National Weather Service Reno Nevada 307 am PDT Thursday Sep 19 2013 Synopsis... Light southeast winds and warmer conditions expected today and another night of below freezing morning lows is possible in the Sierra valleys tonight. A strong low pressure system will move into the Pacific northwest Friday and Saturday, bringing gusty winds, below normal temperatures, and a few showers to the area. Short term... clear skies will prevail across much of the western U.S. As short wave ridging briefly passes through the region. Expecting warmer temperatures this afternoon as winds shift out of the southeast with highs today right around season averages. Lower 80s are forecast across much of western Nevada with middle 70s for Sierra valleys. Thereafter, we will see a Stark regime change as an unseasonably potent low pressure system develops off the West Coast. The main weather impacts this low will provide are strong winds beginning Friday afternoon and temperatures 15 to 20 degrees colder by Saturday. The core of an unseasonably deep upper low (3-4 Standard deviations) will remain offshore of the Pacific northwest on Friday morning, but will begin to send a 100+ knot jet segment across northern California. Winds will begin to strengthen across the ridges through early Friday morning with gusts reaching around 75 miles per hour across the Sierra crest by the afternoon. Gusty winds will also materialize across the foothills and valleys on Friday as a strong surface pressure/thermal gradient and weak downslope signature help mix down winds aloft during the day. Looking like we could see widespread gusts in the 40-45 miles per hour range across Sierra valleys and into Lee side valleys in western Nevada with locally higher values in the typical wind prone areas. These winds may pose hazards to motorists in high profile vehicles especially along the Highway 395/i580 corridor and also for any individuals on area lakes where dangerous boating conditions are anticipated. Critical fire weather conditions are also expected and a Fire Weather Watch remains in place. See the fire weather section for additional details. The peak winds will occur into into Friday night as the peak 700mb flow (around 50-55kts) crosses the Sierra. This jet also Marks the arrival of the strong cold front that will sweep through NE California and northwest Nevada on Saturday where winds will remain gusty. Temperatures will drop considerably with some areas remaining only in the upper 60s across western Nevada and 50s in the Sierra. Do expect rain showers along and behind the front with upwards of a third to a half inch of rainfall possible across the wettest locations mainly near the crest and through Plumas and western Lassen counties. Valley areas in western Nevada will largely be shadowed out but could see a few hundredths to up to a tenth of inch in isolated areas within shower activity as instability increases beneath the cold core of the upper low. Snow levels will dip into the 8000-8500 foot range behind the front so some snow showers will be possible in High Sierra. Overnight lows on Saturday into Sunday morning will dip into the 20s for some Sierra Valley locations. Fuentes Long term...Sunday through Thursday... System for Friday and Saturday will push into the eastern Great Basin by Sunday with dry conditions for the start of next week. The next system in the fast Pacific flow should reach the West Coast by Tuesday night. There is a fair amount of uncertainty in the track of this low due to rapid amplification of the pattern over the northeast Pacific. However do feel confident a trough will push into the Sierra and western Nevada and bring at least a low chance of showers, gusty winds and decreasing temperatures for middle week. Latest model runs are further east with the low dropping from British Columbia into northern Nevada Wednesday. With the track a bit more overland there is less Pacific moisture for the storm to tap into and precipitation amounts are quite a bit less. However the cold air is still very apparent with this system for middle week, which may push snow levels down to 6000-7000 feet and could limit highs to the 50s and low 60s for western Nevada with 40s for the Sierra. Overnight lows may approach freezing for the outlying areas of Reno-Carson-Douglas with low 20s for the colder Sierra valleys Wednesday night and Thursday morning. Brong Fire weather... Fire Weather Watch remains in effect for gusty winds and low humidity across the Lake Tahoe basin, eastern Sierra, northeast California, northwest Nevada and the Sierra front for Friday. Confidence remains high in a low reaching the West Coast Friday with a cold front tracking across northern Nevada Saturday. Winds will begin to increase Friday morning as the jet noses into northern California. Gusts across most locations in the fire watch should easily exceed 30 miles per hour with peak gusts reaching 40 miles per hour for Friday afternoon. Dry air ahead of the system will allow humidity to plummet down to near 10% in the lower elevations and to 15-20% in the mountains. The highest wind gusts should occur overnight Friday into early Saturday morning as the jet core reaches northern California. Downslope wind signatures along the Sierra front and northern Mono County could lead to peak gusts of 50-60 miles per hour in wind prone areas. There will be some overnight recoveries, but probably not enough to decrease threat for critical conditions given the potential for strong wind gusts. Winds will be slow to diminish for Saturday, but increasing humidity and potential for wetting rains in the northern Sierra through western Lassen County should decrease the fire weather threat for Saturday. However stronger winds than Friday may impact zones 453 and 459 as the front slowly crosses western Nevada with afternoon humidity dropping close to 15 percent east of Highway 95. Brong
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