The visible satellite image this morning was stunning, reminiscent of an image from mid-winter (below). The star shows the location of Seattle.
You can see the swirl of clouds around a deep low-pressure center west of British Columbia, a strong front offshore, and unstable air with convective clouds south and southeast of the low.
Impressive.
It is times like this that we should be glad that we have a coastal Doppler radar (thank you, Senator Cantwell), which shows the approaching frontal rain band offshore (see below).
This rain will come in later today, bringing another period of moderate precipitation.
Below is the latest high-resolution UW WRF model forecast of accumulated precipitation through 5 AM Saturday morning.
Very, very wet in the mountains, with large areas getting more than 3 inches.
Rivers are going to surge rapidly, as illustrated by the predicted discharge on the Snoqualmie River near Carnation (below). If you go to Snoqualmie Falls on Sunday, you won't be disappointed.
Another interesting aspect of this event is the high humidity today. Dew points are reaching the mid-60s, making it feel sticky ....reminiscent of the East Coast.
Note: the dew point is the temperature to which air needs to be cooled to reach 100% relative humidity. The higher the dew point, the more moisture the air has.
At SeaTac, the dewpoint today is the highest of the year! See plot below
There are some amateur YouTube sites and some media claiming that this is a highly unusual, record rainstorm.
This is not true.
Having a strong event like this in mid-August has occurred numerous times before. Below is a list of the record one-day totals for mid-August (Aug 4-21) at Seattle.
Yesterday's total of .22 inches was 44th on the list. Today, SeaTac may get a half inch, which is certainly not without precedent.
The PWAT values are indeed record breaking for ANY time of the year. The Weather Prediction Center Day 1 excessive rainfall outlook points this out as well. This is what I was reffering to in my video today.
ReplyDeleteMichael.... I am not talking about PWAT (Precipitable Water) but rainfall. PWAT is very high, but the dynamics of this system are relatively weak; thus the precipitation will not be extreme. We can get high values of PWAT during the summer without much rainfall.....the key to getting heavy rainfall is to have strong uplift from an incoming system, which is MUCH stronger during the winter, when PWAT is generally lower because the atmosphere is cooler..cliff
DeleteCliff, how long until the dewpoints in the 60s abate? I turned on my a/c today just to get a break from it.
ReplyDeleteThe major forecast services called for substantially more precipitation than I’ve observed to this point during this event so the amateurs perhaps aren’t entirely to blame for overshooting the mark. If you actually compare precipitation as measured by a high-quality rain gauge with forecast amounts you’ll find that precipitation forecasts are generally less reliable than temperature forecasts for any given location.
ReplyDeleteWhy did this happen? It seems like it is something that happens now and again - is it weather from Alaska?
ReplyDelete