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Area forecast discussion 
National Weather Service Pueblo Colorado 
258 PM MST Friday Nov 20 2009 


Short term... 
(tonight and saturday) 


..increasing cloudiness Saturday... 


The ridge of high pressure aloft will continue moving east...as a 
weak storm moves through Wyoming and into the plains by late 
Saturday. Used the WRF as a basis of the forecast...as winds 
appeared consistent...and the system kept any precipitation north of 
our County Warning Area through Saturday afternoon. Winds also appeared to be 
reasonable...with some downslope winds along the mountains west of 
the I-25 corridor overnight...which will keep temperatures warmer 
than those expected in the lower areas of the Arkansas River valley. 


With mainly clear skies expected overnight...the High Mountain 
valleys will again cool into the single digits to low teens. Clouds 
will increase Saturday as the system moves a weak cold front across 
mainly the central mountains...but...since the lower levels are 
dry...no precipitation is expected through the day. The main problem 
will be increasing winds across the higher mountains and along the 
eastern slopes ahead of and with the cold front. --Jkh-- 


Long term... 
(saturday night through friday) 


First shortwave will cross the Colorado rockies Sat night. This system 
looks relatively dry...bringing a brief shot of snow to the central 
mountains and dragging a dry cold front through the remainder of the 
area by early Sunday morning. This system is fairly 
progressive...which should keep snowfall amounts on the light side 
across the Sawatch and mosquito ranges. Moisture Shallows out 
quickly along the Continental Divide on Sunday behind the system...though there 
will be enough moisture for some isolated orographic snow showers 
across the higher peaks. Temperatures should be around 5 to 10 degrees cooler 
than the day before...especially across the plains. 


The next upper trough which drops in Sunday night/Monday has the 
potential to be the strongest of the week. There is still some 
variability between the models with 12z NAM and GFS dropping the 
open trough through Wyoming/northern Colorado into the Central Plains...giving 
southern Colorado more of a glancing blow before it closes off and heads 
towards the Upper Middle west. The 00z and 12z European model (ecmwf) and now the 18z 
NAM are stronger and farther west with the southeastward track of 
this system...with European model (ecmwf) the strongest and slowest of the bunch... 
closing off the upper low across western Kansas/eastern Colorado by Monday afternoon. Even 
with the stronger solution...most of the forecast area will be under 
the dry downslope portion of the storm...however northern portions of 
the plains...Palmer Divide and along with the central mountains 
could see some accumulating snows under the developing trowal on 
Monday. Given the uncertainties...will leave the low grade 
isolated probability of precipitation in for the southeast plains Sunday night/Monday. The 
central mountains could see a few inches of accumulation with this 
system as well. 


Regardless of the model...the system should well east of the area by 
Tuesday with a return of dry weather and rebounding temperatures. 


GFS has trended westward with the next round of energy dropping down the 
east side of the upper ridge through the Central Plains Tuesday 
night/early Wednesday. This system will send another front through the southeast 
plains...and which if latest GFS is correct could be accompanied by 
some isolated light snow showers. For now will keep forecast dry 
for the plains as previous runs and European model (ecmwf) keeps the track of this 
system farther off to the east. This should at least bring some 
degree of a cool down for Wednesday. Upper ridge will translate in 
aloft for Thursday before getting cut down and transitioning to zonal 
flow for Friday as next system enters the Pacific northwest. This 
should bring warmer temperatures and a trend towards breezy/windy 
conditions to the area through late next week. -Kt 




&& 


Aviation... 
VFR conditions are expected at all three taf sites through the 
period. Gusty winds may develop along the eastern mountain slopes 
late tonight and early Saturday as a dry cold front moves through 
the area from west to east. The gusty winds are not expected to 
affect the taf sites...but could cause problems for general aviation 
trying to fly from the plains into the mountains. --Jkh-- 


&& 


Pub watches/warnings/advisories... 
none. 
&& 


$$ 


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