textproduct: Reno

KEY MESSAGES

* Afternoon shower and thunderstorm chances each day this week, becoming wider in areal coverage through midweek.

* Abundant moisture and slower storm motions will introduce flash flooding potential from heavy rainfall as the main concern today and tomorrow. * Uncertainty later this week into next weekend on whether the monsoonal pattern will persist or if drier conditions emerge.

DISCUSSION

Currently, the CWA is underneath an upper ridge encompassing generally the western two-thirds of the CONUS with high pressure over the Four Corners region. Model guidance has this pattern persisting today though the high pressure progresses ESE a bit into the Great Plains overnight. With this setup aloft, the CWA will be seeing a good amount of monsoonal moisture continue to flow in today with model PW values ranging between ~0.8-1.2 inches. This will allow storms today to produce heavy rainfall and with models showing slower storm motions out of the S/SE, flash flooding is possible today (especially in southern portions of the CWA where a Flood Watch is in effect). As for how showers and thunderstorms develop today, CAMs are showing them starting to initiate in Mono and Mineral Counties around 1 PM PT. The 40-60% PoP chances then spreads north into the NV Basin and Range as well as the Quad County area in the late afternoon and continues through the evening. Other portions of the CWA see around a 15-25% PoPs chance this evening as well. While precipitation chances diminish overnight, portions of W NV generally see a 10-20% chance of lingering showers going into the early morning hours of Tuesday. With CAMs showing CAPE values under 1000 J/kg, there looks to be a ~20-40% chance for thunderstorms in the NV Basin and Range as well as Mono County this afternoon and evening with around 10-15% elsewhere. Thunderstorms that develop could become borderline severe today and produce strong, erratic outflow wind gusts of 50+ mph. Keep this forecast in mind when making plans today and have a way to receive the latest weather alerts and information. With the flash flooding threat, conditions can become extremely dangerous quickly. If you encounter a flooded roadway, remember: "Turn around, don't drown!"

For Tuesday, another round of showers and thunderstorms (~20-80% chances with the higher end chances in Mono and Mineral Counties) are to be expected along with flash flood potential. With CAMs showing the precipitation coverage a bit more widespread, the area that may see heavy rainfall will include the Greater Reno Area and the Quad Counties as well as portions of the Tahoe Basin in addition to Mono County and the NV Basin and Range. Model PW values are slightly higher on Tuesday than Monday (0.9-1.3 inches) due to monsoonal moisture still flowing in. With slow storm motions generally out of the south, Tuesday looks another day of potential flooding concern. Please watch for forecast updates especially in areas that see heavy rainfall today in case another flood product is needed. Similar CAPE values to those on Monday are seen on Tuesday though the latest RRFS shows pockets of almost 1500 J/kg of CAPE south of US-50, making it second day to watch for stronger thunderstorms. Forecast guidance shows a similar evolution in precipitation to that on Monday with chances starting in Mono County and adjacent portions of NV in the afternoon before before coverage spreads northward through the rest of the day.

Even with this precipitation potential this week, W NV valley high temperatures are forecast to be in the 90s with some portions (Lovelock and Fallon) potentially reaching the triple digits. Sierra communities generally will see highs in the upper 70s to 80s range. On Wednesday, models forecast the high pressure to make it over TX/OK which will take some (but not all of the monsoonal moisture) more eastward. As such, chances for showers and thunderstorms decrease to around 20-40% and are mostly confined to Mono County and the NV Basin & Range at this time. For the rest of the week and going into the weekend, precipitation chances are currently forecast to lower to where it may dry out by the weekend. However, some models show solutions where the high pressure retrogrades back into the Four Corners area, which may cause precipitation chances to rise instead. With this uncertainty, we'll continue to monitor this going forward to see if more models start trending drier or wetter for the late week. -078

AVIATION

VFR conditions are expected for area TAF sites to start today, but sub-VFR conditions may be probable after 20/18Z on account of shower and thunderstorm chances developing within the region (especially near KMMH which sees 50-60% PoPs). Storms that develop will likely cause lower CIGS/VIS with heavy rainfall due to monsoonal moisture flowing into the region. Strong and erratic gusts up to around 40-50 kts may also be possible with thunderstorms today. Will continue to monitor forecast models going forward and amend TAFs as needed with these showers and thunderstorms. Mountain obscurations at area terminals are likely today due to this precipitation as well. Lingering isolated shower chances (~10-20%) are seen in W NV going through the night.

Another round of showers and thunderstorms is expected on Tuesday with similar impacts though coverage may be a bit more widespread than that on Monday. -078

HYDROLOGY

While flooding from heavy rainfall is possible today and Tuesday, there is low confidence in exact locations at this time. Currently, the WPC gives Mono, S. Douglas, S. Lyon, and Mineral County portions of the region a marginal risk (at least 5%) for excessive rainfall on Monday. This marginal risk coverage then spreads north to along US-50 on Tuesday. Slow moving storms may produce heavy rainfall leading to possible localized flash flooding. Please clear drains now if you can to help prevent possible ponding especially in urban areas. Area rivers and streams could see some rises and increased flows with this increased rainfall, but rivers reaching flood stage is currently not forecast. -078

REV Watches/Warnings/Advisories

NV...Flood Watch from 2 PM PDT this afternoon through this evening NVZ001.

CA...Flood Watch from 2 PM PDT this afternoon through this evening CAZ073.