Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 191642
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1042 AM MDT Wed Jul 19 2017

.UPDATE...
Issued at 1042 AM MDT Wed Jul 19 2017

Not many things to change in the forecast. The upper air pattern
is remaining stable with a strong upper ridge dominating the
weather picture across the southern half of the country. The flow
aloft remains weak, and it becomes a matter of monitoring the
amount of sub-tropical moisture moving into the state from the
desert southwest. The mountains and plains are getting strong
solar heating this morning, so I expect clouds and showers to
begin developing over the high country in the next couple hours,
with scattered thunderstorms through the early afternoon. Isolated
showers will be possible on the plains through later in the
afternoon, with storms developing on outflow boundaries from
earlier showers.  Precipitable water values along the i-25
corridor range from 0.7 to 0.9 inch which is slightly above normal
for this time of year. Satellite imagery is showing moderate
southwest flow aloft at high levels, but model soundings show much
weak flow at lower levels. Storms that develop will be slow
moving and capable of locally heavy rainfall along with some gusty
winds. The HRRR has shower activity over the mountains through
about 00z with aband of convection developing from Denver
northeastward to Sterling by 01z which then continues for a couple
more hours. No need for any highlights at this time.

&&

.SHORT TERM...(Today and tonight)
Issued at 315 AM MDT Wed Jul 19 2017

Little change in the weather pattern since yesterday. West-
southwest flow aloft will prevail around an upper level high over
Oklahoma. This will keep monsoon moisture over the area.
Precipitable water values may increase a little today, around an
inch across the lower elevations. Heavy rainfall will be possible
with some of the storms due to the moisture and slow storm
movement. With a large temperature/dew point spread, gusty winds
will likely accompany the convection. Best chance for storms will
be over the higher terrain where scattered thunderstorms are
expected. Convergence along outflow boundaries may trigger
isolated storms over the plains late this afternoon and evening.
Otherwise, there does not appear to be anything to kick off
storms, like convergence along a boundary yesterday.

It will be another warm day with mid to upper 90s across northeast
Colorado. There is a good amount of mid and high cloud over and west
of the area. If more cloud cover prevails than expected, highs may
fall short of the mid 90s. Though expect enough sun to push
temperatures into the mid 90s at least.

.LONG TERM...(Thursday through Tuesday)
Issued at 315 AM MDT Wed Jul 19 2017

Thursday through Friday, the models to show the center of the
upper ridge moving into the central plains states. This will allow
for the plume of monsoonal moisture to move more directly across
the cwa. The forecast soundings show the precipitable water
values approaching an inch by late Thursday afternoon, then around
1.10 inches on Friday. The storm motions will be slow as well so
locally heavy rainfall will be the primary concern. Models vary
quite a bit regarding the CAPES each afternoon, but 500-1500 j/kg
would appear to be a mean value. Over the weekend, the ridge
flattens and stretches across the entire southern half of the U.S.
The flow aloft over Colorado will be a little drier and more
westerly. The best chance of thunderstorms at that time would
appear to be over southern and eastern Colorado, impacting areas
primarily east of I-25 and south of I-76, with lesser coverage to
the north and west. A weak front will push across the area by
the weekend, and likely settle along the Palmer Divide. This
would also help as a focusing mechanism for tstms there. By early
next week, a ridge tries to re-establish itself over the Desert
Southwest. The flow aloft will remain weak and more southwesterly,
allowing for the plume of monsoonal moisture to advect back into
western Colorado. The best pops at that time will be in the
mountains, with more isolated coverage across the northeast
plains. Overall temperatures will be at to slightly above normal
for Thursday and Friday, which is 90 for Denver. High temperatures
will not be as hot the rest of the period, generally be in the
mid to upper 80s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1042 AM MDT Wed Jul 19 2017

Ioslated thunderstorms are expected over the Denver area through
the afternoon, but not necessarily reaching KDEN. Outlflow from
thunderstorms will probably send boundaries out toward KDEN after
21z. Winds will be light and westerly to northerly ahead of shower
development and then become stronger out of the southwest through
the afternoon. Drainage southerly winds are expected overnight.

&&

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

$$

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


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