WX Models Trending Wetter with System Friday into Weekend…Tropical/Subtropical Tap May Surprise A Few Folks…..
Monday November 12, 2012
Posted at 9:13 am by Howard
Another quick update:
QPF from CRFC is about the same at 1.4 inches while the 00z Thursday GFS is a little wetter. ECMWF is holding its own at about 1.70 to 1.90 inches through Monday AM . Over all this is still a relatively warm storm for the high country of Mammoth. Snow levels about 7500 to 8000 feet. Freezing levels about 9K until Saturday night when it drops to 8400 by 10:00pm then 7800 by Sunday 4:00AM. So the cooler air arrives late Saturday night into Sunday AM. That will be the best time for accumulation in town. The snow level will depend upon the rate of cooling per thousand feet. Best guess 7400 by 10pm Sunday and possibly 6500 to 6800 by 4:00am Sunday. 2/3rds of the storm, precip wise will be over with by then.
Still expecting 1 to 2 feet on Mammoth Mtn by Sunday Midnight. 9,000-11,000
Still looking at 1 to 3 inches of snow in town by Sunday Night. Monday looks dry in Southern Mono County
Quick Thursday AM Update
The QPF forecast is for about 1.5 inches of liquid EQ from California Rivers Forecast Center over the crest. Forecast models range from 1.5 to 2.2 with the wetter ECMWF through Monday. So best guess at 10,000 ft or About McCoy Station is for 18 to 24 inches by Monday AM.
The first system is fairly warm and so the Dweebs do not expect much if any accumulation at 8000 feet through Saturday. Cooler air from the next system will begin to arrive late Sunday and into the night. The Snow level will lower during the Sunday PM/Night time frame, however most of the precipitation will have fallen by then. So…..snowfall amounts will be light in town in the 1 to 3 inch range at most. With the “*freezing level” around 9000 feet through Saturday…..snow to water ratios probably lower now in the 8:1 to 9:1 range. That will increase a bit Sunday/night during the colder portion. Best guess at the main lodge is for 6 inches to a foot of wet snow by Monday 12:00 noon. McCoy station between 12 to 24 inches. The upper jet shifts north Monday through Wednesday, however there still may be some light orographic action over the crest… IT will be pretty breezy early next week over the upper elevations with westerly flow aloft..
It looks dry for Thanksgiving Day
*Freezing level is different than the snow level
Wednesday Am Update:
The Quantitative Precipitation Forecast I.E. (QPF) is still modest for the Southern and Central Sierra for the system now spinning up well west of San Diego. CRFC brings only .14 to the Huntington Lake Region and .35 to Yosemite…..”Pretty modest QPF” “Through Saturday AM” for a system with a Subtropical origin, and a 110knot upper jet that taps the ITCZ. However….I did noticed that the new 12Z Wed GFS has the upper jet at 300mb weakening rapidly as the system moves on shore. The 12z Wrf hangs on to the strength a bit longer…. Additionally, the upper jet support on the GFS for the Sunday/Monday AM period is pretty weak…. The Dweebs rarely look at one deterministic run of any model and make drastic changes this far out, only within 24 to 36 hours of the event…..
CRFC Days 4, 5 and 6 add to the amounts with .36 to .65 respectively. So total is between .50 and 1.00
Days 1,2,3 Freezing Level Mammoth is 8500′ @ Night to 9200′ afternoons through Sat AM
Days 4,5,6 Freezing Level Mammoth 8650 Sat AM to 8900 Sat Late afternoon, then 7800′ Sunday AM then 8200 Sunday late afternoon.
Monday AM at Sunrise, 8000′ rising to 9500 by Monday PM..then 9600′ by Tuesday AM.
The 00z ECMWF had 1.5 inches just west of the Crest by Monday AM. The Dweebs will update this afternoon on the EC.
Overall the first system is pretty mild temperature wise and the second system is just a little colder. Snow levels are usually between 500 and 1500 feet below the Freezing level.
At the main lodge because of the freezing level, the snow to water ratio will be 9 or 10:1
At McCoy the ratio will be about 11 to 12:1 as it will be some 3 to 4 degrees colder over all.
If you add orographics it looks like we could still get up to a couple of feet at McCoy Station by Monday AM considering orographics….
Although 15 to 20 inches look more reasonable at the moment by Monday AM above McCoy
The snow will be pretty wet in town……5 to 6+ inches at the village….
Dr Howard and the Dweebs……………………………..:-)
Good morning everyone….
Beautiful day out this this morning with a low of 27 here near the village. WX synopsis shows a weakening ridge over the state that will become dirtier with time. Temps will remain mild here in Mammoth through tomorrow with highs near 50 degrees. Lows in the 20s. Dry weather will remain through Wednesday.
The next sensable change with be an increase of moisture from the SW. As per yesterdays discussion.
The ripping and tearing has begun with the short wave approaching 140W. By this time Wednesday the top portion of the wave is sailing east through the pacific NW while the bottom stronger portion slows and develops a closed center as well as 110knot upper jet. The upper jet is aimed at Pt Conception, Ca and eventually the Southern Sierra will be located in the Front Left Quad exit region. The models have this system forecasted to weaken. However, through the process, it taps into a region of moisture from the ITCZ, and pulls it NE into the Southern Ca coastal areas as well as the Central and Southern Sierra. Now there are two things worth mentioning. The dynamics do weaken with time as the system approaches the coast and the fact that models almost always underestimate the moisture for systems with a subtropical tap leads me to believe that the QPF for the Sierra is under done. The flow of moisture does continue even after the systems dynamics has gone, with orographics continuing through Saturday as the inflow of moisture continues. So the Pump will be primed for the next more dynamic system arriving Sunday night into Monday. Although there are the usual differences this far out between the EC and the GFS. It is becoming more apparent that the colder system for late in the weekend and into early next week could be a real dumper! Stay tuned………..
PS…. CPC recently has stated that El Nino, the warm phase of ENSO will not likely be a factor in this winters weather. We now have a La Nada winter in the making. La Nada winters have a higher bias for tropical or pineapple connections over the Northern half of Ca. The Infamous atmospheric rivers are often times associated with very weak ENSO signals that swing between La Nina…La Nada…to weak El Nino. IE. + (-.05) to neutral to – (+.05C) And they most often are MJO induced, mostly but not always associated with the MJO Phase Space 8
This winter is forecasted to be in that category…..so do not be surprised if an atmospheric river event sets up in either January, February or March over Northern and Central Ca. The only contrary issue to the possibility is that the PDO is in the negative phase.
For those that wish to do some research on past atmospheric events open the following link for a past study. http://184.108.40.206/2005publications/CEC-500-2005-004/CEC-500-2005-004.PDF
Like the Dweebs indicated this morning the models will trend wetter….
New 12Z ECMWF has 2.00 QPF Friday through Monday AM just west of the crest now.
Short wave ridging continues to build over California, for warmer temps through mid-week. Highs yesterday over Mammoth were in the low 40s while lows this morning were some 20 degrees warmer at the Village (5F vs 25F) as compared to the colder valleys, still in the very cold around 10 degrees this morning. Today’s high will jump well into the mid to upper 40s, and by Tuesday/Wednesday in the 50s. Lows will moderate into the 20 and 30s. Winds will be light and it will stay dry through Thursday.
Now comes the Fun………
The Dweebs have been poo-pooing the splitting trof the past few days and are now back peddling a bit, to possibly a lot in the future….
Upstream this morning at a longitude of about 160west, or north of the Kauai is a highly amped ridge that becomes positively tilted so that the upper jet dives south then east and rips the down stream short wave a new one. That is a new separate system that Southern and Central Ca will deal with over the weekend. Now the Dweebs are not being Colloquial here……In the literal sense, this new trof splits off from the old at about 140W….taps well into the ITZ and pulls up quite a bit of tropical and subtropical moisture and brings it into Central and Southern Ca. A closed Anti Cyclone located near Cabo San Lucas, helps to channel the moisture our way. The ECMWF from last nights 00z run brings in about 1.2 inches for the crest between Friday and Sunday PM. The models will probably trend wetter with this in the coming days. The Dweebs will be keeping a Weary Eye out on this development to see if the trend continues. So far…the 0C Iso Therm at 700mb (10,000 ft) is south of us, so it looks like all snow on Mammoth Mt. The snow level may be about 8K or so.
The next weather system is the one that most forecasters are watching most intently. It is an Alaskan storm that will have a lot of punch to it. The EC brings it to Ca in two pieces over several days and the new 12Z Monday GFS sets California up for a series of systems within a log fetch of short waves, some of which tap the ITZ as well.
So the the system that will bring subtropical moisture to California is essence will prime the pump this weekend for the following week. It will be a lot of fun for all the Dweebs to watch it all unfold………………………….. I do not believe that anyone at this time has a real good handle on the longer range (next week) at this time. But Mother Nature is sure shifting into high gear, as a train of storms appear to be in the making….the challenge of which at the moment is their track and how the Sierra will be effected……….