Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 061312 AAA
AFDREV

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
612 AM PDT FRI MAY 6 2016

.UPDATE...
Have increased shower coverage through the day and added some
patchy fog this morning to many valley locations. Very moist
conditions continue and the morning 12Z sounding remains
weakly unstable. As a result,expect another wet day with almost
all locations in Wrn NV and NE CA seeing rain today. It will be
locally heavy and stronger storms will again have the potential to
produce accumulating small hail. More details below...

Showers and isolated thunderstorms continue to fire this morning
across Western NV into the eastern Sierra. The showers and storms
have not been as strong as yesterday, but amounts have been up to
1/4" over 3 hours or so in persistent showers. Currently, there is
a band stretching from Gabbs/Hawthorne northwest to Lassen County
moving west. This band will persist with another tenth to quarter
inch falling this morning.

For this afternoon, expect more showers and thunderstorms to fire.
There is some weak forcing from a E-W jet streak across northern
NV. Also, with the morning sounding showing it unstable, it won`t
take much of a trigger. Any clearing will be brief, but the
insolation would permit stronger storms. Again, be prepared for
another active day. Wallmann

&&

.SYNOPSIS...

Widespread showers with scattered thunderstorms will redevelop
Friday with some of the stronger storms producing small hail and
brief moderate to heavy rain. Unsettled weather will continue into
the weekend with locally heavy rain possible. Drier, warmer weather
returns next week.


&&

.PREVIOUS DISCUSSION... /Issued 224 AM PDT FRI MAY 6 2016/

SYNOPSIS...

Widespread showers with scattered thunderstorms will redevelop
Friday with some of the stronger storms producing small hail and
brief moderate to heavy rain. Unsettled weather will continue into
the weekend with locally heavy rain possible. Drier, warmer
weather returns next week.

SHORT TERM...

Closed upper low along the CA coast early this morning should
continue to move slowly east into southern CA today and across the
southern Great Basin into Utah late Saturday. The proximity of
this low will result in continued instability with widespread
showers and isolated to scattered thunderstorms through Saturday
evening. Coverage will decrease by Sunday afternoon as the upper
low moves east and a weak short wave ridge tries to develop over
the region. Overall few changes were made to pops and weather
types this forecast...but QPF was increased for the Saturday time
frame.

For Friday...the best forcing associated with an upper level jet
streak and vorticity lobe should be across the northern part of
the forecast area north of Interstate 80. The highest Theta-e air
may also reside in that area...aiding in developing more highly
efficient rain producing storms. But that region will also have
the fastest storm motions as mid level flow and bulk shear in the
lower to mid atmosphere will be strong enough to produce organized
cells with gusty winds and small hail. Still...brief moderate to
heavy rain is possible. The slower storm motions are likely to be
south of Interstate 80 where the threat for periods of heavy rain
will be greater. This could result in some minor flooding in
steeper terrain and poor drainage areas. See the Hydro section
below for more details. Gusty outflow winds associated with the
thunderstorms may also produce periods of blowing dust...especially
in the Basin and Range where less precipitation is expected today.
Visibilities could be briefly reduced to less than one-half mile
this afternoon and evening.

For Saturday and Saturday Night...the development of a deformation
axis over western NV and eastern CA is likely Saturday with storm
motions a little slower than previous days. Instability is not
quite as impressive for Saturday and upper level jet support is
less than previous days. But...high Theta-e air signals the
potential for increased precipitation efficiency. The combination
of slow-moving banded precipitation and the high moisture content
of the atmosphere (the forecast precipitable water from the GFS
sounding is 0.80 inches while the NAM sounding shows 0.74 inches;
both are above the moving daily maximum of 0.72 inches from May
7) could result in copious precipitation amounts for some parts of
the forecast area and minor flooding small streams...burn scars in
steep terrain and poor drainage areas. Unfortunately...this
far in advance it is still too early to pinpoint the exact
locations of these heavy bands.

There is also the possibility that any rain in the Sierra will
aid in melting some of the mid/high elevation snow pack as snow
levels climb to near 9000 feet. Total precipitation in the Sierra
from this morning through Sunday could reach greater than 1.50
inches while in the valleys around an inch is possible. That is in
addition to the rain that has already fallen. A Flash Flood Watch
could be needed for Saturday given the high precipitation
efficiency and slower moving cells...but we prefer to let the day
shift Friday take another look at this situation before we make
that decision. One thing to note for Saturday: thunderstorm
coverage could be less than Friday given more widespread
cloudiness early and cooler temperatures limiting surface heating
and low level instability.

Precipitation chances decrease Sunday...but do not end. The upper
low moves well east but a couple of vorticity lobes rotating
around the back of the low along with increased heating due to
less cloud cover should work together and lift residual moisture
enough for isolated to scattered showers and isolated
thunderstorms by Sunday afternoon. Temperatures will likely
rebound from the 50s and 60s Saturday into the the 60s and 70s
Sunday. 20

LONG TERM...Monday through Thursday...
Few changes to the long term, but did pull the mention of showers
Mon-Wed. A ridge will build off the coast with a NW flow aloft
expected through the period. The GFS and EC do show a weak
backdoor front for Tuesday which will slow the warmup, otherwise
do not expect much of an effect.

While there will be plenty of residual moisture, temps aloft are
expected to warm quite a bit Monday. Prog soundings show a strong
cap around 7-600 mb which will keep cumulus development shallow.
This despite the models trying to show rain along the crest. With
the backdoor front Tuesday limiting the low-level warmup, think
it will be a couple more days before we see showers again so left
them in for Thursday. Wallmann

AVIATION...
Showers and isolated thunderstorms will continue this morning.
Some of these will produce moderate to heavy rainfall. Expect MVFR
CIGS and mountain obscuration in any showers and lcl IFR VIS in
heavier showers and storms. Best chances through 18Z will remain
south of I-80 including all fcst terminals.

Showers and sct storms will develop again this afternoon. Some of
the storms could be strong with GS, especially with the low
freezing levels. MVFR CIGS in SHRA with IFR VIS again in
+SHRA/TSRAGS. While all terminals will see at least a couple
showers during the day, the chance of a heavier shower/storm will
be about 30% for each individual terminal. These worst case
conditions would last for about an hour.

Expect the showers and storms to weaken after 03Z tonight,
although some showers will remain overnight. Saturday could see a
significant band of moderate to heavy rain with MVFR/IFR CIGS/VIS
in this band. Location is yet to be determined, but the 00Z GFS/EC
target I-80 and Hwy 50 which would impact KRNO/KCXP/KTVL/KTRK.
Wallmann

HYDROLOGY...

Thunderstorms through Thursday evening produced localized
precipitation amounts of half an inch or greater in some areas
with snow levels approaching 8000 feet at times. This caused some
rises in smaller streams in the Sierra...but no risk of flooding
as yet. With precipitation waning now...stream flow should settle
well within their banks through Friday morning.

Increased precipitation efficiency along with snow levels at or
above 8500 feet for much of the northern Sierra and Nevada
mountain ranges later today will allow for increased snow melt
and run off with rises in some small streams possible this
evening. Snow levels in Mono County will not rise as fast so small
streams there should not rise as much.

More widespread moderate to heavy rain on Saturday will only
exacerbate the situation as this rain falls on already moist soil
and likely causes more snow to melt in the mid/high elevation
snowpack as snow levels rise above 9000 feet in the northern
Sierra and above 8500 feet in Mono County. Small streams around
the Tahoe Basin...across northeast California...along the eastern
flanks of the Carson Range and south into Mono County could
overflow their banks Saturday afternoon and evening causing minor
flooding. Poor drainage areas and areas of steep terrain in recent
burn scars could also experience flooding by Saturday afternoon
due to moderate to heavy rain. No main stem river flooding is
expected at this time...but area rivers will start running quite
high by late Saturday.

As of now we will not issue a Flash Flood Watch. If the forecast
situation evolves into a more widespread thunderstorm event for
Saturday...we may issue a Flash Flood Watch. For now be aware that
minor nuisance-type flooding is possible for Saturday. Anyone
camping or hiking near small streams...or driving near or
otherwise making use of areas that are prone to flooding due to
poor drainage or steep terrain should be alert to the possibility
of flooding for Saturday. 20

&&

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

$$

For more information from the National Weather Service visit...
http://weather.gov/reno



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