textproduct: Reno

KEY MESSAGES

* Widespread showers and thunderstorms continue today with lesser chances Friday, and even lower chances Saturday. Cooler than normal temperatures persist through the start of the weekend.

* Snowfall is likely in the Sierra and mountains in Nevada above 7000 feet today into Friday.

* Temperatures will warm back to near or above normal next week.

DISCUSSION

As the cold core upper low spins its way across California into Nevada, it appears to have begun an elongation process that has stretched the bulk of the precipitation over the northern Sacramento Valley this morning. When referring to guidance in CAM modeling, this appears to align with the formation of a secondary center of circulation that will behave as a double-barrel effect on the overall motion of the main upper low as it tracks eastward. What does all of this mean? Well, the originally advertised track and position of the low will modify slightly, owing to the elongated positioning. As with most forecasting puzzles, this finer detail will mean some elements that would have been a more favorable setup for convection today may be displaced in future model runs. For now, it appears the bulk of the moisture will be strung across central Oregon, along with the best CAPE and vorticity fields. For this reason, we expect the best chances for thunderstorms to exist across the northern Sierra (20-30%) into the Tahoe Basin (20-25%) this afternoon, with lower chances across the Basin and Range (10-20%). Rain amounts will continue to be on the lighter and more transient side, with QPF ranging from a trace up to 0.25" through this evening. Snow amounts will be found above 7000 feet and remain light, with the best accumulations found along the higher Sierra peaks, where an additional 2-4" is expected. While some Sierra passes are closed to traffic, practicing safe winter driving is advised if you encounter slick mountain roads.

If weather systems had feet, this one would be dragging its toes! Cooler temperatures and shower chances will linger into the start of the weekend as the low begins to lift east. While Sierra valleys will be firmly stuck in below freezing morning lows through Saturday, the likelihood of seeing below freezing morning lows across western NV valleys is near zero.

Looking ahead to the tail end of May and the start of June, we resume our regularly scheduled spring warmup in earnest. By the middle of next week we will start seeing 90 degree highs emerge once more across western NV valleys. HRICH

AVIATION

* High chances (80%+) for MVFR to brief IFR in rain showers across the region resuming later this morning and continuing through this afternoon and evening. Terrain obscuration is also expected.

* Thunderstorms are also expected (20-30% chances) for the main terminals today favoring the 20-03Z time frame. Main threats are erratic outflows to 30 knots, lightning, small hail, and heavy rains. By Friday, t-storm chances drop to less than 10% for the main terminals.

* Rain-snow lines vary between 7000-8000 ft, so snow showers can't be ruled out at mountain airfields like TRK/TVL and MMH. Amounts will be light, with a 20-30% chance for up to an inch of snow falling at KMMH. Chris/HRICH

REV Watches/Warnings/Advisories

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