Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA

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271
FXUS66 KHNX 221100
AFDHNX

Area Forecast Discussion
National Weather Service Hanford CA
400 AM PDT Sun Sep 22 2019

.SYNOPSIS...Dry weather can be expected over the district
through Thursday. Temperatures will warm to seasonable
levels today then trend slightly cooler Monday in the wake
of a dry cold front. A major warm up will occur by midweek
with high temperatures near the century mark Wednesday in
the hottest locations of the San Joaquin Valley and desert.
A cold storm system will bring a change to unseasonably cool
and possibly wet weather Friday through next weekend.

&&

.DISCUSSION...The week ahead will bring some wild temperature
swings in addition to some astounding weather extremes. One
week from today many of us may look back in amazement and wonder
how we could transition from Summerlike heat during midweek to
unseasonably cool, unsettled weather at the end of the week and
possibly Winterlike conditions over the high Sierra by next
weekend. We`ll do our best to sort it all out for you in this
discussion.

Today, officially, is the last day of Summer. Thermometer readings
will climb above the 90 degree mark in the San Joaquin valley,
lower foothills and the Kern county desert this afternoon as a
weak ridge of high pressure aloft moves over central California.
When Fall officially arrives at 12:58 am PDT Monday, a cold front
will be approaching from the northwest. This moisture starved
front will sweep southward through our CWA Monday morning with
little more than some mid and high clouds. In its wake, the rest
of Monday will be breezy and slightly cooler than today with
seasonable afternoon temperatures.

A much stronger upper level ridge anchored over the Eastern
Pacific will build into central California Tuesday through
Wednesday and bring a major warming trend. High temperatures
Tuesday will bounce back above the 90 degree mark in the San
Joaquin Valley and the Kern county desert. As the ridge gains
stronger footing over central California Wednesday, temperatures
will soar well into the 90s in the valley and desert. Thermometer
readings could top the century mark in the hottest locations.
That`s pretty close to the records in Fresno and Bakersfield.
(The record high in Fresno for Wednesday is 100 degrees which
last occurred on that date in 2009.  In Bakersfield, the record
high for September 25th is 103, which last occurred on that date
in 1975.)  This might be Summer`s last hurrah before a storm
system in the Gulf of Alaska chases it all away later this week.

That storm will be a major pattern breaker when it arrives here
Friday. As the cold front ahead of this storm approaches from
the north on Thursday, the high pressure ridge will get squashed
and there will be an increase in onshore flow across central
California. A shallow intrusion of marine air will come into
at least the northern half of the San Joaquin Valley by Thursday
afternoon and lower high temperatures back to seasonable levels.
Otherwise, Thursday will still be slightly warmer than normal
over much of the CWA.

That cold front will slip south of our CWA Thursday night and
herald the arrival of a much cooler air mass Friday. Otherwise,
the upper level trough that follows this cold front will deepen
along the West coast Friday through Saturday. In doing so, our
weather will turn sharply cooler/colder and the atmosphere will
become increasingly unstable over the central California interior.
Showers will become likely over the mountains Friday and could
materialize over the lower elevations by Friday afternoon or
evening. As the upper level trough moves inland Saturday, rain
showers could turn to snow showers in the Sierra above 7,000
feet and isolated thunderstorms equipped with small hail could
develop over the San Joaquin Valley and adjacent foothills
Saturday afternoon, especially from Fresno county northward.
Isolated funnel clouds are certainly possible on Saturday as
well. Afternoon temperatures Friday and Saturday may be no
higher than the lower 70s in the San Joaquin Valley and possibly
as cool as the mid 60s. (Records for low max temperatures could
be challenged in the San Joaquin Valley both days depending on
cloud cover.)

The models differ on the placement and the depth of this upper
level trough along the West coast next weekend, so forecast
confidence is low as to where and how much precipitation occurs
over the CWA. The GFS continues to deepen the trough over the
Golden State next Sunday while the ECM displaces the closed low
off the Pacific Northwest coast and places much of central CA
under a relatively drier southwesterly flow aloft. Whatever
the case, our pattern looks potentially wet by Saturday,
especially over the mountains. Hikers and campers in the Sierra
will want to pay close attention to NWS forecasts during the later
part of the week and be prepared for a drastic change to wintry
weather by next weekend with the potential for several inches of
snow in the Sierra above 8,000 feet.

&&


.AVIATION...
VFR conditions will prevail at MCE, MER, FAT, VIS and BFL through
at least the next 24 hours.

&&

.AIR QUALITY ISSUES...
None.



&&

.CERTAINTY...

The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.html for additional information
an/or to provide feedback.

&&

.HNX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Synopsis...Durfee
Public...Durfee
Aviation/Fire weather....BS

weather.gov/hanford



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