Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 302056
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
156 PM PDT Sun Apr 30 2017

.SYNOPSIS...

High pressure will weaken slightly allowing breezy
winds this evening. The ridge rebuilds by the middle of the week
with light winds and above normal temperatures. By late week
cooler and wetter weather may return.

&&

.SHORT TERM...

Above normal temperatures are expected for the next few days as
high pressure remains just off the CA coast. A weak shortwave
drops through the Pac NW and into Eastern NV and Utah tonight,
which will help to increase the winds across the Northern Nevada
Basin and Range late today. You can already see some of the
cumulus clouds forming north of Pyramid Lake and Lovelock in
association with a weak frontal boundary coming down from the
north. Very little to no cold air advection is expected with this
wave, as the colder air gets shifted east of our area.

We expect to see gusty winds up to 35 mph late this afternoon and
into the evening, especially for areas east of US-395. This will
make for some choppy conditions for Pyramid Lake due to the gusty
northwest flow, but duration will not be long enough for a lake
wind advisory as Pyramid closes at sunset. Lighter winds are
expected Monday through Wednesday as the ridge builds overhead. By
Tuesday night, we will see an increase in easterly flow over the
Sierra Crest as a surface high builds over the northern Great
Basin and Rockies.

Low temperatures will be chilly overnight and in the early
mornings due to mostly clear skies and radiation inversions. As
the ridge builds overhead, the temperatures in the upper
elevations will increase to above normal, with some areas above
7500 feet remaining above freezing even overnight. Daytime
temperatures will also be on the increase over the next few days
with highs into the mid/upper 70s and near 80 by Wednesday in
Reno. For the Sierra, we expect to see 60s and near 70 degrees by
Wednesday. Warm temperatures will lead to increases in snowmelt
runoff into rivers and streams. See our Hydrology section below
for more details. Hoon

.LONG TERM...Thursday through the weekend...

Well above average temperatures expected through Thursday as the
ridge axis crosses over California and Nevada. Lower valleys in
western Nevada may reach the low to mid 80s, which would be the
warmest temperatures that we have had so far this year. For the
Sierra, the above average temperatures will impact overnight lows
with many locations staying above freezing. These warmer
temperatures for the second half of the week will contribute to
accelerated snowmelt and hydrology impacts. Please see the
Hydrology section for more details.

By Thursday the ridge breaks down as a strong trough moves into the
West coast. Went ahead and added in slight chances for thunderstorms
for Thursday afternoon and evening along the entire Sierra crest.
Convective heating along with sufficient moisture should be enough
to kick off a few storms. Model soundings for Thursday afternoon and
evening are particularly unstable with lifted indices around -2 to -
4 J/kg across the Sierra and far western Nevada. Forecaster
confidence is low to medium with exact thunderstorm location for
this day. The ridge breakdown combined with the above normal
temperatures and moisture are enough evidence to at least put slight
chances for thunderstorms in the forecast.

After that forecaster confidence remains medium to high for the
transition from warm, dry conditions to wetter, cooler conditions
for the end of the week as the ridge completely breaks down. Models
have been in good agreement with the sharp trough being cut off into
a bowling ball low for somewhere from the CA coast to far eastern
NV, but the exact trajectory of the low is uncertain. Like the
previous forecast discussion mentioned, cutoff lows are extremely
dynamic and the weather that we get will be strictly dictated by
the position of the low.

Where does that leave us? Well like I mentioned before, there is
a high likelihood that the end of next week will not be dry and
warm like this current weekend. Make next weekend`s arrangements
with the idea of cooler, wetter conditions as well as the
potential for some thunderstorms and breezy winds. Cutoff lows
also have the potential produce localized heavy rains, but because
of the low predictability of cutoff lows beyond 3-5 days it will
be hard to pin down those details. Something to keep in mind for
those dealing with general hydrology concerns, such as snowmelt
and ongoing flood mitigation. One of the latest model simulations
is showing the potential for snow even down in Reno (#NoThanks).
-Edan

&&

.AVIATION...

This afternoon and evening gusty northwest winds will develop for
areas east of the Sierra. Winds aloft will also increase which could
result in some turbulence over the ridges.

Generally light north winds on Monday with east to northeast flow
for Tuesday. VFR conditions also return through the middle of the
week. By late Tuesday night there could be stronger winds over the
Sierra ridge tops as easterly flow becomes enhanced which would lead
to another round of potential turbulence over and west of the Sierra.

By Thursday and through next weekend the pattern shifts to wetter
and cooler conditions with the potential for showers returning to
the area.

&&

.HYDROLOGY...

Above normal temperatures into the middle part of the coming week
will lead to increased snowmelt and higher flows on many area
streams and rivers. Flows are already significantly above normal
for this time of year and this increase in temperature will only
exacerbate those conditions. Overnight lows are likely to remain
just above freezing in the higher elevations through much of the
week. This could mean some minor melting in the higher elevations
even at night. There is also a good chance for showers to return
late next week and next weekend. Any additional rainfall could
create more runoff and even higher flows.

Record to near record snow pack in the Sierra will mean a
prolonged period of high flows through the spring and possibly
into early this summer. Peak flow forecasts vary across the region
with the Truckee and Carson peak forecasts falling in the middle
of May while the Walker and Lower Humboldt are forecast to peak
in June. These are peaks for the main river systems...not the
feeder streams. And even after these peaks occur...flows will
remain elevated for an extended period.

A Flood Warning remains in effect above Rye Patch Reservoir on
the Humboldt River. Flood Advisories are in place on portions of
the Truckee River due to high flows from reservoir releases and
snowmelt and in the lower part of the Carson River due to releases
from Lahontan Reservoir.

Remember that these elevated river flows are moving fast and that
water temperatures are cold. The cold waters make hypothermia a
distinct possibility for anyone in the water and the swiftness of
the water can carry someone away rather quickly. In any areas
where flows are high...even areas without warnings or advisories...
bank erosion is possible.


&&

.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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