Scientific Forecaster Discussion
fxus65 kvef 202153
Area forecast discussion
National Weather Service Las Vegas Nevada
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 miles per hour. Thunderstorm
activity should diminish after sunset.
On Saturday the attention shifts to a disturbance/mesoscale convective vortex 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 California 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 mean sea level. Isolated to scattered
thunderstorms can be expected by Saturday afternoon around the
Spotter information statement...spotters are encouraged to report
any significant weather or impacts according to Standard operating