Very wet system headed into the sierra Friday night and should continue through early Sunday am
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