La Niña, associated with cool water over the tropical Pacific, has a significant impact on Northwest weather, influencing temperature, precipitation, and snowfall.
As described below, La Niña has strengthened recently, and some decidedly La Niña weather is now in the forecasts.
As noted in previous blogs, La Niña is associated with cooler-than-normal ocean temperatures over the central tropical Pacific, known as the Nino 3.4 area (see below)
According to the latest observations, we are about to transition from a weak to a moderate La Niña (see figure below). This figure shows the difference from normal of the temperatures in the Nino 3.4 area, with blue colors indicating below-normal temperatures. A moderate La Nina is associated with a cool temperature anomaly larger than .9C.
We are now crossing this threshold to moderate La Niña conditions (see below).
Occasionally, the jet stream breaks through underneath the ridge with a strong cyclone/wind event.
Now, let's look ahead over the next week or so, considering forecast models' predictions.
The forecast of the upper level (500 hPa, about 18,000 ft) heights/pressures for Saturday afternoon shows a big ridge offshore and northwesterly flow over Washington. Classic La Niña pattern.
Tuesday morning? Very similar. La Niña upper air pattern
With a La Niña pattern with northerly flow from Alaska in place, temperatures should be a bit colder than normal over the Northwest, as illustrated by the forecast temperatures at SeaTac over the next few days. Normal is around 50F.... predicted temperatures are several degrees cooler.
Below-freezing temperatures will also occur over the eastern part of Puget Sound country. Keep in mind that temperatures could be even cooler at the surface.
So be ready for the first frost of the season!
The latest forecast of temperature (actually the difference of temperature from normal) from the highly skillful European Center extended forecasting system through January 13th, suggests colder than normal temperatures for the next month and a half.
Get your skis ready!
It's about time for frost in the lowlands Usually most years it comes around this time or a bit earlier (mid November, not late in the month) but as you say, it varies from year to year and when we are in a la nina or El nino year.I would not mind a good snow in the Puget Sound area this year. I recall a couple of years ago when it snowed Christmas eve and again over the holiday week/weekend. It was beautiful with sunny weather on the brilliant white snow but cold.
ReplyDeleteAnyway, it's shaping up to be an interesting Thanksgiving weekend weatherwise with the substantial rains that came through on Thursday over Thanksgiving.
So, does this mean I should be getting a new snow shovel for this winter.
ReplyDeleteWhat are the effects of a stronger La Nina on the high pressure ridge? Does the intensity increase? Does it push further north? Likewise, does a weak la Nina or El nino pull the high pressure ridge south or make it weaker?
ReplyDeleteA lot of us live in places that flood and that is our biggest concern. What does a stronger la Niña mean for us?
ReplyDeleteWhat are the effects of a stronger La Nina on the high pressure ridge? Does the intensity increase? Does it push further north? Likewise, does a weak la Nina or El nino pull the high pressure ridge south or make it weaker?
ReplyDeleteYou mention that the indicated La Nina pattern forecast for this winter could lead to colder than normal temperatures for the Pacific Northwest and this is predicted for the next month or two by the European model. This may not be true for places like Wenatchee or much of the low lying areas of Eastern Washington, where temperatures so far through this November, have been quite a bit above normal. This has been due mainly to warm nights , but also warmer than normal days due to the lack of low clouds which begin to prevail in the Columbia Basin in November and last through winter, usually persisting through the day and keeping daytime temperatures depressed. However, if strong enough fronts come in fairly frequently, this tends to reduce the number of these low cloud days and even though the fronts may have generally cold temperatures, the daytime temperatures actually end up warmer than normal, since there is better mixing and some sunshine at times. As long as these fronts come in fairly often, even on northwest flow, temperatures here in the Wenatchee area will likely end up above normal. However, if the flow becomes more northerly, bringing down Arctic air, or if high pressure settles overhead leading to persistent low clouds, we would end up near or below normal in temperature. It seems as predicted in the next week or two, high pressure will persist over the Eastern Pacific with mainly west to northwest flow and frequent enough frontal passages to reduce the low cloud days and keep temperatures above normal.
ReplyDeleteHere just NE of lake Stevens our first freeze was 29 degrees on Oct. 15. If the latest La Niña forecast is correct it seems to be at odds with the CPC forecast of warmer than normal for the next month. Is this correct?
ReplyDeleteUnfortunately it doesnt tell us when we can strap on the boards at our local ski hills. Not loking promising for the next couple of weeks.
ReplyDeleteIndeed, cold don’t mean much without the precip. Was wet but too warm, now cold and dry in BC. Only had one big storm with colder temps in the past month
DeleteKulharin- yes that is the inherent problem with the PNW when is comes to skiing. Either too warm or too dry, usually.
DeleteThats why tesla invented remote defrost
ReplyDeleteAccording to the Climate Prediction Center at the National Oceanic and Atmospheric Administration (NOAA), we can expect a 40 to 50 percent chance of above-normal precipitation through the second week of December.
ReplyDeleteUnfortunately, we also have a 33 to 40 percent chance of above normal temperatures in the same time frame. That will not help our effort to boost the snowpack in the Cascades.
1. I would privilege the Euro extended over the CPC (which I think still uses GFS?)
Delete2. It’s all about one’s point of view, isn’t it? You could say the CPC predicts a 60 to 67 percent chance of normal/below normal temps during the same period, because that’s exactly the case. Your meteorological glass is half-empty; another person’s is half-full! Both points of view are worth acknowledging, whichever one you prefer.
The morning minimum temperature at my location in Bellingham was 28.5F at 7:39AM - the coldest it’s been since Valentine’s Day. KBLI has only had 3 freezes so far this season - a tie for the 3rd fewest October + November freezes in the POR. The 1995-2024 normal number of freezes for October + November is 11.
ReplyDeleteInterestingly, the 5 years with three or fewer October + November freezes included 2 (1988, 1998) during strong La Nina events, 1 (2016) during a weak La Nina event, and 2 (1962, 2024) during periods of “La Nada”.
The BPA graph is now into the 6th day of almost no wind generated electricity. Most of the coming week isn't looking better. A correlation with La Niña might make a good exercise for an intern with BPA. It is beyond my data retrieval and computer skills.
ReplyDeleteLooks like the foreseeable forecast has been turned on its head with prolonged Spring-like weather ready to stampede. Bummer. Was looking forward to a festive Christmastime with some colder-like weather
ReplyDelete. Is this because of the Polar Vortex affecting mainly the eastern US?