Scientific Forecaster Discussion
fxus65 krev 180920
Area forecast discussion
National Weather Service Reno Nevada
220 am PDT Wed Sep 18 2019
Another low pressure system will bring gusty winds today but the
winds are not expected to be as strong compared to monday's storm.
Temperatures will be well below average into the start of the
weekend, with light rain and high elevation snow showers also
possible through Thursday afternoon. Dry conditions return for the
weekend with a warming trend, then breezy winds by Sunday.
The next frontal system is approaching the region this morning.
Rainfall with this system will spread across the Tahoe basin
through far northeast California this morning with light showers
making their way across western Nevada as well. Increasing
instability and frontal forcing may trigger some thunderstorm
formation with isolated lightning strikes possible across
northeast California and far northwest Nevada this afternoon.
In these areas, rainfall amounts around 0.25" will be possible, with
locally up to 0.50" in heavier bands. Elsewhere, rainfall amounts
will be lighter, with generally 0.10" around the Tahoe basin and
near the Sierra crest, and only trace amounts to a few hundredths
across the remainder of western Nevada and Mono County away from the
crest. Light snow showers will be possible at higher elevations with
snow levels dipping to around 8,500 feet this afternoon.
Winds will also become gusty again ahead of the approaching cold
front, although winds won't be as strong compared to Monday. Gusts
up to 40 mph are possible this afternoon particularly across the
Tahoe basin and through the highway396/i580 corridor. Hazardous
boating conditions can be expected and lake wind advisories have
been issued for both Lake Tahoe and Pyramid Lake.
The wind may also result in isolated areas of critical fire
weather conditions mainly across Mineral County where humidity
values could drop to near 15%. However, the combination of the
strongest winds and lowest humidity does not seem to be widespread
or for a long duration.
For Thursday, brisk northerly flow is expected behind the front.
Lingering moisture and instability, along with upslope flow could
produce additional rain and mountain snow showers, but little
additional precip amounts are expected. High temperatures will be
about 15 degrees below seasonal averages Thursday, mainly in the 60s
across western Nevada and mid to upper 50s for Sierra valleys.
Drier conditions along with a few degrees of warming is expected for
Friday as surface high pressure settles across the region. Highs
look to reach back into the low 70s for western Nevada valleys
and mid 60s for Sierra valleys. Fuentes
Long term...Saturday through next week
The main changes this morning are to continue to increase the threat
of precip for Sunday night into Monday and lower temperatures for
Monday. Ensembles this morning are showing a much higher probability
for the trough affecting the region during that time frame.
This weekend still looks mild with light winds Saturday and Sunday
turning breezy in the afternoon ahead of the trough. The trough is
anticipated to dig southeastward Sunday night into Monday into the
Great Basin. The track and depth of the trough remains in question,
but almost all ensemble members now show the trough. Overall, the
GFS family is deeper and colder while the ec family is weaker and
not as cold. The track varies from something near the Sierra to more
of a slider that ends up in eastern Nevada.
For now, we are adding shower chances areawide during this timeframe
with the best chances for showers north of a Susanville to Lovelock
line. We have also cooled temperatures a few degrees as even the
farther east/weaker solutions support some cooling.
Tue-Wed are a bit more uncertain with what happens to the trough.
Many more ensemble members are cutting off the wave as an upper low
near Southern California. There are still a few that are more
progressive. Our highest confidence during this time period will be
temperatures warming. But the position of the low will dictate
shower chances, if any. We will have ghost pops in there (~10%) to
give US the most flexibility going forward. Looking behind,
ensembles are showing a potentially deeper trough for late next week
or next weekend. X
A few showers will gradually progress southward to near I-80 after
21z. Mostly VFR still, but localized MVFR ceilings in the -shra. The
showers will spread south to be a threat to all terminals by 06z
tonight and continue to be a threat into Thursday. Any showers will
be short-lived and not all that heavy.
The other concern will be gusty afternoon SW winds this afternoon.
Peak gusts of 25-30 kts with mtn wave turbulence to be expected,
especially from 20-06z. Some light to moderate low level wind shear is possible,
with the greatest likelihood around the Tahoe basin including
Nevada...Lake Wind Advisory from 1 PM this afternoon to 8 PM PDT this
evening for Pyramid Lake in nvz004.
Lake Wind Advisory from 11 am this morning to 8 PM PDT this
evening for Lake Tahoe in nvz002.
California...Lake Wind Advisory from 11 am this morning to 8 PM PDT this
evening for Lake Tahoe in caz072.