Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Sacramento California
259 PM PDT Fri may 26 2017
slow warming trend this weekend into early next week. Isolated
afternoon showers or thunderstorms possible over the Sierra into
early next week.
Discussion (today through monday)...
Model analysis and water vapor imagery showed a high pressure
ridge in the eastern Pacific during the early afternoon hours, and
associated dry air was moving into northern California. An exiting
trough of low pressure was present on the northern end of the
Great Basin to the east of the forecast area. Visible satellite
continued to show persistent lower level cloud cover as 925 mb low
off the coast brought lift along with southwest oriented winds to
bring additional cloud cover this afternoon. Radar returns
remained clear of precipitation.
Model forecasts remain consistent in bringing a high amplitude
ridge of high pressure over the west tonight and into the weekend.
As a result, temperatures will gradually warm up to near normal or
a few degrees above normal by Memorial Day. An isolated
thunderstorm is possible for the Sierra ridges south of I-80
Saturday and Sunday afternoon/evening, but limited forcing could
limit development chances. A series of shortwave troughs approach
the forecast area Monday evening could bring enough lift that
will bring better chances for mountain thunderstorms.
Extended discussion (tuesday through friday)
A trough moves through the region Tuesday and Wednesday. Timing
of the trough is uncertain between the models with European model (ecmwf) bringing
the trough in earlier Tuesday than the GFS. Have nudged the
maximum temperatures even lower for Tuesday as model guidance has
continued to trend cooler. Cooling continues Wednesday as the
trough axis moves through, then the low looks to cut off south of
the area on Thursday. 12z GFS continues to show more moisture than
the much drier European model (ecmwf) Tuesday and Wednesday, and the position of
the cut off low will determine whether precipitation chances will
continue through the end of the week. Have continued with the
blend with slight chance of precipitation and thunderstorms over
the higher elevations through Friday. Temperatures will warm again
beginning Thursday to the low to mid 90s for the valley and 60s
to 70s for the mountains. Delta breeze will continue to keep the
Delta area a few degrees cooler than the valley, as well.
Stratus intrusion has lifted in the Central Valley to VFR cigs.
Clouds should clear out by 0-3z Saturday. VFR conditions expected
next 24 hours. Winds generally 10 kts or less for taf sites with
gusts to around 20 kts invof the Delta.