Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 150342
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
942 PM MDT Mon Aug 14 2017

.UPDATE...
Issued at 935 PM MDT Mon Aug 14 2017

Updated first period forecast and forecast grids to account for
the extended line of t-storm activity creeping eastward across the
plains this evening. Storms in the past hour have expanded in
coverage moving in the elongated zone of higher CAPE sitting over
ern Elbert, Lincoln, Washington and Logan Counties. Past hour
storms in the Morgan County area produced copious amounts of
rainfall with radar estimates anywhere from 1.3 to 2.7 inches of
rain across central and eastern sections of that county. A flash
flood warning is presently in effect for east central Morgan
County centered on the city of Brush on the South Platte River.
This line of storms is projected to continue its eastward progress
across remaining eastern sections of the CWA over the next 2-3
hours. Heavy rainfall, small winds and strong gusty winds main
threats. Rainfall rates up to 1.5 inches per hour also a
possibility with some of these storms. Elsewhere, t-storm threat
has pretty much ended with arrival of drier air. Finally, left
mention of patchy/areas of fog late tonight across the northeast
corner of the state with partial clearing.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 308 PM MDT Mon Aug 14 2017

This aftn the lower levels of the atmosphere have dried out with
dewpoints dropping into the 30s at KDEN. The max at DIA has hit 90
before the clouds moved in, the last one since 92 on the 4th. Still
enough mid level moisture around to support a few thunderstorms
this evening. Best CAPE values however will be further east,
ranging from 500-1000 j/kg. Strong storms possible there with
heavy rain and wind gusts in the 50-60 mph range, but weaker
storms elsewhere with less moisture and limited CAPE. Will keep
scattered weaker storms in the high country early this evening,
more isolated over the urban corridor, then scattered further east
where better moisture will be. The flow aloft will be
southwesterly, with a weak upper trough to the northwest of CO,
stretching from western MT into northern NV late around 00z. On
Tuesday it will be cooler and wetter. The trough axis will stretch
from western WY into central NV at 12z. There may be some light
showers in the mountains in the morning especially north of
Interstate 70. By the afternoon, scattered showers and
thunderstorms will spread to the south and east, with the best
pops over along the northern tier counties. Overall, the NAM and
GFS both show weak mid level QG ascent over the region on Tuesday
morning will get more consolidated and shift more into east
central/southeast CO on Tuesday with cooler air moving in from.
the north. This allow weak northeast winds to advect the the
boundary layer theta-e max along the eastern border westward
toward the Urban Corridor in the aftn. Better instability with SPC
placing most of northeast CO in the marginal risk of severe, with
the slight risk along the eastern CO border. NAM12 forecast
soundings for Tuesday range from around 1000 j/kg for the Urban
Corridor to over 2000 j/kg over the northeast plains, with
precipitable water values back over one inch.

.LONG TERM...(Tuesday night through Monday)
Issued at 325 PM MDT Mon Aug 14 2017

The upper level pattern across the western United States will be
undergoing some changes through this week, but the resulting
weather over Colorado will be little changed. A lack of ridging
across the western United States is going to allow mid level
moisture to continue moving across the Rocky Mountain West which
will feed afternoon thunderstorm activity each day. Early in the
forecast period, an upper trough which is over eastern Nevada this
afternoon will be shearing out and moving across northern Colorado
Wednesday morning. A surge of cool temperatures at low levels will
also move into the region that morning. Dynamic forcing associated
with the passing upper disturbance may extend Tuesday evening
showers over the mountains through most of the night. Temperatures
on Wednesday will also be cooler because of the presence of the weak
cold front. Through the latter half of the week, the GFS and ECMWF
show weak upper ridging developing over the southwestern United
States, but the weak mid level flow will also allow a resurgence
of monsoonal flow into the Four Corners region. This will bring
more moisture over Colorado, feeding additional shower development
over the mountains each day. Temperatures will warm back up to
seasonal normals, but the unsettled pattern of afternoon showers
will also prevail. This pattern looks to continue until either a
much stronger ridge builds over the southwest, or a potent upper
trough develops and sweeps down out of Canada or the Pacific
Northwest.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 935 PM MDT Mon Aug 14 2017

VFR conditions anticipated at denver air terminals for the
remainder of the night as skies go from partly cloudy to clear,
and back to partly cloudy with the next wave of mid-level
moisture moving in from the west. Southerly winds will prevail at
speeds of 5 to 13 kts, with the lighter speeds at KBJC.

&&

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

$$

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



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