Above normal temps to continue through mid week then upper trough from Gulf of AK to swing toward the west coast as we approach the weekend…..At this time the trough is dry for the eastern sierra but much cooler weather is expected for the upcoming weekend…Long Range forecasters are going to have a difficult time with the upcoming winters outlook….
Monday September 26, 2016
Posted at 8:36 am by Howard
Wednesday Evening 10:00PM
I have been chatting about the trend of late of ENSO, SST anomalies and the Warm Pool. Since the middle of September, the 30 day ave of the SOI has become increasingly positive, resulting of the strengthening of the trades. So La Nina is strengthening as well. OPIN… It has a chance now to become at least moderate I believe. This is contrary to a lot of what you have been reading that this will be a weak La Nina winter. The Big Blob, the drought blob. and so on and so forth… At least one forecaster has been touting that the Big Blob is going to reestablish over the Easter Gulf of AK, positive PDO style. Even through the Climatic Predication center has that forecasted for November, the Dweebs have serious doubts that it will.
Another bases for the Forecast for the Winter is the Strong Positive phase of the PDO. Looking at the SST pattern across the pacific, it sure does not look all that positive. Water is warm pretty much all across the north pacific with two specific anomalies of mention. One at 155East and the other at 150 west. The only cool patch of water is at the dateline over the north pacific. This is radically different than last winter. Looking at the updated PDO index this evening, Here are the indexes for the past four months. May 2016 2.35, June 2.03 July 1.25 and the lastest month for August just released today .52
I would say that the positive phase of the PDO is trying to flip or at least greatly weaken. We’ll see…. The +PDO is visually noted with a large broad cold stretch of SSTAs from the North Western Pacific eastward to beyond the Hawaiian islands with all the Warm water piled up along the North American Coast from Baja north to the Eastern Gulf of AK. That gradient is gone!!
Now if we start seeing the waters really cool along the west coast northward, that will mean that the PDO has flipped. Not all that uncommon in a La Nina! And….it may be that this incipient La Nina may some how be related to the weakening of the PDO. Regardless, the position of the warm pool now suggests that the eastern pacific adjustment wave in the mean may set up closer to 120west. Much better for snowfall in the sierra. At this time….The Dweebs are becoming less concerned about the Warm Water Blob with each day passing… However, for the record….the models still forecast a positive phase PDO winter and so it is expected to build back.
Wednesday AM: 9/28
Some Changes to earlier thinking;
- Subtropical moisture later in getting into Southern Mono County so Thursday holds the best chance of a few showers or TSRW over Mammoth Area.
- Worth mentioning is that the cooling forecasted, is still on track to begin Thursday then through Monday.
- There has been several runs of both global models which now appear to be in sync showing cold core low dropping into Northern CA Sunday. Comment: It really looks like the GFS from last night has caught up with the ECMWF. The Dweebs just hope that the EC does not back off. 😉
- And….although WSFO-RNO has yet to bring precip to Mono County in their late weekend forecast, the models are becoming increasingly favorable for at least Showers and snow showers later Sunday afternoon and especially Sunday night. Bulk of precipitation is up around highway 80 on the west side where moisture and strong UVM are best with associated upper jet. Both models are also showing another area of lift coming through in the chilly air Monday afternoon/Evening.
Another Comment…..Woo Hoo! Eastern Pacific warm pool did retrograde a bit more yesterday!
Tuesday 9:50 AM
Only change is in the outlook with last nights EC, and this AM s GFS is that the weekend trof is some 40 decameters deeper over California. This may not be all that much for showers this far south but there may be a few. The nature of this trof is two distinct short waves. The lead short wave is now being handled similarly by both models for Saturday afternoon although the Timing is slightly different. What is most different is how the 2nd short wave is being handled. The ECMWF has much more amplitude Saturday into Alaska along 145west. It is the secondary feature (upper low) that being handled much differently between the two models. The ECMWF as a result digs the cold core down the coast to the OR/CA boarder as the main short wave digs south into Southern Ca all the while it becomes negative tilt. The results are a much colder and somewhat wetter scenario for the sierra late Sunday afternoon into Sunday night. One that would have Tioga Pass ramification’s for closing, if not for just a while. On the other hand the GFS takes the same short wave ESE across the pacific NW and into the northern great basin for further cooling and wind but no precipitation. Although there are subsequent short waves that keep us cool from both models, the key will be on the upstream amplitude and more importantly the energy coming off Asia into the western pacific. As a side note, the warm pacific pool is “between” 150 and 140 west. This is where the results of the amplitude carried east from the western pacific is being focused. Big message is that the position of the corresponding eastern pacific ridge is a favorable one for periods of cold short waves and possible high country moderate snowfall during the month of October.
Today Monday…500MB Charts are showing a SW/NE ridge across North Central California with two anti cyclone centers. One over Nevada and the other well west of Northern Baja. Well above normal heights are over the state and thus the warm up will likely to continue another day or two. The upper ridge does break down by mid-week in response to a GOAK Trof digging Southeast. The trof should be good for at least 15 degrees of cooling between this Tuesday and Sunday, with strong gusty winds over the crest next weekend.
At the moment, it is unlikely to bring any precipitation this far south, However, there is a closed low over Northern Baja that will lift NW into Southern California later Tuesday into Wednesday. This system is lifting in response to the GOF trof and there may be some showers from it for Southern CA north to Inyo County and Southern Sierra. It should be mentioned that a similar pattern has been repeated now 3 times this month. It will probably be repeated another two or 3 times…Later in October, these systems should bring some snowfall
High temps will remain in the low to mid 70s in Mammoth through this Wednesday….cooling to the mid upper 50s by Sunday. Lows at night at 8000 feet will range in the 30s this week, then 20s by this weekend.
After next weekend the weather is expected to be a bit cooler than normal into following Monday or Tuesday, although some weak ridging is likely mid-week for milder temps before an even cooler trof moves into California that following weekend. (October 8th)
This is according to the ECMWF Ensemble’s from 00z run 9/26.2016.
Comments about longer range forecasts this Fall.
- There are beginning to be some long-range forecasts coming through and they maybe already in trouble in my estimation. A lot of the Forecasts are based upon the PDO being positive with the big blob of warm SSTAs along the west coast snuggled up over the Eastern GOF like the past 3 to 4 years. They are also based upon a weak La Nina or La Nada. We still do not know for certain where the winter warm pool is really going to set up or how strong it is going to be as we do not know for certain how strong or weak La Nina is going to be. Scripps, although weaker than its forecast this summer, is still forecasting a strong La Nina. The CFS VS2 is forecasting a weak La Nina, but beginning to trend moderate. Remember the trend is your friend in this science. Also look at the SOI, as the trades are really blowing! See: the SOI: https://www.longpaddock.qld.gov.au/seasonalclimateoutlook/southernoscillationindex/index.php Anything in the 20s daily is cranking! The 30 day and 90 days means are rising as well. This bodes well for La Nina to intensify this Fall.
- You can clearly see that the position of the eastern pacific warm pool seems to coincide with the position in the mean of the eastern pacific ridge which suggests a lot of where the Fall and Winter storms are going.
- Late last August, some Winter Forecasters were saying the Ring of warmth (+PDO) would reestablish itself for a dry warm west and a cold wet east…and the guidance clearly shows that by November. However, the current SSTA north pacific warm pool does not. The core of the pool of warmth is located about 145West not 130west and so it is far enough west to allow Short Wave trofs to progress into California in various ways, depending upon the amplitude of the upstream EP ridge. Although it is unlikely that the warm pool retrogrades, if it stays around 140west, that would suggest a quite cold fall for the west with the Long Wave or adjustment wave axis set up east of Eastern Ca,….At about 110west. The set up favorites, cut off west coast lows, Cold lunkers pinching off and dropping south down the Southern CA Coast, and dry inside sliders, depending upon which month we are looking at. So not a wet winter for the sierra but at least the chance of some decent snowfall. This would also suggest a bit wetter than normal snow season for the Rockies.
- Do not forget the MJO between December and March. ENSO neutral years are best for AR events along west coast…..One AR event can bring a half winters worth of precipitation or more! The MJO works on all by itself and does not care so much about where the EP ridge is.