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Area forecast discussion 
National Weather Service Pueblo Colorado 
354 am MST Wednesday Nov 19 2008 


Short term... 
(today and tonight) 


Short term concerns include temperatures along with movement of cold 
front across the plains late tonight. 


Current water vapor imagery and RUC upper air analysis indicating 
weak to moderate westerly flow aloft with flat upper level ridging 
in place across the state at this time. Water vapor imagery also indicating 
faster zonal flow with several embedded waves moving through the 
flow across the Pacific northwest through the northern tier of states. Warm 
air aloft under ridge and Lee trough associated with passing 
northern High Plains wave across central Kansas through the far 
southeast plains... keeping west to northwest flow in place and very mild 
temperatures with readings mainly in the 40s to low 50s across the 
plains and mainly 30s across the higher terrain at this time. 


Today and tonight...westerly flow to continue aloft with Lee trough 
prognosticated to deepen across the I-25 corridor through the late 
morning...allowing for easterly low level upslope flow to develop 
across the eastern plains through the afternoon as surface high pressure 
builds across the Central High plains behind passing wave. However 
with the warm start...have stayed closer to the higher side of 
guidance with temperatures quickly warming through the late morning with 
steady or slowly falling temperatures through the afternoon. With only 
slight cooling aloft...should see temperatures at or slightly cooler out 
west. Main cold frontal boundary currently across southern Montana 
and through the Dakotas prognosticated to slide through southern Wyoming 
around 00z Thursday. Front then continues across the Palmer Divide 
between 3z-6z and through all of southeast Colorado banked up across the 
lower eastern slopes by 12z Thursday. Soundings indicating low levels 
quickly saturating with widespread stratus developing across the 
plains behind frontal passage. Not much upward vertical velocity associated with system with best 
chances of precipitation associated with warm air advection along the lower eastern slopes 
and immediate adjacent plains with soundings indicating light freezing 
drizzle or flurries possible. With likelihood of faster frontal 
movement...have added slight probability of precipitation along and west of the I-25 
corridor after midnight. Best coverage of light freezing precipitation 
expected across the Palmer dvd...could make for sleek roadways for 
the early morning commute. -Mw 


Long term... 
(thursday through tuesday) 


..much colder temperatures southeast Colorado Thursday... 
..Freezing drizzle/fog possible I-25 corridor Thursday/Thursday night... 


Thursday and Thursday night...well advertised much colder 
temperatures across eastern Colorado still appears to be on track. 
Leaned the forecast towards the higher terrain resolution 12km 
NAM-WRF...but the GFS is not too far away from the large scale 
solutions. A 1040-1045mb surface high pressure system will 
continue to push into the northern/Central Plains with eastern Colorado 
on the western side of the air mass. Thursday afternoon's 
temperatures should be 20-30 degrees colder compared to today's 
readings. Model MOS projected high temperatures are now in the 30s 
across the Palmer Divide and lower 40s across southeastern Colorado. The 
new NAM MOS guidance continues to predict 39f for pub and 32-34f 
at cos-aff-mnh. The raw 12km NAM-WRF model maxt has temperatures 
slightly cooler than the MOS readings. Cold front depth will be 
up to 750-700mb...so not anticipating it making past Pikes Peak 
and into the sangre Delaware cristo. As typical with these 
scenarios...the relatively warmer temperatures will be found in 
the central valleys(san luis and upper Arkansas river) where 50s will be 
likely. It is even possible Leadville could be warmer than cos and 
pub. Precipitation will be a challenge. The moisture will be very 
shallow...surface up to maybe 700mb...behind the front. Will 
likely see a very sharp transition from clear sky to cloudy sky 
along the eastern slopes of Pikes Peak...Wet Mountains...and 
southern sangre Delaware cristo mountains. As for precipitation...there 
will be some frontogenetical forcing and some weak orographics. Plan 
to maintain the very low probability of precipitation. Couldn't rule out a few flakes of 
snow...but the primary precipitation will be drizzle per BUFKIT 
sounding analyses. Low level flow becomes east-southeasterly...so 
the southern Palmer Divide and cos will likely be in the LIFR fog 
and ceilings all day. With temperatures in the Lower/Middle 
30s...drizzle and freezing drizzle will be possible Thursday 
morning and possibly throughout the whole day if temperatures 
don't warm much along and west of the I-25 corridor. Surface cp 
air mass across the central 1/3 of the United States begins to 
migrate eastward Thursday night...and will allow for the western 
fringe air mass to retreat eastern Colorado. Cloud ceilings should 
start to break-up and rise...but LIFR-IFR ceilings/visible in 
fog/drizzle-freezing drizzle may continue across the southern 
Palmer Divide/cos through the night given a low level southeast- 
southerly upslope flow. Basically...moisture/cold air still 
trapped under a strengthening inversion aloft. 


Friday through Sunday...the next weather feature continues to be 
prognosticated passing to our north. A Flat Ridge moves back into the 
central rockies Saturday with the potential of another relatively 
"dry" cold frontal passage across eastern Colorado on Sunday. 


Monday and Tuesday...no changes. Metze 


&& 


Aviation... 


VFR conditions expected through between 03z-06z Thursday 
across the eastern plains and for the next 24 hours across western 
portions of the area. A cold front currently moving across southern 
Montana will continue to move south through the day and is expected 
across the Palmer Divide between 3z-6z and through all of southeast Colorado and 
banked up across the lower eastern slopes by 12z Thursday. MVFR and IFR 
ceilings to develop across the plains behind frontal passage. Local LIFR 
conditions along and west of the I-25 corridor with light freezing 
drizzle and freezing fog possible. -Mw 


&& 


Pub watches/warnings/advisories... 


None. 


&& 


$$ 


23/17 

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