Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 271102
Area Forecast Discussion
National Weather Service Sacramento CA
402 AM PDT TUE SEP 27 2016
Strong high pressure will continue hot weather across the region
today. A cool down is expected as an upper level trough moves into
northern California for the rest of the week and into the weekend.
The hot weather pattern will continue across the interior of
NorCal for another day as strong high pressure continues. The
offshore surface pattern is not as strong as 24 hours ago, but
the marine layer has yet to return. A weak Delta Breeze may
develop by this afternoon and may shave a few degrees off today`s
highs compared to Monday.
The Delta Breeze will pick up tonight and Wednesday as the upper
ridge shifts east and a low drops down to off the PacNW coast.
This will mark the beginning of a significant cooling trend across
interior NorCal (and a return of breezy southwest winds) for the
second half of the week from a combination of increased onshore
flow and synoptic cooling associated with the trough. By Friday,
highs across the region are expected to be around 20 degrees
cooler compared to today.
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)
A cool trough from the Gulf of Alaska will bring a period of
typical fall weather for the weekend into early next week. This
means cooler temperatures and unsettled conditions, with periods
of precipitation possible as a series of waves move through the
trough. The initial wave late Friday through Saturday should be
relatively dry and will bring a drop in temperatures to 8 to 11
degrees below normal levels. Mountain winds should be quite
breezy/gusty, though increasing humidity levels will tend to
decrease fire weather concerns.
The next wave arrives Sunday into Monday, but models differ
significantly on timing and how far south this system will go.
Overall there is a trend of this system looking wetter and
shifting further south. Sunday there is a slight chance of
precipitation over the northern mountains and into the northern
Sacramento Valley, with snow levels in that area dropping around
to just below 7000 feet. The best potential for precipitation is
expected to be mid-day Monday, across the mountains and extending
into the central Sacramento Valley. If models continue this trend,
the potential for precipitation may spread across the forecast
area. On Tuesday confidence is low but the general trend appears
that this system should be exiting the area with some lingering
mountain showers. EK
VFR conditions over interior NorCal next 24 hours. Light winds
will prevail across TAF sites.