Area Forecast Discussion
Issued by NWS Reno, NV
FXUS65 KREV 221027
Area Forecast Discussion
National Weather Service Reno NV
327 AM PDT Wed Mar 22 2017
Convective snow showers today, mostly in the Sierra, with the
possibility of isolated thunderstorms through the region this
afternoon. Another storm is likely Friday into Saturday, with
another possible early next week. Neither storm looks very
strong, but could produce some travel impacts for higher passes.
A moderately strong consolidated band of convection is currently
moving east through central California this morning (3 am). The
band is north-south oriented along a weak mid-level cold front.
The trough associated with this front is splitting as it moves
over the region today with nearly all model simulations
dissipating the band as it moves into the the Sierra and is sheared
apart. However, satellite cloud top temperatures and the trajectory
of the mid-level low indicate the possibility this will stay
stronger then modeled as it moves into the Sierra this morning. If
so, snow fall could be fairly heavy for a few hours this morning,
especially right along the Sierra crest.
Either way at least some moderate convective snow showers are
likely this morning through this afternoon with the highest
chances in the Tahoe region this morning moving south into Alpine
and Mono counties in the early afternoon. With the cold pool aloft
this afternoon sufficient instability will again be available for
isolated thunderstorms. Snow levels will be dragged down under
convective precipitation possibly as low as 5000 feet or so. Again
these convective shower will be sporadic with breaks of sunshine
between showers this afternoon. On the high end 3-8 inches of
snow could accumulate (if the convection band stays intact) along
the crest through this afternoon, but most areas would most
likely only see a couple inches. Temperatures should again be warm
enough that snow that sticks to roadways should melt of fairly
quickly below 7000 feet.
Thursday we`ll see a break in the weather as ridging temporarily
builds in and drier air works into the region. On Friday another
round of moisture pushes into the region driven a sharp trough and
northeasterly oriented jet. The trough is fairly progressive but
still retains some splitting nature, as is common this time of
year. Moisture will begin to move into the Sierra during the day
on Friday as the initial upper level front moves in. Snow levels
could start between 5000-6000 feet with cold dry air in place.
Snow levels are expected to rise to 6000-7000 feet during the day
as the bulk of the moisture, with subtropical influence, moves
The secondary front and stronger forcing moves through on
Friday night with snow levels dropping below 6000 feet, but most
of the precipitation will have fallen by then. The cold pool now
only brushes by the region with 700 mb temperatures only briefly
dropping to -6C (cold enough for snow at lake level). Total QPF is
quite a bit lower then expected a few days ago. Currently the total
QPF along the Sierra crest looks to be in the 0.75-1.5" range.
.LONG TERM...Saturday into Tuesday...
Made some adjustments to the long term with respect to precip
potential and temps. The splitting system should be exiting
Saturday and right now the cold pool aloft is looking weaker. I
reduced pops a bit for Saturday, but we should still at least see
scattered showers area wide with snow levels 5-6000 feet.
A break Saturday night into Sunday morning before the next fast
moving system arrives Sunday afternoon. The models are trending
wetter with this system as both the EC and GFS now have it
entraining some subtropical moisture. I have increased the QPF some
and also the threat of precip. In addition, both the EC and GFS show
this system beginning colder than previous systems and a few inches
of snow is possible in the mountains above 6000 feet.
Beyond Sunday night, the GFS and EC diverge with their ensembles
showing the spaghetti as well. They do hit on the same theme of
cooler, splitting systems dropping near or just east of the Sierra
which is a typical early spring pattern. However, the timing of each
is almost 180 degrees out of phase. For example, the GFS has the
Sunday night system splitting more and keeps cold air and precip
around through Monday. The EC has more ridging for Monday before
dropping another slider type system for Tue-Wed while the GFS shows
more ridging. At this point, went with a middle of the road solution
with a few showers around, snow levels 5-6000 feet and temps near
VFR conditions to continue until 14Z or so before the next band of
precip moves in. This band of convection is over the CA Central
Valley and slowly moving east. Expect MVFR/IFR conds in SHSNRA in
the Sierra with areas of it in Western NV from 14-18Z. Afterward,
the band is expected to break down with more sct -SHSNRA and
restrictions. Isolated thunderstorms are also possible after 18Z.
All convection expected to die off by 02Z with VFR conditions
As for winds, KMMH will continue to gust to near 25 kts from the SW,
but elsewhere peak gusts will be 20 kts or less. A quiet day
expected Thursday with VFR conditions before the next storm arrives
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