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afdpub 


Area forecast discussion...updated 
National Weather Service Pueblo Colorado 
927 PM MDT sun Mar 21 2010 


Update... 


Last few runs of both the GFS and NAM have been extremely consistent 
with forecasts of a high quantitative precipitation forecast early Spring storm Tuesday PM through Wednesday PM....so 
have gone ahead with a Winter Storm Watch for the areas most 
likely to see warning criteria snowfall. Highest confidence is for 
the wets and eastern slopes of the eastern ranges including Pikes Peak and 
the Spanish Peaks...where 1-2 feet of snow is looking more and 
more likely. A little less quantitative precipitation forecast for the northern ranges...but based on 
current upstream observation...believe that there will be more than enough 
moisture with this system for warning criteria at the hyr elevs. 
Northern El Paso was borderline...with snow levels initially starting 
out at 6500 feet or higher Tuesday afternoon...but should turn to all 
snow by Tuesday evening...with significant wet snow accums by Wednesday morning. 
Probably a greater likelihood of hazardous travel over I-25 with 
this system than with the last storm. Still a bit of uncertainty 
as to the phasing of the southern storm that is currently well off the 
Baja California coast with the northern system approaching coastal 
British Columbia...however...it looks like enough moisture with the northern branch 
that warning criteria will be met regardless. Plains look very 
wet...with some snow by late Tuesday into Wednesday morning especially at elevs 
above 5k feet. Rose 


&& 


Previous discussion... /issued 303 PM MDT sun Mar 21 2010/ 


Short term... 


(today and tonight) 


An upper ridge will remain over the area tonight...but will be flattened 
over the area by morning morning as a new weather system moves into 
the northern U.S. Rockies and the Pacific northwest. With increasing westerly winds 
over the area for Monday...will see some breezy to windy conditions... 
especially over and near the hyr terrain. With a couple to a few degrees 
more of warming aloft Monday...we should see daytime highs about 10 
degrees above normal over the southeast plains and just a little above 
normal over the high valleys. One concern for tomorrow is low 
relative humidities. It looks as though the southeast plains will 
see humidities of 10-15 percent...but at this time the winds do not 
looks like they will be strong enough in most areas to warrant a 
fire weather highlight. Some areas near the mts could get close to 
meeting the wind criteria. However...with the recent snowfall in 
these areas...it is possible that the fuel conditions are not 
critical. 


Long term... 


(monday night through sunday) 


.Significant winter storm for midweek... 


An upper level storm system will drop south out of the Pacific 
northwest Monday night and will begin impacting southern Colorado 
by Tuesday. The upper level storm system is currently forecast to 
track across The Four Corners area and into New Mexico by 
Wednesday afternoon. Models in general agreement with the storm 
system however there are difference in track and timing. Followed 
a NAM/GFS solution with regards to timing and track. Zonal flow 
ahead of the upper level storm will shift southwesterly by Tuesday 
morning as the trough digs across Utah. Moisture will advect 
northward ahead of the storm...both GFS and NAM have precipitable water values 
over half an inch across the plains by 18z. A lead wave will eject 
across The Rockies early Tuesday with snow increasing across the 
central and western mountains. Models indicating two cold fronts 
will move south over eastern Colorado...a weak front will move 
south across the region early Tuesday morning which will turn the 
flow northeast to easterly across the plains by 18z Tuesday. Not 
expecting too much cold air with this initial front with lower 
level temperatures in the upper 30s to low 40s over the plains. A 
secondary surge of cold air will shift south across the plains 
Tuesday evening with much colder air. 850 mb temperatures are 
forecast to drop to near 0c with 700 mb temperatures down to -10c 
over the plains by Wednesday morning. Expect snow levels to start 
out high...about 8000 feet before falling Tuesday evening behind the 
second front. One thing models are generating with this storm is 
deep moist upslope flow. The current NAM solution has 25-30 knots 
easterly flow through 700 mb from 18z/Tuesday through 12z/Wed. The 
moist upslope flow combined with the strong dynamics associated 
with the upper trough translating across the area will set the 
stage for heavy rain and snowfall Tuesday night and Wednesday. 
Significant snow accumulations are possible across the sangre Delaware 
cristo and Wet Mountain ranges as well as the adjacent plains 
including the southern I-25 corridor. Several inches of snow will 
be possible over the eastern plains by Wednesday as rain changes 
to snow. The upper trough exits the region Wednesday night with 
snow coming to an end by Thursday morning. 


A shortwave ridge will move quickly across The Rockies ahead of 
the next storm system which will impact the area on Saturday and 
Sunday. GFS and European model (ecmwf) are a bit different handling the storm with 
the European model (ecmwf) not as strong and a bit slower. Not looking at the best 
precipitation producer...flow looks to be northerly limiting 
orographic influences. Still do expect to see snow over the 
central and western mountains as well as the Palmer Divide. 
Currently thinking the main issue will be winds. Both GFS and 
European model (ecmwf) are generating very strong winds over the plains...with up 
to 50 kts at 850 mb and 700 mb near the Kansas border. This will 
need to be watched. 88 


Aviation... 


VFR conditions will persist across the area tonight and 
Monday. 


&& 


Pub watches/warnings/advisories... 
Winter Storm Watch from Tuesday afternoon through Wednesday 
afternoon for coz058>063-076-081-082-084. 


Winter Storm Watch from Tuesday evening through Wednesday 
afternoon for coz072>075-077>080-087-088. 


&& 


$$ 


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