Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 232055

Area Forecast Discussion
National Weather Service Reno NV
155 PM PDT Mon Apr 23 2018


Warm afternoon temperatures are expected through Thursday, with a
cool down to near or possibly below average temperatures by next
weekend. Low pressure developing off the California coast will
bring increasing chances for showers and a few thunderstorms from
mid week into the weekend, with breezes increasing by Friday.



Although there are slightly cooler temperatures today with easterly
surface winds and northerly flow aloft, the highs will still be in
the mid 70s for western Nevada and the mid/upper 60s for Sierra
valleys. The surface winds along with the placement of the ridge
will likely limit most thunderstorm development across the Sierra
and western Nevada today, but since a stray thunderstorm in
southern Mono county could develop there is a 10% chance.

With thunderstorms in the forecast for much of the week,
especially in the Sierra, keep in mind that gusty and erratic
winds along with small hail will be a concern with any storms that
develop in the afternoons and evenings. Simulations have remained
fairly consistent with the ridge axis shifting eastward for
Tuesday, allowing for increased potential for thunderstorm
development. Model soundings across the region are fairly unstable
in the low levels, but most north of highway 50 do have a stable
layer aloft which would limit thunderstorm development Tuesday
afternoon. This stable layer is absent for model soundings from
South Lake Tahoe into the southern Sierra across Mono county, so
that is where we expect the best potential for thunderstorm
development Tuesday afternoon for now.

Chances for thunderstorms will stick around on Wednesday afternoon
as well as the ridge axis remains just east of the Sierra.
Maintained slight chances for thunderstorms along much of the Sierra
and northward into the Tahoe Basin and as far north as Lake Davis.
The upper low for the most part is still offshore on Wednesday
afternoon-evening, so any thunderstorms development would largely be
from surface-based convergence and heating. -Edan

.LONG TERM...Thursday onward...

The main focus of concern for the long term forecast is the track
of the upper low off the West Coast late this week. Model
solutions between the ECMWF and the GFS continue to vary.
However, the solutions are indicating that the low will make
landfall along the West Coast near the border of northern CA and
southern OR Thursday into Friday.

Southerly flow ahead of the approaching trough will allow for
increased moisture and instability in western Nevada and the
Sierra. This will bring chances for thunderstorms and showers each
afternoon and evening through Tuesday. The focus for convection
will be along the Sierra and adjacent lower valleys of western
Nevada, as well as the Sweetwater and Pine Nut Ranges. Breezy
conditions can also be expected each afternoon as the thermal
gradient between the Sierra and lower valleys increases below the
upper low.

The operational GFS is now opening the low up into a wave and
quickly bringing it through Oregon Friday night, with a secondary
shortwave carving a large trough over the west by the end of the
weekend. The EC now looks similar to what the operational GFS
looked like yesterday and brings a closed low over California and
Nevada for the weekend, ejecting it eastward as another wave drops
south into the PacNW. Ensemble spread in both models is
significant, to the point nearly each perturbation ends up with a
differing solution. What can be gleaned from this is the weekend
is looking cooler with chances for showers and some thunderstorms.
However, the various features and placement of the low will have
major implications on the exact forecast. -Johnston/Dawn



VFR conditions expected through much of the week except for the
possibility of morning fog at KTRK/Martis Valley.

The only other flight concern will be low chances of afternoon
thunderstorms mainly over the Sierra crest through mid week.
Chances for showers and thunderstorms increase late this week as
an upper low approaches the region. -Johnston/Boyd


.REV Watches/Warnings/Advisories...


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