Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 301000
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
400 AM MDT Fri Jul 30 2021

.SHORT TERM...(Today and tonight)
Issued at 400 AM MDT Fri Jul 30 2021

...One more hot day on the plains, Monsoon rains for the CONTDVD
regions with flash flooding possible...

Currently...skies were mostly clear across the region at 3:00 AM,
with some remnant cloudiness noted over the CONTDVD. To the west of
the fcst area, quite a bit of shower and thunderstorm activity
was still noted over western CO. Additionally, quite a bit of
thunderstorm activity was noted over WY associated with a cold
front which was progressing south.

Mild conditions were noted over the plains at this hour. Temps were
well into the 70s across the lower Ark Rvr valley, with 70s at most
other locations on the plains. 60s were noted in the valleys with
50s and 60s mtns.

Today and Tonight...

Flow aloft will gradually transition during this time period. Deep
southeasterly flow which was previously over the region will become
more southerly by late today. This will allow deep monsoon moisture
to gradually shunt eastward and this will increase the shower and
thunderstorm activity over the higher terrain, especially over the
CONTDVD region. With the southerly flow, storms will likely remain
over the CONTDVD as they move north over the spine of the mtns. This
in turn will allow for an increased threat of flash flooding today,
and a flash flood watch has been issued for the central mountain
region.

It will be hot once again today across the plains with highs around
100 across the lower Ark Rvr valley from KPUB east to the KS border;
90s over the remainder of the plains. Temps in the mtns and valleys
will be cooler due to the expected increase in showers and storms
over this region.

By late this afternoon/early evening a cold front will move into the
Pikes Peak/Palmer Divide region. This will bring an increasing
chance of showers and storms to Teller county by mid/late afternoon
with increasing chances of storms over the entire Pikes Peak region
by early this evening. Some locally heavy showers will be possible.

This front will continue moving down the plains this evening,
bringing an increasing chance of showers and thunderstorms to all of
the southern mountains/San Luis Valley this evening. Most of the
plains east of the I-25 corridor are expected to remain dry.

By late this evening into tonight, showers and storms should
significantly decrease all areas except across the central mountains
where precip activity is anticipated to linger into the nighttime
hours.

.LONG TERM...(Saturday through Thursday)
Issued at 400 AM MDT Fri Jul 30 2021

...Potential for significant flash flooding over the mountains and
valleys on Saturday...

...Flash flood potential each day this weekend into early next
week over the mountains and valleys, and also extending eastward
over the plains for Saturday and Monday...

Saturday...

Recycled, post-frontal low-level moisture will be advected
westward in upslope flow over the plains toward the southeast
mountains. This moisture will phase with the rich monsoonal
moisture in place, surrounding a midlevel ridge over the Rockies
vicinity, to support potentially significant flash flooding.
Diurnally enhanced orographic ascent will foster convective
development over the mountains by mid-day, with activity becoming
widespread during the afternoon across the higher terrain.
Congealing cold pools will eventually descend eastward along the
eastern mountain slopes, facilitating eastward spread of
convection across the Interstate-25 corridor and even farther east
across the plains -- into the late afternoon and evening.
Activity should exhibit a weakening trend with eastward extent
across the plains by late evening.

Given precipitable water values ranging from around 0.9 inch over
the higher terrain of south-central Colorado, to around 1.5
inches over the plains, and the presence of narrow/deep buoyancy
profiles, storms will be highly efficient at rainfall production.
Moreover, individual convective cells should move slowly given
500-mb flow at or below 10 kt. This will be a highly favorable
set-up for flash flooding, as some locations potentially receive
upwards of 3 or 4 inches of rainfall accumulation. While such
accumulations may only be isolated to widely scattered in coverage,
if they were to occur over flood-prone areas across the mountains
and valleys -- especially burn-scar locations and the Chalk
Cliffs region -- and the Interstate-25 corridor, significant flash
flooding would be possible. This includes the potential for roads
to become inundated, mudslides to occur, along with substantial
debris flows. A Flash Flood Watch will likely become required for
Saturday afternoon into Saturday night.

Sunday...

After appreciable convective overturning on Saturday, comparatively
more stable thermodynamic profiles may be in place on Sunday,
particularly in areas where substantial cloudiness lingers. However,
sufficient insolation is expected over the higher terrain to support
terrain-enhanced ascent and convective development for Sunday
afternoon and evening. Adequate lingering moisture will facilitate
the potential for locally heavy rainfall and flash flooding over the
mountains and valleys, especially if this activity were to impact
burn-scar locations and the Chalk Cliffs region. However, this
activity is presently forecast to be principally relegated to the
higher terrain, and perhaps the immediately adjacent plains.
Cooler/more stable conditions farther east should restrict
convective development across a broader portion of the plains.

Monday...

A more substantial flash-flood risk may materialize on Monday,
similar to that on Saturday, following adequate intervening
atmospheric recovery. This would occur as midlevel heights fall,
in response to a low-amplitude wave advancing through the
aforementioned ridge before becoming absorbed into a belt of
northwesterly flow aloft peripheral to a deep trough -- centered
well to the east of the region. In response to these developments,
increased large-scale forcing for ascent may phase with the deep
moisture already in place to support widespread convective
development once again, potentially spreading eastward across the
plains. A heightened flash-flood potential will exist on Monday,
particularly over the mountains and valleys (especially for burn
scars and the Chalk Cliffs region), and perhaps also across the
plains. However, confidence regarding details of the Monday
flash-flood risk are not as high as Saturday, owing to increasing
forecast range from the present and associated lower predictability
regarding the midlevel wave. Nevertheless, antecedent saturated
grounds should tend to increase the overall conditional risk.

Tuesday through Thursday...

Heavy-rainfall and flash-flood potential will persist, but may
become mostly confined to the mountains and valleys. This would be
in response to modest northerly midlevel flow overspreading the
area -- east of a midlevel ridge becoming re-centered over the
southwest states, as depicted by medium-range model guidance. This
would generally prevent diurnal, terrain-enhanced convective
activity from spreading farther east across the plains.

Other forecast factors through the period...

High temperatures are expected to be near to below normal this
weekend, given the widespread convective activity on Saturday and
lingering clouds into Sunday. Temperatures are forecast to rise to
near to above-normal readings next week after Monday, owing to
decreasing convective coverage with the midlevel ridge building west
of the forecast area.

Also, while precipitation-loading in the rich-moisture environment
could support locally gusty winds with collapsing convective cores
this weekend into next week, weak deep-layer shear should
mitigate the severe-thunderstorm risk.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 400 AM MDT Fri Jul 30 2021

VFR is anticipated for a majority of this time period at all 3 TAF
sites, KPUB, KALS and KCOS. The main concern today will be the
return of afternoon and evening storms to the TAF sites,
especially KCOS and KALS. In addition, a cold front will be
affecting KCOS and KPUB early evening. As the front goes by, winds
will shift into the north and will be gusty for 2-3 hours after
the front goes by. At this time we do not anticipate any low cigs
(except with any tsra) at the TAF sites during this fcst period.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from noon MDT today through late tonight for
COZ058>061-063.

&&

$$

SHORT TERM...HODANISH
LONG TERM...COHEN
AVIATION...HODANISH


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