Area Forecast Discussion
Issued by NWS Reno, NV
FXUS65 KREV 042136
Area Forecast Discussion
National Weather Service Reno NV
236 PM PDT WED MAY 4 2016
An increase in showers and thunderstorms is expected tonight and
Thursday as low pressure approaches the California coast. Some of
the storms Thursday could be strong with frequent lightning and
copious amounts of small hail. Unsettled weather will continue
into the weekend with locally heavy rain possible. Drier, warmer
weather returns next week.
Cloud cover, no obvious forcing, and likely some capping in the
mid levels (12Z REV sounding) slowed convective development over
eastern California and western Nevada into early this afternoon.
However, of late, cumulus have begun to bubble up with isolated
showers forming over far western Nevada and northeast California.
Shower coverage is likely to trend up to scattered in the next
couple hours with peak heating. As far as thunderstorms this
evening, coverage looks isolated with fast-moving cells. Small
hail, lightning, brief heavy rain, and gusty winds to 40-45 mph
will be possible with thunderstorms into this evening.
Late tonight and Thursday morning, models have consistently shown
precipitation developing over extreme western/northwestern Nevada
and northeast California as a jet noses into the region ahead of
the potent upper low off the California coast. However, the 18Z
NAM fires up precipitation 3-6 hours later than the 12Z so the
most widespread rain may wind up being Thursday morning rather
that after midnight tonight if the NAM verifies. Upper lapse rates
increase late tonight with a few hundred joules of MUCAPE (weak
instability) so a few nocturnal storms are certainly possible into
early Thursday morning.
Thursday looks like the better day for strong thunderstorms as the
upper low nears with more divergence aloft. The divergence/cooling
aloft should erase the mid-level cap that was in place today, with
instability/CAPE increasing to up to ~800 J/kg or so, especially
north of highway 50 in northeast California and far western
Nevada. Also, the S-N upper jet is in a very favorable position
over central NV and winds aloft support some increased organization
and longevity to storms. Expect widespread showers and storms near
Reno/Tahoe up to Cedarville where instability is greatest, with at
least scattered showers/storms elsewhere by late afternoon and
early evening. Accumulating small hail (with possible brief slick
conditions on hail-covered roads) and brief heavy rains will be
the greatest threats with Thursday`s storms.
Showers and storms to continue into Thursday evening and become
less numerous. Still enough moisture and instability to continue
scattered showers overnight. Friday more showers and storms are
expected with another day of good instability as the low moves
into Southern CA. Forcing won`t be quite as strong, but still
expect some locally heavy rains and some small hail from them.
Snow level will come down somewhat late Thursday night and Friday
as the upper low moves into central and southern California. If
there is any sustained precipitation in the Sierra, higher passes
(above 8000 ft) could see a light accumulation especially if snow
falls before 9 AM Friday. Be sure to check with NDOT (for Mt Rose
Highway) or CALTRANS if traveling over higher passes Thursday
night or Friday morning.
Friday night continues to look intriguing with a deformation band
developing on the NW side of the low. The EC/GFS and less so the
NAM are hitting the Oregon border area into Lassen County. Moderate
confidence in this band location and development. Rainfall amounts
Friday night could approach 0.50" to 0.75" in this band alone.
.LONG TERM...SATURDAY THROUGH WEDNESDAY...
An expansive area of low pressure will provide continued wet and
cool conditions for the remainder of the weekend. Periods of showers
and thunderstorms will continue Saturday and Sunday with conditions
drying by Sunday evening and into early next week as the low finally
departs the region.
Overall, few changes to the ongoing forecast with the upper low
remaining well behaved in deterministic and ensemble model runs. The
main forecast problems for Saturday and Sunday will be determining
the placement of a band of heavier showers and thunderstorms that is
expected to develop as a result of deformation forcing north of the
low. Currently a north-south oriented band of convergence will be
positioned just east of the Sierra mostly across far western Nevada
on Saturday and then shifting east across Pershing and Churchill
counties on Sunday. This forcing is disjointed from the best surface
based instability across far northeast California so do not think
thunderstorm activity will be as potent as earlier in the week.
Nonetheless, mid-level instability should be sufficient to still
produce periods of small hail, cloud to ground lightning strikes,
heavy rainfall, and rises on creeks and streams.
Snow levels will remain quite high through the weekend mainly from
8,500 feet on Saturday rising to near 10,000 feet by Sunday. As
such, any problems from snow will only impact the highest passes
during periods more intense convective cells. Anyone planning
outdoor activities should prepare now for a very active weather
pattern which will include the possibility of lightning and small
The low will finally pull away for the beginning of next week which
should largely provide warmer and drier conditions aside from a few
lingering showers across the Sierra. After a cool weekend,
temperatures will warm quickly next week with high temperatures
warming into the upper 70s and near 80 by midweek across western
Showers and thunderstorms will be on the increase this evening and
Thursday. Expecting showers and storms to increase after 06z as
forcing from an upper level low and jet arrive across the northern
Sierra. This widespread coverage will continue into Thursday.
Storms will be capable of lots of small hail and heavy rain,
especially Thursday when forcing/instability will be strongest.
Since this is a wetter system, potential for severe outflow winds
looks less probable with more impacts expected from heavy rain,
decreased visibility, and abundant small hail.
Potential for continued periods of showers and thunderstorms will
remain through Sunday as the low will be slow to depart the region.
Precipitation will diminish by Sunday evening as the low departs
with drier conditions expected by early next week. Fuentes
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