Area Forecast Discussion
Issued by NWS Las Vegas, NV

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000 FXUS65 KVEF 262144 AFDVEF Area Forecast Discussion National Weather Service Las Vegas NV 244 PM PDT MON SEP 26 2016 .SYNOPSIS...
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An unsettled weather pattern will begin developing as low pressure moves in from the south. Expect scattered shower chances and increased cloud cover for much of the week. Dryer conditions are expected over the weekend.
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&& .SHORT TERM...
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through Wednesday Night. The focus for much of this week continues to be the low that has cut off from a departing trough and sunk southward around the Baja Peninsula. This low continues to entrain moisture which is being pulled up into the Southwest US. Most mesoscale models bring in a push of moisture from the southeast this evening. However, without much northward progress by the low, the atmosphere looks to remain fairly stable through the overnight, thus only clouds and perhaps even some brief breezes are expected tonight. The low really begins its northward progression tomorrow. With continued moisture advection and height falls, at least some instability is likely to develop, mainly across Mohave county, where forcing for ascent will also be the best. Cloud cover will likely inhibit coverage and limit activity to showers with just a few thunderstorms, however, any reduction in cloud cover will likely yield an environment favorable of a few more organized thunderstorms with 20 to 30 knots of easterly shear in central Mohave county between the easterly jet streak to the north and southwesterly jet streak to the south. Wind gusts and small hail would be the main threats under that scenario. As the low continues its trek up the Colorado River Valley, moisture, instability, and lift will all expand in coverage over most of the area. Once again, cloud cover will likely limit instability and keep most activity as isolated to scattered showers with a few lightning strikes here and there. Plenty of wildcards exist that could enhance or inhibit thunderstorm chances. Areas of clearing could enhance instability, as could any shortwaves rotating around the low. Tropical Storm Roslyn might be worth watching, as it could direct more moisture into the low, even without a favorable track for a gulf surge. .LONG TERM...Thursday through Sunday Night. We will continue to deal with a pesky upper level low as well as the remnant moisture from Tropical Storm Roslyn that will be moving up the Colorado River Valley on Thursday. PW values increase fairly substantially on Thursday in the southern half of Mohave County and southeast portion of San Bernardino County with values increasing from around one inch to values of 1.5 inches. I have increased PoPs modestly in those areas on Thursday. The main trough will begin to move onshore in the Pacific Northwest on Friday and provide drier westerly flow to the western two thirds of the area, but moisture and sufficient instability will remain in Lincoln, Clark and Mohave Counties and continue to provide the chance of showers and thunderstorms. By Saturday the trough will begin to move into the Great Basin enabling additional drying. At this point kept a slight chance of showers in the far eastern portions of Lincoln County and northern Mohave County on Saturday as models continue to linger moisture a bit longer. The trough axis will move across the forecast area on Sunday and Sunday night and will provide a few degrees of cooling, bringing temperatures back to near their seasonal normals.
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&& .FIRE WEATHER...
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A low pressure system moving in from the south will increase moisture for most of the area by the middle of the week. Shower and thunderstorm chances will initially enter northwest Arizona Tuesday...overspread the area Wednesday...then decrease as the area dries out from west to east through the end of the week. Some easterly breezes remain possible across the far western Mojave Desert...otherwise expect lighter winds for the rest of the week.
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&& .AVIATION...
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For McCarran...Northeast gusts could persist until sunset, then light and variable winds overnight favoring a west or northwest direction. Tomorrow will bring light winds, increasing clouds, with dry weather for the Las Vegas Valley but a chance of a showers and thunderstorms along the Peach Springs corridor. For the rest of southern Nevada...northwest Arizona...and southeast California...Generally light winds expected area-wide. Some exceptions may be across the western Mojave Desert where east breezes may prevail. Increasing clouds and shower/thunderstorm chances will enter northwest Arizona tomorrow.
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&& .SPOTTER INFORMATION STATEMENT...
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Shower and thunderstorm chances will increase in Mohave County tomorrow, overspread most of the area Wednesday and begin decreasing the rest of the week. Spotters are encouraged to report rainfall amounts and any other significant local weather.
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&& $$ Short Term/Aviation/Fire...Steele Long Term..................Czyzyk For more forecast information...see us on our webpage: http://weather.gov/lasvegas or follow us on Facebook and Twitter

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