National Weather Service Forecast Discussion

000
FXUS65 KBOU 201611
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1011 AM MDT Sat Jul 20 2019

.UPDATE...
Issued at 1011 AM MDT Sat Jul 20 2019

North to northeast winds behind a cold front will continue to
transport moisture into the area today. Cold air advection will
make for slow warming today. Highs are expected to top in the 80s
for most area.

Thunderstorms will return this afternoon with the increase in
moisture. Mixed Layer CAPE reach 1500-2500 J/kg with the highest
CAPE along the Front Range southeast into Lincoln county. Shear
will be marginal for severe storms, but there should be enough for
some severe storms. Expect the initial storms along the Front
Range to pose a hail threat. As storms propagate eastward, winds
will become the main threat. Models are good agreement that storms
will move across the area from mid afternoon through mid evening.
Will bump PoPs into the likely category for the Urban Corridor
and near by plains.

&&

.SHORT TERM...(Today and tonight)
Issued at 311 AM MDT Sat Jul 20 2019

WSW flow aloft will be over the area today thru tonight. For
today, confidence isn`t high with respect to pops or highs across
nern CO. Low cloud imagery shows a front from east central WY
into nwrn NE. This front will reach the WY-NE border around 12z
and then move across the rest of nern CO during the aftn. Thus
will see quite a variance in temps across the plains by aftn.
Readings along the WY-NE border may not get above 80, while
further to the south, highs reach the mid to upper 90s over srn
Lincoln. Along the front range urban corridor, readings may still
reach the upper 80s to lower 90`s around Denver before cooler air
spreads in by mid to late aftn.

As for convection, most of the plains will be capped behind the
front with the lowest CIN values from the foothills across the
Palmer Divide.  Overall, expect sct tstms will develop over the
higher terrain by early to mid aftn and then consolidate into a line
of storms as they move generally eastward across the plain by late
aftn into the evening hours.  MLCAPE values will generally be in the
2000-2500 j/kg range with up to 3500 j/kg over the east central
plains. Mid level flow is around 20 kts with somewhat warm mid
level temps. There will be some severe potential with marginal
large hail initially, however, as storms form into a solid line,
strong winds from wet microburst activity may evolve across
portions of the east central plains. Also, will likely see heavy
rain with some spots getting an inch or more as the storms move
across.

Overnight, a well defined disturbance now over swrn Utah, will move
across nrn CO.  This feature could bring a chc of showers and storms
to the higher terrain overnight.  Over the plains, if the airmass is
worked over by aftn and evening storms, not sure how much additional
activity there will be with the disturbance late tonight.

.LONG TERM...(Sunday through Friday)
Issued at 334 AM MDT Sat Jul 20 2019

Sunday through Thursday upper level high pressure will be
centered over the Four Corners Region with the CWA being under the
influence of a north to northwesterly flow aloft. Recycled
monsoonal moisture trapped underneath the high, combined with
daytime heating, and an occasional upper level disturbance will
produce scattered afternoon and evening showers and storms through
the period. The far northeastern plains may be the exception and
see only isolated activity due to lower instability. Upslope flow
behind a frontal passage late Sunday may result in more numerous
activity across the foothills, adjacent plains and Palmer Divide.
With PW`s between 1.00" and 1.25", some of the storms could
produce heavy rainfall Sunday afternoon and evening. The storms
should be moving at a pretty good pace which should limit the
flash flood potential. Soundings are also showing CAPES over 1000
J/KG and some shear which could support one or two severe storms.
However, 500 mb temperatures around 20 degrees F may limit hail
size to below severe limits.

A cooler airmass behind the front should keep Monday`s high
temperatures on the plains only in the 70s with limited
precipitation chances due to a possible cap. Showers and storms
will be more likely further to the south and west where greater
moisture convergence and instability exist. This includes the
foothills, South Park and areas from southern Metro Denver south
across the Palmer Divide. Some of the storms could produce heavy
rainfall and small hail. In addition, there is the potential for
localized flash flooding over South Park due to slow storm
movement. A warming trend is expected into the middle of the week
with highs reaching the 90 degree mark on the plains by Wednesday.

On Thursday, the upper level ridge begins to shift south into the
Desert Southwest with possibly another cold front moving across
the northeastern plains. As a result, the chance of storms is
expected to continue through the end of the work week with
temperatures on the plains dropping back into the 80s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1011 AM MDT Sat Jul 20 2019

Northerly winds behind a cold front will turn to the northeast
through the day. Scattered thunderstorms will start to form around
20Z over the higher terrain to the west of the Denver. The storms
will spread east through the rest of the afternoon and evening.
If KDEN takes a direct hit from a stronger storm, visibilities may
briefly drop to 3 miles with mvfr ceilings. Outflow winds of 40
to 50 knots and hail may also occur.

For this evening, the HRRR continues to show additional weaker
storms thru 04Z. Outflow boundaries will continue to produce
chaotic winds through the early evening hours. Would expect winds
to become more southerly by 06z.

Low clouds are expected to form after 06Z over parts of eastern
Colorado. There is a chance these low clouds make it into the
Denver area.

&&

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

$$

UPDATE...Meier
SHORT TERM...RPK
LONG TERM...jk
AVIATION...Meier

NWS BOU Office Area Forecast Discussion