Area forecast discussion
National Weather Service Sacramento California
939 PM PDT Friday may 24 2013
Short term discussion...
Upper low continues to spin over Washington this evening just like
the past few days. This is keeping a dry...but cool northwest flow
over norcal. Skies are generally clear...although a few patchy high
clouds are passing over areas north of Red Bluff. Temperatures at
9 PM are generally in the low 60's and low 70's at valley
locations...warmest to the north. These readings are similar to
yesterday at this time. Forecasted overnight lows in the low 50's
look on track and no evening update will be needed.
Previous discussion...
Strong blocking pattern over western noam will dominate norcal weather
through the Holiday weekend...in what could end-up being "memorable"
if the models and forecast weather (especially qpf) verify for our County Warning Area.
Mild west-southwesterly flow S of the upper low over the Pacific northwest will continue
into norcal on Sat. A weak short wave will rotate across the far north
through this evening...spreading some high cloudiness over the area.
But the air mass is forecast to remain stable. That may change
Sat/sun afternoons across the far northern mountains with the forecast of
increasing instability as successively stronger short waves move
over the area. Moisture is marginal Sat...but a little more moisture
is forecast on sun and we have increased the areal coverage of
probability of precipitation with an inclusion of possible thunder eastern Shasta/western Plumas
counties including Lassen park area. Synoptic cooling will also
lower maximum temperatures on sun.
Monday may turn out to crack the top 5 wettest Memorial days in dts
(downtown sac) if the models verify. Energy from the Gulf of Alaska is
forecast to phase with the blocking low...with the energy moving
southeastward Monday/Tuesday over CA/NV. Greater areal coverage of showers is
expected on Monday/Monday night...with virtually all of our County Warning Area expected to
see some showers. Showers should decrease on Tuesday. Any quantitative precipitation forecast .08 inch
or more would crack the top 5 wettest Memorial days for dts...and
our latest quantitative precipitation forecast grids show a little more than a tenth of an inch
for the Monday period.
The sref plume average temperatures are forecasting some cool maxes for
Monday as well...again possibly cracking some of the top 5 coolest
Memorial days. However...the latest plume spreads have become
less clustered around the mean...resulting in low confidence that
a record "cool high" would occur on that day. In addition...the
naefs table shows the negative anomalies of the Standard pressure
charts occurring in the very near term with positive anomalies
returning sun/Mon. Still...maximum temperatures are forecast to range about
10 to 16 degree below normal on Monday. Jhm
Extended discussion (tuesday through friday)
Trough starts shifting to the east on Tuesday tapering off the
showers and warming temperatures a few degrees. Temperatures are
expected to warm into the middle 70s in the valley and upper 40s to
upper 50s in the mountains. Another low moves into the Pacific
northwest on Wednesday for continued chance of showers over the
northern mountains. Temperatures will still remain about 5 to 10
degrees below normal for this time of year. The low shifts to the
east on Thursday for a slight chance of lingering showers over the
northern mountains and a little warmer temperatures. The 12z
European model (ecmwf) builds the ridge off the West Coast on Friday but the 12z
GFS keeps a broad trough over the area. But either way it looks
like it may dry for next Friday and warmer but how much warmer
will depend on how much heights rise over the area. The forecast
for now warms temperatures in the middle 80s in the valley and 60s in
the mountains which is nearing normal for this time of year.
&&
Aviation...
VFR conditions continue across interior northern California
through Saturday. A weak wave will move across the far north
tonight into Saturday bringing more clouds and a slight chance of
Saturday afternoon showers over the northern mountains. Winds
generally 5 to 15 knots at taf sites. Light to moderate west to
southwest winds over ridgetops.
&&
Sto watches/warnings/advisories...
none.
&&
$$
