Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211016
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
416 AM MDT Mon Aug 21 2017

.SHORT TERM...(Today and tonight)
Issued at 416 AM MDT Mon Aug 21 2017

Satellite loop shows mainly high and thin cirrus across the
forecast area, but overall trend has been for more thinning.
Therefore, outside of a couple narrow bands, eclipse viewing
should be relatively unobstructed. There is patchy dense fog over
the northeastern corner of the state, and with additional travel
loads this morning feel an advisory for dense fog is warranted.
This is expected to burn off 8-9 AM with gradual dissipation of
the stratus before the eclipse.

For this afternoon, sufficient destabilization of the atmosphere
may be limited to the mountains and Palmer Divide area given
relatively deep north/northeast flow on the plains. There is also
drying working in from the northwest so see most showers and
storms later this afternoon into early evening being confined to
the mountains along/south of I-70 and then east across the Palmer
Divide. The far eastern plains still have an opportunity for
deeper and stronger convection given more moisture and
instability, but overall threat is shifting slightly south/east of
our forecast area as low level convergence zones pushes south
faster than earlier forecast. Will lower PoPs slightly from
Denver northward to account for the drying from the north.
Of interesting note, the Experimental HRRR shows about 2-5F
cooling associated with the eclipse and significant reduction of
short wave radiation 17Z-18Z. Have opted to show a slight cooldown
during this period in the temperature grids, then a quick rebound
by 20Z.

.LONG TERM...(Tuesday through Sunday)
Issued at 416 AM MDT Mon Aug 21 2017

Weak upslope flow early Tuesday morning may produce patchy fog
across the plains, but at this point it seems like stratus will be
more likely. Some light showers may fall early in the morning,
especially along and east of the Divide. A stronger upslope push
is expected in the afternoon to increase shower and storm activity
especially in upslope favored areas, with the far eastern plains
likely not seeing any activity until that evening. Temperatures
will be cooler east of the Divide, with the plains cooling to
below seasonal norms. Readings should be in the low to mid 80s. A
weak speed max will push into the area Tuesday night to keep the
slight chance of showers and storms over the far eastern plains.

Additional moisture will be drawn up from the desert southwest
Wednesday and Thursday as an upper low off the southern
California coast lifts northeast. Storm coverage will increase and
temperatures will warm back up. As the trough passes over the
state Thursday, expect slightly stronger and wetter storms.

Slight subsidence behind the departing trough will bring less
instability for Friday, but still expecting some activity.
Temperatures will then take a cooling trend as a couple shortwave
troughs originating near the US/Canada border pushes southeast.
Not much moisture associated with these so expecting not much more
than slightly cooler temperatures and isolated diurnally driven
storms. The upper ridge will be building back over the Western US
with drier and warmer conditions possible for early next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 416 AM MDT Mon Aug 21 2017

VFR conditions will prevail. Any fog early this morning will
remain well away from the Front Range airports and over the
northeastern corner of the state. Chance of thunderstorms is
only about 10% 21Z-03Z, with a little higher 20-30% chance of
gusty outflow winds. Most activity should stay south/west of the
metro airports. For later tonight, some stratus with IFR/MVFR
ceilings should develop on the plains, perhaps approaching KDEN
toward 12Z. Will continue to monitor that. Winds will become
north/northeast 10-15 knots 17Z-18Z, and then may transition to
light/variable toward 02Z with potential for weak Denver cyclone
wind pattern through early Tuesday.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 8 AM MDT this morning for COZ048-050-
051.
&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Kriederman
AVIATION...Barjenbruch



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