000
Fxus65 krev 272200 cca
Afdrev
Area forecast discussion
National weather service reno nv
158 pm pst tue nov 27 2012
Three things to know upfront...
* forecast confidence in the overall pattern is high.
* threat of strong winds for reno/tahoe increasing thurs night
And friday.
* high snow level storms friday through sunday should minimize
Travel impacts over sierra but heavy rain could create rises in
Lower elevation streams.
.Short term...
No major changes to the forecast today, though confidence is
Increasing in periods of heavy precip for the sierra and high
Winds in the lee wednesday-friday. We`ll be issuing a high wind
Watch for tahoe, reno, mono zones thurs night and friday, but no
Snow advisories/watches for the sierra since snow levels are
Likely to be too high for major impacts.
First storm is on track to swing through tomorrow with a period
Of hvy precip in the sierra. Negative tilt trof and thin moisture
Ribbon suggest a quick hit with only a few inches of wet snow
Above 6500 ft. Mslp gradient and increasing flow aloft will result
In gusty winds area wide as well. Lake wind advisories will be
Posted.
Brief lull in systems thursday but it won`t be much of a break wx
Wise with winds increasing during the day. More substantial wind
Threat for tahoe and lee side looks to be thurs night and friday,
With 700mb flow near 60 kts, precip banking up west side of plumas
County, and decent mtn wave/downslope signatures showing up even
In gfs. Sref plume diagrams also indicate period of high winds in
Lee, so we`ve gone ahead with a watch. This has the potential of
Being a rather strong wind event late thurs night into
Friday...Definitely worth keeping an eye on.
Good atmospheric river setup with this second storm friday into
Early saturday will raise snow levels resulting in mainly rain for
Areas below 7500 ft. Potentially 2-4" liquid for crest areas north
Of tahoe; amounts dropping off rapidly to the south. We`ve issued
A hydro outlook to address potential rises in streams and rivers
Due to this heavy rain. Spillover chances into western nv are only
Modest with shadowing signals showing up in gfs/ec data but we`ve
Kept high chance pops for reno/carson area due to uncertainty.
Snow amounts in sierra could be up to a foot, but it would be
Above 8000-8500 ft for the most part, with only localized impacts
To travel.
Cs
.Long term...Saturday through monday...
Potential continues to increase for a significant rainfall event
In the sierra...Northeast california and far western nevada with
Snow levels rising above 8000 feet saturday afternoon through
Sunday morning. The large scale pattern remains unchanged, with a
Deep and warm subtropical plume (atmospheric river) pushing into
Northern california saturday night, with a front passing through
The sierra and western nevada sunday.
The main forecast issues are snow levels and rainfall amounts,
Which will dictate runoff at high elevations, and factor into the
Urban and small stream flood potential. Latest models runs are in
Good agreement in snow levels rising well above 8000 feet. A few
Model runs have shown snow levels for the tahoe basin and mono
County, may rise to 11,000 feet prior to the frontal passage and
During the period of heaviest precipitation saturday night and
Early sunday.
We do want to emphasize main-stem river flooding (truckee,
Walker, carson and susan rivers) is unlikely at this time due to
Ample reservoir storage relatively dry soil conditions. However
Those living near rivers, creeks and streams will want to remain
Aware of the forecasts through the weekend as river levels will be
On the rise.
Rain will intensify the northern sierra saturday, with light rain
Pushing across into western nevada. The period of highest snow
Levels and heaviest rain is focused from saturday night into
Sunday afternoon as the front moves through the sierra and western
Nevada. Potential is there for 6 or more inches of rain from
Western lassen county southward to along the sierra crest from the
Tahoe basin to mono county. Farther east, 2-4 inches are possible
In the tahoe basin to the foothills just west of highway 395, with
Up to an inch on the western nevada valley floors. There are a few
Factors which could produce more rainfall, especially if the front
Moves through the region slowly and warm rain processes increase
Precipitation efficiency as the front interacts with atmospheric
River.
Once the front passes snow levels should drop to near 5000 feet
Well north of i-80, near 6000 feet for reno-tahoe and near 7000
Feet south of highway 50. However the event will be ending as the
Snow levels drops, so significant snow accumulations may not occur
With this event.
High pressure is forecast to build over the sierra and western
Nevada monday and tuesday, with warm and dry conditions. Models do
Hint at a second warm moisture plume reaching the west coast for
The middle of next week. Brong
&&
.Aviation...
High pressure will bring vfr conditions, light winds and a high
Clouds through tonight. A fast moving system will bring period of
(roughly 6 hours) moderate to heavy rain/snow in the tahoe basin
And northeast california after 18z wednesday. Across western
Nevada rain and gusty winds are possible wednesday afternoon.
Conditions should fall to mvfr in rain for the tahoe basin and
Northern sierra terminals. Snow is unlikely to accumulate on
Runways below 6500 feet.
Much stronger winds will reach areas south of portola to lovelock
Thursday night and friday. Surface gusts may exceed 50 kts,
Especially at mammoth and perhaps reno-carson-minden. Certainly a
High potential for mountain waves, turbulent approaches and low
Level wind shear at all terminals.
A period of heavy rain is likely in the sierra and far western
Nevada, with high freezing levels, saturday night into sunday. Brong
&&
.Rev watches/warnings/advisories...
Nv...Lake wind advisory from 10 am to 7 pm pst wednesday for pyramid
Lake in nvz004.
High wind watch from thursday evening through friday evening
Nvz002-003.
Lake wind advisory from 10 am to 7 pm pst wednesday for lake
Tahoe in nvz002.
Ca...High wind watch from thursday evening through friday evening
Caz072-073.
Lake wind advisory from 10 am to 7 pm pst wednesday for lake
Tahoe in caz072.
&&
$$