Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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455
FXUS65 KBOU 211807
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1207 PM MDT THU JUL 21 2016

.UPDATE...
Issued at 1207 PM MDT Thu Jul 21 2016

Upstream area of cloudiness is an area of slight cooling and
moistening aloft that will move over the mountains this afternoon
and the plains tonight. This should enable decent convective
coverage in an otherwise capped environment. CAPEs around 400 J/kg
over the mountains up to 800 J/kg on the plains. So updrafts
should be weak with plenty of moisture available, and slow but
steady storm motions. In short, a similar environment to
yesterday. The main threat is heavy rain, but this should be
limited to 1-2 inches in 1-2 hours with the heaviest storm. Given
the cloudy environment with weak forcing most of the rain should
be much lighter than that. Could be some hail with the strongest
pusles and some wind with any larger scale organization this
evening, but both of those threats look pretty small.

Main changes at this time were to raise POPs a bit for a better
chance of light amounts, especially over the mountains this
afternoon and the plains this evening with the expected timing of
the forcing/more favorable environment passing over.

&&

.SHORT TERM...(Today and tonight)
Issued at 235 AM MDT Thu Jul 21 2016

Persistent upper high remains anchored over Oklahoma and Texas
Panhandle with a resultant Southwest flow aloft over Colorado.
Water vapor imagery showing swath of moisture continues to be
steered into Colorado from New Mexico and Arizona. Precipitable
water values continue to remain just over an inch over the Front
Range and near 1.25" over the western slope of Colorado. The upper
high is progged to shift slowly Westward into New Mexico by later
tonight but the moist plume still expected to remain over Northern
Colorado with little overall change expected. Appears to be a
weak surge over Wyoming which will move over NE Colorado this
morning with a weak NE winds behind the surge. This may help focus
storms on the Palmer Divide providing for some weak convergence
and focus for storms.

In fact, high resolution models including the HRRR continue to
focus showers/storms today over mountains and Palmer Divide
during the afternoon. Outflow will likely trigger more isolated
storms over the nearby plains by late in the day. Overall CAPE
values from 500-1000j/kg so again today severe threat is low with marginal
updraft strength and low shear. Heavy rain will be the main threat
with always the potential for potential flooding issues. Temperatures
again will be very similar to Wednesday`s readings. Persistence
forecast is the way to go!

.LONG TERM...(Friday through Wednesday)
Issued at 151 AM MDT Thu Jul 21 2016

The upper ridge will continue retrograding west on Friday while
being flattened as an upper shortwave trough pushes east across
the Northern Rockies. Temperatures will remain above normal for
this time of year with diurnally driven storms beginning in the
mountains around noon then spreading east across the plains by mid
afternoon and over the far eastern plains and into Nebraska and
Kansas in the evening and overnight. Expect locally heavy rainfall
from these storms and small hail will be possible as PW values are
around 1.5 inches.

The upper trough will push a cool front down the plains Saturday
morning. This will bring slightly cooler temperatures and keep
storms mainly focused over the high terrain and areas over the
plains south of I-70 as the northern plains will remain somewhat
capped in the post frontal airmass. The front will also bring in
slightly drier air from the north, pushing the more moist air
south. Therefore storms may not be such heavy rain as we`ve been
used to over the last several days.

On Sunday, high surface pressure over the Great Plains will bring
back the low-level moisture in east to southeasterly flow and
allow for cooler daytime max temperatures. This will combine with
a disturbance aloft to bring more widespread storms across the
plains, with locally heavy rainfall again, while the high country
will be slightly drier.

The upper ridge will slowly begin to build back north and west
Monday through Wednesday bringing warming temperatures and slight
drying, though still expect daily afternoon and evening storms.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1207 PM MDT Thu Jul 21 2016

Scattered thunderstorms are expected in the Denver area from about
22z until 04z. Some of the storms could produce localized limited
visibilities and lower ceilings, but the main threat will again be
periods of variable winds gusting up to 30 knots. Similar threats
are expected from storms late Friday afternoon and evening.

&&

.BOU Watches/Warnings/Advisories...
None.
&&

$$

UPDATE...Gimmestad
SHORT TERM...Entrekin
LONG TERM...Kriederman
AVIATION...Gimmestad



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