textproduct: Reno

KEY MESSAGES

* Increased breezes and low humidity will lead to elevated fire weather concerns this afternoon, especially for northeast CA and northwest NV.

* Seasonably warm and mainly dry conditions prevail through this weekend, with increased cloud cover Saturday night and Sunday.

* Periods of monsoonal moisture return next week, renewing chances for showers and thunderstorms, with potential for localized heavy rain.

DISCUSSION

Another dry and warm day prevails for eastern CA and western NV with a modest SW flow aloft over the Sierra while an area of low pressure off the northwest Washington coast moves slowly northward into SW Canada. Meanwhile, a large high pressure ridge continues to extend from the Rockies to the central US. We'll still have elevated fire weather concerns across northeast CA and far northwest NV this afternoon as wind gusts increase to 25-30 mph with brief gusts to 35 mph while humidity bottoms out in the 8-12% range. For Saturday, the wind gust speeds edge downward a bit while humidity won't be quite as low, but it remains important to avoid activities that can cause a spark, with ongoing fires in northeast CA.

As the weekend progresses, we'll start to see a gradual shift to a monsoon-type pattern, with the first indications being the arrival of more widespread mid-high clouds late Saturday through Sunday. There are low probabilities (10% or less) for a few narrow shower bands forming Saturday night into Sunday morning across parts of northeast CA and far northwest NV, with a few higher resolution guidance sources now indicating this potential. With low levels remaining relatively dry, the most likely outcome would be virga or just a few sprinkles reaching the ground. Similar low-end chances (near 10%) for light showers could return Sunday afternoon and extend from northeast CA into the Sierra and Mineral County, but confidence is on the lower side for any meaningful rain amounts reaching the ground, with no significant forcing evident on the latest guidance.

Next week from Monday onward, the large high pressure ridge is projected to drift southward and extend from the Four Corners region to the south central US. This will bring a more southerly flow aloft, with deeper moisture advancing into eastern CA/western NV. For Monday afternoon, the best instability and potential for showers and t-storms currently favors areas south of US-50. Then for Tuesday-Wednesday, the risk for showers and afternoon/evening t-storms expands northward across the region as surface dew points rise into the 40s and lower 50s. While this moist pattern can lead to storms capable of producing heavy rainfall and increase concerns for localized flash flooding, a common limiting factor if forcing isn't sufficient is an overdevelopment of thicker cloud cover. This in turn cuts off the instability and leaves more areas with periods of mainly light rain, and cooler daytime highs by up to 10 degrees.

Later next week, the ensemble guidance spread increases with a near equal split between a return of drier southwest flow vs. a continuing influence of deeper monsoonal moisture into the region. As a result, overall confidence is lower and the current forecast will take a mid-range approach with a gradual decrease of shower and t-storm chances initially for northeast CA then to northwest/far western NV and the Tahoe basin, but not yet clearing out of west central NV or Mono County by next Friday.

Aside from the aforementioned potential for several degrees of cooling if we get a day or two with thicker cloud cover and/or patchy rain, daytime temperatures for the upcoming week will generally remain near mid-late July averages. This keeps highs in the 90s for lower elevations, with a few sites in west central NV within reach of 100 degrees especially Sunday and Monday. Sierra communities can expect highs mainly in the 80s. However, overnight lows will be warmer than average due to increased moisture and cloud cover starting Saturday night, mainly in the 60s-lower 70s for the lower elevations and upper 40s-50s for the Sierra. MJD

AVIATION

VFR conditions continue across all main terminals through this weekend, although mid and higher level cloud cover increases Saturday night-Sunday. Main concern today and Saturday will be afternoon SW-W wind gusts up to 25 kts (except a bit lighter for KTVL/KTRK) ramping up between 21-23Z and winding down between 03-05Z. MJD

REV Watches/Warnings/Advisories

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