Excessive Heat in California, September 4 to 7, 2020

Area Forecast Discussion
National Weather Service Las Vegas NV
1022 AM PDT Fri Sep 4 2020

.SYNOPSIS...Dangerously hot temperatures will grip much of the
region through Labor Day weekend as high pressure sprawls across the
western states. Abrupt cooling will occur Tuesday along with gusty
north winds as a low pressure system dives out of western Canada into
the Four Corners Region.
&&

.UPDATE...No changes made to the going forecast this morning with
increasing heat expected today through Monday.  Temperatures
expected to be near record levels through Monday with a big cooldown
for the middle of next week.

.SHORT TERM...Today through Labor Day.

A strong ridge of high pressure was already centered over Nevada and
surrounding states. This ridge will remain nearly stationary and
strengthen slightly through Sunday leading to record or near record
temperatures and dangerously hot conditions. The ridge will be
nudged toward the West Coast by Labor Day in response to energy
diving out of British Columbia on the west side of a very broad
trough digging over the Canada/U.S. border. However, temperatures
will not change much until Tuesday. Excessive Heat Warnings and
Advisories remain in effect through Labor Day.
&&

.LONG TERM...Tuesday through Friday.

Unfortunately still quite a bit of uncertainty regarding the long
term forecast and whether or not temperatures will become more fall-
like or stay stuck in summer. There remains quite a bit of intra-
model uncertainty, with the ECMWF still holding onto a 10 degree
standard deviation for potential highs on Tuesday. That said, the
ECMWF and GFS Ensemble means appear to be moving toward each other,
if only slightly. While the ECMWF mean still indicates a digging
trough, and ultimately a closed low over the Four Corners on
Tuesday, the GEFS has a more westward trajectory of the incoming
trough across the Intermountain West. Regardless, it appears that
temperatures will drop below Excessive Heat criteria on Tuesday. How
far temperatures will drop will depend on how westward the incoming
trough digs.

In addition to temperatures midweek, the position of the incoming
trough will also determine wind and wind gust intensity. Due to the
bone-dry lower levels, if the ECMWF's forecast wind gusts come to
fruition, we will have another increased, critical fire danger
concern over the region. Slowly but surely, forecast models are
coming to a resolution.

Wednesday onward, the digging trough will push eastward through the
region, allowing the ridge off the California Coast to build and
temperatures to increase once again.
&&

.CLIMATE...
DAILY RECORD HIGH MAXIMUM TEMPERATURES

               FRI 9/4      SAT 9/5      SUN 9/6      MON 9/7
Las Vegas, NV  111 (1947)*  109 (1977)*  110 (1955)*  108 (1977)*
Bishop, CA     103 (1955)*  103 (1955)*  103 (1955)*  100 (1955)*
Barstow, CA    110 (1955)*  110 (1955)*  110 (1955)*  109 (1955)*
Needles, CA    116 (2019)*  114 (1923)*  114 (1924)*  116 (1923)*
Kingman, AZ    104 (2019)*  104 (1932)*  104 (1955)*  105 (1932)*
Death Valley   120 (1955)*  119 (2017)*  119 (1955)*  121 (1932)*

*-Current forecast is close to the record.
&&

.AVIATION...For McCarran...Hot temperatures, clear skies, and light
winds following typical diurnal trends through the period. Afternoon
temps well in excess of 100 degrees will result in high density
altitude.

For the rest of southern Nevada, northwest Arizona and southeast
California...Light winds following typical diurnal trends with
occasional smoke around the Sierra Nevada the only interruption to
clear skies. Hot afternoon temperatures will result in high density
altitudes across the entire region.
&&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&

SHORT TERM...Adair
LONG TERM...Varian
AVIATION...Steele
UPDATE...Berc

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