By Rod Hill on 2022-05-09
The first 8 days of May have racked up a rain surplus of .86" with total rainfall of 1.49" which is well on the way to surpassing the monthly average of 2.51" at PDX. Temperatures through the first week of the month are averaging 2-3 degrees below normal. Mother's Day alone saw a high temperature 15 degrees below normal with a high of only 53 degrees. Combined weather model outlooks show good confidence of a cooler and wetter than normal weather pattern lasting through at least June 20th.
Outdoor Memorial Day Weekend plans may be in Jeopardy with a cold upper low tracking the back half of the holiday and into the 1st of June. The European model below shows the cold low along the Northwest coast on May 31st. This pattern of "winter like" cold lows dropping down from the north is exactly what we saw in April and so far this month of May. What forecasters call upper pressure heights in the 40s is typical for January but highly unusual for May. The resulting cold air aloft is leading to hefty rain totals and high temps in the 50s, which are close to record cold-high temps for this time of year.
A similar active, cool wet pattern shows up June 9th and again on June 16th. The blue shading represents lower than normal pressure heights which leads to cool temperatures. The pattern also leads to rainy weather.
The July upper flow map indicates a more normal temperature pattern. The weak trough along the west coast may lead to humid, unstable days with an increased chance for convective rainfall. A similar pattern sets up for August. The July pressure map does finally place the jet stream north into Canada, which would bring a more normal summer pattern too much of the USA. (To locate the summer jet pressure height, trace the 576 contour line across southern Canada.)
The main HEAT DOME this summer is expected to develop over Texas, the plains states and possibly into the Mississippi River Valley or the heart of the midwest. Not saying we will not have 100 degree days this summer locally in Portland and Salem, but at this time I see no clear "heat" signals that would make our local summer unusually hot. Since the summer of 2000, Portland is averaging 15, 90-days each year. Let's hope this summer at least stays under 20 total hot days.
Summer outlook conclusion: June cooler then normal with normal to above rainfall, July near normal temps and rainfall, August shows the best chance for above normal temperatures, but as mentioned there are no signs pointing to historic heat. It will likely take a somewhat hot August and September to push the number of 90-degree days this year above 15.
Rod Hill
Snowpack Shows Parts of Oregon in Good Shape