Area Forecast Discussion
Issued by NWS Reno, NV

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577 FXUS65 KREV 190931 AFDREV Area Forecast Discussion National Weather Service Reno NV 231 AM PDT Mon Apr 19 2021 .SYNOPSIS...
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Dry and warm spring conditions continue today. A low pressure system will then drop into the area Tuesday and Wednesday with cooler temperatures, increased winds and chances for showers. A few thunderstorms are also possible. Drier and warmer conditions return later this week, with a wetter storm is possible by late next weekend.
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&& .DISCUSSION...
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Another day like Sunday is in store today with the main difference being a turn to a more west-northwest wind this afternoon and high temperatures about 5 degrees warmer (upper 60s Sierra valleys to mid-upper 70s in warmer lower elevations). Model consensus is reasonably good in dropping a compact upper low into northeast CA Tuesday, with the system moving south along/just west of the Sierra early Tuesday night before turning east across southern NV Wednesday. Marginal instability and forcing will be sufficient for scattered showers/isolated thunderstorms along its track with some of the scenarios still painting some locally stronger cells and decent QPF signatures over northeast CA, from about Truckee northward into Lassen County. While overall QPF amounts will be 0.20" or less and in many cases just a few hundredths, amounts may exceed 0.50" with stronger clusters of storms. Showers will likely decrease going into the late evening and overnight hours Tuesday night as forcing and heating wane. On Wednesday, north winds will be advecting drier and more stable air into western NV and northeast CA. This will limit shower/storm potential mainly to the Sierra south of Lake Tahoe, with northeast steering currents favoring the west slopes. However, outflow could still force a few storms east of the crest into the Highway 395 corridor of Mono County. Surface pressure/thermal gradients tighten ahead of this low in the eastern Sierra Tuesday afternoon. Wind gusts approaching 35 mph and dry air will bring elevated fire weather concerns, especially to southern Mono/Mineral counties (see fire weather discussion for more information). Otherwise, expect cooler and more seasonal temperatures both Tuesday and Wednesday. A few showers may linger in the Sierra close to Mammoth Lakes Thursday, otherwise a shortwave ridge will build into the region Thu-Fri for warmer and drier conditions. West winds will begin to increase Friday afternoon as surface thermal gradients begin to increase again with the warmer afternoon temperatures. A couple of the ensemble clusters continue to favor a trough over the eastern Pacific this weekend with the GFS ensemble IVT probabilities indicating plenty of moisture available, although it points the main plume between 40-45N. The national blend of models was increasingly wet for the Sierra, and the forecast maintained chance POPs and light-moderate QPF. However, there is at least one cluster that is drier and a lot still depends on how the tropics (specifically Typhoon Surigae east of the Philippines) phase with the progressive westerly flow into North America. Definitely worth watching as we could use the precipitation! Hohmann
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&& .AVIATION...
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VFR conditions today with late day west winds 10-15 kts along the eastern Sierra slopes to about Hwy 95. Elsewhere, winds will be more northwest to north, also 10-15 kts. A compact low pressure system will drop through the area Tuesday- Tuesday evening for a chance of showers and slight chance of a thunderstorm. The chances for a thunderstorm at KTVL-KTRK-KRNO- KCXP-KMEV late Tuesday afternoon-early Tuesday evening is around 15%. West winds 15-20 kts with gusts to 30 kts will be possible along the eastern Sierra Tuesday afternoon, including KMMH. Hohmann
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&& .FIRE WEATHER...
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A weak area of low pressure will drop into the region Tuesday into Wednesday, bringing showers and isolated thunder to parts of eastern CA and western NV. Humidity values will be relatively high so if any lightning strikes occur they are unlikely to ignite any significant fires. Farther south in Mineral and southern Mono counties, wind gusts could reach 30-35 mph Tuesday afternoon. These gusty west to northwest winds combined with very dry conditions (RH 5-15%) will create localized critical fire weather conditions in areas with dry carry-over fuels from prior years. The main areas of concern include the US-95 corridor near and south of Walker Lake, and across Long/Chalfant/Round valleys and Swall Meadows in southern Mono County. Breezy north winds will continue for these areas into Wednesday, but temperatures will cool with humidity increasing, along with a chance of showers especially for Mono County. MJD
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&& .REV Watches/Warnings/Advisories... NV...None. CA...None. && $$ For more information from the National Weather Service visit... http://weather.gov/reno

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