textproduct: Reno

KEY MESSAGES

* Cool, showery and breezy conditions prevail today with isolated afternoon thunder and minor snow impacts for Sierra passes.

* Shower and thunder chances slowly decrease Monday and Tuesday, with a gradual warming trend.

* Expect drier and warmer weather for mid-late week, then shower chances may return by late next weekend.

DISCUSSION

The upper low that brought areas of light mountain snow and valley rain to Mono-Mineral counties is departing eastward into south central NV. Meanwhile, a broader low pressure trough currently producing rain showers in northeast CA will drop southward across much of CA/NV this afternoon and persist through early this week. Cold air aloft associated with this trough will bring increased instability for scattered showers and isolated thunderstorms this afternoon, favoring areas from Susanville- Pyramid Lake-Fallon northward where chances for thunder increase to near 25%. With the cooler air mass keeping highs mainly in the 50s today for lower elevations, some of these storms will be capable of producing minor accumulations of pellets/very small hail.

Along the Sierra, upslope flow will support shower bands mainly near and west of the crest with snow levels between 5500-6000 feet this morning edging up to 6000-6500 feet this afternoon. While snow accumulations will be sparse during the daytime hours, a well-placed band could bring light amounts up to 2" and slick travel for the main Sierra passes (Donner/Echo summits) especially for the morning or evening hours. Across the remainder of western NV, shower coverage will be more sparse this afternoon. Thunder chances for the eastern Sierra into western NV from Reno-Fallon southward are lower, generally 10-15%. Brisk west-northwest winds with afternoon gusts 25-35 mph will make today more fall-like, with isolated choppy conditions on area lakes.

For Monday, a near-repeat of afternoon shower activity is anticipated, although instability decreases compared to today with best chances for thunder (15-20%) east of US-95 in west central NV, and generally around 10% elsewhere. Shower coverage and precip amounts decrease in comparison to today, while snow levels in the Sierra edge upward to near 7000 feet by Monday afternoon, limiting travel impacts over the main passes.

This trough pattern is projected to hang on through Tuesday, and high resolution guidance shows another round of isolated afternoon showers mainly near the Sierra. As temperatures warm up by 5-10 degrees above Monday's highs and Sierra snow levels rise to 7500-8000 feet, snow travel impacts are not expected for main passes.

From Wednesday-Friday, a high pressure ridge builds into CA/NV and continues the warming trend, with highs climbing to near 80 degrees for lower elevations and near 70 for Sierra communities by the end of the week. Dry weather and lighter winds will also prevail, although cumulus buildups may yield a slim 5-10% chance of brief showers each afternoon near the Sierra crest.

Next weekend looks to start out warm and mainly dry, but medium range guidance is hinting at another closed upper low dropping into the western US. Confidence is lower on this system's track, with some scenarios tracking the low farther west/off the west coast. At this time, our forecast indicates a return of shower/isolated thunder chances and a few degrees of cooling by Sunday. MJD

AVIATION

Rain and mountain snow showers continue to be the main weather concern for the region today and Monday, favoring the Sierra terminals where brief periods of MVFR/IFR in -SHRASN could begin as early as 17-18Z and continue until 03Z each day. For western NV terminals, VFR conditions likely prevail through Monday, although expect periods of terrain obscuration each afternoon with showers in the vicinity.

Low-end risk for isolated thunder affecting the main terminals (10-15% chance) between 20-02Z this afternoon, then edging downward to around 10% for the similar time frame Monday afternoon.

West breezes increase today with gusts 25-30 kt for western NV terminals and around 20 kt for Sierra terminals mainly between 18-04Z, followed by lighter winds (gusts 15-20 kt) Monday. FL100 wind gusts of 30-35 kt could produce isolated mountain wave turbulence this afternoon-evening. MJD

REV Watches/Warnings/Advisories

NV...None. CA...None.