FXUS65 KLKN 212101
Area Forecast Discussion
National Weather Service Elko NV
201 PM PDT Wed Mar 21 2018
.SYNOPSIS...Abundant Pacific moisture will move across the region
through Thursday night bringing valley rain and mountain snow.
.SHORT TERM...Tonight through Saturday. Mostly cloudy across the
region as a very moist air mass is pushing in across California
and into western Nevada. Valley rains and high elevation snow will
increase tonight into Thursday with moderate QPF amounts expected.
Ahead of this systems frontal passage, southerly winds will become
breezy on Thursday. Strongest winds will be over east-central NV.
A wind advisory has been issued for White Pine County for
Thursday. Strongest winds will be over higher terrain. Snow levels
will remain above 8000 feet through Thursday afternoon, then begin
to lower toward valley floors Thursday evening from northwest to
southeast across the CWA into Thursday night. Most areas will be
dry late Friday morning into the afternoon, however a little more
lighter precipitation is expected into Friday evening, mainly
across northeastern NV. Cooler on Saturday with scattered snow
showers across the region.
.LONG TERM...Saturday night through Wednesday. The weekend and
next week should see a closed low translate across northern NV
this weekend before moving southward to Arizona early next week.
The system then begins to cut off from the flow with the low
remaining over the desert southwest through the week This system
looks to remain fairly moist through the weekend which should
continue showers across Nevada through Sunday. The main region of
showers should be around the upper level of the low center in
northern NV. The atmospheric profile will be cold enough that the
showers should be snow. This snow will not last as diurnal heating
will quickly melt any accumulations in the lower elevations. As
the system moves southward it will draw dry air into the region
drawing down the shower activity. South Central NV may still see
some showers during the week as the flow around the low center may
still move a little moisture to that area. NV can see gusty
afternoon winds each day with the passage of this system.
Temperatures should warm through the week as a ridge starts to
build across NV with the low moving to AZ.
.AVIATION...A storm system is passing through the region bringing
cloud decks and rain showers to all terminals. Cloud decks should
range between MVFR and VFR with the chance for IFR during the
overnight hours. The clouds will cause mountain obscuration
conditions through out NV. Rain showers will lower visibility with
MVFR visibilities possible in heavier showers.
.HYDROLOGY...Rainfall will intensify from tonight through early
Friday. Storm total rain of a quarter inch to a half inch are
likely across the region, with locally higher amounts of an inch
or so possible by Friday morning. Product RNOESFLKN has more
information on this event.
Wind Advisory from 9 AM to 8 PM PDT Thursday for White Pine
FXUS65 KVEF 220410 AAA
Area Forecast Discussion
National Weather Service Las Vegas NV
915 PM PDT Wed Mar 21 2018
.SYNOPSIS...Rain and high elevation snow will increase northwest
of Interstate 15 tonight, with periods of heavy rainfall possible
across the Sierra and Owens Valley. Rain will spread southeast
across the entire region Thursday, with improving conditions
expected Friday into early next week.
.UPDATE...Deep plume of subtropical moisture currently slamming into
southern California with impressive rainfall totals so far. Rainfall
amounts over the western slopes of the Sierra mainly range from
0.50" to 1.00" with a few locations over that. Over the eastern
slopes and the Owens Valley rainfall amounts have generally been
lighter with a quarter to half an inch. Overnight, the deeper
moisture plume will remain generally over northern San Bernardino
and Inyo Counties before starting to shift southward Thursday
morning. That will turn more attention to the lower deserts with
precipitation spreading across much of the Mojave Desert and
southern Great Basin. The best window for rain in the Las Vegas
Valley looks to be late Thursday morning through much of the
afternoon. Rainfall amounts still don't look heavy, but amounts
ranging from a tenth to a quarter of an inch look good with higher
amounts in the mountains. Models are also showing increasing winds
across the area, but with significant precipitation drag the wind
speeds should be kept lower. Areas such as the Morongo Valley could
see some gusty winds off the Little San Bernardino Mountains as they
have a higher potential of seeing downslope winds during the day. At
this time will not make any changes as the forecast timing looks
242 PM PDT Wed Mar 21 2018
.SHORT TERM...through Thursday night. First couple of waves of
moisture rolling into the western Mojave Desert have been producing
light showers today as anticipated. About an inch of rain has fallen
in the high Sierra, with much lesser amounts thus far in the Owens
Valley. The Flood Watch still looks reasonable in this area, and the
Winter Weather Advisory seems okay as well since precip is likely to
be ongoing when snow levels fall below the resort level during the
day Thursday. Satellite loop and area radars showed thicker
clouds/possible light showers moving from eastern SBD Co. into
southern Clark County as of 2 PM, with more significant radar
returns limited to western SBD Co. and areas farther west. Models
suggest that this area will fill in overnight and lift north as the
mid level flow turns a bit more southerly in advance of the
approaching circulation near 29N 137W. Thus, trimmed back PoPs from
Las Vegas southward overnight, as the main focus should be farther
north. The main moisture plume should reach the I-15 corridor early
Thursday afternoon, and swing southeast rather quickly as the trough
axis approaches and turns the flow more westerly with time. High
resolution models still suggest a very impressive gradient in precip
totals from the mountain peaks to the valley floors. Raised total
forecast amounts to over two inches at the peak of the Spring
Mountains, most of which will be rain in the populated areas, with
snow confined to the highest peaks. Also issued a Wind Advisory for
Lincoln County Thursday, where strong pre-trough southerly winds are
most likely. Models have been trending toward moving the moisture
plume out of the area more quickly, so reduced PoPs in the southwest
third to half of the area Thursday night.
.LONG TERM...Friday through Wednesday.
By Friday, much of what is left of the moisture plume will be north
and east of the area. Models still indicate a weak shortwave will
move across the area early Friday. The GFS/ECMWF are in slightly
better agreement on the strength of this feature. Even with somewhat
limited moisture kept slight chances of showers/snow showers mainly
for eastern Lincoln County and the Arizona Strip through Friday
afternoon. A fair amount of instability will be across southern
Nevada and northwest Arizona Friday afternoon, as such decided to
put slight chance of isolated thunderstorms/thunder snow Friday
By Friday evening, dry southwest flow ahead of a broad upper low
will move over the region pushing any residual moisture eastward and
bring breezy to gusty southwest winds. Both the GFS/ECMWF have a
shortwave pushing into northern California and across the Great
Basin Saturday-Sunday, but the timing, location, and intensity of
this feature still remains uncertain. Generally, with limited
moisture the only potential impacts looks like increased SW winds
SAT and some slight chances of precip Sunday mainly north of Clark
County. Beyond Sunday afternoon confidence is low as models become
vastly different. Temperatures will be a few degrees below normal to
start off the weekend before dropping a bit more behind a cold front
Sunday. Otherwise, expect fair weather with partly cloudy to mostly
clear skies through much of the weekend and into early next week.
.AVIATION...For McCarran...South to southwest winds gusting 20 to 25
knots will continue through sunset, then lull to around 10 knots
overnight before increasing again Thursday morning. Lower ceilings
around 060 will arrive late Thursday morning, with an outside chance
of a shower pulling the ceilings down to 030 and restricting
visibility. Heavier showers and MVFR conditions will become more
likely Thursday afternoon before rain chances end Thursday night.
For the rest of southern Nevada, northwest Arizona and southeast
California...Rain will increase overnight in areas mainly northwest
of I-15, with associated low ceilings and terrain obscuration. Lower
clouds and rain chances will spread to nearly the entire area
Thursday afternoon, and then rain chances will end and clouds will
decrease from west to east Thursday night into Friday morning.
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures. Rainfall and flooding reports are appreciated during
periods of weather later this week.
For more forecast information...see us on our webpage:
http://weather.gov/lasvegas or follow us on Facebook and Twitter
FXUS65 KREV 220500 AAA
Area Forecast Discussion...UPDATED
National Weather Service Reno NV
1000 PM PDT Wed Mar 21 2018
Regional radar mosaic continues to show precipitation increasing
across central CA in association with main moisture push. QPF
amounts have not been too impressive so far east of the Sierra
Crest but this will be changing as rain/high elevation snow
increases in both areal coverage and intensity between 06Z-09Z and
continues through Thursday morning. The last few radar images show
precipitation beginning to spill over into the Tahoe Basin and
eastern Sierra of Mono County.
Profilers and radar associated bright bands indicate snow levels
in the 9000-9500 ft MSL underneath this band of precipitation west
of the Sierra while surface temperatures indicate snow levels
along the eastern Sierra ranging from 7500-8000 ft MSL. So given
what is going on farther west, these snow levels may rise some as
the main moisture and precipitation plume arrives overnight but
probably not more than about 500 feet. So current projected snow
levels and QPF seem reasonable. Streams responded well to our
earlier round of precipitation and we expect them to respond even
more overnight for areas below 7000-7500 feet. So the threat for
flooding along smaller creeks and streams and on burn scars will
increase significantly over the next few hours. Hohmann
.PREVIOUS DISCUSSION... /Issued 113 PM PDT Wed Mar 21 2018/
An atmospheric river type storm will produce significant
precipitation tonight into Thursday. This will bring periods of
heavy valley rain and heavy high Sierra snow along with gusty
winds. The weekend will be colder with snow showers possible down
to all valley floors. Drier conditions are looking more likely for
Early Wednesday afternoon saw a bit of minor break between the
precipitation associated with warm air advection Tuesday night
into early Wednesday and the incoming main portion of the storm.
That portion will impact most of our area this evening through
Thursday night...but a few areas are already seeing the initial
precipitation with this part of the storm. The warm air advection
part of the storm performed better than expected in terms of
rainfall production and the break today was not as defined as we
thought it would be. Thus we have already seen more precipitation
than we expected this early.
That brings us to tonight and Thursday...and what to expect going
forward. Model solutions still pull the main upper level jet north
with increased upper level divergence from Mono County north into
northeast California. That leads to increased QPF again with
slightly higher snow levels. These adjustments were made for
tonight and early Thursday. There is still the question of how
much precipitation will spill over with the jet oriented more
south to north tonight. It does start to push east Thursday and
that puts western Nevada in a more favorable area for increased
QPF as instability increases through the day.
We did consider adding slight chance for thunderstorms to Thursday
as instability increases. But there is a lack of cold air aloft
until late in the day. The best potential for thunder looks to be
in the Sierra and northeast California. We will hold off including
it for now...but a few isolated rumbles of thunder are not out of
So the main points for the next 36 hours are:
- The total amount of liquid precipitation has been raised with
the highest totals...approaching another 4 1/2 to 5
inches...along the Sierra Crest. Another 2 1/2 to near 3 inches
is possible near Lake Tahoe with around 3 inches possible west
of Highway 395 in Mono County below 7500 feet. Lassen and Plumas
counties could see from another half inch in the far eastern
parts of the counties to as much as 2 1/2 inches in the western
areas. Western Nevada could pick up from around half an inch to
as much 1.30 inches in the western foothills.
- Snow will be confined to areas above 7000 feet due to high snow
levels. Snow levels start well above 7500 feet in general and
remain there until Thursday morning when cold air starts to push
in from the north. By the time the snow levels fall below 7000
feet late Thursday most of the precipitation will have ended.
Totals above 7000 feet in the Tahoe Basin could reach 2 to 4
feet...near 5 feet at the crest. In Mono County...totals above
7500 feet should range from 2 to 4 feet with totals in excess
of 5 feet near the crest.
- Winds will not be as big a factor. Gusts up to 40 mph are still
possible into early this evening...but once the rain spills
over in earnest...the winds should decrease in Western Nevada.
Winter Storm Warnings remain in effect for the higher elevations
of the Tahoe area and Mono County with a Lake Wind Advisory into
Thursday for Pyramid Lake. Flood Watches also remain in effect.
The Hydrology section will cover that a bit more.
LONG TERM...Friday onward...
No big changes with the long term forecast.
Model simulations still show a break in precipitation until Friday
afternoon and evening ahead of a cold front and the next storm.
Winds will increase ahead of the cold front with choppy conditions
on area lakes and possible travel concerns for high profile vehicles
along with turbulence for aviation. Precipitation chances will
remain north of Interstate 80 through Friday afternoon, but will
spread southward as the cold front advances toward the I80 corridor
by Saturday morning. Snow levels will be down to all valley floors
with light snow accumulations possible by sunrise on Saturday,
especially north and along the I80 corridor.
Another shortwave drops through the Sierra and western Nevada for
Saturday evening into Sunday morning. Some timing differences still
exist with this final shortwave, but generally anyone traveling over
the weekend should plan on snow showers and travel slow downs,
especially across the Sierra passes. Considering we are getting into
the latter part of March, most road impacts from these lighter snows
will be limited to the overnight and early morning hours outside of
higher elevation mountain passes.
A ridge begins to build off the west coast next week leading to a
drying trend. Cool, northerly flow will dominate the first portion
of the week until temperatures gradually moderate to near or
slightly above normal by the end of the week. -Edan
IFR conditions should become widespread this evening and overnight
in northeast California and the Sierra as a significant storm
spreads high elevation snow and lower elevation rain across the
forecast area. By late tonight and early Thursday MVFR conditions
are likely in western Nevada with brief IFR possible in the
Gusty winds of up to 40 mph are possible early this evening...but
as the heavier rain spills into western Nevada the winds should
subside. Still...there will continued to be strong winds aloft
with turbulence along and east of the mountains.
Snow levels in the storm remain quite high until Thursday evening.
By late Thursday night and early Friday morning...a few inches of
slushy accumulation are possible at the Sierra terminals.
After a brief break Friday...another fast moving system could
bring snow showers down to the valleys floors by Saturday
morning. Stronger winds are possible Friday ahead of this system
with gusts possibly as high as 45 mph in the valleys north of
Highway 50. A more substantial storm is shaping up for Sunday and
Sunday night with snow possible down to the lowest valley floors.
Rain Tuesday night into Wednesday morning was more than expected.
This should aid in ripening the snow pack in the Sierra valleys
and increasing soil moisture in the lower valleys and western
Nevada and northeast California where snow is not present.
Expected heavy rain later tonight and into Thursday...with
relatively high snow levels...should increase the runoff
potential. We have already seen some rapid responses on small
streams in basins that picked up quite a bit of rain last night.
Responses should be magnified tonight and Thursday...especially in
the basins that already received heavy rain. This includes the
Sierra below 7500 feet and northeast California along with
streams that drain the east side of the Carson Range in western
Nevada. The other challenge in this situation is heavy rain
ponding or redirecting runoff in areas where there is sufficient
snow to block storm drains. In these areas...the melting portions
of the snowpack will also increase runoff. Recently burned areas
will be another place to watch if the rain intensity becomes very
heavy for an extended period of time. The only mainstem rivers of
concern right now are the Susan River and Middle Fork Feather
River. Both of these should see mostly rain in their headwaters.
We will keep Flood Watches in effect for northeast California and
parts of the Sierra below the snow line. We will not...at this
time...include western Nevada...but it is not out of the question
to see rises on small streams that cause minor flooding in areas
adjacent to the small streams. We could see some minor ponding in
poor drainages areas around the urban centers and low water
crossings in western Nevada as well.
NV...Flood Watch through late Thursday night below 7000 feet in
Winter Storm Warning until 5 AM PDT Friday above 7000 feet in
Lake Wind Advisory until 8 PM PDT Thursday for Pyramid Lake in
CA...Flood Watch through late Thursday night CAZ071.
Flood Watch through late Thursday night below 7500 feet in
Winter Storm Warning until 5 AM PDT Friday above 7500 feet in
Flood Watch through late Thursday night below 7000 feet in
Winter Storm Warning until 5 AM PDT Friday above 7000 feet in
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