Excessive Heat in California, August 14 to 20, 2020

Area Forecast Discussion
National Weather Service Sacramento CA
206 AM PDT Fri Aug 14 2020

.SYNOPSIS...
Dangerous and prolonged heatwave will impact the region through
the middle of next week. Daytime temperatures will be 10 to 20
degrees above normal with limited overnight relief. Slight chance
of afternoon thunderstorms over the mountains this weekend into
Monday.

&&

.DISCUSSION...
The dangerous and prolonged heatwave arrives today. Excessive
Heat Warning goes into effect for the entire Central Valley
beginning this afternoon, and continues through through 9 PM PDT
next week Wednesday.

A strong and broad upper level ridge residing over the Desert
Southwest and Great Basin is responsible for this extended period
of excessive heat. Temperatures at 850 mb will warm to the 27 to
30 deg C range over the weekend and into the first half of next
week, and will result in maximum surface temperatures on the order
of 100 to 110 deg F Valley-wide. Ensemble means from the ECMWF
and GFS even suggest a remarkable 110+ for the Sacramento area
around Monday/Tuesday. It's quite conceivable that Sacramento
could match/exceed 105 for six consecutive afternoons, and perhaps
10 days at/above 100. These highs equate to about 10 to 20 deg F
above middle August climatology. Overnight lows will be oppressive
as temperatures hold in the 70s to low 80s well into next week.

Subtropical moisture will continue to entrain in the clockwise
flow around this upper level ridge, and will bring periodic
mid/high clouds to the region through the weekend. This moisture
could help initiate some isolated mountain thunderstorms near the
Sierra crest through Monday afternoon. Furthermore, these clouds
could help dampen peak temperatures through Sunday, but
conversely, would also hold overnight minimum temperatures higher
than officially forecast. Regardless, it will be hot - extremely
and dangerously hot for an extended period of time, even for
Central Valley summer standards. The heat risk will be high to
very high for much of the region through at least Wednesday of
next week.

This will not be a short-lived heatwave. The Excessive Heat
Warning is in effect for six days and five nights through next
week Wednesday 9 PM PDT. A combination of the extended duration,
relentless afternoon heat, and poor overnight cooling is what
will compound the severity of this heatwave. Heat is the number
one weather-related killer in the United States. Take the
necessary precautions to protect yourself from this extreme heat:

 * Stay hydrated and avoid caffeinated and alcoholic beverages.
 * Use air conditioning.
 * Take frequent breaks in the shade if you must be outdoors.
 * Wear light-colored and lightweight clothing.
 * Recognize the signs and symptoms of heat exhaustion and heat
   stroke. A heat stroke is a medical emergency; dial 9-1-1!
 * Check up on neighbors and relatives.
 * Ensure pets and livestock have shelter and water.
 * Never leave a person or pet unattended in a parked vehicle: look
   before you lock!
 * Wear a life jacket in the water.

Please be safe, and beat the heat!

// Rowe

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...
Minimal changes to the extended forecast as models continue to
depict high pressure dominating the forecast. Unfortunately, this
means we'll see triple digit heat for the Valley and foothills
through the extended period. Guidance does show a broad trough
slowly digging into western BC; however, we'll still be
experiencing the influence of high pressure. The "good" news is
that this will drop high temperatures by a few degrees, with most
areas being in the 100 to 105 range on Friday. Overnight lows
during this time frame are expected to be miserable as well, with
most areas ranging from the 70s to near 80s.

With that being said, it's important to re-iterate the danger of
this heat event. Know the signs of heat illness, drink plenty of
water, stay in air-conditioned rooms, check on your neighbors, the
elderly, children and pets. If you're traveling with children
and/or pets, look before you lock ever leave so that they're never
left unattended in vehicles.

This very dangerous heat event will have impacts on the general
population. Please learn the symptoms of excessive heat exposure,
drink plenty of water, stay in an air-conditioned rooms, and
never leave pets and children unattended in vehicles.

Some moisture will remain in place over the area on Tuesday. This
will lead to some instability over the higher elevations. There
is no forcing but the terrain could be enough to kick off an
isolated storm or two in the afternoon near the Sierra crest. No
thunderstorms are expected after Tuesday.

&&

.AVIATION...

Quiet conditions are forecast of interior northern CA for the
next 24 hours. Expect to see VFR conditions with winds generally
below 12 kt. &&

.STO WATCHES/WARNINGS/ADVISORIES...

Excessive Heat Warning from noon today to 9 PM PDT Wednesday for
Carquinez Strait and Delta-Central Sacramento Valley-Motherlode-
Mountains Southwestern Shasta County to Western Colusa County-
Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-
Northern San Joaquin Valley-Southern Sacramento Valley.

&&