Wednesday December 15, 2010
Posted at 9:55 am by Howard
Lots of good ingredients coming together for quite a bit of precip this weekend. The well touted subtropical jet will play quite the part the next 7 days in putting a good dent in the annual snow and water totals for the high country.
This mornings 12z GFS still showed the REX block at the dateline and the long wave trof at 143w, smack dab in the middle of the Gulf of AK. The polar jet extends from 160W through Northern California along 35 to 40 N. So what we have is one big pacific ocean “Lake Effect” with the subtropical and polar jets pretty much coupled off shore. A nice mix for Sierra Cement!
QPF: HPC has a walloping 9+ inches for the period Wednesday Am through Monday AM with the main emphasis Saturday through Monday. Lead forecasters at WSFO-RNO are a bit more conservative at 6 Inches.
The big question revolves around the snow levels. The consensus at the moment with the forecasters up in Reno is that the precip will be in the form of snow Friday night changing to rain below 8500 ft in the Town of Mammoth Saturday Afternoon then changing back to Snow Saturday night with the snow level back down to 7ooo or 7500 feet.
All forecasters will be very interested in seeing the 12z Saturday Oakland sounding to get a more exact idea on whether this will be snow or rain in town.
2:15 pm Update
Here is an excerpt from the latest EFD from the NWS Camp Springs MD
ONSHORE STRONG ZONAL MID LEVEL PACIFIC FLOW WILL SHEAR IN ENERGY IN
PIECES WITH ONE BETTER DEFINED FRONT COMING IN AROUND MONDAY.
EXPECT HEAVY PRECIPITATION INTO NORTHERN AND CENTRAL CALIFORNIA AND ESPECIALLY THE CENTRAL
SIERRA REACHING SOUTHERN CA SUNDAY AND MONDAY. TOTALS OVER THE WEEK MAY EXCEED 10-12 INCHES LIQUID EQUIVALENT WITH HIGH AMOUNTS FALLING AS SNOW IN THE SIERRA.
THE CENTRAL SIERRA QPF GUIDANCE EXCEEDS 16 INCHES LIQUID OVER A 4 DAY
PERIOD. THIS MOISTURE WILL EXTEND EASTWARD INTO THE GREAT BASIN AND ROCKIES OVER THE WEEK END WITH LOCALIZED HEAVY ROCKY MOUNTAIN SNOW IN UT/WY AND CO. AS A DEEPER EASTERN PACIFIC TROF EVOLVES LATE PERIOD AND RIDGING BUILDS OVER CENTRAL CONUS EXPECT STRONGER PACIFIC INFLOW
TO SHIFT BACK NORTHWARDS TARGETING NORTHERN CA AND OR.
Is this hype?
See Wednesday’s Complete discussion
Here is some criteria for snowfall in the sounding;
I. Micro-physical processes
A. Oakland sounding
1. There must be a temperature in the column at or below
-15C between 650mb and 500mb (dendritic growth zone)
2. Critical temps at 700mb at or below -2c
3. The Air Mass saturated 650mb down to 500mb and lower.
4. There must be UVM! (upward vertical motion)
Stay Tuned…………..The Dweeber…………………..:-)
Reference Glossary of Weather Terms
Pattern change underway with first system to bring light to moderate amounts to the high country tonight…..then major storm for the weekend into next week!
Tuesday December 14, 2010
Posted at 9:10 am by Howard
After a small storm tonight…… (3 to 6 inches in the village) and 6 to 12 inches over the crest….
The long awaited shift from dry weather to wet will arrive Friday as a strong upper jet coming off Asia will have the effect of displacing the dateline upper ridge far enough east to get the central west coast and California wet again. The big emphasizes is on the REX configuration of the central pacific upper ridge where the upper low south of the ridge will provide for some pretty rich juice to be entrained into the west coast trof, beginning Friday night into Sunday. Looking at the precipitate water loop, there are some PWA areas west of Hawaii up to 1.75 out there that will head for the central west coast this weekend. High moisture flux and upslope conditions along the frontal boundary should support heavy snow from the Central Sierra north. HPC QPF has 5+ inches for the crest by Sunday. It should also be noted that 1000mb/500mb thicknesses are between 558dm and 564dm. So this will be definitely be Sierra Cement over the upper elevations this weekend and could possibly be rain at times in the town of Mammoth. The Dweebs will fine tune snow levels later this week. The models keep changing on the idea on the amount of rain we will have in town. A good look at the Oakland sounding Friday afternoon should help. Hopefully, Cylke’s micro-physical processes will come to the rescue!
Next week continues to be wet with snow over the upper elevations…..The Dweebs will have to keep a weary eye on the subtropical ridge over the Rockies to see when everything shifts back to the north. Will it be Mid week or as late as Christmas?
Dr Howard and the Dweebs…………………..:-)
Reference Glossary of Weather Terms
Monday December 13, 2010
Posted at 9:24 am by Howard
The long wave pattern will change over the next week…however one resounding fact remains…..the snow level will be higher then normal for the month of December. Why?? The long wave trof is too far west along with the long wave positive height anomaly near the dateline. Until these features shift east….we will most likely be more effected by the subtropical jet then the polar jet. The best that we can hope for is the right rear entry region of the polar jet. The MJO seems stuck in Phase 5. The Dweebs are looking forward to the new CPC weekly discussion today to shed light on the matter. If the MJO would continue to track eastward and remain as strong as it currently is, that would have a profound effect in dislodging the current ridge/trof positions. That most unlikely will not happen because of La Nina and how far west the Negative SSTA’s are. The MJO will probably die or at least significantly weaken over the graveyard of the warm waters of the Maritime continent.
Monday Am update:
The new 12z Monday GFS does show a strong Asian Jet having the effect of temporarily shifting the long wave features east some 1000mi. That is how they accomplish all the precip between Friday and the following Wednesday. This is just a temporary eastward shift as the pattern retrogrades back again some 1000 to 1500mi before Christmas. Using the operational 12z GFS run this AM, we ridge up again after mid week next week….possibly through the end of the year!
1. The snow level will be about 8000 during the day Tuesday then 7000 feet Tuesday night… with it lowing to near 6500 after midnight. Mammoth Mountain should get 6 to 12 inches….with the village….4 to 8 inches. This will be mainly a Tuesday night snow event for the town…… highs in the upper 30s Tuesday at the village.
2. A split in the upper flow will give a bit of a break Thursday. Snow showers still possible but the main short wave is coming in split.
3. The new 12z GFS is now very wet for the weekend beginning Friday and continues though Monday am. Several feet of snow is expected over the Sierra this weekend. 1st guesstimates, 4 to 5 feet over the crest. (This may be bumped up later) There appears from this model run…. plenty of snowfall for the plows in town as well.
The new guidance is colder now with the upper jet a bit further south. So….. A pretty much non stop dump (with some breaks) is portrayed beginning later Friday through Sunday night. The upper flow continues natural to Sierra through Tuesday night with excellent orographics. The grand fennalli comes in Tuesday/night associated with a 996mb surface low W of the Bay area. That is being portrayed by the new Monday12z GFS as the grand daddy storm that will really dump in a short period of time. There after, if the longest guidance is correct…..we should gradually ridge up, as the long wave features retrograde west. Christmas looks fair at this time……
Dr Howard and the Dweebs……………………..:-)
Reference Glossary of Weather Terms