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KEY MESSAGES

* Much cooler conditions are expected today through Thursday, with highs 15 to 20 degrees below late May averages. * Gusty winds will bring aviation and recreation concerns today through Wednesday morning.

* Shower and isolated thunderstorm chances return today with the highest overall chances Wednesday through Thursday, including light snow accumulations in the Sierra.

DISCUSSION

Gusty winds are ongoing as a cold front makes its entry into far northeast CA/northwest NV. While there will be some lulls in valley areas through the pre-dawn hours, it won't take long for the gusts to mix down to the surface as the front continues marching southward today. Lake Wind Advisories will be in effect for most area lakes through at least this afternoon as wind gusts range from 30-40 mph (with some gusts to 45 mph south of US-50). For Pyramid and Walker lakes, a more northwest-north wind direction along the longer axis of these lakes will keep choppy conditions going overnight into Wednesday morning.

With the upper low and cold front both dropping southward into CA/NV today, shower activity will spread into northeast CA/northwest NV this morning, with more isolated activity moving into the Tahoe basin and far western NV this afternoon. By tonight, a band of rain showers is most likely to form across west central NV, mainly near and east of US-95. Isolated lightning could accompany some of the showers this afternoon as colder air aloft near the low's center provides a bit more instability, as probability of thunder increases to 20-30% from western Lassen County southward to the northern Tahoe basin. Snow levels settle around 6500 ft for the Tahoe basin through this evening, although the sparse shower coverage isn't likely to yield any accumulating snow prior to Wednesday.

For Wednesday and Thursday, chilly fall-like weather will prevail with widespread cloud coverage keeping temperatures below 60 degrees even in lower elevations Wednesday, and not much recovery on Thursday. Bands of showers with embedded lightning will continue rotating around the main upper low as it meanders around eastern CA-western NV, before this low lifts out and departs on Friday. While the eventual track of this low will determine where heavier precip occurs, the probability of receiving liquid totals of at least 0.10" is quite high (80% or greater) regionwide. For higher amounts of at least 0.50", the best chances (40-75%) are showing up along the eastern Sierra and northward into Lassen County/Surprise Valley, but even western NV valleys have a 20-40% chance of receiving two-day totals of least 0.50".

For the Sierra, snow levels could drop as low as 5500-6000 feet by early Wednesday morning, then fluctuate between 6500-7500 ft from Wednesday afternoon through Thursday morning, before rising above 8000 feet by Thursday afternoon. The latest snowfall forecast has trended upward a bit especially for the higher peaks and passes of Mono County (Sonora, Tioga, and Mammoth Mountain), where overall totals could end up in the 4-8" range. For the Tahoe region, around 2" of snow is projected for Mt. Rose Summit, with less than 1" for other main passes. A rain-snow mix could occur at lower Sierra elevations down to Lake Tahoe level, but we're not anticipating any impactful snow amounts at this time.

For Friday through this weekend, temperatures will rebound with lingering shower chances mainly north of I-80 through Saturday, as highs return to end of May averages by Sunday. Further warming and dry conditions are likely for early next week as highs return to the 80s for western NV valleys and 70s for Sierra communities. MJD

AVIATION

Windy conditions with widespread turbulence continue today as a cold front passes through the region, with periods of LLWS most likely this morning when stronger FL100 wind gusts of 60-70 kt are expected. Winds shift to a W-NW direction for most terminals (except KTVL remains SSW) with gusts up to around 25-30 kt until around 03Z this evening, with lighter winds overnight and through Wednesday-Thursday.

Otherwise, VFR conditions will prevail although light showers may begin to produce short-duration terrain obscurations for the Tahoe and far western NV terminals as soon as this afternoon. Chances for rain showers increase Wednesday-Thursday that could bring MVFR conditions at times with longer periods of terrain obscurations. MJD

FIRE WEATHER

* Gusty winds continue today and shift to a more northwest direction, although humidity will be increasing as a cold front sweeps through the region. However, one area to watch is southern Mineral County and the US-6 corridor in southeast Mono County, which could see a short duration of near-critical wind and humidity conditions this afternoon.

* Fire weather concerns become minimal Wednesday and Thursday due to much higher humidity and well below average temperatures, with increasing chances of showers producing wetting rainfall. MJD

REV Watches/Warnings/Advisories

NV...Lake Wind Advisory until 2 PM PDT this afternoon NVZ002.

Lake Wind Advisory from 2 PM this afternoon to 5 AM PDT Wednesday NVZ001.

Lake Wind Advisory until 5 PM PDT this afternoon NVZ003.

Lake Wind Advisory from 5 AM early this morning to 11 AM PDT Wednesday NVZ004.

CA...Lake Wind Advisory until 2 PM PDT this afternoon CAZ072.

Lake Wind Advisory from 8 AM this morning to 5 PM PDT this afternoon CAZ073.