Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 312232
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
332 PM PDT TUE MAY 31 2016

.SYNOPSIS...
Very warm weather expected this week as high pressure strengthens.

&&

.DISCUSSION...
Early (first of the) season heat wave unfolding over interior Norcal
with max temps some 10-18 degrees or so above normal for the rest
of the week. Strong subsidence from the Ern Pac high pressure cell
shifted inland today has squashed the marine layer... suppressed
mtn convection and trended max temps upward an additional 5 degrees
or so from yesterday with the likelihood of initial triple digit
max temps in the Valley today. Bias Corrected Consensus of the Max
T models suggested a >70-99% chance of at least reaching the
century mark in the Valley today. 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 today are
for KRDD/KSAC 103 in 2001...for DTS 106 in 2001...and for KSCK 107
in 2001.

The high pressure cell is forecast to shift into Wrn NV/SErn CA on
Wed as a trof works its way into the Pac NW. This feature is nearing
135W between 40-50N at press time...and is forecast to move into the
Pac NW on Wed.  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 some of the guidance shows as the marine layer
will remain shallow which reduces the cooling effects in the Srn Sac
Valley...aka "no freon". Also...timing may be an issue as the max
temps may be reached before the ameliorating effects of the
Breeze arrives. The strong thermal contrast from a couple of days
of heating in the Valley and the colder sea water may also create
a sufficient gradient to allow for air to flow inland through the
Strait.

Generally though, the heat will continue through Sat as 850 mbs
temps are forecast to remain in the low to mid 20s deg C and the
ridge axis persists over the Desert SW and Great Basin. Dry
adiabatic descent from 850 mbs would yield max temps at least in
the mid 90s to around 103 for example.

For Thu thru Sat...the ridge is forecast to amplify slightly with a
bump in 850 mbs temps which should push max temps a little higher
and up above 100. In addition...these warm 850 mbs temps also
suggest strong "thermal belt" areas with very mild/warm overnite
mins.

Limited convection potential expected in our CWA mtn areas for
the rest of the week until the flow backs to the SE...possibly
during the weekend. In the short term...convection from the
passing trof on Wed is forecast to remain N of Shasta Co in the
surrounding Siskiyou/Trinity county areas.    JHM

&&
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)

Models shift strong upper ridge into the Great Basin Saturday as
upper low approaches the SoCal coast. Some instability depicted
over the Sierra Nevada Saturday to support a slight chance of
afternoon showers or thunderstorms. Low is forecast to track across
California Sunday into Monday but models differ with exact track
and how quickly it progresses through. Thus forecast confidence
decreases during this period but pattern suggests at least a
slight chance of showers and thunderstorms for Interior NorCal.
Models then point to a drier southwesterly flow regime for
Tuesday. Cooling expected through the extended forecast period
with Central valley highs lowering to the upper 80s to lower 90s
by Tuesday.
&&

.AVIATION...

Upr high ovr NorCal with acyc flow alf bcmg SWly Wed as high
movs E into Grt Basin. VFR conds ovr Intr NorCal nxt 24 hrs with
sfc wnds genly lgt exc lcl SWly gsts to 25 kts poss thru Delta
aftns into eve. In Cntrl Vly, aftn density altitudes gtr than
2500 ft.

&&

.STO Watches/Warnings/Advisories...
None.
&&

$$



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