Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sacramento California
315 am PDT Sat Sep 5 2015
dry with near normal temperatures by Sunday. Locally breezy north
to east wind expected over the weekend. Continued dry next week
with temperatures warming to above normal.
Discussion (today through monday)...
water vapor imagery showing upper low pushing into the Great Basin
this morning with progressing upper ridge offshore. At the
surface, high pressure from the eastern Pacific is building
through Oregon into the Great Basin. As a result, the north-S surface
pressure gradient is tightening and will result in some locally
breezy north to northeast wind over interior norcal today.
Strongest winds are expected along western portions of the
Sacramento Valley and into the coastal range. Given strength of
low level gradient and limited upper level support, I.E., Lack of
proper phasing, wind speeds look to remain below advisory
criteria. Air mass will dry and warm today under increasing subsidence.
High temperatures this afternoon will continue about 5 degrees
below normal with mid 80s for the Central Valley.
Heights and thicknesses will gradually increase over interior
norcal through early next week. Locally gusty north to east wind
will continue Sunday into early Monday, then surface pressure
gradient and upper level support weakens. Low daytime humidities
and areas of poor overnight relative humidity recovery, combined with locally
gusty wind will increase fire potential this weekend.
Extended discussion (wednesday through saturday)
Slightly positively anomalous ridge expected throughout extended
forecast period. Hot and dry weather with temperatures forecasted
to reach well above normal by the end of the week. Drying
northerly winds caused by pressure rises over the Pacific northwest will
result in very poor overnight humidity recovery, especially over
the ridges and foothills.
The question will be whether a Delta flow develops and how strong
it will be if it does. Surface progs indicate that a thermal
trough will retreat to the coast with downslope winds overnight
over the western slopes of the Sierra nevadas. The thermal
gradient that develops over the region may eventually result in
some flow over the Delta, but questions remain on the depth of the
marine layer. MOS temperatures are trending towards climatology
late in the forecast period, except for Saturday, and have
basically followed persistence.
Northwesterly flow aloft with VFR conds over interior norcal next 24 hours. Local northerly
surface wind gusts to 25 kts today.