Area Forecast Discussion
Issued by NWS Pueblo, CO

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593
FXUS65 KPUB 211726
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
1126 AM MDT Mon May 21 2018

.SHORT TERM...(Today and tonight)
Issued at 346 AM MDT Mon May 21 2018

Currently...

Variable, mostly mid level, cloudiness was moving over the region at
3 am. Some fog was likely occuring over the northeastern sections of
Kiowa county, and some lower clouds were noted over some of the mtns
and valleys across the region. A few sprinkles were likely occurring
south of Pueblo to Walsenburg.

On the large scale, a broad closed 500 mb low was moving onshore of
the central CA coast. Broad SW flow was noted east of this low. Sat
pix show quite a bit of moisture advecting north from New Mexico
into Colo.

Today...

Guidance showing most of the shower and thunderstorm activity that
will occur over the region today will occur generally along and
south of the US-50 corridor, as the moisture to the south moves into
Colorado. Activity will get going by late morning over the SW mtns
and develop/move east during the mid afternoon time period. Showers
are expected to occur relatively early in the afternoon on the
plains along a weak surface boundary that will extend from roughly
KTAD to KLHX. Showers are also expected over the San Luis Valley
(SLV) by afternoon. Overall, the heaviest precip will likely fall
over the sw mtns today.

Thunderstorms today are not expected to be severe, but gusty winds
and small hail will be possible as max temps will be in the 70s and
80s over the plains and 60s valleys. This will lead to CAPE values
around 1000 on most of the plains, with higher values over the far
eastern Plains. Deep shear will be 20-30 knts.

Tonight...

Precip chances are likely to remain over the region into the
nighttime hours, especially over the mountains/valleys along and
south of US-50. Scattered showers will likely be ongoing even into
the early morning hours across the sw mtns. Over the remainder of
the region precip will be more isolated.

Temps tonight will fall into the 50s across the plains, 40s valleys
and 20s and 30s mtns. Some very high light snow accumulations are
expected (2-3"). /Hodanish

.LONG TERM...(Tuesday through Sunday)
Issued at 346 AM MDT Mon May 21 2018

Tuesday...By Tuesday morning, a closed upper low will be centered
over southern Nevada and will slowly lift to the northeast during
the day. The low will bring another day of moderate southerly low-
mid level flow, which will continue to draw increased moisture into
southern Colorado. Favorable moisture combined with intense daytime
heating will lead to scattered thunderstorm development over all
mountain areas during the afternoon, with isolated storms spreading
into the high valleys and eastern plains. Given only moderate
instability plus weak flow aloft (leading to weak deep layer shear),
severe storms are not expected. However, storms will be capable of
producing frequent lightning, small hail, and brief gusty winds.
Temperatures on Tuesday will be slightly warmer, with highs in the
mid 80s across the plains, and mid to upper 70s in Colorado Springs
and the high valleys. Winds at the surface will increase out of the
south to 15-25 mph across the eastern plains by early evening,
gusting to 30 mph.

Wednesday through Thursday...Models remain in agreement on lifting
the upper low northeast on Wednesday north of Colorado, which
evolves into an open wave on Thursday as it advances into the
northern US plains. In it`s wake, a ridge begins to build over
Colorado. As the upper level energy lifts northeast during the day
Wednesday, flow throughout the atmosphere becomes southwesterly.
The southwest flow draws considerably drier air over the state,
which mixes to the surface during the afternoon/evening. Gusty
southwest winds will also mix to the surface, and combine with low
RH values to create areas of critical fire weather conditions across
the San Luis Valley and parts of the eastern plains. The need for
highlights will depend on the state of fuels at that time, which
will be influenced by precip over the next few days. Only isolated
showers and thunderstorms are expected over the higher terrain given
a lack of moisture. As the upper energy advances east, north of
Colorado on Thursday, flow becomes more westerly over the state. Dry
air will once again mix to the surface during the afternoon, but
winds will be weaker, so critical fire weather conditions appear
less likely. Thunderstorm activity will remain sparse, with isolated
coverage over parts of the mountains, and possibly far eastern
plains along a dryline. Temperatures will be even warmer during this
period, with highs in the upper 80s to mid 90s across the plains and
mid 70s to mid 80s across the high valleys and Colorado Springs area.

Friday through Sunday...Models continue to agree on bringing another
upper low just offshore the central California coast by Friday and
onshore Saturday as a ridge builds over Colorado. Slight
timing/position differences remain, however, in the progression of
the low between the GFS and ECMWF, with the GFS now being the faster
and southern of the two solutions. The GFS is also faster than it
has been in previous days, with the recent solution building the
ridge axis further east over Colorado, leading to less precip than
was present in previous runs. GEFS members from the latest run are
also in fairly good agreement on the position of the ridge over
Colorado. Given only minor differences in guidance, have moderate
confidence in only isolated to scattered afternoon thunderstorms
over the mountains each day, with isolated storm chances over the
eastern plains. The fire threat appears to be low both days, with
higher RH values and weaker wind speeds forecast. Both GFS and ECMWF
lift the energy into the Great Basin on Sunday, possibly increasing
southerly/southeast low-level flow over eastern Colorado and
increasing moisture near a dry line. High temperatures are likely
to remain at least in the 80s across the plains during this
period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1121 AM MDT Mon May 21 2018

Scattered thunderstorms will continue to develop over the southern
mountains this afternoon, spreading northeastward into the KALS
TAF site by early afternoon...and potentially to near the KCOS and
KPUB terminals during the mid-late afternoon. Have introduced a
VCTS group for KPUB as thunderstorm coverage still looks best
south of highway 50. Have left VCTS mention out of the KCOS TAF
for now due to very low probabilities of impacting the terminal.
Main threat with thunderstorms today will be small hail, erratic
wind gusts to 40 kts and brief heavy rainfall. Thunderstorms
chances will decrease at the terminals after 02z though a few
lingering showers will be possible across the mountains through at
least midnight. CIGS should remain VFR through the night with a
high cirrus deck persisting into Tuesday morning. -KT

&&

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

$$

SHORT TERM...HODANISH
LONG TERM...LINE
AVIATION...KT



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