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Area forecast discussion 
National Weather Service Las Vegas Nevada
225 PM PDT sun Apr 19 2015 area of weak low pressure off the California coast
will sink south tonight through Tuesday. This will help trigger
showers and thunderstorms mainly over the higher terrain during the
afternoon and evening hours each day. The greatest chance will be
over the Sierra Nevada. This low moves inland Tuesday across
Southern California. Two additional systems are expected to pass
near or across the area between Tuesday night and Saturday bringing
additional chances of showers along with decreasing temperatures.

Short term...tonight through Tuesday night.

The current upper-air pattern depicts a deep trough across the
central Continental U.S. With a weak area of low pressure off the northern
California coast. With our area stuck between these two features our
winds have been rather light and temperatures have reached the 80s
aross lower elevations once again. We are also seeing a little more
cumulus development over the southern Sierra and mountains of
southern Nevada. Cannot rule out showers or even a thunderstorm for
these locations, with the Sierra Nevada having the best chance.

The area of weak low pressure off northern California will slide
south along the coast tomorrow and eventually push inland over
Southern California late Monday night and Tuesday, as a stronger
trough approaches the West Coast. This weak low will continue to
provide enough instability for the best chance of showers and a few
thunderstorms over the southern Sierra and White Mountains Monday,
mainly during the afternoon and early evening hours. Shower and
isolated thunderstorm chances will also remain possible across the
higher elevations of southern Nevada and perhaps northern Mohave
County. Chances then spread to higher elevations of southeast
California for Tuesday, as the low moves inland. Temperatures will
remain above normal yet trend cooler from Monday to Tuesday. With
the upper low /albeit weak/ sitting over Southern California and
southern Nevada Tuesday night, shower chances may continue overnight
across mainly higher elevations of Inyo County and perhaps western
San Bernardino County. This weak low will eventually merge with the
approaching stronger trough for Wednesday.

Long term...Wednesday morning through Sunday.

The models are in pretty good agreement with the overall pattern
during this time frame. A low pressure system will be centered off
the central California coast Wednesday with a somewhat moist
diffluent flow over the forecast area. I kept slight chance to
chance probability of precipitation over most of the forecast area with temperatures cooling
roughly five degrees compared to Tuesday. The low is still expected
to move inland Thursday with moisture and dynamic forcing
increasing. For now I kept broad brushed chance probability of precipitation across the
entire forecast area with a few more degrees of cooling. It
continues to be difficult to pinpoint a location or locations that
will see the most significant precipitation but models hint at
possibly the Sierra and Spring Mountains. The models keep things
fairly progressive with the low/trough moving east to the southern
rockies by Friday. However...the models do hang on to some moisture
and another weaker trough moving in from the west by Friday will
keep a chance of showers in the forecast Thursday night and Friday
especially north of Las Vegas. The area will gradually dry out over
the weekend as zonal flow Saturday is followed by ridging Sunday.
Showers are not expected in any portion of the County Warning Area by Sunday and
temperatures will warm back up above normal.

Aviation...for McCarran...light and variable winds will transition
to southwest drainage this evening. Afternoon cumulus clouds will
diminish. Winds should once again be variable/light Monday morning
and favor an easterly wind late morning and afternoon. Guidance is
indicating a stronger southerly wind push for Monday evening.
Cumulus to around 12kft can be expected again Monday afternoon and
early evening, with a chance of rain showers over the Spring Mountains and
Sheep Range.

For the rest of southern Nevada...northwest Arizona...and southeast
California...expect diurnal wind trends at all taf sites through the
taf period...with slightly enhanced west winds at kdag. Skies will
be clear at all taf sites with the exception of kbih where scattered-broken
250 can be expected with a few cloud bases as low as 8k-12k feet in
the late afternoon and early evening hours. Isolated rain showers and thunderstorms and rain
are possible over the southern Sierra Nevada, White Mountains and
the Spring Mountains and Sheep Range.

Spotter information statement...spotters should report according to
Standard operating procedures.


Short term/aviation...paddock
long term...Harrison

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