Weather Service Report


870 
FXUS65 KVEF 202153
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
253 PM PDT Fri Jul 20 2018

.SYNOPSIS...Moist and unstable air will remain over the region 
through the end of the week providing fuel for afternoon and evening 
thunderstorms...especially over the mountains. Next week, a heatwave 
develops with very hot temperatures expected Tuesday through 
Thursday along with lowering thunderstorm chances.
&&


.SHORT TERM...Tonight through Sunday.

A moist and unstable airmass remains in place over the area today. 
Diffluent flow over the Sierra and Inyo County mountains has 
initiated thunderstorms fairly early and should allow scattered 
convection to continue over the same areas throughout the 
afternoon/early evening; localized flash flooding will be the 
concern for the Sierra. Elsewhere, convection has been increasing 
over the higher terrain. Highest CAPE (1000-1500 J/kg) will be 
focused across southern Inyo, San Bernardino, Clark, and Mohave 
Counties; strongest storms will be favored in these areas. Large 
DCAPE values will overlap areas of high instability. Thus, 
thunderstorms that develop will pose a microburst threat (very 
strong, sudden winds) along with an isolated flooding. Generally,
storm motion will be southerly around 5-10 MPH. Thunderstorm 
activity should diminish after sunset.

On Saturday the attention shifts to a disturbance/MCV riding along 
the western periphery of an eastward moving ridge. Model guidance 
has been fairly consistent with this feature for the last couple of 
runs and brings it into the forecast area by Saturday morning. With 
this impulse progged to advance northward and combine with diurnally 
driven convection, PoPs and sky were increased across eastern 
SanBern, southern Mohave, Clark, and Lincoln Counties. Temperatures 
were lowered slightly to account for added cloud cover on Saturday. 

By Sunday, the disturbance (what's left of it) should track 
northeastward into Utah around the ridge. Moderate moisture will 
remain in place and allow for diurnally driven convection over the 
higher terrain. Temperatures will be warmer Sunday compared to 
Saturday as cloud cover will be less and ridging begins to 
retrograde back over the southwest. Generally, temperatures will be 
near normal through the weekend. 

.LONG TERM...Monday through Thursday

Strong high center progged to shift westward next week with 
temperatures expected to peak Tuesday-Thursday. Late collaboration
with offices that cover the deserts of southern CA it was agreed 
upon to issue an Excessive Heat Warning early to help agencies get
an early start on preparations. Confidence moderate to high for 
this event that far out so my southern Nevada and northwest 
Arizona zones were upgraded to a warning as well. For the Spring 
Mtns and Sheep Range, a heat advisory was issued. 
&&


.AVIATION...For McCarran...Thunderstorms moving to the north 
around 10 mph over the mountains south of Las Vegas will likely move 
near or over the terminal during the late afternoon...producing 
gusty and erratic winds for the terminal area. Influences from 
thunderstorms will diminish with sunset this evening and more 
tranquil conditions are expected overnight through early Saturday 
morning. Showers or thunderstorms will be possible near the Las 
Vegas Valley again by Saturday afternoon.

For the rest of southern Nevada, northwest Arizona and southeast 
California...Thunderstorms over the mountains around the region will 
move to the north around 10-15 knots and expand in coverage through 
late afternoon into early evening. Storms should largely dissipate 
around sunset and fairly tranquil conditions will remain overnight 
with remnant cloud bases above 12 kft MSL. Isolated to scattered 
thunderstorms can be expected by Saturday afternoon around the 
region. 
&&


.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&

$$

SHORT TERM...Boothe
LONG TERM....Pierce
AVIATION.....Adair

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Western Regional Climate Center, wrcc@dri.edu