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Area forecast discussion 
National Weather Service Las Vegas Nevada
830 PM PDT Thursday Aug 21 2014

Synopsis...a circulation moving from Southern California into
southwest Arizona will continue toward The Four Corners region
Friday. A few lingering storms may occur over northwest Arizona
Friday. A broad area of low pressure brushing northern Nevada will
lead to dry conditions with temperatures a little below normal
across the entire region through the middle of next week.
&&

Update...
convection dissipated rather early this evening. Still have a few
showers in northern Mohave County...and with some deformation across
mainly Mohave County overnight...we could still see some isolated
precipitation. Otherwise we will now dry out from west to east as this
upper low pushes into Arizona. The ongoing forecast handles this
pretty well...just made a few minor updates to the near-term
forecast.
&&

Aviation...for McCarran...prevailing wind direction will be from
the south overnight. Drier air arrives Friday although southwest
winds will increase with gusts up to 25 kts possible.

For the rest of southern Nevada...northwest Arizona...and southeast
California...winds will favor diurnal trends overnight once any
influence from outflow boundaries diminishes. A dry southwest flow
will spread across the region Friday leading to mostly clear
conditions with southwest winds gusting around 25 knots in the
afternoon.
&&

Spotter information statement...spotter activation is not expected
at this time.
&&

Previous discussion...
330 PM PDT Thursday Aug 21 2014

Short term...through Saturday night

Convection started early across southern Nevada and northwest
Arizona but was waning this afternoon. As the closed upper low moves
from far Southern California into western Arizona this evening...middle
level flow will become northeast to north across southern Nevada and
eastern San Bernardino County. Storm development will continue to
wane this evening on the back side of the system but cannot
completely rule out additional thunderstorms from Clark County
southward through late this evening. The low is forecast to slowly
open up and lift toward The Four Corners region Friday as a long
wave trough digs into northern Nevada then moves into the northern
intermountain region Saturday. The resulting dry southwest flow will
scour out most of the moisture across our County Warning Area Friday though a few
thunderstorms may still occur over Mohave County. Showers ahead of
the front associated with the northern Great Basin trough may brush
northern Lincoln County Friday night through Saturday but the
majority of moisture and forcing will be to the north and east of
Lincoln County. Temperatures will remain below normal under the
influence of these low pressure systems.



Long term...Sunday through Thursday night.

An interesting pattern is shown for the first half of next week,
especially if you go full blast with the 00z operational run of the
European model (ecmwf). At this point, since that model is so out there in left
field, I have given it only limited weight with this morning's
forecast. That said, the European model (ecmwf) has a good track record of deviating
from the norm and being the first to pick up things, so the best
course of action is to see what trend are shown in the next few
model runs and adjust based on that.

For Sunday, broad troughing in the middle and upper levels is shown to
our north, with a second trough axis waiting in the wings to swoop
on down. Our area looks to be a in more a quasi-westerly flow.
Overall, the pattern supports a dry forecast with high temperatures near
normal.

Things get more complicated in the Monday through Wednesday time
frame. The 00z operational European model (ecmwf) drops the next trough into norcal
and forms a closed middle/upper level low that floats east eventually
across the northern half of Nevada on Tuesday and Wednesday. This
low would keep US much cooler and potentially even draw northward
moisture that could trigger showers and thunderstorms especially in
the eastern half of the area. This solution has some support from a
few of the 00z GFS ensembles. The second solution is what we saw on
previous runs of the European model (ecmwf) and the latest and previous runs of the
GFS, Gem and dgex which brings the trough through Monday into
Tuesday across Utah. There is some chance this trough could be deep
enough to clip northern Lincoln County with a few showers or at
least increased clouds and this was placed in there for Tuesday
afternoon/evening. Otherwise I left the forecast dry but did go
ahead and trim temperatures by a few degrees given the uncertainty. This
places them near to a hair below normal. Either way the pattern
looks more like that of late September to early October versus late
August.
&&

$$

Update/aviation...paddock
short term...Adair
long term...stachelski

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