Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 170231
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
831 PM MDT Mon Apr 16 2018

.UPDATE...
Issued at 820 PM MDT Mon Apr 16 2018

Main concerns will be Critical Fire Weather and high wind
potential on the plains for Tuesday. Have already updated and
expanded the high wind watch to include much of the northeast
plains, including Denver in a high wind watch for Tuesday
afternoon and early evening hours. Strong upper trof and cold
front will sweep across Colorado during the day on Tuesday with
strong subsident flow kicking in behind it. QG fields showing
impressive +40-55mb/hr descent behind the trof. In addition,
tightening surface pressure gradient across the state increasing
to near 16mb from GJT to DEN. Given 50kt of wind is just above the
surface, won`t take much to get the high winds with sufficient
mixing expected. For now will go with the additional areas to a
watch but wouldn`t be surprised to see widespread high winds from
Denver eastward through the plains. Surface winds will already by
increasing by later tonight ahead of the trof from the southwest
over the mountains and foothills.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 231 PM MDT Mon Apr 16 2018

A prefrontal airmass will move in tonight leading to lows in the
upper 40s over the plains and cooler across the far northeast
corner because of snow cover with low in the lower 30s. Over the
mountains lows should be in the mid 20 and 30s. Tuesday`s highs
are expected to be in the 60s on the plains with 30 to 40 degrees
F over the mountains.

A trough will deepen over the mountains late tonight bringing
gusty winds, to 60 mph, and a chance of snow showers. Tuesday
morning the snow showers will become likely for the high mountains
and winds will spread down the the lower elevations blanketing
Northeast Colorado by afternoon. Areas near the northern boarder
will have a slight chance of rain or snow from afternoon to
evening. Due to the high winds expected, a High Wind Watch has
been issued for eastern Elbert and Lincoln Counties.

.LONG TERM...(Tuesday night through Monday)
Issued at 231 PM MDT Mon Apr 16 2018

Tuesday night into Wednesday a positively tilted trough will be over
eastern CO with the surface low over Kansas. Model cross-sections
show continued, deep moisture in the higher terrain with some edging
out over the foothills Tuesday evening. Most areas along the base of
the foothills will stay dry with the plains seeing no precip late
Tuesday given the increased NW flow and downsloping. A few inches of
additional snow will be possible over the mountains into early
Wednesday.

For Wednesday into Thursday an upper level ridge combined with
increased subsidence will bring a warm and drying trend.
Temperatures for Wednesday and Thursday will be closer to seasonal
normals with highs in the mid to upper 60s. For Wednesday, an
increased pressure gradient will keep gusty winds on the
plains...especially over the far NE section and near the Wyoming
border. Sustained winds of 10 to 15 mph with some gusting up to 30
mph will be possible by Wednesday afternoon. For Thursday upper
level ridging will be firmly in place with temperatures inching up
into the upper 60s on the plains and 30s to 40s in the mountains.
Mid-level winds will switch to the SW ahead of the next upper level
trough over the west coast of California. Moisture fields are dry
through Thursday, however the surface low that develops over the
four corners region by Thursday night will help to pull some low and
mid level moisture from the Gulf over the eastern portions of the
state. Models are indicating the possibility of a Denver Convergence
zone by Thursday night with the increased SE push. There is some
diffluence aloft overnight Thursday that could help to bring
scattered nocturnal thunderstorms to the plains.

By Friday morning (12z) the upper level low will be over the four
corners region with the low center just slightly varying between
models. It will then progress over the CO/NM border pulling
increased moisture up from the Gulf impacting eastern CO through
Saturday morning. Model cross sections show moisture increasing
through 400 mb with decent QG ascent with -31 mb/hr over the eastern
plains by Friday night. A surface low develops over SE CO by Friday
evening with a cold front bringing winds on the plains into a more
favorable ENE direction. This will enhance upslope flow over the
Front range by Friday evening into the overnight hours. Upper air
soundings are showing precipitation starting out as rain Friday
afternoon and turning over to snow by midnight with the help of the
front and increased upslope. Instability looks high with near moist
adiabatic lapse rates. At this time, the GFS is the most bullish on
QPF with the EC not too far behind. Expect decent rainfall on the
plains before it changes over to a wet snow overnight into Saturday.
This system could also bring higher snowfall amounts in the
mountains Friday and Saturday. Will need to continue to monitor
timing and placement of the low system as this could turn into a
decent weather-maker for NE Colorado.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 820 PM MDT Mon Apr 16 2018

Surface winds finally returning to more normal southwest winds as
surface cyclone played havoc with the winds from late afternoon.
Big impact will be the increasing southwest winds Tuesday morning
and then shifting and increasing to the northwest in the
afternoon. Potential for high winds close to 50kt at KDEN/KAPA
during the afternoon with frontal passage and increased subsident
flow. winds will very slowly decrease Tuesday evening.

&&

.FIRE WEATHER...
Issued at 231 PM MDT Mon Apr 16 2018

The Red Flag Warning has been allowed to continue for the Palmer
Divide on Tuesday due to expected strong winds and low humidity
leading to extreme fire danger.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Tuesday morning through Tuesday evening for
COZ040>051.

Red Flag Warning from 10 AM to 8 PM MDT Tuesday for COZ241-
245>247.

&&

$$

UPDATE...Entrekin
SHORT TERM...Sullivan
LONG TERM...Bowen
AVIATION...Entrekin
FIRE WEATHER...Sullivan


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