Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Reno Nevada
211 PM PDT Monday Jul 6 2015
Low pressure near the California coast will slowly move onshore
and bring the threat for thunderstorms through the week,
especially during the afternoon and evening. The highest
probability of strong thunderstorms will occur today and tomorrow,
but locally heavy rainfall will be possible any day this week.
Atmospheric conditions remain in place today for strong
thunderstorms to develop this afternoon and evening. A Flash
Flood Watch remains in effect for the eastern Sierra and western
Nevada from Reno-Sparks south to Lyon-Mineral counties where the
coverage of thunderstorms is expected to be greatest. Locations
in northeast California and western Nevada that are north and east of this
area could also see isolated storms producing brief heavy rain,
and may actually have a better chance for strong thunderstorms to
create hail up to one inch in diameter and strong outflow winds
50-60 miles per hour.
The morning atmospheric sounding at the Reno forecast office
showed steep middle-level lapse rates but with a cap around 600 mb.
This cap is expected to erode by middle-afternoon as temperatures
heat up allowing convection to become deeper and stronger. Though
not strong, there is also moderate 0-6k shear this afternoon
which increases the potential for longer-lasting strong updrafts
within any storms.
The active thunderstorm pattern will continue all week as a low
pressure system slowly moves east over CA/NV. Current satellite
estimates show abundant moisture offshore which will provide a
moist southwest flow aloft Tuesday-Wednesday. By Tuesday, the low
will have moved far enough onshore to increase the potential for
upper impulses to influence thunderstorm activity. Current models
show potential for an impulse to arrive early Tuesday morning with
a stronger upper wave for afternoon. Timing these impulses is
difficult but another Flash Flood Watch may be warranted for
Tuesday afternoon. The only limiting factor could be if the
morning impulse creates enough cloud cover to limit instability
during the afternoon.
For Wednesday, a broad area of slow rising motion in the
northeast quadrant of the upper-low should lead to an increase in
cloud cover and rain showers but could lead to a decrease in the
number of strong thunderstorms producing heavy rain. However,
model guidance continues to show the potential for strong
instability, and any cloud breaks would again provide a threat for
strong thunderstorms and locally heavy rain Wednesday afternoon
and evening. Jcm
Long term...Thursday through Monday...
An upper low off the central California coast will move inland
across Nevada by Thursday afternoon. This will provide much cooler
temperatures with a better potential to see widespread precipitation
across the region. Overall looking for ample moisture/cloud cover to
spread inland with the low which may inhibit instability and lead to
more widespread shower activity with isolated storm coverage. The
increased clouds could also keep high temperatures in the upper 70s
to lower 80s across western Nevada with upper 60s to lower 70s
across Sierra valleys. Main changes to the forecast for Thursday
were to increase precipitation chances, increase cloud cover, and also to
lower high temperatures.
An upper low will then develop just off the West Coast by Friday
with additional chances for showers and storms across the Sierra and
into far northwestern Nevada. The low will maintain chances for
showers and storms on Saturday but chances will slip mainly across
the northern forecast area roughly north of Interstate 80. By
Sunday, model guidance introduces a dry southwest flow which will
transition US into a drier pattern into early next week. High
temperatures look to return to near seasonable levels with upper 80s
across western Nevada and middle to upper 70s across the Sierra. Fuentes
Thunderstorms over the Sierra and northeast California will become
stronger and spread eastward this afternoon and evening. Erratic
outflow winds up to 50 kts and low visibility due to heavy rain are the
main aviation threats from these Storms. Mountain obscuration is
also likely especially near the crest of the Sierra. Storms should
become less intense after 0900 PDT but showers may persist
Expect similar conditions tomorrow (tuesday), except thunderstorms
may start earlier than today, especially over the Sierra where
storms may initiate by mid-morning. Jcm
Nevada...Flash Flood Watch until 9 PM PDT this evening nvz001>003.
California...Flash Flood Watch until 9 PM PDT this evening caz072-073.
For more information from the National Weather Service visit...
http://weather.Gov/Reno (all lower case)