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414
FXUS66 KSTO 290918
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
218 AM PDT Wed May 29 2024

.SYNOPSIS...
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Hot and dry weather with breezy north winds bring locally
elevated fire conditions today and tomorrow. Afternoon highs well
above normal expected Thursday and Friday, with Friday expected to
be the warmest. Slight cool down on Saturday and Sunday, then a
warmup to possible triple digits next week.
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.DISCUSSION...
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Breezy northerly winds are already being observed in the
northern Sacramento Valley early this morning. Some passing high
clouds are also being observed just north of Willows. Northerly
winds are expected to strengthen as we move through the early
morning/afternoon hours, as a trough axis moves through the area
and tightens the pressure gradients as upper level ridging
develops in the Pacific and strengthens the northerly flow. North
to west winds of 15 to 20 mph are expected today along the central
and northern Sacramento Valley, along the I-5 corridor. Gusts of
30 mph are also possible, especially during the morning hours.
High temperatures should be slightly warmer today with Valley
highs in the upper 80s to low 90s and cooler 60s to 80s for the
higher elevations. Daytime humidity values will be in the single
digits and teens across the northern and central Sacramento
Valley, so elevated fire weather risk exists for today across the
Valley.

Tomorrow, northerly winds will increase in the morning hours once
again as the upper level ridging continues to build in the
Pacific and the upper level trough moves eastward. Similar
northerly wind speeds of 15-25 mph are possible, along with 30 mph
wind gusts. The National Blend of Models (NBM) advertises around
a 20-50% chance of a 40 mph wind gust along the I-5 corridor
tomorrow. Additionally, low humidity values of single digits and
teens exist, so another day of elevated fire weather risk exists.
Easier fire starts will be possible in the Valley. High
temperatures will increase as well, to low to mid 90s for the
Sacramento Valley, prompting areas of widespread Moderate
HeatRisk.

Onshore flow returns to the area late Friday afternoon, as our
upper level heights will flatten and enter a westerly/zonal
component. This will help ease the winds across the northern and
central Sacramento Valleys, but the Delta will still experience
breezy winds of up to 20 mph. High temperatures will once again be
in the mid to upper 90s for the Valley, with the Delta remaining
in the low 90s, again prompting widespread Moderate HeatRisk for
areas mainly and north of I-80. NBM probabilities of reaching 100
degrees are 20-60% for the aforementioned areas. Saturday, we
will see some minor relief from the high temperatures as weak
troughing overtakes the area and onshore flow will continue,
prompting breezy conditions in the Delta once again.
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.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)...

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Sunday will see similar high temperatures as Saturday, with highs
in the mid 80s to low 90s for the Delta and Valley, with cooler
60s to 80s for the foothills/mountains. As we move into the next
work week, our upper level pattern will once again flatten out in
response to upper level ridging building offshore. Ensembles
project the ridge to continue to strengthen and move inland
as we move through the week. High temperatures will increase
in response to the strengthening ridge over the area. The NBM is
advertising highs in the low 90s in the Valley on Monday, with 60s
to low 80s for the higher elevations.

Tuesday our high temperatures will increase, with higher
probabilities (40-60%) of reaching 100 degrees for areas from
Sacramento northward. Widespread areas of Moderate HeatRisk and
isolated Major HeatRisk are forecast for Tuesday. Wednesday
appears to currently have the greatest potential for widespread
triple digit temperatures across the Valley. The upper level ridge
is forecast to deepen Wednesday over the area, creating a quasi
Omega Blocking pattern with troughing in the Gulf of Alaska and
troughing in the eastern US, so high temperatures will continue
to climb. Cluster Analysis reveals good agreement in this pattern
manifesting, so it is possible that we may retain warmer than
normal temperatures for an extended period of time.

Right now, widespread Major HeatRisk exists for the central and
northern Sacramento Valley with Moderate HeatRisk for other areas.
Current NBM probabilities of reaching 100 degrees are around
50-90% for the Valley on Wednesday. Continued dry and mostly clear
weather is anticipated during the extended period.
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&&

.AVIATION...

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VFR conditions next 24 hours. Areas of northerly surface wind
gusts 20-30 kts in the Central Valley, strongest 15Z until about
00Z Thursday. Lighter winds elsewhere.
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&&

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

$$