Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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462
FXUS65 KBOU 192048
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
248 PM MDT Thu Apr 19 2018

.SHORT TERM...(This evening through Friday)
Issued at 237 PM MDT Thu Apr 19 2018

Upper level low over California and Nevada will track east the
next 24 hours and be centered over Colorado Friday afternoon.
Surface low pressure over the Great Basin will continue to bring
gusty south- southeast winds to the eastern plains tonight with
gusts to 45 mph. The gusty winds will result in mild overnight
lows for many places. Models are in good agreement showing the
left exit region of the jet producing an area of showers over far
eastern Colorado late tonight and Friday morning. A second of area
of precipitation is expected over the Central Colorado tonight
due to diffluence aloft ahead of the approaching upper level low.

South-southeast surface winds continue into Friday as the surface
low and upper level low near the region. This will pump moisture
into the area. Clouds will thicken and lower through the day due
to the increasing moisture and lift. Expect QG ascent to bring
rain and snow to much of the area Friday afternoon. Will upgrade
the Winter Storm Watch to a Warning for the mountains. Snowfall
amounts are marginal for warning criteria. However models indicate
airmass over the mountains becomes unstable with CAPE up to 500
J/kg. Because of this, will go with the warning with some areas
seeing a quick round of heavy snow. Tougher call on how much snow
will fall in the foothills. Snow level starts off high, around
8500 feet and lowers during the afternoon. Period of northeast
upslope winds is short and not that strong, so will go with a
Winter Weather Advisory for the the foothills.

.LONG TERM...(Friday night through Thursday)
Issued at 237 PM MDT Thu Apr 19 2018

For Friday night into Saturday the low pressure system will be in
place over Colorado and stacked through 300 mb. At this time
confidence is high that the mountains and higher foothills will see
decent snow accumulations into Saturday evening. However,
temperature profiles on the plains continue to be tricky. Latest GFS
continues to be on the warmer side with the NAM as the outlier on
the cold side. The 00z EC is in the middle so will most likely lean
to this solution. A surface low to the south over NM will move
eastward increasing NE flow over the plains and keeping much of the
NE region under the deformation zone. This set-up combined with the
stacked and slower low progression could keep precipitation falling
into Saturday evening. At this time QPF totals through 18z Saturday
for the Urban corridor and east are between three quarters of a inch
up to an inch on the EC with less over the east side of DIA and
increasing as you go toward the KS border with the help of increased
lift. Wet bulb zero levels show a decreasing trend after 00z Saturday
with the EC dropping between 5800 and 6000 by 12z Saturday. Between
03 and 06z the cold push from the NE will reach back to the
foothills that will help to cool and saturate the column through 300
mb. Models are indicating cold air damming against the northern
foothills that could significantly add to snow amounts in this area
through Saturday morning. By 18z Saturday the low pressure system
will start to transition to the SE over the TX panhandle while
maintaining the def zone over the east and NE portions of the state.
This will continue light to moderate snowfall into the afternoon
hours. As the storm transitions east-southeastward increasing
subsidence behind it with WAA increasing. This will help to clear
out conditions by the later afternoon hours on Saturday helping to
push daytime temperatures on the plains into the upper 40s to low
50s.

For Sunday into Monday upper level ridging will increase helping to
warm areas back into the 60s with 70s possible by Monday. By Monday
night a shortwave will skirt over the northern portion of the state
bringing snow to the mountains with a slight chance of rain to the
NE plains by early Tuesday morning. The active NW pattern will
continue through mid week bringing additional chances of
precipitation to the region.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 237 PM MDT Thu Apr 19 2018

VFR conditions will prevail through tonight. Low clouds move in
Friday morning, after 15Z with ceilings falling to 3000 to 6000
feet. Ceilings will continue to lower aftet 18Z, with rain likely.
South-southeast winds will continue through tonight. Wind speeds
will increase late this afternoon and evening, with gusts of 30-40
knots at KDEN/KAPA, 22-08z. Winds will be much weaker at KBJC and
generally be northerly.

&&

.FIRE WEATHER...
Issued at 237 PM MDT Thu Apr 19 2018

Gusty south-southeast winds continue east of I-25 through this
afternoon and tonight. The strongest winds are expected late this
afternoon and this evening. Relative humidities will fall into the
lower to mid teens late this afternoon. Will allow the Red Flag
Warning expire early this evening as relative humidities slowly
climb. However, overnight relative humdity recovery will be poor
tonight due to the windy conditions.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for COZ214-216-
240>247.

Winter Weather Advisory from 6 AM Friday to noon MDT Saturday
for COZ031-035-036.

Winter Storm Warning from 6 AM Friday to noon MDT Saturday for
COZ033-034.

&&

$$

SHORT TERM...Meier
LONG TERM...Bowen
AVIATION...Meier
FIRE WEATHER...Meier



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