October to Turn Colder Next Week as Western Canadian Short Wave Digs into Western Great Basin bringing a few inches of snow over the upper elevations of the Central Sierra…..Between today and the rest of the week enjoy Mammoth’s Excellent Indian Summer Weather!
Thursday October 24, 2013
Posted at 5:18 am by Howard
Models have come around to the thinking of the ECMWF (European model) that the system will take a more westerly trek with the upper jet off shore and allowing the Front Rt exit region to do its magic by providing lift and vorticity over and near the coastal waters of the far eastern pacific. This bodes well for more significant accumulations now for the Sierra with a good 3 to 6 inches possible beginning Monday morning through Tuesday night. The new 12z NAM shows a slowing of the system over California, which if correct would keep the showers going possibly into Wednesday AM over the Southern Sierra. So the Dweebs are predicting 3 to 6 inches over the upper elevations beginning Monday AM through Tuesday night. The snow level will begin about 8500 but lower rapidly Monday to 5000ft.
It is likely that Tioga and Senora passes will close early Monday AM…so visitors in the eastern sierra plan accordingly….
Dr Howard and the Dweebs……………………..:-)
ECMWF has been the most consistent the past 3 runs showing the upper center of the 500mb geopotential heights centered near Susanville 5:00am Monday with the upper jet off the west coast. The GFS is now trending in that direction with the upper jet axis forecasted last night to be along the NV/CA border Monday and with this afternoons run, it is displaced west over the Sacramento valley. This is the compromise that the dweebs believed would happen. However…what may happen if it digs even further west like the ECMWF…..??? The 12z ECMWF puts the bull’s-eye back over Mammoth Lakes….
Update in the AM….
Stay Tuned…….Were almost 48 hours away>>>>>>
Latest guidance once again has gone there separate ways with the 00z run of the GFS centered near the NE Nevada Border and Southern Idaho Tuesday afternoon, while on the ECMWF, the Center swings SE from North of Tahoe Tuesday AM and is near Bishop, Ca by Tuesday at 5:00pm. This is the main reason why the big differences in precipitation for the Central Sierra Eastern Slopes, whereby the GFS model has a few snow showers and the ECMWF has a Solid 6 inches in some areas. In fact in the Tahoe area, it forecasts about an inch of Water EQ on the west side over the crest. That’s about 10 to 12 inches of snow. So here we are Friday morning with still……A low confidence forecast for snowfall for the Monday night/Tuesday period.
What do the Dweebs think? I think that there are enough short term ECMWF ENSEMBLE Runs to argue against the greater odds of the GFS for it being totally Dry.
Thus a compromise between the two……1 to 3 inches for that time frame. If there is much more…the EC was correct. If little or nothing accumulates, the GFS was correct. In that the 12z Friday GFS was not available at the time of this discussion, I will update if necessary.
As another point not mentioned above, I took a quick look at the 200 MB Potential Heights for 00z Tuesday from last nights run of the ECMWF. The Front Right Exit region is clearly off shore. The nose of the upper jet “is off the Central Ca coast”. This is the reason why the EC is so much wetter then the GFS.
Dweebs will update later today.
Remember……………Forecast models are not perfect……Just forgiven……………;-)
Dr Howard and the Dweebs……………………………………..:-)
Both EC and GFS are much closer this afternoon with a closed low over the Great Basin Monday night and Tuesday. So Snow Showers and light accumulation is expected. The EC is still in my estimation over done with well over 6 inches of snow for Mammoth Mt by Tuesday night. The GFS is still skimpy with maybe an inch.
More in the morning………………
Dr Howard and the Dweebs………………..:-)
The Dweebs had a look at the precip forecast from the deterministic 00z Thursday ECMWF for the area around Mammoth. It showed a total of .8 to .9 of an inch of QPF. This is very likely over done. It accomplishes this by a further west set up of the upper low between Mammoth and SFO Monday night. The GFS has only a trace (.01) within the same period of time. Its set up has the upper center over Central Idaho with the upper flow over land. Clearly, with the further westerly track of the deterministic ECMWF, there is more opportunity of the upper flow to get over water Tuesday and this is why it is wetter. However the ECMWF Ensembles is more like the GFS this mornings. So….Chances are that there will be a compromise with the upper center closer to the Sierra but to the east of it….still limiting the QPF. The GFS track is being favored by NWS as they only have a slight chance of snow showers at this time. Lets take a look out over the western pacific to see what is causing the Amplification up-stream…..
There are two tropical storms. One is a super typhoon. Both will become extra tropical and phase with the westerlies. This is what amplifies the down stream trof/ridge combo and drives the downstream short wave out of western Canada Sunday Night into Washington state. To the Dweebs…..The phasing of the TS’s looks constructive; IE ahead of the next upstream short wave coming off Asia. That would argue for more amplification and thus a track more toward the EC. Will Update in the AM.
Although little change in the weather under a ridge of high pressure is expected through weeks end…..Amplification of the eastern pacific ridge near 140West will bring a classic inside slider to the high country Monday through Tuesday night.
Temperatures will drop a good 20 degrees from current temps and along with the cold will come wind as well. Confidence in some light snowfall is increasing as the ECMWF model from last night run is now more or less in line with both the GEM and GFS. Therefore, expect snow showers to develop anytime after Monday afternoon. High temperatures will continue in the low 60s through Sunday then fall to the low 40s by Tuesday, Night time’s lows in the 30s will fall into the teens by Tuesday and into Wednesday AM. Thereafter, upper ridging will build back in for All Hallows Eve and continue into the first few days of November. So a return of fair weather with warmer temps expected for the end of October into early November.
Dr Howard and the Dweebs…………………………:-)