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000 
FXUS65 KBOU 241907
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1207 PM MST Tue Jan 24 2017

.UPDATE...
Issued at 1157 AM MST Tue Jan 24 2017

A mix of freezing drizzle and freezing fog around a frontal 
boundary settled along the foothills and Palmer Divide has 
resulted in icy conditions and several accidents late this 
morning. As a result have issued a freezing fog advisory until 2 
pm this afternoon. The icy conditions will persist until 21z then 
increasing moisture in the mid level moist is expected to overrun 
the post frontal airmass. this should be enough to end freezing 
pcpn transition the advisory area over to snow showers later this 
aftn. the main area of concern in the foothills will be in 
Douglas, Jefferson and Boulder Counties below 7500 feet.

UPDATE Issued at 1006 AM MST Tue Jan 24 2017

fog spreading into the urban corridor this morning following the
passage of a cold front. high temperatures have likely already
been met with steady reading the rest of the day. Fog should 
continue through 19-20z then visibilities and cigs should  
gradually improve this afternoon as the sfc low over central KS 
shifts east. Have updated the grids to include fog and adjusted
temperatures as well. snow showers as well but still likely no
more than a dusting this aftn.

&&

.SHORT TERM...(Today and tonight)
Issued at 330 AM MST Tue Jan 24 2017

Latest satellite analysis shows upper low spinning just west of
Casper Wyoming, with another piece of energy now pushing northeast
from the Four Corners area. The main cold front has hung up in 
east central Wyoming into the Nebraska panhandle as some pressure 
falls were still noted into southeast Wyoming. Better falls were 
seen under the short wave in the Four Corners. As that shortwave 
lifts out, should see stronger pressure rise/fall couplet develop 
finally allowing front to surge southward through northeast 
Colorado. Behind that, shallow anticyclonic upslope develops in a 
slightly unstable atmosphere, so expect scattered snow showers to 
develop across the plains and I-25 corridor later this morning. 
Still not entire sure about how this unfolds but feel at least 
scattered PoPs would be warranted in this scenario. Any showers 
that develop may drop brief moderate snowfall with a quick dusting
to 1 inch possible. 

Into late this afternoon and evening, the anticyclonic upslope 
component would have a tendency to increase and deepen. While most
synoptic scale energy is departing and low levels begin to dry, 
there still appears to be sufficient instability under the upper 
trough to keep the chance of snow showers in the forecast. Most 
likely during this time frame there would be a focus toward the 
Front Range foothills from Boulder southward. On the northeast 
plains it should turn drier but as system organizes in Nebraska 
would expect some wrap around moisture to bring an inch or so of 
snow to the far northeast corner of the state. Chance of snow on
the plains will decrease late this evening.

In the mountains, expect mostly light snow off and on through
tonight with modest orographics and moisture. Will leave existing
advisory for zone 31 in place, while most mountain locations
should pick up another 1-4 inches through tonight.  

.LONG TERM...(Wednesday through Monday)
Issued at 330 AM MST Tue Jan 24 2017

Drier and warmer conditions for the extended period. Wednesday
will see increased moisture behind the trough with mostly cloudy
skies through the morning slowly scattering out by the late
afternoon as increased subsidence returns. Flow from the north on
the plains provided by the exiting surface low over Eastern Kansas
could bring a slight chance of snow to the far NE plains counties
and the mountains into the evening hours. Some light accumulation
will be possible in the mountains with little to none on the
plains. Temperatures will be cooler on Wednesday behind the front
with highs hovering right around freezing and overnight 
temperatures into Thursday in the single digits to low teens. 

Thursday will see the building in of a surface high that will
dominate the mesoscale picture for most of the extended period.
There will be enough moisture in the mountains for a slight chance
of snow on Thursday but POPS will decrease substantially by the 
evening. Temperatures on Thursday will increase into the upper 30s
and then to normal by the weekend with a chance of above normal 
temperatures in the 50s by Monday under a moderately strong ridge.
With the surface high dominating most of the Western portions of 
the CONUS with strong flow out of the north provided by the trough
over the Great Lakes some increased winds will be possible over 
the plains with gusts reaching into the 30s by the weekend. 
Otherwise conditions will be dry under partly cloudy skies.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1006 AM MST Tue Jan 24 2017

IFR cigs/vsbys expected until 19z with a gradual improvement to
MVFR cigs/vsbys until 21z. patchy freezing fog/freezing drizzle
until 19z as well, mixing with snow showers as well. ILS cigs this
23z-03z then VFR conditions. 


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Freezing Fog Advisory until 2 PM MST this afternoon for COZ035-
036-039>041.

Winter Weather Advisory until 5 PM MST this afternoon for COZ031.

&&

$$

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