Reno Area Technical Forecast Discussion

Technical Forecast Discussion

FXUS65 KREV 190953

Area Forecast Discussion
National Weather Service Reno NV
253 AM PDT Sat Aug 19 2017


Thunderstorms remain possible each day through the middle of next
week. Storms this afternoon and Sunday will again develop over
the Sierra, but we will see increasing coverage across the Pine
Nut and Virginia ranges in western Nevada. Flash flooding will
become more of a threat late this weekend and into early next
week. Temperatures through the weekend will remain above average
with weak afternoon breezes each afternoon.



A closed low off the southern California coast will provide chances
for showers and thunderstorms through the weekend and into early
next week. Storms will be favored again through the Sierra with the
best chances occurring across Alpine and northern Mono counties.
We could see some increased development in western Nevada this
afternoon and Sunday as moisture slowly increases through the
weekend. Favored locations for storm formation would be elevated
terrain such as the Pine Nut and Virgina ranges.

Storms over the next couple days will have very little motion, as
the steering flow aloft remains weak. This means that storms will be
capable of producing heavy rainfall with localized areas of flash
flooding particularly in steep terrain and recent burn scars. The
flash flooding threat will increase into early next week as
moisture works its way in. If you have outdoor plans through the
weekend, monitor for thunderstorm potential in the forecast and
updates through the afternoon.

Areas such as sections of I-80 near the Farad burn scar is
particularly vulnerable to flash flooding and debris flows as was
the case yesterday afternoon. Additional heavy rainfall on this
burn scar could produce the same results through the first half
of next week.

Gusty outflow winds are also expected in and near showers and storms
as storm bases remain relatively high and won`t lower until deep
moisture moves into the region late Monday. In terms of eclipse
viewing, this is an encouraging sign of preventing a solid cloud
deck from obscuring the sky. So far, partly cloudy conditions
look to prevail Monday morning.

Otherwise above average highs will continue into early next week
with western Nevada valleys reaching into the mid 90s while Sierra
valleys warm to the mid 80s. Fuentes

.LONG TERM...Tuesday and beyond...

The large scale pattern for the early part of the week features an
area of low pressure sitting off the southern California coast. This
brings increased south to southeast flow to the eastern Sierra and
western Nevada helping to advect modified monsoonal moisture
northward. This will bring an increase in thunderstorm coverage,
with Tuesday into Wednesday looking interesting.

On Tuesday, the position of the low allows for large scale
divergence aloft, which is excellent for thunderstorm development.
PWATs rise to around 0.8-0.9", which climatologically lends itself
to increased flash flood risk, especially given the light steering
flow. Instability continues overnight into Wednesday with showers
and embedded thunderstorms possible overnight. Wednesday also could
be another very active thunderstorm day as the low slowly opens and
shifts eastward bringing an increase to upper level lapse rates.
PWATs are forecast to increase to around 1", with light steering
flow, so once again flash flooding will be a concern. The one caveat
is that if we end up with extensive cloud cover Wednesday, which is
possible given the situation, we may not realize the full
instability potential. This may be a wait and see type day where it
could go big or it may end up cloudy, cool, and showery with
embedded isolated thunderstorms.

Heading into the end of the week, the low off the southern California
coast weakens and is absorbed into the large scale flow as a
stronger area of low pressure dives through the Pacific Northwest.
This will bring drier westerly flow to the region and increased
afternoon breezes. There may be enough lingering moisture and
instability across central Nevada eastward for a stray
thunderstorm to form Thursday. By Friday and into the weekend,
storm chances look minimal if not non-existent as most ensemble
members are indicating a large ridge building across the west.



Greatest threat for aviators will be isolated showers and
thunderstorms this afternoon, mainly along the Sierra and western
Nevada Sierra front. Storms are likely to form after 21z today,
dissipating between 03-05z. Brief periods of heavy rain, gusty and
erratic outflow winds can be expected with lesser chances for a hail
threat. Localized terrain obscuration is a concern along with short
periods of MVFR-IFR conditions under the rain core of the storms.

Chances and most likely timing for a thunderstorm to impact or be in
the vicinity of a terminal site:

KRNO and KCXP: 20 percent, 21z-03z
KTRK and KTVL: 25 percent, 21z-01z
KMMH: 30 percent, 21z-03z
KLOL and KNFL: 20 percent, 00z-05z

Thunderstorm chances and coverage will increase through the weekend
and into the first half of next week.

Otherwise, expect VFR conditions over the weekend with afternoon
westerly breezes of 8-12 kts. If it rains at KTRK, the airfield is
likely to see fog develop overnight into the early morning hours.


.REV Watches/Warnings/Advisories...



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