Cold in California, June 30, 2020

Area Forecast Discussion
National Weather Service Sacramento CA
217 PM PDT Tue Jun 30 2020

.SYNOPSIS...
Temperatures around seasonal averages this week, with dry weather
continuing.

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.DISCUSSION...
The synoptic pattern continues to maintain a strong upper ridge
anchored over the eastern Pacific (140W longitude) with a broad
negatively-tilted trough across the Upper Intermountain West.
Height gradients between these two features has weakened and
turned more north-northwesterly. A pressure difference of 5 mb or
so remains between KRDD and KMFR which has kept brief northerly
breezes around 10 to 15 mph at times over the northern Sacramento
Valley. Dew point depressions are a bit higher in this location
given the augmented downsloping flow.

Aside from fair weather cumulus fields over the higher terrain,
nearly cloudless skies are evident on visible satellite imagery
over interior northern California. Early afternoon temperatures
have reached the upper 80s, locally into the low 90s with numbers
likely to rise another 2 to 4 degrees given further diurnal
heating. With little change in 1000-500 mb thicknesses and 850-mb
temperatures, similar highs are anticipated for Wednesday.

On a broad sense, troughing is forecast to extend over much of
western Canada into the Pacific Northwest through the remainder of
the work week. Embedded shortwaves circulating about this
extensive trough will hold any building ridges at bay.
Consequently, daily temperatures should remain at, or slightly
below climatology heading into early July. As one such impulse
digs toward the Washington coast, increasing onshore flow off the
Delta should lower temperatures a bit on Thursday and Friday.
Delta influenced locations can expect highs into the upper 80s to
low 90s. Periods of breezy west-southwesterly winds are likely in
the Delta, possibly gusting 20 to 30 mph at times. ~BRO
&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)...
For the holiday weekend, a building upper ridge across the Four
Corners and Southern/Central Plains will expand westward in time.
This should bolster mid-level heights enough over northern
California to raise temperatures back into the mid to upper 90s.
On Sunday, with forecast 850-mb temperatures likely to return to
the 22 to 24C range, dry adiabatic mixing to the surface would
carry highs to around the century mark. This would especially be
the case over the northern Sacramento Valley. Heading into early
next week, how much troughing remains off the Pacific Northwest
coast vs. the strength of the Four Corners ridge will dictate
whether the warm up continues. Global ensembles support enough
troughing to keep temperatures closer to seasonal averages. A dry
weather pattern will continue. ~BRO
&&

.AVIATION...
VFR conditions are forecast over the next 24 hours for interior
northern CA. Winds are forecast to generally be below 12kt, with
the exception being the Delta and nearby areas where gusts reach
25 kt.
&&

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