Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 211733
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
1133 AM MDT Mon Aug 21 2017

.SHORT TERM...(Today and tonight)
Issued at 352 AM MDT Mon Aug 21 2017

Monsoon moisture has increased across the area as southerly flow has
advected higher precipitable waters northward between a ridge of
high pressure across the southern states and an upper low off the
southern coast of CA.  Precipitable waters from satellite derived
AMSU SSM/I show values running around 100-140 percent of normal
across the southern mountains and southeast plains, with generally
80-100 percent of normal across the northwest portions of the area.
Several slow moving disturbances are evident in the moisture plume
aloft, one moving through NE NM headed towards the southeast corner
of CO and into KS.  Another is back across northwest NM which will
shear off to the northwest across southwestern CO later this
afternoon.

First forecast concern will be cloud cover near the eclipse time.
Models had been showing a fairly distinct dry slot (evident in WV
pics across central NM lifting northeastward into southern CO and
the I-25 corridor through the late morning.  00z runs still show
this feature, but upper level RH fields are not quite as dry, and
soundings suggest at least a thin cirrus layer around 15k-20k ft may
persist through the afternoon.  Another observation that does not
bode well for complete clearing is the amount of convection still
ongoing across northern NM which will be sending up convective
debris cloudiness through at least the first part of the morning.
Overall, its going to be a close call...though it does still look
probable that the cirrus will thin sufficiently with some breaks
towards noon to get a view of the eclipse across portions of the I-
25 corridor and southeast CO plains. Some of the mountain areas and
far southeast corner of the state may still see some obscured
conditions under a thicker layer of mid/high cloudiness. Will just
have to wait and see how this evolves.

By noon...should start to see thunderstorms develop across the
mountains then spread off into the adjacent plains and develop along
the surface trof axis farther east. CAPE values are highest (1000+
J/kg) across the far southeast plains though shears look too weak
for a severe thunderstorm threat.  Main concern will be the
potential for locally heavy rainfall.  Will see a variety of storm
motions today given the complex flow pattern across the area.  Any
storms that develop across the southeast corner of the state will
move off to the east northeast...while storms over the mountains
within the lighter flow regime around north side of orphaned
cyclonic circulation across NW NM will be drifting westward.
Meanwhile a cold front will drop southward through the plains with
isolated storms firing along/behind it this evening. Will have to
watch burn scars closely for the potential for flash flooding,
especially for Hayden and Junkins.  Have kept temperatures today on
the cool side given some cloud cover and at least a period of
reduced solar heating.

Thunderstorms will gradually diminish overnight though may last
longest across the mountains.  Will keep overnight lows on the mild
side given frontal passage and some breezy winds across the
plains...and some persistent high cloudiness across the rest of the
area. -KT

.LONG TERM...(Tuesday through Sunday)
Issued at 352 AM MDT Mon Aug 21 2017

Tuesday-Thursday...Active weather pattern continues to be progged
across the area, especially for areas over and near the higher
terrain. Monsoonal moisture progged to increase within the generally
weak west to southwest flow aloft, as upper high pressure builds
across the southern Rockies and into the southern High Plains.
Models still indicate a cold front dropping south through the plains
late Monday night, which could keep a few storms possible across
eastern Colorado early Tuesday morning. Developing upslope behind
the front should drop back temperatures some for Tuesday, likely
keeping the far southeast plains too stable to support afternoon and
evening convection. Meanwhile, a minor wave caught up in the flow
aloft should help to bring scattered to numerous showers and storms
for the mountains and adjacent plains Tuesday afternoon and evening.
With some training of storms, especially across the eastern
mountains, will see an enhanced threat for flash flooding on burn
scars. Moisture continues to move across the area Wednesday and
Thursday, keeping daily chances of showers and storms, with the best
coverage for areas over and near the higher terrain. Locally heavy
rainfall and the potential for flash flooding remain the main
threats from storms, with temperatures expected to be at or slightly
cooler than late summer averages.

Friday-Sunday...Upper high slowly retrogrades back across the Great
Basin, with flow aloft becoming more northerly into the weekend.
Should see drier slowly moving back into the area with decreasing
coverage and intensity of diurnal convection expected into early
next week. However, there looks to be another cold front sliding
across the eastern plains on Saturday, with upslope flow a return of
low level moisture, owning to an uptick in convection Saturday,
especially across the eastern mountains and plains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1126 AM MDT Mon Aug 21 2017

Thunderstorms will develop over the mountains 18z-20z...then
drift across the lower elevations/adjacent plains late this
afternoon and into the evening. Will carry VCTS this afternoon
and early this evening at all 3 terminal sites, with lowest chance
at KPUB. VFR cigs along with locally heavy rainfall and erratic
gusty winds up to 45 kts will be the primary storm threats.
Thunderstorms will diminish this evening with winds shifting to
the north at both KCOS and KPUB as a cold front moves through.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...KT
LONG TERM...MW
AVIATION...PETERSEN


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