I wanted to update a couple things since Melissa’s discussion this morning. First of all, we ended up keeping that small low and front right over the area for most of the day. That’s the reason why we saw gray skies and plenty of drizzle for the Willamette Valley and north half of the coast. All areas picked up less than 1/10th of an inch, if any.
This afternoon’s model runs showed an overwhelming switch. Generally I check four models: The NAM, the GFS, the ECMWF, and the GEM. It isn’t very common that these all perfectly agree, so changes from run to run happen quite frequently. This afternoon’s runs, however, had all four models shifting the mid-week ridge south and pointing the jetstream right at us. Generally we think of ridge scenarios and drier, warmer periods. Sometimes, however, that is not the case. In fact, when we are sitting at the top of a ridge with the jetstream pointing right at us, we’ll get airflow coming off the water for most of the atmospheric column. That’s the reason why recent model runs are now putting chances of showers in for Monday through Friday, where originally it was just Monday and Tuesday.
I’m not going to jump on this pattern just yet, since it is the first run. Right now the biggest change is for Wednesday, whereas showers Thursday and Friday are very isolated. There is a good chance this could change in tonight’s model runs and the pattern will not show back up this week. Keep checking in here on the blog as we get model runs in over the weekend, and we’ll see if the pattern holds.
— Meteorologist Megan Taylor