Scientific Forecaster Discussion
fxus66 ksto 182200
Area forecast discussion
National Weather Service Sacramento California
300 PM PDT Thu Jul 18 2019
Slight cooling tomorrow, followed by a slight warm up early next
week. Breezy winds through the Delta and over the Sierra crest at
Little in the way of sensible weather through the weekend. Dry
weather and mostly clear skies look to persist. Slightly cooler
temperatures will be seen tomorrow with highs ranging from the
upper 80s in the southern Sacramento Valley to the upper 90s in
the north. Slight troughing over the area will give way to an
amplifying high pressure over the Great Basin by late weekend.
Added a slight chance for an isolated thunderstorm over the Sierra
crest over Tuolumne/apline counties Saturday night as the trough
moves out. The Delta breeze continues through the weekend keeping
low temperatures around this area in the low 60s.
Extended discussion (monday through thursday)...
12z gefs/00z eps 500 mb height anomaly progs very similar in amplifying
the ridge axis of the 4-corners high well into the wrn half of
Canada and into Alaska at the onset of the efp, followed by a flattening
of the ridge over nrn rockys/wrn Canada later next week. The
flattening of the ridge to our north results in a westward expansion of
the ridge offshore, replacing the weakening nern pac cyclone.
Seasonable temps forecast for Mon/Tue with a warming trend into the
latter half of the week as 850 mbs temps warm into the mid 20s deg c
over much of our County Warning Area. Dry adiabatic descent of these temps should
result in some triple digit heat in The Vly from mid week into next
weekend. Daily Max temps for smf from the GFS ensemble shows temps
in the upper 90s early in the week, reaching into the 100s Wed thru
the end of the month with a high of 105 on Sat. Meanwhile, the
ecm ensemble shows temps in the mid 90s Mon/Tue, warming into the
upper 90s Wed, then low 100s Thu through sun with a high of 104 on
Sat. During the 6-10 day, Jul 23-27 period, the CPC has calculated
a 57% chance of a Max hi (heat index) of 100, and 85-90% chance
of >100 (102+) at rbl and sck. These occurrences will more likely
occur near the end of this period and into the weekend.
A couple of surges of monsoon moisture are forecast during the
period, one on Mon, and the other Wed/Thu, as the steering flow
strengthens around the 4-corners high. An increase in humidity is
likely with this moisture surge, and may also lead to convection
near the Sierra crest, mainly S of the Tahoe area. In general, the
SW flow aloft will keep the moisture shunted to the east side of our
County Warning Area and will tend to carry storms to the NE of our County Warning Area.
Expect strong thermal belts to develop in the foothills overnite
and some warm overnite mins in the 60s and 70s later in the week.
VFR sky clear-sct250 conditions next 24 hours. Occasional southwest wind
gusts 25-35 kts vicinity Carquinez Strait/delta; otherwise,
sustained winds generally below 15 knots.