Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 161549
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
949 AM MDT Sun Apr 16 2017

.UPDATE...
Issued at 939 AM MDT Sun Apr 16 2017

Northern Colorado remains under a moderate west to southwest flow
aloft. Airmass is still relatively dry with pw values around a
third of an inch and a bit higher over the eastern plains. There
is a modest southeast low level flow on the plains which is
bringing higher low level moisture into the area with even some
increasing low clouds over Lincoln and southern portions of Elbert
Counties. With this flow patter, Denver cyclone and convergence
zone developing and looks to be the focus for isolated showers and
thunderstorms this afternoon. Looks like most of the activity will
be just east and south of the Denver area, mainly over the Palmer
Divide. CAPE values in the 400-800j/kg so any storms will likely
be under severe limits. Previous forecast has this focus area
already well in hand and only minimal changes needed to forecast.
Too dry really for much of any convection especially further west
into the mountains.

&&

.SHORT TERM...(Today and tonight)
Issued at 301 AM MDT Sun Apr 16 2017

A flat upper level ridge of high pressure will be over Colorado
through tonight with a light to moderate westerly flow aloft.
Mid level qg ascent nearly neutral this aftn through tonight. In
the mountains, it will be dry with mainly high level moisture
moving over the region. Overall the sfc pressure gradient across
the area will be fairly weak, so strongest winds in the mountains
will be near the ridgetops and diurnally driven in the valleys.
Across the northeast plains, generally dry and mild with
temperatures around 5 degrees warmer than yesterday. Generally
southeasterly winds across the plains today which should help
induce a Denver cyclone. A few thunderstorms may develop along the
resulting convergence line, mainly south and east of Denver late
this afternoon and evening. Boundary layer computed CAPES in the
200-600 j/kg range around 00Z. Not much to the west except maybe
west and southwest of the Denver area. Better low level moisture
gradually advecting northwestward into the cwa overnight. Could
see some patchy fog developing across the northeast plains late
tonight.

.LONG TERM...(Monday through Saturday)
Issued at 301 AM MDT Sun Apr 16 2017

An upper level trough will move across the Northern Rockies Monday
with a surface low tracking across Wyoming. A trailing dry line
will move across eastern Colorado Monday afternoon and evening.
Airmass will be moist and unstable enough for thunderstorms east
of the dry line over the far eastern plains. Other than
convergence along the dry line, forcing will be weak. At this
time, thinking isolated thunderstorms will be possible along and
east of the dry line. With CAPE up to 1000 J/kg, a few of the
storms could be strong with hail size approaching one inch. The
chance for storms will move east of the state along with the dry
line Monday evening. Fire Danger will be elevated Monday west of
the dry line due to gusty west winds and low relative humidity.
Will continue with the Fire Weather Watch for Monday.

Southwest flow aloft will prevail over the region Tuesday around
an upper level ridge over the south central part of the country.
Moisture will start to increase as its transported from the
Pacific. There could be a few showers over the mountains Tuesday
afternoon. The best chance for precipitation over the mountains
will be Tuesday night and Wednesday when the jet passes over the
state. Temperatures will remain mild over the area under this
pattern.

Strong west-southwest flow aloft will continue to produce snow
over the mountains with scattered rain showers in the valleys
Wednesday. Cold air advection will lead to good lapse rates and
should result in orographic snow over the mountains. A northerly
behind a cold front will bringing cooler air into the state. The
ECMWF shows light QPF over the plains Wednesday afternoon. This
is likely due to it becoming slight unstable during the afternoon
and will have low pops in the forecast.

Short wave ridging moves across the state Wednesday night and
early Thursday. This should bring precipitation to an end
Wednesday evening. The next Pacific system moves into the Great
Basin Thursday afternoon. This may result in the scattered
showers and thunderstorms over the mountains and along the Front
Range. Will continue with the scattered pops for Thursday
afternoon.

Models then show this trough strengthening into a closed low
Thursday night. The 00z ECMWF has shifted to the north with this
system. It shows a closed low over eastern Utah Thursday night.
Then it tracks across southern Colorado Friday. A favorable track
for significant precipitation along the Front Range. The GFS is
farther south and would favor southern Colorado for heavier
precipitation. Thursday night and Friday are expected to be wet
regardless of the model, just how much is the question. Snow
level starts off above 10000 feet Thursday evening and then falls
into the foothills by Friday morning. Can`t rule out snow for the
Front Range and near by plains on the tail end of this storm late
Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 939 AM MDT Sun Apr 16 2017

Increasing south to southeast winds at kden/kapa this morning with
low level southeast flow on the plains. Set up for denver cyclone
developing and this will likely turn winds more north to northwest
especially at bjc and even KDEN later this afternoon. Will make
some adjustments to the wind forecast for this afternoon.
Convergence boundary set up to be just east of kden to kapa line
and will keep thunder out of forecast for now.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Monday afternoon through Monday evening
for COZ240-241-245.

&&

$$

UPDATE...Entrekin
SHORT TERM...Cooper
LONG TERM...Meier
AVIATION...Entrekin



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