Scientific Forecaster Discussion
fxus65 krev 190942
Area forecast discussion
National Weather Service Reno Nevada
242 am PDT Thu Jul 19 2018
Hot temperatures continue through the end of the week. Isolated
thunderstorms for portions of Mono and Mineral counties will
expand in coverage northward across much of the Sierra and western
Nevada this weekend with locally heavy rainfall possible. These
storms will also bring a slight cooling trend, however it will
remain seasonably warm.
The heat remains the main weather focus today with many western
Nevada valleys expected to reach triple digit highs again while
Sierra valleys reach near 90. The heat is thanks to an expansive
upper level ridge of high pressure across the southwest US with
its axis extending through Nevada and California.
This axis will gradually shift eastward over the next few days
which will allow temperatures to decrease a few degrees but hot
nonetheless with mid to upper 90s expected into the weekend.
The main impact of the ridge sliding eastward is that it will
allow moisture to return to the region and increase mid-level
instability. As a result, we will see increasing chances and
coverage for thunderstorms heading into the weekend.
Chances for storms this afternoon will be concentrated mainly
south of Highway 50 but as moisture streams northward, storms
will increase through the Tahoe basin, Carson Valley, Reno-
Sparks and roughly south of I-80 through the western Nevada basin
and range by Saturday. Hybrid type thunderstorms which may
produce isolated dry lightning strikes will transition to wetter
storms by Friday with Saturday seeing the best potential for
wet thunderstorms areawide. The S-SW steering flow, ample
moisture, and increased instability could focus heavy rainfall
particularly along the Sierra, Pine nut and Virginia ranges
Saturday afternoon which would increase the concern for flash
flooding in areas of steep terrain, drainages, and recent burn
scars. Some of these storms could persist through Saturday night.
Smoke and haze mainly from the Ferguson fire in California will
continue to impact the region, possibly through the end of the
work week. The rain from anticipated thunderstorms could help to
decrease particulate matter in the air and improve air quality.
The smoke forecast will be dependent on how actively fires burn
and could also change if new fires start. Check with your County
for the latest air quality. Fuentes
Long term...Sunday through Wednesday...
The upper ridge centered over the southern rockies Sunday will
retrograde westward and encompass the entire Desert Southwest and
Great Basin by the middle of next week. This will result in a
gradual decrease in thunderstorms and another round of very hot
temperatures next week.
For sun-Mon, we are still looking at plenty of moisture being
advected into the region on a south flow on the western periphery of
upper ridge. There continues to be indications of a couple of upper
level waves moving northward through the area late Sunday and
again Monday. Thunderstorms may be ongoing Sunday morning,
especially south of Highway 50 with extensive cloud cover farther
north. As a result there may be a lull in the activity during the
day Sunday before the first wave arrives and thunderstorms
increase and expand north Sunday evening into early Monday
morning. More storms are likely along the eastern Sierra and far
western Nevada for Monday afternoon and evening as deep moisture
remains in place and another potential wave arrives. Slow storm
motions both sun-Mon will bring an increased risk for flash
flooding, especially near steep terrain and burn scars.
Temperatures will be a little closer to normal Sunday before
beginning to inch upward Monday as upper ridge gets closer.
By Tue-Wed, thunderstorms will become noticeably more localized and
confined mainly to the higher terrain along the eastern Sierra as
temperatures aloft warm. While the core of highest heights will be
south of our area, 700mb temperatures will climb to 18-19c and help
push temperatures back up over 100 degrees for western Nevada valleys.
VFR conditions will prevail for the next couple of days although
areas of haze and smoke aloft from the Ferguson fire will likely
continue, especially near the Sierra between ktvl and kban where
MVFR visibility was reported Wednesday afternoon. Late afternoon-
evening wind gusts around 20 knots are expected along the US-395
corridor through Friday with lighter winds elsewhere. Storm coverage
will expand north to near US-50 today, then across the I-80 corridor
by Friday, with the greatest coverage expected this weekend. Many of
these storms will bring heavy rain, reduced visibility, mountain
obscurations and gusty outflow winds. Mjd
Nevada...heat advisory until 9 PM PDT this evening nvz003-004.
Heat advisory until 9 PM PDT this evening nvz005.
California...heat advisory until 9 PM PDT this evening caz070.