textproduct: Reno

KEY MESSAGES

* Seasonably warm temperatures are forecast for the region through this week.

* Areas of increased cloud cover prevail today with chances for isolated showers and thunderstorms beginning near the Eastern Sierra this afternoon before spreading northward going into the night.

* Periods of monsoonal moisture will keep shower and thunderstorm chances with potential for localized heavy rain this week. Best overall storm chances favor Monday afternoon through Wednesday.

DISCUSSION

For today, forecast guidance depicts a high pressure ridge centered over the Four Corners region yielding a south-southwesterly flow over the CWA. This ridge is projected to strengthen on Monday and Tuesday, which turns the CWA's upper flow more southerly. On Wednesday, the high pressure controlling the upper ridge travels more towards OK/TX, which then changes the CWA's upper flow to southwesterly with low pressure developing off the Pacific Coast. While forecast guidance diverges a bit for the rest of the week, the popular solution appears to at least keep the CWA underneath the influence of the ridge. With this pattern aloft, area high temperatures generally stay near the seasonal normal temperatures for mid-July. W NV valleys are forecast to be in the 90s through the week with some portions such as Lovelock and Fallon nearing or even reaching the century mark. Sierra communities expect highs ranging between the upper 70s and the 80s. This pattern though will allow for a good amount of overnight cloud cover through at least the first half of the week, which will keep low temperatures about 5-15 degrees above mid-July normals.

This aforementioned ridge pattern will bring in monsoonal moisture to the region starting today which can already be seen moving into the SW CONUS in the latest IR water vapor satellite imagery. With this moisture, cloud cover will increase through the day and cause shower and thunderstorm chances within the region. CAMs are showing a ~15% chance for isolated light showers this morning in NE CA down to around the Tahoe Basin that expect to taper off by the late morning. But in the afternoon, Mono and Alpine Counties as well as adjacent portions of NV begin to see a 25-50% chance for showers and non-severe thunderstorms around 1-2 PM PDT. Going into the late afternoon, chances diminish to around 25% and spread into the north including the Reno-Sparks area. Shower chances for the region then lower even more to around 15% overnight before ending early Monday morning. There still is potential that the widespread development of clouds will inhibit convection in the evening and overnight hours following the afternoon thunderstorms that could pop up in the Eastern Sierra.

For Monday and Tuesday, more showers and thunderstorms are expected with monsoonal moisture continuing to flow into the region. Models are continuing to show PW values exceeding 1 inch on both days with portions of W NV surpassing 1.25 inches on Tuesday. This means that thunderstorms that do develop will be capable of heavy rainfall. Expected storm motion continues to be on the slower side, so this points to the potential for flash flooding to occur within the region. On Monday, a ~50-70% chance for showers and thunderstorms begins once again in the Eastern Sierra and adjacent portions of NV in the afternoon. These chances lower a bit to around 40-60% and also spread more into the NV Basin and Range by the evening with the Quad County area seeing around a 25% chance. Precipitation chances then mostly taper off overnight though there still is around a 10- 15% chance for a lingering shower in portions of W NV. On Tuesday, more widespread shower and thunderstorm chances (20-80% with the higher end chances in the Eastern Sierra) are currently forecast. With the aforementioned heavy rainfall potential, this is looking right now to be the most probable day for flash flooding within the area (just ahead of Monday in the upcoming days). Please continue to monitor the forecast as more details become available in case preparations need to be made for your area.

Daily shower and thunderstorm chances will continue in the CWA Wednesday onward though they diminish each day and are considerably less than the chances seen early week (20-40% on Wednesday and up to around 20% for the remaining days). The precipitation coverage currently is forecast to be confined mostly to Mono County and the NV Basin and Range on these days. However, there is some uncertainty in the evolution of the high pressure ridge as some models do show it retrograding back to over the Four Corners by the end of the week. Will continue to monitor this going forward in case trends begin to show more monsoonal moisture flowing into the region later in the week. -078

AVIATION

VFR conditions are currently forecast for today and tonight for all area TAF sites. Monsoonal moisture is expected to push into the region starting today allowing for increased mid-high level cloud cover. Models also are showing shower chances to begin in the Eastern Sierra around 19/20-21Z that will spread into the Sierra Front by 19/23Z-20/00Z. Shower and thunderstorm chances then expect to increase going into Monday and Tuesday within the region bringing potential impacts including heavy rainfall, more frequent lighting, and outflow gusts of 30+ kts. Seasonably warm daytime high temperatures may continue density altitude concerns through the week. -078

REV Watches/Warnings/Advisories

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