surface to 85° F or even higher. But it’s early April and there will be a few high clouds, so 75-80 sounds reasonable. I’m sure that it will feel a little bit “summer-like” since we haven’t been this warm yet.  Enjoy it, because we won’t see another day like it for quite some time!

Rain returns Friday, with a sharp cold front. By 5pm the 850s are already below 0 C, indicative of an abrupt return to cool conditions (i.e. 50s in the lowlands).

Saturday is when the “cold side” of spring rears its head.  A very cold trough dives down over the Western U.S., extending deep into California and Nevada.  This is the exact pattern responsible for our cold and snowy weather in winter. By 11am Sunday the coldest air has arrived, with 850mb temps over Portland just under -7° C!  In midwinter this would mean highs only in the upper 30s to near 40…but in the 2nd week of April, the sun angle guarantees much warmer conditions at the surface.  At least 45 degrees even with solid clouds, or close to 50 with ample sunbreaks.

The cold pattern is expected to linger from Saturday through at least Monday, with plenty of shower activity. Some models have even shown low pressure centers coming ashore south of Portland on Sunday or Monday. Anytime between late November and early March, this would almost certainly mean snow for Portland and NW Oregon, with a cold east wind pushing in from the Gorge.  But on April 9-11? Any snow accumulations on the valley floors seem most unlikely.  For fun I’ll show you the 18z GFS for 132 hours, that’s total snowfall through 11pm Monday. Notice about 3″ in Portland, maybe 4-5″ in my Orchards neighborhood, and a truly historic April snowstorm in the northern Coast Range!  This is why I don’t like the GFS for our lowland snow forecasts…

I don’t have snow maps for the Euro, unfortunately. But the WRF is looking a lot more reasonable: several inches in the Coast Range but nothing significant in the valley.

My gut instinct is that soggy flakes may come down to 500′ or even lower Saturday or Sunday night if there is shower activity. But real sticking will probably only make it down to the 1,000 foot level. So the tops of the West Hills in Portland might get a dusting if they are a bit lucky.  Sticking snow is likely in the Coast Range and Cascade foothills Saturday through Monday though. And eastern Oregon might get significant rain and snow as well…woo-hoo!

Hope you enjoy getting nearly 30 degrees colder in just 48 hours! -Karl