After a long period of dryness, western Washington and Oregon are finally seeing significant rain.
The 7 a.m. radar image shows a mass of rain extending roughly from Seattle to Portland, some of moderate intensity (yellow). This rainfall comes from an unusual direction: from the east.
At the same time, infrared satellite images show extensive clouds throughout the region, some convective clouds clearly. But none of them are deep enough for lightning.
As of 8 a.m., there has been substantial 24-hour rainfall in the Cascades and southwestern Washington (see below)
NOAA’s latest HRRR forecast for cumulative rainfall from 5 a.m. Friday through 8 p.m. tonight, predicts up to about half an inch of rain from the Olympics to the southern Cascades.
Admission
This situation has not been particularly well forecast. On Wednesday afternoon, our model predicts rain further north (total rainfall for the 72 hours ending at 5 a.m. Saturday is shown below).
On Thursday morning, our main tool for understanding forecast uncertainty…, a collection of high-resolution forecasts, began to show a chance of rain with about half of the members in the forecast. The set will see significant rainfall (see cumulative precipitation chart for projections starting Thursday 5AM, time ascending to the right). Each line is a pattern, the black line is the average of all of them.
Cumulative rainfall at SeaTac
By last night, the population was wet (see forecast below).
The bottom line is that the models have problems initiating weak perturbations associated with this relatively small, modest-scale rain area. I will check out this event to better understand its evolution.
