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FXUS65 KREV 152110 AFDREV

Area Forecast Discussion National Weather Service Reno NV 210 PM PDT Wed May 15 2024

SYNOPSIS

Unseasonably warm temperatures will persist this week with breezes returning each afternoon Thursday through the weekend.
Other than a slight chance of showers and thunderstorms in the eastern Sierra south of Highway 50 on Saturday, conditions will stay dry. Low pressure will bring more seasonal temperatures next week with a low potential for showers.

DISCUSSION

KEY POINTS:

* Unseasonably warm temperatures this week, peaking Thursday afternoon when highs could approach 90 degrees for warmest lower valleys.

* Afternoon breezes (typical of early summer) return Thursday and continue into the weekend. Nothing crazy, but locally choppy lake waters and impacts to activities more sensitive to wind.

* 15-25% chance of showers and thunderstorms Saturday, mainly south of Markleeville. Otherwise, dry conditions will prevail through the weekend.

THROUGH FRIDAY:

An upper ridge tonight and Thursday will flatten Friday in response to a northern stream shortwave moving through the PacNW.
500 mb heights and 700 mb temperatures peak Thursday then fall back several degrees Friday behind a weak front moving through the Great Basin. So confidence is high that Thursday will be our warmest day with temperatures falling back a few degrees Friday. A few spots still have an opportunity to reach 90 degrees Thursday.
Latest statistical guidance places Reno-Tahoe Intl Airport at a 50/50 chance of hitting 90 degrees, which would be 16 degrees above normal. The heat risk will be in the minor category, so anyone extremely sensitive to heat should stay hydrated and limit activity during the hottest part of the day. Nighttime temperatures tonight and Thursday night will also stay quite mild, especially in thermal belts where humidity recovery will be poor (25-35% range). Breezy SW-W winds return Thursday afternoon and evening and turn more N-NE Friday. Wind gusts will generally be 25-30 mph, strongest north of Hwy 50 for Thursday and across the Basin and Range on Friday.

WEEKEND AND BEYOND:

We are looking at a troughy pattern developing this weekend into next week which will allow for a gradual cooling trend. While there is still a lot of spread in the temperature guidance Sunday and beyond, there is strong ensemble support for temperatures returning to within 5 degrees of normal by Monday- Tuesday (60-80% chance). Shower chances look rather meager through early next week as moisture and the main upper support stay just to our north. An upper low off the southern CA coast has also trended a bit more southerly which leaves more uncertainty in convective potential. The blended guidance was rather absent of PoPs Saturday afternoon despite the ECS/GEFS showing a decent QPF signature at both KBAN/KMMH. Temperatures remain around 10 degrees above normal in an area of deformation there, so we painted some low end chances (15-25%) along the eastern Sierra south of Markleeville eastward into southern Lyon/Mineral counties. Shower chances next week will depend on how far south the northern stream energy drives, but guidance currently favors northeast CA-far northwest NV next Tuesday-Wednesday. Breezy daytime winds will persist this weekend into the middle of next week as we transition to a cooler pattern.

Hohmann

AVIATION

* 24-HR Operating Period (through 17/00Z): VFR. Light N-NE winds early this evening will diminish overnight then shift to the W 10-15 kts with gusts up to 25 kts after 21Z Thursday.

* Friday-Weekend: A couple of weak fronts will push through and bring a continuation of daytime breezes, gusts 20-30 kts at times this weekend. 15-25% chance of showers/thunderstorms eastern Sierra Saturday afternoon, potentially impacting KMMH- KBAN-KHTH.

Hohmann

HYDROLOGY

Unseasonably warm daytime temperatures and mild nights, combined with higher solar angles, longer days, and limited cloud cover, will continue to increase snowmelt rates late week. Even the higher elevation deeper snow areas have begun to melt in earnest.

This rapid melt will lead to elevated flows with rivers and streams running cold and fast, most notably in areas draining significant terrain over ~7500 feet from Lake Tahoe south through Mono County. Rivers and streams in this area will remain high through the weekend, with the highest flows likely Thursday into Saturday. Cooler temperatures and a depleting snow-covered contributing area will help reduce flows somewhat Sunday into early next week.

While these high and cold flows can be hazardous to recreationalists, flooding is very unlikely. Remember the highest flows are significantly lagged from the heat of the day and can often occur at night.

More steady high flows will also continue along the Lower Humboldt, with additional rises likely in very late May or early June.

Please use extra caution around local rivers and streams which will be running fast and cold and can be very hazardous.

REV Watches/Warnings/Advisories
NV...None.
CA...None.

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