textproduct: Reno

KEY MESSAGES

* Afternoon shower and thunderstorm chances are forecast through Wednesday, with a drier pattern more likely returning by late week.

* Abundant moisture and slower storm motions will allow flash flooding potential from heavy rainfall to be the main concern today. * Typical July warmth, breezy afternoons and drier conditions may produce elevated fire weather conditions at times later this week and into the weekend.

DISCUSSION

Last night's showers have carried into this morning according to the most recent radar returns. The latest run of the HREF shows showers becoming more isolated with chances lowering to around ~15% in NE CA, far NW NV, and near the Sierra crest in Alpine and Mono Counties through the late morning. While other areas of the CWA may see a break from precipitation chances this morning, the CWA remains underneath the influence of a high pressure ridge and having a southerly flow aloft bringing in more monsoonal moisture today. The latest model PW values continue to max out at around 0.9-1.3 inches today though some models are showing areas of up to around 1.5 inches in the NV Basin and Range. With CAMs showing another round of showers and thunderstorms today, these well-above normal values mean that heavy rainfall is possible once again. Storm motions expect to be slow as well so there is a Flash Flood threat within the region, especially if there are training thunderstorms. Refer to the current Flood Watch product and the Hydrology section for more details. With the flash flooding threat, conditions can become extremely dangerous quickly. If you encounter a flooded roadway, remember: "Turn around, don't drown!"

Forecast guidance is showing cloud cover lessening going through the this morning in portions of S. Mono County as well as over the NV Basin and Range, which will allow for more diurnal heating in these areas and increasing instability for convection. Models reflect this with CAPE values between 500-1500 J/kg today, so stronger thunderstorms that do develop today could also produce strong outflow wind gusts of 50+ mph and small hail. The NBM probabilities for thunder across the region today are around 20-60% with the higher end chances in the aforementioned areas. As for precipitation chances today, areas along and south of I-80 have around 50-90% chance with portions to the north having around a 20-50% chance. Aside from the morning precipitation, the HREF has showers and thunderstorms initiating in the Eastern Sierra by around 11-12 PM PDT with coverage spreading northward going through the afternoon and evening. While chances taper down overnight, portions of W NV north of US-50 see a 10-20% chance of lingering showers going into Wednesday morning. Please stay weather aware today and have a way to receive the latest weather alerts.

For Wednesday, CAMs are showing around a 15-40% chance for afternoon showers and thunderstorms with the higher end chances in Mono County and adjacent portions of Mineral County. Other areas highlighted for these precipitation chances include Eastern Pershing and Churchill Counties, along the OR border, and the Reno-Sparks area as well. However, forecast guidance is showing that bulk of the monsoonal moisture will shift eastward with high pressure moving into OK/TX. Model PW values come down to around 0.5-0.8 inches on Wednesday, which brings the flooding threat down a bit (though there some heavy rainfall may still be possible with thunderstorms). Will continue to monitor these flooding chances especially with rainfall occurring in the previous two days.

For the rest of the week and going into the weekend, afternoon precipitation chances gradually diminish though portions of Mono County and the NV Basin and Range may see 10-20% chances through Saturday. Forecast winds will increase on Thursday and going through the weekend with afternoon gusts up to around 25-35 mph possible. Daytime high temperatures for the W NV valleys will be in the 90s with some portions reaching the triple digits for the latter half of the week. Sierra communities have highs generally in the 80s. As conditions dry out with these temperatures, the increased winds may allow for elevated fire weather concerns especially in NE CA and NW NV. -078

AVIATION

VFR conditions are expected at all area TAF sites through around 21/18Z with low shower chances (10-20%) in the Sierra and near the OR border. After 21/18Z, widespread showers and thunderstorms are expected in the region. NBM thunder probabilities increase to around 40-50% for all TAF sites. Direct impacts from thunderstorms today could produce brief MVFR/IFR visibility from heavy rainfall, mountain obscuration, small hail, and erratic outflow gusts approaching 40 kt. Precipitation chances should diminish after 22/06Z though lingering showers are possible in W NV. Lesser chances (20-40%) for showers and thunderstorms are seen on Wednesday in the Sierra and Sierra Front with drier conditions forecast through the latter half of the week. -078

HYDROLOGY

* A Flood Watch remains in effect today from noon-11 PM for the Tahoe Basin and Reno-Carson City-Minden corridor as well as Mono, Mineral, and southern Lyon Counties. The WPC has introduced a Slight Risk (at least 15%) for excessive rainfall covering Mono and Mineral Counties as well as southern Lyon County in their latest outlook for today. Remaining areas along and south of US-50 are in a Marginal Risk (at least 5%) for excessive rainfall for today as well. Today's primary flash flood corridor extends from Mono County through the Walker, Smith, and Mason Valleys into Mineral and southern Lyon Counties as well as north into the Carson Valley, eastern Tahoe slopes, Virginia Range, and Reno-Sparks area. Individual storm tracks remain uncertain, but repeated development could produce flash flooding near steep terrain, burn scars, normally dry channels, and urban areas. Clear drains where possible to limit urban ponding. Area rivers and streams could see rapid rises and increased sediment loads with localized heavy rain, but no river flooding is expected.

-Bardsley/Johnston/078

REV Watches/Warnings/Advisories

NV...Flood Watch from noon PDT today through this evening NVZ001>003.

CA...Flood Watch from noon PDT today through this evening CAZ072-073.