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Area forecast discussion 
National Weather Service Austin/San Antonio Texas 
401 PM CST Wednesday Dec 2 2009 


Discussion... 
cold air advection will continue tonight into Friday ahead of the 
approaching upper level trough and result in temperatures well 
below normal across much of the area. A quick look at the surface 
observations across the central and northern plains shows 3pm 
temperatures in the 20s and 30s...with a few spots in the upper 
teens. Dewpoint temperatures in the teens are common in this 
airmass...which will build into our area going into Friday. 


The large trough taking shape across the northern plains will lift 
NE over the next 48-72h. At the same time...shortwave energy will 
move around the base...across the southern rockies Thursday and 
across our area Friday. A coastal trough is forecast to deepen 
Thursday night in response to the approaching upper level short 
wave trough. The forecast position and magnitude of the coastal 
trough will be a big player in the snow forecast. There are some 
differences among the 12z model suite with regard to the coastal 
trough...with the 12z GFS more bullish on the quantitative precipitation forecast...especially 
across our southeast counties. The 12z GFS forecast soundings for our southeast 
counties show classic snow traces Friday...so precipitation will likely 
be all snow. Our forecast snowfall amounts are generally a blend 
of the 12z nam12 and gfs40 snowfall amount output...minus a 
quarter to half inch for anticipated melting. Will pass on a 
Winter Storm Watch for now given our forecast amounts and 
uncertainty with forecast coastal trough evolution...but a watch 
may be necessary with later model runs. For now...have updated the 
Special Weather Statement and created web graphics to highlight 
the snow forecast. In addition...a hard freeze is forecast Friday 
night into Saturday morning and a freeze warning will likely be 
required. 


The high amplitude synoptic pattern currently in place is forecast 
to be replaced with a near zonal pattern across the southern U.S. 
By 12z Monday. Another front is forecast to push through 12z 
Monday...with a quick turn-around and another front Tuesday night. 


Temperatures will generally be below to well below normal for the 
next seven days. We're forecasting new record low maximum temperatures Friday 
for the entire area...and will likely see a few new record low 
temperatures on Saturday morning. 


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