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Area forecast discussion 
National Weather Service Reno Nevada
326 am PDT Monday may 4 2015


Warm temperatures and chances for showers and thunderstorms will
continue this afternoon. A low pressure system dropping out of the
Gulf of Alaska will bring an unsettled weather pattern by midweek
with more widespread shower activity. Daytime temperatures as much
as 20 degrees cooler from Monday to Thursday.


Short term...

The persistent weather pattern we've seen over the weekend will
continue one more day before we transition to a cooler and wetter
pattern by midweek. For this afternoon we will see shower and
thunderstorm development with the best potential again existing
across Mono, Mineral and southern Lyon counties. Instability does
look a little more favorable farther north than compared to
yesterday so could see some development into the Tahoe basin and
also northern Lassen County. Gusty outflow winds appear to be the
main impact with any development today as a dry subcloud mixed layer
persists. Can generally expect erratic outflow winds up to 45 miles per hour in
and near shower and thunderstorm activity today. Westerly steering
flow should diminish precipitation chances across the Sierra by
late afternoon with the best potential for storms shifting across
Mineral and Churchill counties.

An upper low crossing over the Pacific northwest on Tuesday will
introduce a drier southwesterly flow across northern California and
Nevada. This should result in breezy west to northwest winds at the
surface with gusts up to 25 to 30 miles per hour. Most residual moisture,
instability and thunderstorm chances will be confined farther south
mainly across Mono and Mineral counties. Temperatures will also cool
about 5 degrees on Tuesday leaving still pleasant high temperatures
in the middle 70s across western Nevada and middle 60s for the Sierra.

The core of the upper low begins to cross the southern Oregon border
by Wednesday. This will yield middle-level instability and dynamic
forcing via vorticity advection to develop some elevated convection
across far northeastern California and northwestern Nevada. Areas
south of Interstate 80 are nearly void of surface based instability
and will be south of the main dynamic forcing region. Models are
still showing some run variability in the placement of the core of
the low which would in turn yield some greater uncertainty in the
extent of the instability and forcing across our southern zones.
As such, will not remove thunderstorm wording across these areas
at this time. Better confidence exists however in experiencing
temperatures about 10 degrees cooler Wednesday afternoon along
with stronger northwesterly winds with gusts near 30 miles per hour. Fuentes

Long term...Thursday through Monday...

No major changes were made to the forecast this morning as forecaster
confidence continues to increase for much cooler and wetter
conditions for the end of the week. Models are in decent agreement
with bringing a trough across the Sierra and western Nevada for
Thursday and Friday. Main impacts from this trough will be a
noticeable drop in maximum temperatures from Wednesday through
Friday, as well as some decent chances for precipitation across the
entire region.

Highs on Thursday will drop about 10 to 15 degrees from Wednesday
with many locations in the 50s. Widespread cloudy and rainy
conditions could result in even lower than forecast high
temperatures for Thursday and Friday. These cooler conditions will
result in lower snow levels across the Sierra for the end of the
work week as well. Snow and/or ice pellet accumulations will be
possible on roadways, so anyone working or recreating outdoors in
the mountains should prepare for winter-like conditions.

Although forecaster confidence is medium to high for a wetter
pattern on Thursday and Friday for the region, the placement and
amount of precipitation is more uncertain. Latest model solutions
show precipitation band setting up on Thursday afternoon anywhere
from the I-80 corridor to as far south as Mono County. Higher
precipitation amounts will occur wherever this bands eventually sets
up, but differences between the operational models make this
difficult to nail down for now. By the weekend, forecast models are
hinting at a slight warmup but the GFS/European model (ecmwf) exhibit differences
with the large scale setup of the shortwave ridge and another
incoming trough so forecaster confidence is low. Weishahn


another round of isolated thunderstorms will be possible today with
best chances south of Highway 50. Storms will be capable of moderate
rain, small hail and gusty outflow winds up to 35 kts. Storms that
develop along the Sierra crest and Pine Nut Mountains will move
eastward as westerlies establish this afternoon. Low chances for
Sierra terminals to have a thunderstorm in their vicinity. Higher
probabilities for vicinity thunderstorms exist for knfl and klol
through 04z. Weishahn


Rev watches/warnings/advisories...


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