Reno Area Technical Forecast Discussion

Technical Forecast Discussion

FXUS65 KREV 291010

Area Forecast Discussion
National Weather Service Reno NV
310 AM PDT Sat Apr 29 2017


Warmer and drier conditions will continue through the weekend as
high pressure starts to build across the area. This high pressure
will weaken slightly early next week and allow slightly stronger
winds late Sunday into early Monday and a brief cool down Tuesday.
The ridge tries to rebuild by the middle of next week with above
normal temperatures before sliding east. By late next week into
next weekend there could be showers over portions of the region.



Overall...the short term forecast is one of relative calm weather
with only temperature fluctuations as the primary concern after
today. For today...the main story continues to be gusty east to
northeast winds at the ridge top level. Winds are decreasing a bit
across the ridges in the Sierra this morning...but remain stronger
than guidance given the thermal gradient in place with cooler air
to the east and slightly warmer air to the west of the Sierra. The
upper level jet support is moving east as a ridge builds. This...
along with some move toward equalizing the thermal gradient...will
lead to a lessening of the easterly winds over the ridges through
the day.

Temperatures warm today and Sunday as the ridge builds. Highs are
likely to reach the lower to mid 60s today in the lower valleys
and the upper 50s to lower 60s in the Sierra valleys. By Sunday
highs reach the 70s in the lower valleys and mid 60s in the Sierra
valleys. Given the thermal profiles from forecast soundings...the
overnight lows at the ridge level were warmed a bit each day.

There are some model differences by Sunday night/Monday. The NAM
holds the ridge in place with warmer temperatures while the GFS
shows the ridge retrograding slightly as another short wave trough
carves its way southeast through the Great Basin and Intermountain
West. This would support slightly cooler highs for Monday...cooler
further Tuesday...and an increase in northwest flow over the
region. The forecast was leaning this way already and that was
continued. West-northwest surface winds were increased slightly
for Sunday evening ahead of this wave...especially from the
Surprise Valley southeast across the Western Nevada Basin and
Range. Monday`s winds may need to increase a bit more as well if
this solution intensifies.

.LONG TERM...Tuesday through next week...

By Tuesday the ridge will begin to amplify and shift over the
western U.S. bringing light winds and rising temperatures through
midweek. The ridge axis is most amplified over the southwest U.S.
Wednesday, with high temperatures likely peaking Wednesday or
Thursday, depending on how quickly the ridge begins to break
down. Temperatures could peak about 10 degrees above average with
highs in western Nevada reaching near 80 degrees, with low 70`s
possible in the Sierra.

The progressive flow and lack of strong height anomalies point
towards a ridge that won`t remain in place long. There is
significant disagreement among the global models in how the ridge
breaks down over the west, however, there is good agreement that
it does break down going into next weekend.

By the end of next week forecast confidence on a particular
outcome becomes much lower due to the lack of a strong height
anomaly pattern and the extent to which global models struggle
during the spring transition period. What can be said though is
that a clean ridge of high pressure most likely won`t loiter over
the region for an extended period of time, and that troughing over
the western U.S. again looks likely. This will bring increasing
chances for precipitation and probably near normal temperatures
back to the region. -Zach



Strong east winds over the ridges...especially around the Tahoe
Basin...will mean a good chance for turbulence aloft early this
morning. By late afternoon the flow aloft lessens as a ridge
begins to build. Light winds at the surface and a lack of moisture
should make for rather benign flying conditions at the terminals for the increased winds off the surface this morning.

VFR and light winds continue into early Sunday. Surface winds are
likely to increase a bit by late Sunday...especially east of the
Sierra. Winds turn back to the east aloft by late Monday into
Tuesday with another round of turbulence over the mountain ridges



A warming trend through the weekend will lead to increased
snowmelt and higher flows on many area streams by Sunday. Flows
are already significantly above normal for this time of year on
many streams and area rivers and this increase in temperature will
only exacerbate those conditions. A brief cool down Tuesday may
slow the runoff before warmer highs return by the middle of next
week into the latter part of the week and next weekend. And to
that the possibility of showers returning to the forecast for late
next week and the weekend. Any additional rainfall has the
potential to 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 system peak forecasts falling in the
middle of May while the Walker and Lower Humboldt systems 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. In any areas where flows are high...even
areas without warnings or erosion is possible
and caution should be used near streams and rivers.

Remember also that these elevated flows are moving faster than
average and the water temperatures are quite cool. At Sparks
yesterday the Truckee had a temperature variance from a low of
about 43 to a high of 48. The cold waters make hypothermia a
distinct possibility if anyone gets in the water. And the
swiftness of the streams and rivers can easily carry someone away
rather quickly.


.REV Watches/Warnings/Advisories...


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