Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Las Vegas Nevada
343 am PDT Tuesday Jul 29 2014
Synopsis...monsoon moisture will remain in place mainly across
northwest Arizona and southern Nevada through the week leading to
isolated thunderstorms mainly confined to the higher terrain.
Temperatures will return to near normal Wednesday and Thursday.
There still looks to be an upswing in thunderstorms over the weekend.
Short term...through Thursday night...
water vapor shows a shortwave lifting northeast into southwest Utah
with an anticyclonic circulation over northwest Nevada early this
morning. An area of convergence/deformation between these two
systems is roughly aligned from northern Inyo County east through
northern Lincoln County. Radar/surface observations showing light
rain showers in this boundary from northern Inyo County east through
northern Lincoln County. Since midnight, two sites in Esmeralda
County (goldfield and dyer) have recorded around a tenth of an inch.
Otherwise, rainfall totals have amounted to only a few hundredths.
The boundary is prognosticated to gradually weaken throughout the day but
we are still expecting another day of terrain driven convection.
Regional integrated precipitable water values have changed little
from yesterday but that should change throughout the day as some
drier air moves in from the southwest. Since we are not looking at
the areal coverage of storms compared to yesterday will not be going
with any watch. That said, locally heavy rain would be the primary
concern with any thunderstorm. NAM the preferred model continues to
advertise slow drying leading to a gradual decrease in terrain
driven thunderstorm coverage Wednesday and Thursday.
Long term...Friday through Tuesday.
Friday now looks like it may be the least active day of the week
across our area for showers and thunderstorms as the flow aloft
remains from the southwest and drier air continues to work east
across the area. Instability remains the best across the far
northern County warning forecast area and eastern Mohave County and that is where we
continued to confine a slight chance for afternoon and evening
storms to with heating and terrain driving activity along with any
boundaries that form. Otherwise expect near seasonable temperatures with
Just in time for the weekend things look to get interesting once
again as the focus turns to an inverted trough or some sort of
vorticity maximum or lobe floating northwest around the ridge axis
aloft centered near The Four Corners. The 00z operational runs of
the GFS, European model (ecmwf) and Gem now seem to be slower in bringing this
feature up and delay it more until Saturday afternoon into Saturday
night. However, an influx of moisture is prognosticated to eject north
Friday night and this should set this stage for an uptick in shower
and thunderstorm activity on Saturday, possibly starting in the
morning. At this point, it would appear the eastern half of the area
would be the most active as the better moisture gets into these
areas first. Then by Saturday night into Sunday as the inverted
trough or vorticity maximum or lobe moves north across our area
things could get even more interesting with the potential for
showers and thunderstorms even at night as the presence of this
feature as well as better 0-6 km bulk shear values could also
support more organized or stronger convective activity on Sunday.
Precipitable waters are prognosticated to be near 1.50 inch across the southeast County warning forecast area
which will mean the atmosphere will have plenty of juice to unload
heavy rainfall all weekend in stronger storms. Thus an increased
threat for flash flooding will exist. The one thing in this
scenarios that is a tough call even shorter in to the event is how
much cloud cover will be around as this would limit heating and
could result in more of a showers and low grade thunderstorm event.
Temperatures should be several degrees below normal although any gain in
the Comfort factor department will be offset by increased humidity.
Sunday night into Monday, I went ahead and bumped up probability of precipitation slightly
as it seems models are now slower with drying across the area in the
wake of the ejecting feature. Drier air should continue to spread in
from the west on Tuesday. Activity these days should be more terrain
and boundary driven and thus I kept probability of precipitation greatest over the higher
terrain especially in the northern and eastern County warning forecast area. Temperatures should
trend closer to normal as sunshine should be more generous.
Aviation...for McCarran...scattered showers and thunderstorms will
be confined mainly to the surrounding mountains this afternoon and
evening. Once developed storms will likely impact all the corridors
at some point. Winds will favor southerly overnight before becoming
light and variable. Southerly winds will return by late afternoon
with the potential of outflow wind affecting all Las Vegas Valley
For the rest of southern Nevada...northwest Arizona...and southeast
California...rain showers will persist from northern Inyo County
through south central Nevada into the morning. Typical southerly
winds with a few gusts are expected this afternoon. Isolated to
scattered thunderstorms are once again possible across Inyo
County...southern Nevada...and northwest Arizona.
Spotter information statement...spotter activation is not expected
at this time. However...spotters are encouraged to report any
significant weather conditions according to Standard operating
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