Area Forecast Discussion
Issued by NWS Reno, NV
Issued by NWS Reno, NV
499 FXUS65 KREV 181916 AFDREV Area Forecast Discussion National Weather Service Reno NV 1216 PM PDT Wed Sep 18 2024 .SYNOPSIS... * Low pressure will bring scattered showers and thunderstorms this afternoon through Thursday, with snow in higher Sierra elevations. * Well-below average temperatures continue through Thursday. * A warming and drying trend starts on Friday with near to above average temperatures returning next week. && .DISCUSSION... The main weather event for the upcoming week arrives this afternoon through Thursday, as an upper low moving southward along the CA coast generates an area of deformation/upper divergence across the eastern Sierra into parts of western NV. While isolated cells are currently developing near the Sierra, the primary time frame for best coverage will be from 2-8 PM. As for location of the heaviest rainfall, the high resolution guidance favors areas from Carson City southward to Douglas, Lyon, Alpine/far northern Mono counties, and also north of Tahoe from I-80 to eastern Sierra County. We`ll be keeping an eye on the Davis and Bear Fire burn areas, where the risk of flooding or debris flow may be enhanced if heavier rainfall rain rates occur. Bands of showers and possible embedded thunder will linger into the overnight hours across parts of far western NV and the eastern Sierra, with the focus gradually shifting to areas near and south of US-50 as the upper low continues its southward trek. Then for Thursday, these similar areas south of US-50 will have the best overall afternoon shower/thunder chances, with most cells moving from east to west. For the duration of this event, the highest probability of 1/2" or more total rainfall (35-70%) are favoring eastern CA from eastern Sierra County southward across the Tahoe basin to Alpine/northern Mono counties, and western NV in Douglas/southern Lyon counties. This probability for at least 1/2" of rain is not quite as high, but still a meaningful 20-40% for the Reno-Carson area, the remainder of Lyon County and much of Mineral County. For higher Sierra elevations, the risk of accumulating snow continues, mainly for Mono County where snow levels mainly between 9000-10000 feet could impact the higher seasonal passes (Sonora, Tioga) and the upper portion of CA-203 beyond the Mammoth Mountain entrance. With the cold core of the upper low remaining west of the Sierra, the snowfall amounts in the advisory area will be more limited to heavier shower bands that linger tonight into Thursday morning. Afternoon accumulations will be harder to come by with the higher sun angles and precip likely to occur in short bursts, as opposed to persistent larger scale snow areas. Also for the Sierra ridges, a period of slightly enhanced NE-E winds (gusts 30-40 mph) are anticipated from Thursday morning through early Friday. This weather system will depart with leftover showers diminishing Thursday night, followed by a drier weather pattern from Friday through the middle of next week. Temperatures will begin a slow recovery starting Friday through the weekend (highs mid-70s to near 80) with high pressure off the west coast keeping a light north-northwest flow aloft. Then as the high shifts eastward into the Great Basin next week, further warming is expected in lower elevations with highs returning to the mid 80s by the middle of next week, along with typical afternoon SW-W breezes. MJD && .AVIATION... Periods of SHRA/TSRA are expected through 04Z this evening, with a 20-35% chance of lightning for all the main terminals, except slightly lower (10-20%) at KRNO and KMMH. Mountain top obscurations will occur, while the stronger cells could produce brief periods of MVFR conditions in CIGS/VIS. Snow is less likely to occur at KMMH (less than 10% for any accumulations) with snow levels mainly near or above 9000 feet. For Thursday, the best shower/thunder chances shift southward with 15-30% chance of lightning from KMEV/KTVL southward to KMMH, dropping to 5-10% northward to KRNO/KTRK mainly between 19-04Z. Again, the stronger cells will be capable of producing MVFR conditions, with mountain top obscurations likely continuing into Thursday evening. With the exception of brief gusts up to 25 kt near t-storms, light winds will prevail through the remainder of the week, with VFR conditions prevailing from Friday onward, other than some early morning fog around KTRK each day into the weekend. MJD && .REV Watches/Warnings/Advisories... NV...None. CA...Winter Weather Advisory from 2 PM this afternoon to 8 PM PDT Thursday CAZ073. && $$