Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211644
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1044 AM MDT Sat Apr 21 2018

.UPDATE...
Issued at 1044 AM MDT Sat Apr 21 2018

The wrap-around flow behind the departing upper level low is
producing a persistent band of light snow along the Front Range
this morning. Some areas are picking up light accumulations on
grassy surfaces, but roads are staying bare and wet, even the well
travelled routes in the mountains. Web cameras at Camern Pass and
Willow Creek Pass do show some accumulation. The center of the
upper circulation is now moving into the Oklahoma Panhandle and
will continue its eastward track through this evening. Conditions
over northeast Colorado should be slow to improve as cool, moist
air continues coming into the state. HRRR runs indicate that
precipitation will be coming to an end shortly, but radar trends
show a pretty good fetch of precipitation that extends all the way
to north of Scottsbluff, in the Nebraska Panhandle. Will not make
any changes to the forecast, as a gradual improving trend is
already advertised. Since roads in the mountains are staying in
pretty good shape, and no heavier shower activity is expected,
will cancel the Winter Weather Advisory shortly.

As precipitation winds down this afternoon and some clearing is
possible tonight, the moist airmass may produce areas of fog
overnight. Will be assessing the amount of fog to expect in
preparation for the afternoon forecast package.

&&

.SHORT TERM...(Today and tonight)
Issued at 440 AM MDT Sat Apr 21 2018

Low center wobbling near Pueblo at this hour and has produced a
nice band of precipitation wrapping around the north side over
northern Colorado. Pesky tongue of dry air aloft continues to
extend to near Denver. The tip of this filled with convection for
a few hours, which is when we had our snow around Denver, but this
adjustment since waned and it looks like the best lift today will
be mainly north and east of Denver. Those areas should have steady
light precipitation this morning that gradually fades during the
middle of the day as the comma cloud gets cut off from its
moisture source and weakens. Areas further south, including
Denver, should just have very light precipitation assisted a
little by light upslope northerly winds. Models are keeping some
weak convection in the remnant moisture pool as it rotates
southward across eastern Colorado this afternoon. Some have one
batch of light showers over the plains and another in the
convergence over the foothills, while others appear to have drier
and/or stabilized over the mountains by mid afternoon. Current
forecasts have low PoPs roughly coinciding with that pattern, so
they look good. It`s currently cold enough for snow almost
everywhere, but not sticking to much below 5-6 thousand feet. With
a few degrees of warming early this morning, the plains should go
back to rain. With the persistent clouds today, I lowered our high
temperatures a little, in line with consensus guidance.

Fairly quick clearing on tap for this evening, though some clouds
may remain over the mountains. With a moist ground and not so much
heating today, there should be areas of fog developing after
midnight except in areas with drainage winds. Lows on the plains
will be near or a little below freezing.

.LONG TERM...(Sunday through Friday)
Issued at 440 AM MDT Sat Apr 21 2018

Sunday and Sunday night, the ridge axis will over the state with
a weak westerly flow over the cwa. The models generate a little
qpf over the mountains in the afternoon and evening, so will keep chc
pops there until 03z. Monday and Monday night, the ridge axis
will shift to the east with the westerly flow aloft increasing.
Breezy southerly winds in the afternoon will allow for temperatures
to climb back in the mid 60s to lower 70s. The next system, over
southwestern MT midday Monday, will slow down and split as it
approaches Colorado. Models generate weak mid level qg ascent with
the trough axis still to the north of CO by 12z Tuesday. The
models develop showers in the mountains Monday afternoon, then
spread showers eastward along the WY/NE borders Monday evening is
a cold front moves into the northeast plains. By 06z Tuesday, the
cold front will be parked along the foothills and Palmer Divide,
with isolated to scattered showers across the Urban Corridor and
northeast plains. It will be cooler on Tuesday but remain
unsettled, with a jet max over the cwa and the mid level trough
axis stretched along the northern CO border. The trough axis
slides to the south by Tuesday evening, with a drier northerly
flow over the region Tuesday night into Wednesday. The pattern
will remain fairly progressive. A ridge axis over northeast CO at
00Z Thursday, will shift south and east Wednesday night. Then another
short wave trough will drop out of the northern Rockies and
across the cwa Wednesday night and Thursday morning. This will
result in slightly cooler temperatures and another chance for
pcpn across the area. By Thursday evening, a drier northerly flow
will develop as the system passes to the south and east of the
area. A dry northerly flow aloft is then progged to be over
northeast CO on Friday and Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1044 AM MDT Sat Apr 21 2018

Low ceilings persist at the Denver area airports late this morning
and a band of light snow continues along the I-25 corridor. Most
recently, echo strength on radar seems to be decreasing, so an end
to the light precipitation and gradually lifting ceilings may
occur in the next couple hours. Still expect to see ceilings
remain in the 1000-2000 foot AGL range through the afternoon with
a few breaks in the clouds late in the afternoon. Further
improvement is expected this evening, but clearing skies and light
winds may combine with the low level moisture that is in place to
produce areas of fog overnight and through tomorrow morning. This
could lead to more IFR/LIFR conditions after midnight tonight.

Regarding the light snow fall this morning, no accumulations are
expected as the snow is melting as it hits the ground.
Temperatures should also climb to the mid and upper 30s through
the afternoon.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...Dankers
SHORT TERM...Gimmestad
LONG TERM...Cooper
AVIATION...Dankers



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