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311
FXUS66 KSTO 202150
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
250 PM PDT Thu Jun 20 2024



.SYNOPSIS...
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Dry weather continues, with a warming trend over the next couple
of days resulting in Moderate HeatRisk Friday-Monday. Hottest
temperatures of the week will be on Saturday with widespread
triple digits. After Saturday, there will be slow cooling trend
to start next week, but temperature will remain above normal.
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&&

Key Points:
- Widespread Moderate HeatRisk is expected from Friday through
  Monday, with areas of Major HeatRisk Friday-Saturday
- Onshore flow will promote good overnight humidity recovery,
  minimizing fire weather concerns this weekend.
- A Heat Advisory is in effect from 11 am to 8 pm Saturday with
 Widespread Moderate HeatRisk and areas of Major HeatRisk in the
 Valley and foothills on Saturday; Highs in the triple digits.

Short-Term Discussion (Today THROUGH Sunday)...
Clear skies with a few passing mid- to high level clouds are
being observed across Northern California this afternoon via GOES-
West Visible Imagery. An upper level trough will start to break
down as we transition to a ridging pattern by Friday. As a result,
a warming trend will continue today, peaking on Saturday with
widespread Moderate HeatRisk expected Friday through Monday, with
areas of Major HeatRisk Friday and Saturday mainly over the Sierra
foothills & northern Sacramento Valley. The National Blend of
Models (NBM) is indicating a 80-100% chance of temperatures
greater than 100 degrees F throughout most of the Valley on
Saturday. While daytime relative humidities will be in the teens
and 20s, weak onshore flow will allow overnight relative
humidities ranging from 50-80 percent with the highest percentages
in the Vicinity Delta. This onshore flow pattern will minimize
significant fire weather concerns during this upcoming period of
elevated high temperatures and keep high temperatures cooler
around the Delta on Saturday.

By Sunday, a trough is expected to move through the Pacific
Northwest resulting in increased southwesterly flow. This will
translate into a more robust Delta breeze on Sunday with gusts
15-25 mph through the Valley. Slightly cooler temperatures will
follow, but Moderate HeatRisk is expected to continue across most
of the Valley and foothills through Monday.

&&

.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
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Moderate HeatRisk continues Monday with slightly cooler
temperatures. Clusters and ensembles depict an upper-level high
pressure that extends over Northern California Monday through
Tuesday which will continue elevated, above-normal high
temperatures throughout the Valley. The National Blend of Models
(NBM) is indicating 25-65% chance of high temperatures greater
than 100 degrees on Wednesday, with the highest probabilities
(greater than 50%) in the northern Sacramento Valley. Onshore flow
continues through the extended period as a weak trough moves
begins to influence the area on Thursday which will work to keep
temperatures around the Delta and Sacramento Metro Area a few
degrees cooler.
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&&

.AVIATION...
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VFR conditions continue over interior NorCal over the next 24
hours. Surface wind will be mainly below 12 kts except vicinity of
Delta, with southwesterly surface wind gusts to 25 kts. Low
marine stratus clouds will be limited to the far western Delta
08z-14z.
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&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM to 8 PM PDT Saturday for Central
Sacramento Valley-Motherlode-Mountains Southwestern Shasta
County to Western Colusa County-Northern Sacramento Valley-
Northern San Joaquin Valley-Southern Sacramento Valley.

&&

$$