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Area forecast discussion
National Weather Service Sacramento California
314 PM PDT Mon Oct 21 2019



Synopsis...
breezy conditions at times, especially Wednesday into Thursday
when elevated fire weather concerns are expected. Dry conditions
and above normal temperatures forecast for the next week.

&&

Discussion...
a warm and dry week is in store for interior northern California.
High pressure centered over the eastern Pacific builds slightly
into norcal, allowing daytime temperatures to rise to around 5 to
15 degrees above normal for late October. Valley highs will peak
in the mid to upper 80s this week with the mountains ranging from
the upper 50s to low 70s. Mostly clear skies will allow overnight
temperatures to still cool to near normal, though some locations
especially in the foothills will remain above normal.

The main concern this week is enhanced fire weather conditions.
Gusty north winds today have increased fire weather concerns. Many
valley locations have reported wind gusts around 20 to 30 mph.
Winds are expected to decrease this evening. Conditions are dry
today with minimum humidity values in the 20s to 30s. However,
good overnight recoveries are expected with most locations
reaching 40 to 70 percent.

Hot yet fairly calm conditions are forecast Tuesday before ensemble
models suggest another round of fire weather concerns Wednesday
into Thursday. This is expected to be a stronger wind event as a
weather system digging into the Great Basin area tightens surface
gradients across norcal. Sustained winds 15 to 25 mph with gusts
up to 30 to 40 mph are forecast Wednesday into early Thursday,
with locally higher gusts in wind prone areas. Confidence is a
little low in specific timing of the strong winds as run to run
agreement with ensemble models is inconsistent with this,
especially for the winds on Thursday. Generally, strong northerly winds
will begin in the valley and far northern mountains Wednesday
morning, shifting to easterly winds in the Sierra overnight
Wednesday into early Thursday. Gusty winds could remain through
Thursday afternoon.

Conditions will also be extremely dry Wednesday and Thursday. This
is due in part to the above normal temperatures expected across
the area. The north winds today and Wednesday through Thursday
will also increase drying. Relative humidity values on Wednesday
will be in the teens to upper 20s, drying significantly on
Thursday to mainly widespread teens. Poor overnight recoveries
are forecast Wednesday night with most locations in the teens to
30 percent.

Hec

&&

Extended discussion (friday through monday)...
temperatures are forecast to go from hot to cool over the weekend
with dry conditions expected to prevail. High pressure in place
over the western US will keep temperatures above average on Friday
with sunny skies and relatively light winds. Saturday the ridge
is forecast to weaken as a trough is expected to dive down into
the Great Basin from the Gulf of Alaska / western Canada area.

Forecast models are not in great agreement about this weather
system. The GFS keeps the trough broad and well to our east. The
European model (ecmwf) is presenting a more concerning pattern with the center of
the low situated much closer to the California / Nevada border, yielding the
potential for a strong northerly wind event. The European model (ecmwf) ensemble
gust matrix is rather excited about the Prospect of gusts over 40
miles per hour Sunday afternoon and evening at the Sacramento international
Airport. However, the GFS is not indicating winds this strong at
all.

If the region of low pressure dives southward close to the California /
Nevada border, then we could have some very dry and windy conditions
over our area for the Sunday to Monday timeframe. However, if the
trough slides southward further to the east, we may not see much
of an impact at all. Models are in agreement however, with the
general northerly flow pattern late this week and into early next
week. This will be something to watch as we get closer in time.
This system will also act to reduce synoptic thicknesses over our
region and bring down temperatures to below normal by the start of
next week.

&&

Aviation...
VFR conditions the next 24 hours at taf sites. Generally
northerly sustained winds 5 to 15 knots. Gusty north winds up to
25 kts in the valley today should diminish by Sundown.

&&

Sto watches/warnings/advisories...
Fire Weather Watch from late Tuesday night through Thursday
afternoon for Carquinez Strait and Delta-central Sacramento
Valley in Glenn, Colusa, Yuba, northern Sutter, and Butte County
below 1000 ft-eastern Mendocino nf-eastern portion of
Shasta/Trinity nf-Lake County portion of lake-Napa-Sonoma unit-
northern motherlode from 1000 to 3000 ft. Includes portions of
Nevada-Yuba-Placer-Amador and Eldorado units-northern Sacramento
Valley to southern Tehama County line below 1000 ft-northern San
Joaquin Valley in San Joaquin and Stanislaus counties below 1000
ft-northern Sierra foothills from 1000 to 3000 ft. Includes
portions of Shasta-Trinity and Butte units-northern Sierra
including Lassen np and Plumas and Lassen nf/S west of the
Sierra crest (west of Evans Peak-Grizzly Peak-beckworth peak)-
northern Sierra including the Tahoe and Eldorado nf/S west of
the Sierra crest-southeast edge Shasta-Trinity nf and western
portions of Tehama-Glenn unit-southern Sacramento Valley in Yolo-
Sacramento far western Placer, southern Sutter and Solano County
below 1000 ft-Stanislaus nf west of the Sierra crest.

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