Area Forecast Discussion

FXUS65 KBOU 180930
Area Forecast Discussion
National Weather Service Denver/Boulder CO
330 AM MDT Sun Mar 18 2018
.SHORT TERM...(Today and tonight)
Issued at 327 AM MDT Sun Mar 18 2018
A vigorous upper level trough will move from the Great Basin across 
Colorado with a closed low developing over sern CO/nern NM by early 
this evening.  The low will then move quickly into the srn plains by 
late tonight.  Overall will see decent mid level ascent as the 
trough moves across later today and this evening with favorable 
lapse rates.  Soundings show enough instability for some tstms as 
well later this aftn and evening.
At the sfc, a low will intensify over sern CO this aftn and then 
move eastward tonight. Low lvl flow over nern CO will become 
mainly northerly this evening with gusty winds overnight. Big 
question still remains as to how fast rain will change to snow at 
lower elevations. Buffer soundings range from 03z along the front 
range to around midnight further east. The wildcard is expected 
convection which could turn rain to snow an hour or two earlier. 
This would lead to potentially higher snow amounts than what I'm 
currently forecasting. Thus overall confidence is still rather low
as to what may transpire. Naturally if convection ends up being 
snow, snowfall rates of 2 to 3 inches per hour could occur for a 
few hours in some places from Denver east and south. With 
northerly low lvl flow my highest confidence would be over the 
Palmer Divide towards Limon so will issue an advisory for those 
areas. Other areas further north (Denver Metro for example) may 
need an advisory as well but as mentioned abvove confidence is not
as high.
For later tonight the upper level system will move quickly eastward 
with snow ending from west to east across the plains overnight.  In 
the mountains orographic component will be favorable overnight and 
cross-sections still show quite a bit of moisture so expect periods 
of lighter snow will continue through the night. 
.LONG TERM...(Monday through Saturday)
Issued at 327 AM MDT Sun Mar 18 2018
Storm system will be shifting east rather quickly and exiting the
eastern plains Monday morning. Still expect some light snow and
blowing snow over the eastern plains through mid to late morning,
but additional accumulations should be an inch or less. In the
mountains, scattered snow showers will likely continue off/on
through the day with modest orographics, moisture, and decent
instability. By afternoon, enough daytime heating and 
destabilization combining with cold advection aloft may allow a 
few light snow showers to spread from the higher terrain back
into the I-25 Corridor. Gusty north/northwest winds will continue
across the plains with gusts to 35-40 mph expected.
By Monday night, mainly dry conditions should prevail although
there's still sufficient mid level moisture to keep a few snow
showers in the forecast across the mountains. Don't expect more
than an inch or so of accumulation.  
For Tuesday and Wednesday, look for drier and warmer weather to
redevelop as a flat upper level ridge builds over the Central
Rockies. Temperatures should rebound to above normal levels by
Wednesday as 700 mb temps warm above 0C. That should push highs
into the lower 60s over most of the plains.  
Warm advection continues into Thursday when highs should push into
the lower 70s across the plains. Meanwhile, in the mountains a
subtropical plume of moisture arrives which should bring mostly
light rain and snow showers given the warm advection and southwest
flow aloft. There is an opportunity for accumulating snowfall
Thursday night into Friday across the mountains, depending on 
strength of an embedded short wave and cold advection aloft. 
Medium range models including the EC and GFS are still showing
potential for cooling and a chance of rain/snow by next weekend.
So far models seem rather progressive, but there's still potential
for a deeper trough development. 
.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 327 AM MDT Sun Mar 18 2018
A sfc low will intenisfy over the Palmer Divide today so winds 
should become more northeast by midday thru the aftn.  Expect 
showers and a few tstms will begin to develop by 21z and continue 
into the evening hours.  At this time expect rain to change to snow 
around 8 pm or so.  Accumulations up to 2 inches will be possible 
with some potential up to 4 inches due to convection.  Snow should 
gradually diminish by midnight with only some lighter snow between 
midnight and 3 am.  Winds this evening will become north to 
northwest at 15 to 25 mph with gusts up to 35 mph.  Winds should 
gradually decrease around midnight. 
Issued at 327 AM MDT Sun Mar 18 2018
Elevated fire danger will develop over Lincoln county this afternoon 
due to gusty south to southwest winds and low humidity levels.  Fire 
danger will decrease this evening as a cold front moves across.
Winter Weather Advisory from noon today to noon MDT Monday for 
Winter Weather Advisory from 7 PM this evening to 6 AM MDT 
Monday for COZ041-046.
LONG TERM...Barjenbruch