Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 192134
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
334 PM MDT Wed Jul 19 2017

.SHORT TERM...(This evening through Thursday)
Issued at 334 PM MDT Wed Jul 19 2017

The upper ridge aloft remains over the south central plains with
weak southerly flow aloft in place across Colorado. Slow moving
thunderstorms have developed over the mountain areas, with locally
heavy rain occurring. Outflow boundaries from these storms may
still generate some thunderstorms on the adjacent plains through
the evening. GPS precipitable water values are in the 0.70 to 0.80
range, so the threat of heavy rain is reduced from some of the
past days.

Overnight, showers will dissipate and skies will clear out. On
Thursday, we will be keeping an eye on a circulation moving out of
west Texas this afternoon. This circulation will be moving over
Colorado tomorrow, and will affect the development of showers
through the day. Monsoonal moisture will be present, so it is
possible that thunderstorms will be capable of producing heavy
rainfall. The situation will be similar to the past several
afternoons. Model QPF fields are not producing especially large
amounts of rainfall, so it won`t be necessary for any highlights
up to this point. The threat will need to be watched out for.

.LONG TERM...(Thursday night through Wednesday)
Issued at 334 PM MDT Wed Jul 19 2017

A shortwave moving across the top of the ridge will stream across
the northern area Thursday night. This will keep scattered storms
across the area that evening decreasing after midnight. With PW
values of 1.1 to 1.5 across the northern plains, and CAPE values
around 1000 J/kg near the state border, will likely see a few
strong to severe strength storms with heavy rain, strong outflow
winds and hail. PW values of 0.75-1.0 inches over the mountains
will keep the threat of heavy rain in the evening.

Confidence in the effects of this upcoming monsoonal moisture
plume is wavering due to models performance. The GFS seems too wet
with its precipitation in regard to it specific humidity and PW
fields, where the NAM seems too dry with respect to its fields.
But overall, the specific humidity is slightly lower than what was
being shown yesterday. Still confident we`ll see heavier rain and
a greater spatial coverage of storms. On Friday, we`ll have a
front pushing down as well from the north to help provide a focus.
PW values of 1.3 to 1.5 inches and CAPE of 1000 to 2000 will allow
for strong to possible severe strength storms again, with brief
heavy rain and strong outflow again with some hail possible.
Mountains will again be under the threat of localized flooding
under stronger storms. Temperatures will be cooler by a few
degrees from increased cloud cover.

Saturday and Sunday will cool back to seasonal normals as a couple
shortwaves push the ridge south. The main moisture plume sinks
south as well, carrying with it the heavier rain threat. Still
expecting scattered showers and storms across the area, especially
south of I-76 and I-70 and down near the Palmer Divide.

Monday through Wednesday should feature a return to warmer
temperatures as the ridge builds back north. Moisture will build
back in to the area, though not as much as we`ll see Thursday and
Friday. This should result in better coverage of storms in the
mountains and a slight chance over the plains.

&&

.HYDROLOGY...
Issued at 334 PM MDT Wed Jul 19 2017

An easterly wave moving over southwestern Texas this afternoon
will be moving over Colorado through the day Thursday. This will
generate showers and thunderstorms from late morning onward. High
moisture levels and slow general storm motion will result in
locally heavy rainfall Thursday afternoon.

With monsoonal moisture pushing into the region, and moderate
storm movements, stronger storms on Thursday night will be able to
produce rainfall rates of 1/2" in 30 minutes or less. Higher
moisture levels and slower speeds on Friday will allow storms to
be able to produce rainfall rates of 3/4" in 30 minutes or less.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 334 PM MDT Wed Jul 19 2017

Storms over the foothills are slow to move off of the higher
terrain up to this point. Isolated thunderstorms will be possible
over the Denver area through this evening. Locally heavy rain and
gusty outflow winds will be possible. Southerly drainage winds are
expected overnight. Another round of showers are expected Thursday
afternoon, with another threat of heavy rainfall.

&&

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

$$

SHORT TERM...Dankers
LONG TERM...Kriederman
HYDROLOGY...Dankers/Kriederman
AVIATION...Dankers



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