747 
fxus65 kpub 211005 
afdpub 


Area forecast discussion 
National Weather Service Pueblo Colorado 
405 am MDT Thursday Aug 21 2008 


Short term... 
(today and tonight) 


Currently...low clouds and fog are over eastern El Paso County and 
extend eastward into parts of western Kiowa County. Fog image also 
shows a patch of low clouds and fog near Pueblo. Surface pressure 
charts indicate a weak Lee trough developing just to the east of the 
Interstate 25 corridor...with a stronger surface trough over 
northeast Colorado and into Wyoming. Suspect the south to north 
pressure gradient is just strong enough to develop weak south to 
southeast flow resulting in low clouds and fog over the southern 
slopes of Palmer Divide. Other area of low clouds and fog is just 
east of Baca County...and satellite loop does not show this area 
moving into Colorado. 


Today and tonight...the next shortwave moves from the Pacific 
northwest this morning into central Wyoming by Friday morning. Lee 
trough will strengthen during the day...and anticipate any areas of 
low clouds and fog to dissipate by 8 am over the region. 
Temperatures at 700mb warm to 14c to 18c by the afternoon. Only 
made minor adjustments to the temperatures...with highs reaching 
into the 90s over much of the plains. With some warming aloft and 
absence of any shortwave...confined probability of precipitation to the mountains and parts 
of the Interstate 25 corridor during the afternoon and early 
evening. Latest NAM has convective available potential energy around 1500 j/kg near the Kansas 
border during the afternoon...but model soundings look capped and 
there is the absence of a shortwave to trigger convection. Kept 
probability of precipitation out of the plains for today...and day shift can evaluate the 
addition of probability of precipitation. --Pgw-- 


Long term... 
(friday through wednesday) 


..active thunderstorm pattern possible Sat and sun... 


Friday...middle to upper level high pressure system will be parked 
just east of The Four Corners area....while a relatively vigorous 
system moves across the northern rockies and northern plains. 
Model projections continue to support a shallow cold front moving 
into northeastern Colorado/northwestern Kansas. Surface-lower tropopause flow 
anticipated to be relatively weak...so the mountain-plains 
easterly flow will likely develop across southeast Colorado. It could be 
a pretty warm day with 700mb temperatures around +18c across much 
of southern Colorado. With mixing...surface dew points will likely tank 
into the 30s and possibly upper 20s along the I-25 corridor and 
portions of the mountains/high valleys. Maintain some very low 
probability of precipitation/weather across the mountains/high valleys for high cloud-base moist 
convection and from the Teller County/Palmer Divide into east 
central Colorado just along and behind the frontal boundary. Models 
continue to support the development of a mesoscale convective 
system(mcs) across northeastern Colorado/southwestern NE/northwestern Kansas 
Friday night as midlevel warm air advection strengths behind the 
surface frontal boundary. This could send the frontal boundary and 
any mesoscale convective system outflow boundaries south southwestward late Friday night. 


Saturday and Sunday...the location of the frontal boundary will be 
key to all the sensible weather across the southeastern Colorado 
mountains and plains during these forecast periods. Some interesting 
weather possible. Middle to upper level high pressure system 
centered just east of The Four Corners area with minor midlevel 
shortwave troughs rotating around the high and through Colorado. Some 
kind of shallow frontal boundary should be against the eastern Colorado 
mountains and along the Colorado-nm-OK borders. There could be 
sufficient amounts of low level moisture with surface dew points 
in the 50s/60s across eastern Colorado. Potential for surface-based 
convective available potential energy to be 1k-3k j/kg and lifted indices of 0c to -5c across the 
southeastern Colorado mountains and plains...if the air mass can 
destabilize by Saturday afternoon. The wildcard is always the 
instability and any shortwave trough to enhance convection in 
these patterns. Could potentially see isolated to scattered 
showers/thunderstorms develop over the high country and along the 
frontal boundary in the southeast Colorado plains Saturday afternoon and 
then evolve into a nocturnal mesoscale convective system across the southeast Colorado plains 
and southward Saturday night. Organized strong to severe thunderstorms 
will be possible given the potential convective energy and the 
0-6km bulk shears of 25-40kts. Large hail and damaging winds could 
be possible. Given the relatively strong cape...available vertical 
shear...and moist low levels...a tornado could not be ruled out 
somewhere across southeast Colorado along any low level convergent 
boundary. As previously mentioned...nocturnal mesoscale convective system possible with 
plenty of energy available...0-6km MUCAPE of 2k-3k j/kg just 
behind the frontal/outflow boundary. Another potential 
thunderstorm impact will be heavy rain given george's k-indices of 
40-45c...700-500mb specific humidity values 6-7 g/kg...wet 
bulb/freezing level heights 12k-14k feet mean sea level...and cell movement of 
10kts or less...especially with cell mergers/training. The latest 
06z/21 NAM-WRF continues to support this weather scenario for 
Saturday afternoon and night...and that's roughly 8 model runs 
now. Stayed closer to the relatively cooler temperatures on Sat... 
but noted mav/GFS MOS much much warmer. Always tough to pindown 
these mesoscale events greater than 12-24 hours out. On Sunday... 
returned the forecast to more of a diurnal shower/thunderstorm 
forecast over the mountains/high valleys possible getting into the 
eastern Colorado plains. 


Monday through Wednesday...these forecast periods do not hold any 
significant pattern changes...so will maintain the diurnal 
convective precipitation and temperatures generally around or 
slight above average August readings. Metze 


&& 


Aviation... 


MVFR and IFR conditions from low clouds and fog are possible at 
kpub and kcos until middle morning. Otherwise VFR conditions will be 
over the region. Isolated afternoon and early evening thunderstorms 
are possible over the mountains and Interstate 25 corridor. --Pgw-- 


&& 


Pub watches/warnings/advisories... 


None. 


&& 


$$ 


06/17 

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