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Area forecast discussion...updated 
National Weather Service Pueblo Colorado 
921 PM MDT Wednesday Mar 17 2010 


Update... 


Have updated the zones/grids and current west-southwest to reflect most 
recent NAM guidance. 00z NAM continues to reflect the 'weaker' 18z 
solution...which is somewhat at odds with the 12z GFS. So...will 
not make any wholesale changes until other 00z guidance surfaces. 
However...snow amounts still look fairly consistent so have 
updated the west-southwest to include more specific snow information and increase 
probability of precipitation over the watch area. The eastern mountains...including the 
wets...rmparts...and sangres...look to be the safest bet for 
warning criteria...especially the eastern slopes. North to NE winds will 
pile up the snow on Friday...with 8-12 inches a safe bet most spots. 
Could locally see 18-20 over parts of the wets...La Veta area...and 
possibly Pikes Peak. Monument Hill looking pretty scary for travel 
Friday morning...with at least a short period of heavy wind-driven 
snow that is likely to result in low visibilities and treacherous 
roads. Wildcard continues to be the central mountains...without 
good orographic flow the models struggling to be consistent with 
quantitative precipitation forecast. Various runs have shown the potential from anywhere from 3 to 
18 inches of snow over the dvd. With good dendritic growth 
potential...think the totals will probably be more on the hyr 
side...but warning criteria still not a given for the western zones. 
Interestingly...with latest NAM continuing the trend of lighter 700 mb 
winds from the north Friday morning...potential for isentropic processes is 
gaining ground...and his could spell more snow than previously 
expected for the cos and pub area. Certainly a busy next 24 h 
expected as this late winter storm moves in to our region. Rose 




&& 


Previous discussion... /issued 300 PM MDT Wednesday Mar 17 2010/ 


Short term... 
(tonight and thursday) 


The biggest problem tonight and Thursday is the amount of 
cloudiness...which will effect overnight low temperatures 
in the High Mountain valleys. At this time...expect some 
cirrus to remain across the area...keeping low temperatures 
.Especially in the high country about 5 to 10 degrees 
above what would normally occur. Some light downslope winds 
are expected to keep the night rather mild over the plains... 
with the usual colder air pockets in low lying areas and where 
any snow is still lingering. 


With increasing westerly winds Thursday...expect temperatures 
to warm to above normal in most areas away from snow cover. 
Increasing cloudiness is expected late in the day as a storm system 
moves toward our area. -Jkh- 


Long term... 
(thursday night through wednesday) 


Main forecast concern continues to be the system for Friday and 
Saturday. 


Thursday night through Saturday...the next system to affect the 
state comes as a fast-moving open wave starting late Thursday 
night...with it dropping down out of Canada and across the northern 
rockies. The system never develops into a closed low...but does 
deliver a strong shot of cold air. 700 mb temperatures of +4c Thursday evening becomes 
-12c in a short 24 hours. So...isolated to low scattered probability of precipitation to start 
out along the Continental Divide Thursday evening...then spreads to all of the higher 
terrain and Palmer dvd within 6-12 hours as a surface cold front is 
forecast to drop south across the Palmer dvd right around midnight. 
Models indicate the front will race south and reach the nm state 
line before noon...and maximum temperatures on Friday will most likley occur early 
to middle morning. Looking at the dynamics of this system...two waves 
of energy/upward lift will sweep across the forecast area...one Friday 
afternoon and the other late Friday night. Using a blend of model quantitative precipitation forecast...and 
halving the amount...produces an impressive potential for snow 
across the higher elevations and S foothills. Therefore...went ahead 
and issued a Winter Storm Watch late Thursday night through late Friday 
night to acknowledge the significant snowfall potential but still 
take into account uncertainties. The trough axis is expected to exit 
the state by midday Sat...with cool northwest flow settling in behind it 
and precipitation diminishing. 


Sunday and Monday...gradual warming and dry conditions expected as 
Post-system northwest flow aloft transitions into a ridge of high pressure for 
Colorado to start the next work week. 


Tuesday and Wednesday...long range models tend to agree on bringing 
another upper low system down across the desert SW on Tuesday...then 
sweeps it across nm and into Texas on Wednesday. If this solution holds 
true...and current forecast grids reflect this thinking...then one 
more warm day on Tuesday ahead of the system as SW flow across the 4 
corners increases...then increasing cloudiness and probability of precipitation with cooler 
temperatures on Wednesday. 27 


Aviation... 
VFR conditions through tomorrow at all terminals. -Jkh- 


&& 


Pub watches/warnings/advisories... 
Winter Storm Watch from Friday morning through late Friday night 
for coz072>076-078>080-087-088. 


Winter Storm Watch from late Thursday night through late Friday 
night for coz058-060-063-066-068-081-082-084. 


&& 


$$ 


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