September is a meteorological transitional month in the Northwest. The jet stream starts to strengthen and move south, while we begin to feel the effects of the first autumn-like fronts of the season.
The climatology of precipitation in Seattle illustrated this. The first shows the probability of getting a real wetting: 0.10 inch or more. The driest period is roughly July 10 to August 10. Things moisten a bit through the end of September, followed by the "great wetting" in October.
A modest Pacific front is now approaching and will reach our region tomorrow.
Below is a satellite image this (Saturday) morning. There are some low clouds along the coast, but the front is offshore and moving eastward. A weak disturbance is found behind the front, followed by post-frontal showers.
This satellite image reveals that the air behind the front is not very cold--which is typical for mid-September. Cold air is associated with deep, cumulus activity, which is absent.
How do I know this? The infrared satellite image at the same time (below), which measures the temperature of the cloud (cold is white and high), indicates relatively warm/shallow clouds behind the front.
Now, let's look at the latest UW WRF model forecast for precipitation (color shading) and low-level winds with the front.
This afternoon, the front is offshore. There is a large wind shift with it!
As the Pacific air wraps around the Olympics, a Puget Sound Convergence Zone will form over the north Sound, with precipitation north of Seattle
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Looks like another bust. Darn those models!
ReplyDeleteWhy do you say this?
DeleteI would be interested in some discussion of whether we would expect the forcing of global warming to manifest as 'Turing Patterns' and cause anomalies or model biases at a larger geospatial scale than 'microclimates' but a smaller scale than 'regional fixtures' like the Convergence Zone.
DeleteI mention this possibility because perceptions of model bias vs. natural variability in stationary data are not the only possibilities on the table for discussion of AGW. A third possibility is that 'bands' (like zebra stripes) or 'spots' (like on a leopard) could naturally develop under climate forcing, and so one person would see a 'model bias' in the local climate in one direction, and a few miles away another observer could see a 'model bias' in the other direction, and both would be evidence for AGW *without* even without any changes in the local climate. The change or inhomogeneity would be spatial, with or without secular changes in climate averages and variability.
Has this been discussed already? I know the development of Turing patterns has been predicted by some groups working on the AMOC topic.
Yep, here too. Barely a sprinkle in Maple Leaf North Seattle. Glad someone got rain from this system, though. Bet it didn't think it made much of an impact on putting out those fires - they seem to be very persistent and what precipitation we've gotten hasn't done much to ameliorate the exceptional dryness.
DeleteI feel like the poster above. I live right by the lower sugarloaf fire (3 miles away) and every model I have seen this spring/summer has fallen short by a lot as far as precipitation. Some people are hoping to catch up on rainfall as it may be pertinent to their homes not burning down. On a side note... Cliff, just curious if when looking at total acres burned in an average year, is there anyway to differentiate between arcres burned and actual fuels burned? I am just curious if although we are below average on acres burned, if we are above or below on fuels burned. I am just thinking acres isn't necessary the best tool for measuring wildfires across the state.
ReplyDeleteI'm looking forward to monsoon season. This long summer has been ...BORING! Ha ha. Incidentally, I've found it interesting that - at least here along the North Fork Nooksack River - 1970 seems to have been quite a bit drier, if the river's USGS flow history is correct (and there's no reason to think those stats were wrong). There was also quite a long dry spell in the mid 1930's, given the flow records through those years. Anyone thinking this summer (or 2023) were unique: I don't think so. Range of normal is a pretty wide swath in the Pacific Northwest.
ReplyDeleteTypical rain moving in from the Pacific is not the monsoon. The monsoon has ended for the year.
DeleteYeah, the Monsoon brings weather from the Gulf of Mexico (Yes, Mexico) and brings subtropical rain and thunderstorms to the SW and sometimes, to the Eastern Cascades. The monsoon rarely reaches the western side of the state; for us, atmospheric rivers (aka the Pineapple Express) brings the heaviest rains. I hope we get another one soon.
DeleteWhat's with the random mid-80s forecast for Tuesday?
ReplyDeleteI wondered about too. Still saying 88 as of now at 10:40 Sunday
DeleteEven the coast could be approaching 80 tomorrow. What is up with that? Its only going to be for a day, but its still unusual.
DeleteEast winds.
DeleteThank you for this excellent post. It provided valuable insight into local weather and has greatly improved my understanding.
ReplyDeleteSo much for moderate precipitation. Here on the central Oregon coast we had torrential rain for at least 3 hours last night. From containers left outside I’d say at least 2 inches. Strong winds to go along with it.
ReplyDeleteIs that why we haven't seen much rain here at one of Seattle suburbs? I was hoping that it helps the garden. 😄
DeleteAnd Western WA stayed completely dry today, nary a drop of rain to be found.
DeleteAs of 4:30pm today we have received. 55" of rain and it continues, were a few miles north of Arlington. It appears the convergence zone picked northern Snohomish county to park most of today
ReplyDeleteVery appointed, no rain in South Bellevue. My grass so wanted the water. Lots of wind though.
ReplyDeleteThere was a LOT of rain around western WA...but not in the rain shadow of the Olympics....exactly what the models predicted!...cliff
DeleteAgreed, we’re in the SnoValley and got .05” of rain, not nearly the half-inch we were promised.
DeleteTypical misunderstanding..
Delete1. Forecast is for rain.
2. It didn't rain right here at my house.
3. Forecast was wrong.
It rained for at least a good 8-10 hours at the coast Saturday night into very early Sunday morning. Not sure how much precipitation fell, but it was a nice change.
DeleteWell that was a bust for central puget sound. Of the three forecast for significant rain here two have not panned out and none of the wildfires have been put out. Now we have strong east winds coming with fire warnings issued.
ReplyDeletePlease look at the forecasts more carefully...the models did show the dry conditions over central puget sound
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