Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 181200
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
600 AM MDT Thu May 18 2017

.SHORT TERM...(Today and tonight)
Issued at 559 AM MDT Thu May 18 2017

...Mountain Snow...Showers and Thunderstorms...A Few Possibly Severe
on the Plains...

Complex weather pattern with multiple concerns.  Intense low
pressure system currently spinning over Salt City area is ejecting a
major shortwave northeast across the 4 corners this morning.  This
shortwave will bring a round of precipitation to the area this
morning, falling as snow above 6500-7000 feet and rain showers
below. In addition, there will be embedded thunderstorms in all of
this with occasional lightning activity noted through the night
across southern Colorado.  This morning, snow has been falling down
to about 6500 feet with snow noted in web cams at Woodland Park,
down Ute Pass and across northern El Paso County including Monument,
Black Forest, and the northern reaches of Colorado Springs.  Roads,
in large part, look just wet or slushy with the most slush appearing
on the roadway in Monument.  The Cheyenne Mountain snow stake at
9440 feet was showing about 2 inches at 5 am.  It looked like
Woodland Park and the higher reaches of Ute Pass and Monument all
had about the same, just eye-balling it.  Wet snow will continue to
fall above 6500-7000 feet across the Pikes Peak region through the
morning and possibly early afternoon and then begin to decrease.
What will happen overnight remains in question as new model runs
coming in this morning are changing things up on us.  Old runs had
precipitation continuing across mainly the Pikes Peak Region
overnight while new runs are shifting the focus for precipitation
much farther south.  This is due to a shift, a big shift, in the
track of the upper low.  Old runs took it across the Palmer Divide
late tonight.  New runs are taking it across northern New Mexico.
This appears to be the result of the intensity of the ejecting
shortwave that is headed our way this morning.  It is so strong that
it may cause the parent upper low over Salt Lake City to get
dumbbelled strongly southeastward into northern New Mexico.  If this
happens, the focus for precipitation will shift south tonight,
bringing a much bigger threat of precipitation to the southern tier
of the forecast area than previously thought.  It would also shift
the focus away from the northern tier, including the Pikes Peak
Region.  So, have started trending that way in this morning`s
forecasts. But, with this being such a late breaking change in the
models, there is much uncertainty.  It could still work out the way
that was previously thought.  For now, it is best to go with a
Winter Storm Watch for the Palmer Divide and all of the eastern
mountains areas, not knowing exactly where the heaviest snow will
fall. Very challenging to figure it out when things are changing at
the last minute.  Just don`t have the confidence one way or the
other.

Another concern today will be the potential for severe weather over
the far eastern plains this afternoon.  Several high res model runs
are showing the potential for severe storm develop across the plains
east of the I-25 corridor in the afternoon, and possibly early in
the afternoon. The Storm Prediction Center has this area in the
marginal risk area at this time but it will be close.  There will be
a ribbon of decent CAPE out there.  There will also be good shear
and instability across the plains.  Couple this with good lift from
the upper low and there could be some severe weather.  Large hail
and strong winds will be the main risks but there is also potential
for a tornado. Will have to monitor things closely in the afternoon.

Another possible concern with this storm is the potential for heavy
rain on burn scars.  Older model runs suggested a low potential for
this.  But, with recent runs, the risk for burn scar flooding has
increased.  There could be some north to south training convection
over the burn scars this morning.  The Waldo Canyon scar may be
alright with primarily snow falling across the scar.  However, the
scars farther south, such as the Junkins and Hayden Pass scars, may
be subject to training rain showers which could lead to problems.
Will have to monitor this closely today as well.

.LONG TERM...(Friday through Wednesday)
Issued at 559 AM MDT Thu May 18 2017

Some relatively major revisions were needed due to computer
simulations/real time data indicating that storm system will be
heading further south than earlier anticipated.

Meteorological focus remains on the amount of impact that upper
systems in combination with north to northeasterly surface surges
will provide the forecast district during the longer term.

Primary meteorological challenges continue to include, but are
not limited to temperatures, pops, qpf, snow amounts over
primarily higher terrain locations and gusty winds at times.

As alluded to earlier, latest computer simulations(especially the
HRRR and NAM), PV analysis and forecast model soundings now
indicate that closed upper low will track a couple of hundred
miles further south than earlier projected with the closed upper
low now expected to move across northern New Mexico Friday before
moving into western Kansas by Friday evening and then shifting
into South Dakota Saturday. Recent GFS also trending further south
with the upper low but not as far south as the NAM and HRRR.

Due to the further southern track of the upper low, have issued a
Winter Storm Watch for the Sangre de Cristo Mountains, Wet
Mountains, Northern El Paso County and the upper Huerfano River
Basin Below 7500 Feet from 06Z Friday to 00Z Saturday. In
addition, existing inherited winter weather highlights remain in
place over the forecast district into Friday.

Then, from Saturday into Wednesday, upper impulses interacting with
northerly/northeasterly surface surges at times will be capable of
producing periods of showers and thunderstorms as well as higher
elevation snow at times in combination with generally below
seasonal later May temperatures.

Below seasonal temperatures are still anticipated over the
forecast district from Thursday into the weekend with temperatures
then attempting to climb closer to mid to late May climatological
averages next week. It still appears that minimum temperatures
challenging the freezing mark will be possible over many
Interstate 25 corridor locations both Friday and Saturday morning,
although several recent computer simulations have begun backing
off on the depth of the colder air during this time-frame.

Finally, the highest potential of stronger gradient winds during
the longer term are anticipated Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 559 AM MDT Thu May 18 2017

Major spring storm will track across the flight area over the next
24 hours.  System will bring widespread MVFR to LIFR flight
conditions to the area, particularly from the I-25 corridor
westward.  Activity east of the corridor will tend to be more
scattered.  Snow levels will be around 6500 to 7000 feet with rain
below.  Embedded thunderstorms producing hail and wind will be mixed
at times.  Also, a tornado cannot be ruled out across the far
southeast Colorado plains during the afternoon from severe
convection.

The KCOS, KPUB and KALS TAF sites can all expect bouts of
precipitation over the next 24 hours leading to periods of MVFR to
LIFR flight conditions.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...

Winter Storm Watch from late tonight through Friday afternoon
for COZ072>075-079-080-084-087.

Winter Weather Advisory until 6 PM MDT Friday for COZ058>060-066-
068-081.

Winter Storm Warning until 6 PM MDT Friday for COZ082.

&&

$$



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