textproduct: Reno

KEY MESSAGES

* Showers and thunderstorms become widespread this afternoon with primary risks of heavy rain capable of flash flooding and frequent lightning, along with outflow wind gusts and hail.

* Isolated showers and thunderstorms may return Friday afternoon but with a much lower risk of flash flooding.

* Drier conditions prevail this weekend through early next week with temperatures a few degrees below mid-August averages.

DISCUSSION

* An area of low pressure off the southern CA coast is currently producing isolated showers and t-storms in the San Joaquin valley. The more southerly position of this low will keep most forcing through mid-morning south and west of the Sierra and western NV, with precip limited to isolated showers and less than 10% chance of lightning.

* By late morning through early afternoon, this low then ejects northward toward the Sierra, providing more substantial forcing to combine with the moisture in place, with decent instability (CAPE values between 500-1000 J/kg). Higher resolution guidance continues to support rapid t-storm development between 10 AM-12 noon for the eastern Sierra, then between noon and 2 PM for far western NV including areas around the Bug and Stallion fires. These storms could develop into more persistent clusters as they march across the remainder of western NV through the rest of this afternoon, although some areas will miss out on more intense rainfall due to a broader cloud shield spreading out from these clusters and reducing heating/instability. Although most of the cells are expected to push east or northeast, rebuilding on the back side and outflow interactions could prolong the storm threat back to near the US-395 corridor and the Bug/Stallion fires until about 6-7 PM.

* While heavy rainfall (rates of 1-2+"/hour) capable of flash flooding and frequent lightning are the primary risks, strong to isolated severe wind gusts and potential for accumulating hail (mainly small but can't rule out 1" hail size either) are also in the mix with these storms.

* Later this evening, leftover showers wind down in west central NV with the low exiting to the north of CA/NV. Then for Friday, a weaker trough shortwave hangs back near the CA coast and provides a bit of instability along with residual moisture. While flooding risks are lower given weaker forcing and decreasing PW values compared to today, isolated PM showers and t-storms could form with up to 20% chance for the eastern Sierra and far western NV, and about 30% chance near US-95.

* For the weekend into early next week, a quieter weather pattern prevails with a modest SW flow over the Sierra keeping mainly dry and mild conditions, as temperatures settle in the 80s to near 90 degrees for lower elevations and 70s for Sierra communities. The next chance for showers and increased breezes may return around the middle of next week, but confidence is lower. MJD

AVIATION

* Showers and t-storms increase after 18Z for the eastern Sierra including KMMH, and after 20Z for KRNO-KCXP-KMEV, with the threat (above 50% chance) continuing through 01-03Z. These storms will produce periods of MVFR/IFR conditions with heavy rain, frequent lightning, and erratic gusts to 35 kt. The Tahoe area terminals (KTVL/KTRK) are more likely to be on the western fringe of these storms with less than 20% chance of direct impacts between 18-22Z, and decreasing further.

* For Friday through the weekend, VFR conditions prevail with SW-W gusts generally below 20 kt. Only exception may be a lingering 10-20% chance of a brief shower or t-storm near KRNO-KCXP-KMEV- KMMH Friday afternoon. MJD

FIRE WEATHER

* With improved humidity recovery over the Tahoe basin and the best forcing associated with the low off the CA coast remaining south and west of the Sierra crest, the risk for dry lightning strikes has decreased. Therefore we have cancelled the Fire Weather Watch.

* Primary concerns are with thunderstorms today producing heavy rains, strong outflow winds. While dry lightning potential is low due to the much higher humidity with surface dew points in the 40s-50s, a few lightning fires could ignite from strikes on receptive vegetation outside the rain cores.

* Flood Watch in effect through this evening for increased potential of flash flooding, mud slides, and debris flows on current and recent burn areas, including the Bug and Stallion Fires just north of Reno. Stallion Fire probably slightly higher risk with steeper terrain involved, but any rainfall can create hazardous conditions for movement of fire personnel. Rainfall rates over 1"/hour are expected from any storms this afternoon.

* Outflow winds producing sudden shifts in fire activity and direction are also a concern this afternoon. Latest high resolution models indicate potential for gusts of 40 MPH close to active fires, and over 50 MPH farther east toward the US-95 corridor.

* While some drying returns this weekend, humidity won't drop near the extreme dry levels prior to this storm event. Afternoon minimums look to range from 15-25% with good to excellent overnight recoveries. Winds will be on the lighter side with typical PM zephyr breezes producing gusts 20-25 mph, but not expecting any stronger wind patterns into early next week. MJD

REV Watches/Warnings/Advisories

NV...Flood Watch through this evening NVZ001-003.

Flood Watch from 1 PM PDT this afternoon through this evening NVZ004.

CA...Flood Watch through this evening CAZ073.