414
FXUS66 KSTO 302122
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
222 PM PDT Thu May 30 2024



.SYNOPSIS...
Elevated fire risk this afternoon due to breezy northerly winds
and low humidity values. Warming trend continues, with Friday
expected to be the warmest day this week. Slight cooldown
Saturday through Monday, then chances increase for triple digit
high temperatures by mid-week.

&&

.DISCUSSION...

Discussion at a Glance
- There is a 40-60% chance of Sacramento Valley climbing into the
  triple digits on Friday, followed by a slight cool down
  Saturday-Monday and increased onshore flow.
- A significant heat event is expected Wednesday & Thursday
  bringing Major HeatRisk for the Valley & Foothills and a high
  likelihood (70-95%) for widespread triple digit high
  temperatures in the Valley.
- Prepare for elevated daytime highs & overnight lows Wednesday &
  Thursday and reconsider outdoor activities during the hottest
  part of the day (3:00-7:00 pm).


SHORT TERM DISCUSSION
Taking a peak outside the window (and looking at GOES- West
visible imagery) it`s another sunny day with a few high clouds
across interior Northern California. North winds continue to gust
20-25 mph through the Sacramento Valley where peak gusts today
reached 25-35 mph (30mph+ gusts closer to Redding & Red Bluff).
Relative humidity (RH) values remain in the teens & low 20s across
the Valley this afternoon. As we head into the evening, winds
will weaken through the Valley and a weak Delta breeze kicks in
later this evening as humidity values increase especially around
the central Sacramento and northern San Joaquin Valleys.

On Friday, temperatures will increase as an upper level ridge
moves inland with Valley highs in the mid- upper 90s, with
approximately a 40-60% chance of exceeding 100 for portions of the
central and northern Sacramento Valley. Onshore flow will help
keep the Delta in the low 90s for high temperatures and aid in
overnight recovery (cooler temperatures and higher humidity
values). Widespread Moderate HeatRisk will overtake the
northern/western Sacramento Valley, while the Delta will remain in
Minor HeatRisk. RH values will still be in the 10-20% range for
the Valley, but wind speeds will be lower and west-south winds
will overtake the area Friday afternoon. More pronounced Delta
breeze is expected in the evening hours with gusts 15-25 mph
through the Delta & Sacramento Metro Area.

A brief "cool down" (highs in the low to mid 90s for the Valley,
mid 80s for the Delta, and cooler upper 60s to low 80s for the
foothills and mountains) is in store for this weekend as a weak
upper level trough moves eastward. Most of the forecast area will
be in Minor HeatRisk on Saturday & Sunday, with isolated spots of
Moderate HeatRisk, mainly from Yuba City north into Redding.
Upper level troughing is then forecast to build in the Gulf of
Alaska, and flatten our heights out into a more zonal pattern late
Sunday.

//Forrest

&&

.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Zonal flow aloft will lead to slight cooling on Monday, with
Valley temperatures in the mid to upper 80s and low 60s to low 80s
in the foothills.

Ensembles and cluster analysis reveal an amplifying upper level
ridge pattern over the area next week, bringing the potential for
a significant heat event. The EFI continues to highlight
anomalous maximum and minimum temperatures during this timeframe.
Guidance is good agreement that this pattern may last beyond the
extended forecast period.

By Tuesday, daytime temperatures in the Valley are expected to be
in the upper 90s to around 100, with areas of Major HeatRisk in
the Central Sacramento Valley. NBM probabilities of reaching 100
degrees are currently around 40-65% for the Valley on Tuesday.
There is a high likelihood (70-95% probability) of seeing
widespread triple digits in the Valley Wednesday-Thursday, with
Valley highs potentially climbing into the 100-1007 degree range.
Limited overnight relief is expected with lows in the mid 60s to
mid 70s, mainly across the northern/central Sacramento Valley and
foothills. Therefore, widespread Major HeatRisk is expected across
most of the Valley and foothills Wednesday and Thursday. Major
HeatRisk affects everyone without effective cooling and/or
adequate hydration. Consider canceling outdoor activities during
the heat of the day.

&&

.AVIATION...

VFR conditions expected over the next 24 hours. North winds
gusting up to 25 kts through the northern Sacramento Valley
through 00Z Friday. Sustained surface winds under 12 kts
everywhere else.
&&

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

$$