Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 302221
Area Forecast Discussion
National Weather Service Sacramento CA
321 PM PDT MON MAY 30 2016
Very warm weather expected this week as high pressure strengthens.
A very warm week ahead with max temps some 10-18 degrees or so above
normal over much of interior Norcal.
High pressure cell just off the CA coast forecast to shift inland on
Tue...with the ridge axis shifting into Wrn NV/SErn CA on Wed. Max
temps this afternoon trending up to 4 deg or so warmer than 24hrs ago
at 20z...so today should warm into the mid to upper 90s in the Valley...
with more warming to come this week.
850 mbs temps are forecast to be in the low to mid 20s deg C through Fri
with the ridge axis persisting over the Desert SW and Great Basin
maintaining the very warm temps after mid week. Dry adiabatic descent
from 850 mbs would yield max temps at least in the mid 90s to around
103 for example. There may be enough of a Delta "trickle" on Wed with
the ridge axis shifting Ewd to allow form some slight cooling through
the Carquinez Strait and into the Srn Sac Vly. However...we don`t
expect maxes to cool as much as the guidance shows...and have
generally adjusted a few of the temps upward and just below 100 in
the Delta-influenced areas. However on Thu...the ridge is forecast
to amplify slightly with a bump in 850 mbs temps which should push
max temps a little higher and up near or little above 100. In
addition...these warm 850 mbs temps also suggest strong "thermal
belt" areas with very mild/warm overnite mins.
Darkening in the water vapor imagery off the coast indicates strong
subsidence which should also move inland on Tue. This will squash
the marine layer...limit the influence of the Delta Breeze and result
in max temps some 10-17 degrees above normal on Tue...and possibly
the first 100+ reading this season. Bias corrected consensus of
the Max T models suggests a >70-99% chance of at least reaching
the century mark in the Valley on Tue. The average date for the
first 100 at DTS is around June 18/19...close to the summer solstice...
and for the RDD area around June 9. Max temp records for the date...
May 31 are for KRDD/KSAC 103 in 2001...for DTS 106 in 2001...and
for KSCK 107 in 2001.
Just a slight chance of some late day shower/storm activity along
the Sierra Crest S of Tahoe and over the Shasta Co mtns on Wed as
the flow turns Wly on top of the ridge...otherwise little if any
late day/early evening shower and thunderstorm activity is expected
over the mtns in our CWA this week until the flow backs to the
SE...possibly this weekend. JHM
.EXTENDED DISCUSSION (Friday THROUGH Monday)
Strong high pressure will dominate through the end of the work
week into the start of the weekend with well above normal
temperatures...triple digit Valley temperatures. Models continue
to advertise a closed upper low transitioning into a negative-tilt
trough moving northeast onto the central CA coast impacting
interior northern CA this weekend Saturday into Monday with
potential mountain showers and thunderstorms. Regardless, the
region will experience some relief from the heat with
temperatures on Sunday around 5 to 10 degrees cooler than
Saturday and increasing flow through the Delta. JClapp/CEO
VFR conditions for TAF sites with light winds. Density altitudes
will be increasing throughout the week due to hot temperatures.