Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 271038
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
438 AM MDT Thu Apr 27 2017

.SHORT TERM...(Today and tonight)
Issued at 438 AM MDT Thu Apr 27 2017

Water vapor and upper air analysis shows the sharp upper level jet
streak pushing toward the Four Corners area, with broad upper
level divergence noted over Colorado. One band of lighter
precipitation was reaching the mountains, but another stronger and
more convective band associated with strong cold advection will
reach the mountains shortly after daybreak. This band is well
defined on the satellite imagery over northeast Utah at 3 AM. As
orographics and instability increase with the onset of cold
advection, snowfall rates may briefly hit 1-2 inches per hour
across the northern mountains between 7 and 10 AM, with conditions
expected to improve by the noon hour.

The chance of showers will also increase on the plains this
morning with the increase of Q-G lift and the convective nature
of this next band. Have increased PoPs into the likely category
for the most part. Showers may tend to organize as they spread
east across the plains, aided by low and mid level moisture
convergence. Despite the cool temperatures today, enough
instability with the strong cold advection aloft and 500 mb cold
pool of -25C approaching to support a few thunderstorms. The
higher probabilities will be on the eastern plains as heart of
lift arrives later in the morning/early afternoon there, during
peak heating.

For tonight, snow showers will likely continue in the mountains
although for the most part expect them to decrease in intensity
with lower precipitable water and specific humidity. With the jet
axis still to our south, can`t rule out another couple inches and
some travel impacts into the night. Won`t adjust the Winter
Weather Advisory any later at this point given the lighter
intensities expected. On the plains, best chance of rain will
shift to the far northeast corner with downslope drier air pushing
across the rest of the plains and I-25 corridor.

.LONG TERM...(Friday through Wednesday)
Issued at 438 AM MDT Thu Apr 27 2017

Friday night through Saturday will be an active period as a potent
late season storm affects the entire state. Each of the mid-range
models are in decent agreement in swinging an upper low from
eastern Utah, over the Four Corners Region and then across
northern New Mexico. At low levels, a strong cold front will drop
out of Wyoming and across eastern Colorado Friday evening. Strong
and deep upslope flow will develop behind the front, and all the
ingredients should be in place for a night time of snow along the
Front Range and down to the Palmer Divide. 700 mb temperatures are
forecast to drop to about -10C, which will be cold enough for snow
levels to drop down to 5000 feet. Model QPF fields show between
and half inch and one inch of liquid equivalent, which should
deliver a decent shot of moisture to the region. As the snow falls
Friday night, roads shouldn`t be impacted too much, but snow
sticking to recently leafed out vegetation may lead to breaking
tree branches. The two areas that will see more signifcant
accumulations will be the foothills and over the Palmer Divide.
Snow accumulations of 4 to 10 inches will be possible. Will issue
a Winter Storm Watch for those areas, since there is still some
uncertainty on the the exact track of the upper low. If the low
dives farther south than forecast, then the areas with heaviest
precipitation would shift further south, to southeast Colroado and
northeast New Mexico.

The effects of the storm will be felt strongest Friday night and
Saturday morning, with the storm moving out onto the southern
plains. Colorado will remain under cool and unsettled conditions,
leading to some afternoon and evening shower activity due to
daytime heating. Sunday could see another batch of diurnal shower
activity as cool northwesterly flow aloft continues. Cyclonic
northwesterly flow is actually forecast through about Wednesday.
This will keep the chance of afternoon shower activity in for
forecast through then. For the latter half of the week, ridging
finally builds over the southwestern U.S. with drier and warmer
conditions eventually spreading across Colorado.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 438 AM MDT Thu Apr 27 2017

VFR conditions will prevail for the most part, but expect showers
to spread off the mountains and push across the Denver metro area
airports through 18Z. Could see a couple periods of MVFR visibility
reduction down to 5 miles and ceilings near 3000 feet with a
couple heavier showers or an isolated thunderstorm. Chance of
showers will decrease to 30-40% 19Z-23Z with a lower 20% chance of
a thunderstorm. Then mostly dry conditions expected to develop by
01Z with ceilings lifting and breaking. Denver cyclone in place
this morning but sufficient T/Td spreads should keep fog from
forming. Light northerly winds developing through 12Z, and then
increasing to 10-15 knots through the afternoon. Potential
variable winds with gusts to 25 knots near any showers or storms.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM MDT this evening for COZ031-
033-034.

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Dankers
AVIATION...Barjenbruch


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