Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 271539
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
839 AM PDT TUE SEP 27 2016

.SYNOPSIS...An area of low pressure will slowly move up the Gulf of
California and into southeast California by tomorrow afternoon
before lifting into the Great Basin on Thursday. Scattered showers
and thunderstorms will be possible across the area through Thursday
before becoming more localized later in the week. Temperatures will
generally be within few degrees of normal into Saturday.
&&

.UPDATE...Showers trying to move through southern Mohave county and
Colorado River valley having a hard time this morning. An area of
light rain closer to Flagstaff will move towards southern Mohave
county in the next few hours with better chances of reaching the
ground. Cloudy skies look to limit instability with just a few
showers around and only slight chances of a thunderstorm or two by
this afternoon. Overall forecast in good shape, so no updates
planned this morning.
&&

.PREV DISCUSSION...
Issued at 250 AM PDT TUE SEP 27 2016


.SHORT TERM...through Thursday Night.

One area of low pressure is currently located at the northern
portion of the Gulf of California. With that location, easterly flow
is dominant across Mohave and San Bernardino Counties and mid to
high level cloud cover has been enhancing overnight along with a few
light radar returns of which are not yet likely producing any precip
at the surface. During the day expect continued moistening with the
best opportunity of showers and thunderstorms over southeast San
Bernardino, southern Clark and Mohave Counties. The NCAR ensembles
and local hi res models all show a similar depiction with the
operational HRRR being much drier. As the low lifts into southeast
California on Wednesday, a more substantial push of moisture will
advance northward through Mohave County and into southern Nevada
during the day. Most models are indicating modest instability with a
few hundred J/kg and lifted indices of 0 to minus 2. The NAM was
indicating the most instability with values nearly doubled.  Expect
Wednesday to be the wettest day across the region with isolated to
scattered thunderstorms across the forecast area and more numerous
showers and storms in Mohave County and the higher terrain of
southern Nevada where brief heavier downpours are possible. The
upper low lifts northward and into central Nevada during the day on
Thursday. Meanwhile, moisture associated with Tropical Storm Roslyn
will work its way into Arizona during the day on Thursday. This will
keep the chance of showers and thunderstorms over Mohave County and
the potential for a more significant rain producer. However, models
are currently keeping the bulk of the moisture further to the east
and in central and eastern Arizona.

.LONG TERM...Friday through Monday Night.

The weather pattern looks to remain active in the extended period
with the possibility of additional troughing influencing the region.
On Friday...southwesterly flow aloft along with some lingering
moisture and instability may promote some isolated to scattered
mountain shower activity across Clark...Lincoln..and Mohave counties
but increasing subsidence and drying aloft should keep things
closely tied to the terrain through the day. Model agreement
decreases over the weekend with ECMWF suggesting a fairly
significant trough digging into the western US while the GFS is
considerably weaker and keeps most of the energy further to our
north. Both solutions would favor breezy conditions and a cooling
trend of some magnitude late in the weekend into early next week.
However...the ECMWF would support a stronger wind episode over the
weekend along with greater cooling associated with a more marked
cold frontal passage. For now I`ve maintained a dry forecast with
modest cooling Sunday into Monday with temperatures falling a few
degrees below normal. I`ve also bumped up wind speeds across the
region as nod towards the ECMWF. If the EC solution maintains some
consistency temperatures may be tweaked downward further as the
event approaches.
&&

.FIRE WEATHER... A low pressure system moving in from the south
today will increase moisture for most of the area by Wednesday.
Shower and thunderstorm chances will initially enter northwest
Arizona and southeast California today...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. There is the potential for a
stronger wind event over the weekend and will be monitoring for
potential fire weather concerns.
&&

.AVIATION...For McCarran...Generally light and variable winds
for the rest of the night. Today will bring light northeast winds,
increasing clouds, with dry weather for the Las Vegas Valley but a
chance of a showers and thunderstorms along the Peach Springs
corridor. Shower and thunderstorm chances increase on Wednesday.

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 and southeast California today.
Shower and thunderstorm chances increase across the area on
Wednesday.
&&

&&

$$

Update.....................Steele
Short Term/Aviation/Fire...Czyzyk
Long Term..................Outler

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