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Area forecast discussion 
National Weather Service Pueblo Colorado 
332 am MST Thursday Jan 8 2009 


Short term... 
(today and tonight) 


..main short term concerns remain temperatures... 


Current water vapor imagery and RUC upper air analysis indicating 
moderate west to northwest flow aloft across the region with next 
system to affect the area moving onshore across the Pacific northwest coast 
at this time. At the surface...Lee troughing persists across the I-25 corridor 
keeping breezy and warm westerly downslope flow with temperatures 
mainly in the 30s to lower 40s along and west of the I-25 corridor 
at this time. Current temperatures across the rest of the plains and higher 
terrain also rather mild for early January with readings in the 20s 
and 30s with single digits and teens across the San Luis valley 
at this time. 


Today...moderating westerly flow across the region as short wave 
ridging builds across the state with Pacific northwest system digging into the 
northern Great Basin. Models continue to indicate warm air aloft 
building across the area with 700 mb temperatures warming to between 5c and 7c 
across the plains and with the warm start to the day along with 
mostly sunny skies...should see highs in 50s to middle 60s across the 
eastern mts and plains. 


Tonight...increasing westerly flow prognosticated across the state as 
northern Great Basin trough and associated cold front continues 
to dig across The Rockies. Lee trough deepens across the I-25 
corridor through the evening and kicks out across the eastern plains 
overnight in advance of cold front moving into northeast Colorado by 
12z Friday. This will keep breezy westerly flow and with continued warm 
air aloft...will see very mild overnight lows...especially along and 
west of the I-25 corridor and have warmed current grids to match. 
Models indicate moisture increasing late in the period across the 
northern and central mts...and with good orographics and increasing 
upward vertical velocity ahead of trough...should see snow developing across the western 
Mosquito Range after midnight and have increased probability of precipitation to high 
chances at this time. -Mw 


Long term... 
(friday through thursday) 


..unsettled weather Friday and Friday night... 
..Accumulating snow possible along and west I-25 into the 
mountains Friday and Friday night... 


Friday...longwave trough moving through the Great Basin/northern 
Rocky Mountains begins to take aim on the central rockies. This 
weather feature is currently noted just off the Pacific northwest 
coastline on satellite water vapor imagery and RUC model upper air 
analyses. Upper level jet streak will be over much of Colorado Friday 
morning with relatively vigorous westerly flow. This always play 
havoc with early morning temperatures. There will be a mountain 
wave...but it doesn't appear to be all that strong...however...gap 
flow areas like Canon City-Pueblo and La Veta Pass-Walsenburg 
could see breezy-windy conditions Friday morning...especially if 
mixing occurs during the morning. The relatively stronger winds 
should be around mountain top/"free-air" areas given the stronger 
winds aloft...so have ajusted winds upward in the digital forecast 
database since the model grids seem a little too weak. It still 
appears high temperatures will be in the morning across southeastern 
Colorado with temperatures shooting up into the 50s just before the cold 
front starts settling into the area Friday afternoon. 700mb 
temperature are prognosticated to cool across southeastern Colorado through the 
day. Also...adjusted Alamosa temperatures up considering 20-30kts 
of wind around 700mb through at least early afternoon and could 
shoot temperatures up due to turbulent mixing. NAM-WRF/met MOS has 
been too cool at kals. Now for preciptation chances...will 
probably see two areas. First...the vigorous west-northwesterly 
flow will likely continue orographic driven(with some synoptic 
ascent from the weather system) across the sawatch/Mosquito 
Mountain ranges in Chaffee/Lake County. Futher south along the 
Continental Divide...moisture content and/or poor orographic 
component shouldn't lead to much quantitative precipitation forecast. With the trough axis halfway 
through Colorado by 00z/10...the 06z/08 12km NAM-WRF is developing 
precipitation across the eastern Colorado mountains and just west of the 
I-25 corridor between 1pm-5pm. Will probably see showers 
developing as the rain-snow line will be tricky given the strength 
of the diabatic/evaporative cooling processes. Initially...it may 
be difficult to get snow below 5k feet mean sea level given the relatively 
"dry" sub-cloud layer...so it may start as virga...sprinkles...light 
rain...or light rain/light snow around 6k or 5k feet mean sea level Friday 
afternoon. Furthermore...initially...much of the snow that falls 
first will likely melt given the above normal temperatures... 
unless the snow showers are extremely intense. Midlevel lapse 
rates are prognosticated to be 6.0-7.0 c/km...so not an extremely intense 
lapse rate. Snowfall amounts could be 1-2" across our eastern 
mountains and 1-5" across the sawatch/mosquito mountains above 
9000 feet in Chaffee/lake counties...and could maybe see a 
hit-N-miss 1-2" snow showers across the Southwest Mountains. Might 
need a Winter Weather Advisory for zones coz058>coz060...but will 
let future shifts re-analyze the situation. 


Friday night...this forecast continues to have the higher 
probability of precipitation...but it is looking less and less 
impressive of a system. The aforementioned snow showers will 
likely expanded across the eastern Colorado mountains into the I-25 
corridor as the associated weather system literally races through 
Colorado. Models are consistent over the past few runs of moving the 
middle/upper level trough east and south of Colorado by 06z/10 Sat. The 
focus of the more intense preciptation might be from the Wet 
Mountains to the southern foothills/Raton Mesa. Wind direction 
will be the key on the precipitation intensity/qpf/snow amounts. 
Some hints of a northeasterly wind from surface-700mb...but the 
latest 12km NAM-WRF is more northerly. Could see 1-6" across the 
southern foothills from Walsenburg-Trinidad-Raton Mesa over to 
Cuchara...and we might need an advisory...mainly for Friday late 
afternoon/evening. Maintained some relatively light amounts...around 
1" elsewhere to the north and west...but again not overly 
impressed how the weather system is setting up. Also...limiting 
the quantitative precipitation forecast/snow amounts will be the speed of the system...mainly 
Friday afternoon/evening east of the Continental Divide. Kept 
preciptation going much of the night...but my gut says it will all 
be done by midnight with clearing sky Friday overnight. 


Saturday...NAM-WRF...GFS...and European model (ecmwf) all have the aforementioned 
weather system well to our east and south early Saturday morning. 
Went with zero pops/wx...and added more sunshine to the forecast 
given the relatively drier air aloft. Relatively vigorous 
northwest-north flow returns by Saturday afternoon...so brisk- 
windy conditions could exist for the higher terrain and near the 
mountains. Current temperatures look on track. 


Sunday through Thursday...vigorous northwest-northerly flow 
returns through at least Wednesday. This spells little or no 
preciptation...except around the sawatch/Mosquito Mountain ranges 
in Lake County. Could see more breezy-windy...sometimes very 
windy...across the higher terrain and eastern slopes of Pikes 
Peak...western El Paso County...and Pueblo County Sunday through 
Wednesday. Temperatures will primarily be at or above average 
readings for January. Interesting note about the Wednesday night 
through Friday forecast...the European model (ecmwf) has been consistent with 
taking a very cold Arctic air mass from Canada into the Heartland 
of the United States Wednesday through Friday. The European model (ecmwf) has a 
1050 mb surface high into the northern plains Wednesday and 
Central Plains by Thursday. The western fringe of this Arctic air 
mass could affect eastern Colorado. The European model (ecmwf) has the cold frontal 
boundary oozing into eastern Colorado Wednesday night and "locking-in" 
across eastern Colorado Thursday-Thursday night. The GFS is much weaker 
with the system. Obviously its too early...but something to keep 
an eye on for next week. Metze 


&& 


Aviation... 


VFR conditions expected to continue at all taf sites for the next 24 
hours. Breezy west winds will along and west of the I-25 corridor this 
afternoon will spread out across the rest of the plains overnight in 
advance of a cold front moving across northeast Colorado early 
Friday morning. -Mw 


&& 


Pub watches/warnings/advisories... 


None. 


&& 


$$ 


23/17 

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