116
FXUS66 KSTO 230908
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
208 AM PDT Mon Sep 23 2024

.Synopsis...
Hot and dry weather with periodically breezy northerly winds and
elevated fire weather concerns persist through Tuesday, with a
brief cool down to near normal and a return to onshore flow
expected through midweek. Breezy northerly winds and warming
temperatures then return once again late week into next weekend.

&&

.Discussion...
Within diffuse north-northeasterly flow aloft at this time, some
upper level cloud cover is beginning to filter into interior NorCal
from the northeast. Little appreciable impacts are expected, but
areas of more persistent cloud cover may stay a few degrees warmer
overnight. Otherwise, light, northerly surface winds prevail early
this morning and are expected to become breezy to locally gusty
throughout the Valley after sunrise. Gusts of 15 to 25 mph will be
possible, with highest probabilities of gusts exceeding 25 mph (20%
to 40%) expected along and west of the Interstate 5 corridor through
mid afternoon. Alongside the locally gusty northerly winds, limited
overnight humidity recovery and daytime minimum humidity values into
the teens to single digits are anticipated as well. This will result
in at least a window of elevated fire weather conditions from mid
morning into the afternoon hours where strongest winds and lowest
humidity overlap (generally Interstate 5 westward in the
central/northern Sacramento Valley).

Aside from the potential for fire weather concerns, broad ridging
aloft will allow above normal temperatures to continue for Today and
Tuesday. High temperatures in the mid 90s to lower triple digits are
expected across the Delta, Valley, and foothills, with 80s to 90s at
higher elevations. Despite the favorable pattern, current
probabilities of high temperatures exceeding 100F run around 15% to
25%, with highest probabilities in the northern Sacramento Valley
today shifting to the Delta, southern Sacramento and northern San
Joaquin Valleys on Tuesday. As a result, fairly widespread Moderate
HeatRisk is anticipated across the Delta, Valley, and foothills for
today and Tuesday.

A transitional period in the upper level pattern is then expected to
evolve from late Tuesday through midweek. A region of broad
troughing from the Gulf of Alaska looks to deepen toward the Pacific
Northwest at the same time a shortwave off the coast of SoCal begins
to deepen into a weak closed low on Wednesday. This will correspond
to the aforementioned broad ridging aloft from early this week being
pushed eastward through midweek. A notable drop in temperatures
looks to accompany this brief pattern shift, with Delta, Valley, and
foothills high temperatures falling into the 80s to low 90s for
Wednesday and Thursday. Despite the presence of troughing in the
vicinity of interior NorCal, a lack of appreciable moisture and
generally unfavorable positioning for lift as the systems progress,
will keep precipitation chance minimal at most. Best chances at this
time for any precipitation are expected Wednesday afternoon and
evening for the northern Sacramento Valley as the two regions of
troughing phase together and move eastward, but even still,
probabilities of precipitation greater than 0.01" remain less than
10% at this time. Rather, the most appreciable impacts aside from
cooler temperatures will be the return of onshore flow and more
favorable humidity recovery through Thursday.

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)...
Current ensemble cluster analysis trends continue to hint at a
return of increasing heights aloft late week into next weekend.
While the rising heights look to occur within mostly stagnant
zonal flow aloft, a warming trend toward above normal temperatures
is becoming more likely through the end of the month. With no
appreciable ridging to reinforce the heat though, high
temperatures for the Delta, Valley, and foothills look to settle
in the low to mid 90s from Friday into the weekend at this time,
with 80s to low 90s at higher elevations. The primary concern with
this pattern will be the shift from onshore surface flow to
predominantly northerly surface flow. With resultant, periodically
breezy northerly winds and the combination of daytime humidity
into the teens to 20s and limited overnight recovery, some
elevated fire weather concerns may be possible.

&&

.AVIATION...
VFR conditions next 24 hrs. Surface wind gusts generally below 12
kts except local northerly gusts 15-20 kts northern Sacramento
Valley 15Z thru about 20Z.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$