Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Las Vegas Nevada
905 PM PDT Tuesday Oct 13 2015
Synopsis...one more day of near record high temperatures expected
Wednesday before we move into an unsettled weather pattern. An area
of low pressure will move through the region Thursday and Friday
followed by a second system Saturday and Sunday. The result will be
an increasing chance of showers and thunderstorms across most of the
area. High temperatures will also trend down closer to normal
Update...a few cirrus may have edged into Morongo Valley and
Landers from what can be picked up by infrared satellite but
otherwise there is not a cloud around this evening across the area.
I went ahead and adjusted the sky cover down significantly based on
the latest trends for the rest of tonight. We should still see an
increase in high clouds from the west later tonight into Wednesday
morning but the arrival looks delayed.
Otherwise, 2 record high maximums were tied and one was set today
and once again we will ask what season this is tomorrow across the
area as we again take a run at record high maximums. The main
challenge to assess with the 00z models tonight will be how quickly
any real push of moisture with the low offshore arrives as we still
see a big spread in timing and just how wet things get with this
first low. The main time frame on the 00z operational GFS is
Thursday into Friday but the 12z European model (ecmwf) was still relatively dry on
Aviation...for McCarran...winds will mainly be 6 kts or less and
favor typical diurnal trends through Wednesday evening. Clear
tonight with few-scattered clouds at or above 25k feet and few bases as low as 10k
feet Wednesday afternoon. An unsettled weather pattern will bring
the potential for rain showers/thunderstorms and rain to the area late Wednesday night through
Monday afternoon including ceilings and visibility reduced to MVFR or lower as
well as the potential for mountain obscurations.
For the rest of southern Nevada...northwest Arizona...and southeast
California...winds will mainly be 10 kts or less and favor typical
diurnal trends through Wednesday evening. Few-scattered clouds at or above 25k
feet tonight with a few bases as low as 8k-12k feet this afternoon and
evening. Isolated rain showers are possible over the southern Sierra mainly
between 20z today and 03z Wednesday. An unsettled weather pattern
will bring the potential for rain showers/thunderstorms and rain to the area Wednesday through
Monday night including ceilings and visibility reduced to MVFR or lower as
well as the potential for mountain obscurations.
issued at 300 PM PDT Tuesday Oct 13 2015
Short term...through Friday night.
Upper low off the Southern California coast has helped pushed
moisture into the region over the past 12 hours as we have started
to see a few more cumulus clouds across the southern and western
portions of the County Warning Area. Before we start to see the full effects of the
low as it approaches the area we will see another day of light winds
and near record high temperatures across most of the area on
Wednesday. As the low slowly moves closer to the coast Wednesday we
will start to see moisture increase over the far western areas of
the County Warning Area. This moisture combined with some weak instability should be
enough to generate a few showers over the Sierra and White Mountains
in Inyo County during the afternoon. Moisture is then expected to
spread west overnight with showers possible early Thursday morning
across western San Bernardino County along with the Owens Valley.
Scattered showers and isolated thunderstorms are expected over most
areas Thursday as the low drags in plenty of moisture. Precipitable water values
over the southern half of the County Warning Area are forecast to be over an inch
with some areas over an inch and a quarter. Although this system is
not quite as dynamic as the system last week there is still the
possibility of seeing isolated strong thunderstorms along with
localized areas of flash flooding. Along with the additional clouds
and scattered showers temperatures should be about 10 degrees lower
than on Wednesday and hopefully the start of temperatures remaining
below 90 until at least next April.
Once the low moves inland it will be slow to go anywhere and showers
and thunderstorms will remain over the area through Friday and most
areas should see between a quarter and half an inch of rain with
some isolated locations seeing close to an inch of rain.
Precipitation is forecast to start dissipating from the northwest
Friday night with scattered showers still remaining over the
southern and eastern half of the area.
Since this low originated from the lower latitudes there is very
little cold air associated with it. Snow levels are expected to
remain fairly high Thursday and Friday with only the highest peaks
above 10000 feet seeing any snow.
Long term...Saturday through Tuesday.
First low that comes into Southern California during the short term
period will have weakened leaving a broad trough across the region
Saturday. Air mass will be primed with abnormally high precipitable
water values for mid-October. Under this pattern instability
showers/slight chance of thunderstorms should be more numerous over the
higher terrain with a slight chance or low end chance for the valleys.
An upstream trough approaching the West Coast is forecast to split
with southern stream energy digging southeast into Southern
California Saturday night-Sunday...again establishing a trough
across the area. The last few runs of the GFS/Gem starting to trend
toward the deeper/slower European model (ecmwf) solution. With confidence increasing
decided to bump up probability of precipitation...especially for the higher terrain. The
trough starts to weaken/shear apart as it slowly shifts through
southern Nevada/western Arizona Monday and finally into central
Arizona Tuesday. Drier northwest flow starts spreading into northern
California/western Nevada late Tuesday as ridge builds inland.
Snow levels will be lower with the second trough. They will start
out around 10000 feet in the southern Sierra Saturday then lower to
8500-9000 feet briefly Sunday. For the Spring Mountains/Sheep Range
the snow level will briefly lower to 8500-9000 feet Sunday night.
After enduring this rather warm work week look for some relief
with below normal temperatures expected Saturday-Tuesday.
Climate...near record or record breaking high maximum temperatures
are expected across the area again on Wednesday. Values
are listed below.
Location 10/14 record
Las Vegas 96/1950
desert rock 92/1991
Montana Charleston 78/1989
Death Valley 108/1991
Record high minimum temperatures are also possible for Las Vegas
each day through Saturday.
* tie from previous years.
Spotter information statement...spotter activation will not be needed
today. Spotter activation may be required Wednesday through Monday.
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