textproduct: Reno

KEY MESSAGES

* Well above normal temperatures with light winds and valley inversions persist through Saturday.

* A weakening Pacific low brings gusty ridgetop winds, scattered showers, and low end thunderstorm chances Saturday afternoon through Monday.

* A brief lull and partial warmup Tuesday and Wednesday may be followed by another disturbance with renewed shower chances mid to late next week.

DISCUSSION

Today-Saturday: Anomalous High Pressure

* Heights continue to build as a subtropical ridge expands north from the Baja/Desert Southwest, keeping conditions dry and unusually warm through Saturday. Highs run about 10-15 degrees above normal, with Reno having a 65% chance of reaching 70 degrees today and an 80% chance Saturday. Sierra valleys will also warm notably into the upper 50s to low 60s, though the coldest basins will run cooler under stronger inversions. Weak synoptic gradients favor light, terrain-driven winds and strong nighttime inversions, while a persistent veil of mid/high clouds should provide enough longwave insulation to keep freezing fog limited to patchy, localized Sierra valley pockets.

Saturday afternoon-Monday: Approaching Storm and Shower/Thunderstorm Potential

* A compact cold-core low approaches Saturday, de-amplifying the ridge and tightening 700 hPa gradients with increasing ridge winds and deeper moisture. Southwest ridge gusts will ramp up Saturday morning into the afternoon, on the order of 60-70 mph, consistent with 700 hPa winds around 30-35 kts. Strong surface heating ahead of the low combined with cold air aloft maintains steep mid-level lapse rates, with MUCAPE roughly 400-600 J/kg supporting weak to modest conditional instability by the afternoon. A 500 hPa vorticity maximum and associated PVA/height falls provide modest synoptic-scale ascent, with orographic ascent favoring convective initiation along the western Sierra slopes, then drifting into northeast California, the Sierra north of Highway 50, and parts of far western Nevada. Expect isolated showers and a 15-30% chance of mainly terrain-driven, pulse-type thunderstorms Saturday afternoon/evening, then a transition to scattered rain/snow showers Sunday into Monday (high elevation snow/valley rain) as the low fills and weakens.

Long Term Outlook: Tuesday and Beyond

* Ensemble means keep anomalously high heights anchored over the Desert Southwest with a lingering offshore trough/low, supporting a brief lull and partial warm-up Tuesday into Wednesday before additional weak shortwaves rotate inland later in the week. Confidence is higher in the synoptic-scale setup, but lower on the timing/track of individual waves and any resulting precipitation chances.

-Johnston

AVIATION

Patchy FZFG has developed early this morning at KTRK. This fog will continue to generate IFR to LIFR conditions through at least 16-18Z Friday. Besides this, VFR conditions with mid to high level cloud cover will prevail through the next 24 hours with light, terrain driven winds. The only caveat to this, will be another chance for patchy FZFG at Truckee from 08-16Z Saturday.

A storm will affect the region Saturday through Monday, increasing winds aloft (FL100 winds 30-35 kts), introducing potential turbulence, and bringing chances for light rain showers and even thunderstorms (15-30% chance mainly Saturday afternoon).

-Johnston

AVALANCHE

Weather impacts to avalanche center terrain will be dominated by continued warm temperatures through Saturday, followed by a windy, showery period late Saturday through Monday with limited high- elevation snowfall.

* Temperatures: Highs remain well above normal through Saturday. Modest cooling occurs Sunday into Monday.

* Snow Levels/SLR/SWE: Snow levels remain very high through Saturday evening (9000-10000 ft), then fall to around 6500-7000 ft Sunday night into Monday. Probabilities of at least 1 inch of snowfall above 8000 ft are around 40-60% during this time period, with SLRs on the order of 9-12:1. Overall SWE contributions remain modest, roughly 0.10-0.30 inches along the Sierra crest through Monday.

* Winds: Southwest ridgetop winds increase sharply late Saturday morning through Saturday evening, with gusts 60-70 mph likely. Winds remain breezy into Sunday, gradually easing Monday.

* Thunderstorms: Saturday afternoon/evening carries a 15-30% chance of terrain-focused thunderstorms, before activity transitions to more widespread but generally light/scattered showers Sunday into Monday.

-Johnston

HYDROLOGY

The Middle Fork Feather River near Portola has risen above monitor stage and has likely crested, with a gradual recession underway. While flooding is not currently expected, flows remain elevated and may respond quickly to continued snowmelt and any weekend showers/thunderstorms.

Most other waterways have generally crested as well, yet cold, fast water persists. Use extra caution near rivers and creeks.

Warm temperatures will sustain snowmelt into the weekend, and even modest rainfall could renew rises. Latest river forecasts and observations are available at www.cnrfc.noaa.gov

-Johnston/TB

REV Watches/Warnings/Advisories

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