Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 182037

Area Forecast Discussion
National Weather Service Denver/Boulder CO
237 PM MDT Wed Apr 18 2018

.SHORT TERM...(This evening through Thursday)
Issued at 237 PM MDT Wed Apr 18 2018

Upper level ridge will reside over Colorado tonight. Mostly clear
skies, dry airmass, and light winds will result in chilly
overnight lows. Readings are expected to fall into the mid 20s to
lower 30s. The upper level ridge will shift east of Colorado as an
upper level low moves onto the California coast. This low will
bring the next round of precipitation later in the week. Southwest
flow aloft will increase Thursday as the upper level low nears
the region. At the surface, a low forms over the Great Basin and
produces gusty south- southeast winds over eastern Colorado. Gusts
to 40 mph will be possible during the late afternoon. The south-
southeast winds will slowly increase moisture. This should keep
relative humidities in the upper teens to lower 20s Thursday
afternoon and above Red Flag criteria.

.LONG TERM...(Thursday night through Wednesday)
Issued at 237 PM MDT Wed Apr 18 2018

For Thursday night into Friday the closed low will be over southern
Utah by 00z Friday and become stacked by 12z over central Utah
pulling moisture over CO from the south. Upper levels will become
more diffluent with the approaching jet as precipitation increases
across the western portions of the state and higher terrain.
Instability increases over the mountains through Friday morning
bringing rain and snow showers with a chance of thunderstorms. QG
lift increases steadily Friday with upwards of -20 to -30 mb of
ascent by Friday evening. At this time thermal profiles indicate
cooling in the mid levels Friday evening but still fairly warm on
the plains in the low levels. Expect precipitation to fall as rain
initially then possibly change over to a rain and snow mix late
Friday night. At this time current model soundings show a cooling
column with the frontal passage and increasing cooler NE flow. This
could be enough combined with the enhanced lift to change rain over
to snow on the plains by early Saturday morning. By Saturday morning
the low pressure system will begin to transition southeastward
pulling moisture and keeping the east and northeastern portions of
the state in the deformation zone and with continued precipitation
through the afternoon hours on Saturday. Subsidence will start to
increase by Saturday afternoon as the low center pushes into the TX
panhandle. Snow will linger over the mountains through Saturday
night into Sunday but clear out over the plains by Saturday evening.
Current accumulation projections have 4 to 8 inches over the higher
foothills will the help of increased upslope some areas could see up
to 10 inches. For the higher terrain amounts could be in the 6 to 12
inch range by late Saturday. At lower elevations it will be hard to
pinpoint amounts with the changeover timing and duration still in
question, however, models are showing up to half and inch or
slightly more for QPF by Saturday afternoon.

Sunday will see a gradual clearing with just light snow over the
higher terrain as upper level ridging moves in. This gradual warming
trend will bring highs back into the mid to upper 60s on Sunday and
near 70 by Monday. The next disturbance is projected to move into
the area on Tuesday but timing still varies between models.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 237 PM MDT Wed Apr 18 2018

VFR conditions will prevail through the next 24 hours under
mostly clear skies. North to northeast winds will turn clockwise
through early evening. Winds will end up southeast around 03Z, and
remain southeasterly through Thursday. Wind speeds increase
Thursday with gusts to 30-35 knots possible after 18Z Thursday.


Issued at 237 PM MDT Wed Apr 18 2018

South-southeast winds will increase ahead of a low pressure
system over the Great Basin Thursday. By afternoon, wind gusts up
to 40 mph are expected over the eastern plains. Moisture will
slowly increase due to the south-southeast winds transporting low
level moisture into the area. This is expected to keep relative
humidities in the upper teens to lower 20s, above Red Flag




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