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fxus64 ksjt 211149 
afdsjt 


Area forecast discussion 
National Weather Service San Angelo Texas 
549 am CST Sat Nov 21 2009 


Discussion... 


See the 12z aviation discussion below. 


&& 


Aviation... 


The low level /850-925mb/ winds are out of the north and east this 
morning. This is allowing for some higher low level moisture to 
advect back to the south and west across the Big Country this 
morning and will result in at least tempo IFR/LIFR conditions 
through 16z at kabi. MVFR conditions over central Texas may also make 
it as far west as kbbd through 17z. After the low ceilings/fog burn off 
later this morning...VFR conditions will prevail with light winds. 
NAM model soundings indicate that there may be a return of some 
IFR ceilings after 06z tonight at kbbd and kjct. Since this is toward the 
end of the period...will insert a scattered cloud group for now. 


Lacy 


&& 


Previous discussion... /issued 331 am CST Sat Nov 21 2009/ 


Short term... 


Much of the middle/upper cloudiness over the Big Country and Heartland 
early this morning will move east of the region by sunrise...as 
upper low in central Texas also moves east. Winds will be light and 
variable early this morning...but shift to the south at 5 to 10 
miles per hour...as a weak Lee trough develops. 


Went close to GFS MOS guidance today in middle of the airmass and 
full sun. Guidance is usually close in such situations. However 
went lower than guidance tonight....south of the Big Country... 
where good nighttime radiational conditions develop...especially in 
low lying areas and river valleys. 


04 


Long term... 


The forecast pattern in the long term continues to look dry for 
our area. Temperatures Sunday will be warmer than today. Lows 
Sunday night will also not be as cool. Boundary layer should 
stay mixed across our northern counties...and low cloud development/ 
advancement is indicated by early Monday morning across much of 
the area south of Interstate 20. Highs Monday are expected to be 
around 10 degrees above normal with some thermal ridging indicated 
ahead of approaching cold front. 


Overall...the GFS and European model (ecmwf) models indicate that an upper trough 
will deepen into the northern/central planis Monday...with an 
upper low and trough progressing toward the middle-Mississippi Valley 
on Tuesday. Though the GFS and European model (ecmwf) still have some differences 
with timing and placement...both models show the associated cold 
front dropping south across west central Texas Monday night. Will 
be a dry cold frontal passage for our area...regardless of the 
specific model differences. Cooler airmass will follow this frontal 
passage and reside in our region Tuesday. 


Wednesday and Thursday...the GFS is more aggressive in diving 
another shortwave into the Midwest and carving out a deep trough 
into the eastern part of the country by late next week. Depending 
on how this pattern evolves...may see a reinforcing surge of 
cooler air into our area. Appears at this time...however...that 
the bulk of the cold air advection would be to our northeast and 
east. 


19 


&& 


Preliminary point temps/pops... 
Abilene 65 44 71 47 76 / 0 0 0 0 0 
San Angelo 67 42 73 47 76 / 0 0 0 0 0 
Junction 66 36 73 46 74 / 0 0 0 0 0 


&& 


Sjt watches/warnings/advisories... 
none. 
&& 


$$