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Area forecast discussion 
National Weather Service Reno Nevada
304 am PDT Friday Jul 31 2015

Synopsis...

Moisture will spread north across the region today and bring a
chance for showers and thunderstorms mainly near the Sierra and in
western Nevada south of Highway 50, with gusty outflow winds and
lightning induced fire starts possible. The best overall shower
and thunderstorm potential is expected for this weekend, with
locally heavy rainfall and flooding becoming the main threats.

&&

Short term...

Middle and high level moisture continues to spread north across
California and Nevada through the early morning. Another weak
impulse farther south across Inyo and Nye counties is being
picked up by the latest NAM and hrrr guidance, which spread some
showers across Mono, alpine and southern Mineral counties during
the early and middle morning.

For the remainder of today, favored areas for afternoon convection
appear to be limited to areas near the Sierra from Mono County
northward to western Lassen County, and in western Nevada south of
Highway 50. Elsewhere, thicker cloud cover spreading across
western Nevada and northeast California during the day combined with dry east
flow near the surface may produce conditions too stable for
forming or sustaining convection that moves north of Highway 50.
However, outflows from cells that develop near the Sierra could
push across western Nevada and bring a short period of stronger wind
gusts by late afternoon or early evening. Most activity will
diminish tonight, although a few brief cells can't be ruled out
mainly south of Highway 50 as moisture continues to increase
overnight.

The main convective potential is expected this weekend as moisture
continues to surge northward. While cloud cover could still disrupt
convective development, there appears to be a larger window of
heating on Saturday, along with rising dew points contributing to
more instability. A stronger upper level disturbance is also
projected to move north across the Sierra with another disturbance
tracking northward across central Nevada. These features would provide
additional forcing and increase shower and thunderstorm coverage
which may hold together through Saturday night. The current
shortwave tracks are favoring some overnight precipitation across the
Tahoe basin and the Reno-Carson City vicinity, although this could
vary since the track of these disturbances are likely to change
with upcoming model runs.

For Sunday, another round of showers and thunderstorms is probable
with very moist and unstable conditions remaining. If full
instability is realized, then some strong storms with heavy rain
would develop. However, there could be too much leftover cloud
cover from Saturday night's activity which limits heating and
cell strength on Sunday. This limiting factor is more pronounced
on the GFS which is holding maximum temperatures down to the middle-upper 80s
across western Nevada. We didn't make much change to the current
Sunday forecast with chance probability of precipitation kept over most areas, since
there is a lot of uncertainty with the details of where convection
eventually occurs. Mjd

Long term...Monday through Thursday...

The overall idea for next week's forecast has not changed, but did
make some changes to the details. Drier southwest flow is expected
to begin Monday and continue through the week. Some moisture will be
left over Monday for some showers and thunderstorms. However, pushed
the best chances to Mono/Mineral where the southwest flow will be
weakest. While it won't dry out quickly, the Zephyr acts to limit
thunderstorm development behind its leading edge. I would not be
surprised if the Tahoe basin is completely dry as early as Monday
and possibly the Sierra front outside the Pine nuts.

Tuesday through Thursday, dry southwest flow will continue. One
thing to note is that there is another wave embedded in the flow for
Tuesday that could back the flow to the south over Mono/Mineral and
keep thunderstorms possible there. The ec is showing this idea,
while the GFS is dry. Will keep Tuesday dry for now until there is
more consistency.

As for the winds, they look to be fairly typical for midsummer with
an afternoon/evening Zephyr each day and gusts 25-30 miles per hour.
Temperatures will also cool back closer to average if not a little
below. Wallmann

&&

Aviation...

VFR conditions as monsoonal moisture streams north today with
broken middle and high clouds. A few light showers possible this
morning with isolated showers and thunderstorms this afternoon
along and just east of the Sierra. Coverage may be more over Mono
County including kmmh, but this will be dependent on cloud cover
this morning. Main threat will be gusty outflow winds 40+ kts and
associated wind shear.

More clouds tonight before a potential repeat on Saturday. Moisture
increases, but the storm coverage will be dependent on cloud cover.
Wallmann

&&

Fire weather...

Main concern will be lightning today with storms as moisture
continues to increase. Cloud cover is fairly extensive this
morning so coverage is likely to remain isolated. Storms will
start dry and become wet/dry hybrids as the day progresses. As we
move into Saturday, moisture will continue to increase and expect
hybrid storms that day. Given the dryness and heat preceding, it
could be a potentially active day. However, cloud cover looks like
it might be extensive that would reduce the instability and
coverage of storms. Given the uncertainty, will not issue a Fire
Weather Watch for dry lightning.

As we move into Sunday, more moisture will be present and storms
will be slow moving. At that point, heavy rain will be the bigger
concern although a few starts outside the cores will remain
possible. Humidity will also be higher too with minimums likely to
remain above 20% in western Nevada and 30% in the Sierra. Dry southwest
flow is expected next week with a few storms possible Monday. Winds
next week look to be typical zephyrs with gusts 25-30 miles per hour. Wallmann

&&

Rev watches/warnings/advisories...
Nevada...none.
California...none.
&&

$$

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