Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 231738
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
1138 AM MDT Wed May 23 2018

.SHORT TERM...(Today and tonight)
Issued at 444 AM MDT Wed May 23 2018

...Isolated Storms and High Fire Danger...

Dry, southwest flow will bring Red Flag conditions to the San Luis
Valley today.  Winds gusting above 25 mph, relative humidity below
15 percent and dry fuels will provide conditions favorable for the
rapid ignition, growth and spread of fires.  Outdoor burning or any
other activities that could accidentally start a wildfire should be
postponed.

Another round of afternoon and evening thunderstorms is expected
across southern Colorado today.  The best chance for storms today
will be across the plains and primarily along and east of a line
from Trinidad through La Junta.  A marginal severe threat exists
along and east of this line today.  This area will likely see pre-
storm CAPEs of 1500-2000 J/kg and LIs of -4 to -6 before storm
initiation around 1 pm. This should be adequate for a few pulse
severe storms capable of 1" diameter hail and 60 mph winds along
with locally heavy rain and lightning.  Shear values don`t look all
that great, however.  Model projections only have 0-6km bulk values
at 25-35 kts across the plains.  500 mb wind speeds are progged at
SW 30-35 kts but surface winds are only progged at S-SW 15-20 kts.
If surface winds end up being more from the SE, we could certainly
end up with better shear and a better potential for rotating storms.
Will have to monitor that through the day.  But for now, it mainly
looks like a pulse severe wind/hail threat for the plains today.
Convection looks pretty minimal over the mountains and west today as
dry southwest flow spreads over the region.  It`ll be a warm one
everywhere with afternoon highs 5-10 degrees above average at most
locations.

.LONG TERM...(Thursday through Tuesday)
Issued at 444 AM MDT Wed May 23 2018

Synopsis:

The upper level low that has been affecting the region will
propagate to the northeast of Colorado at the beginning of the
forecast period. Thursday, a ridge will build over southern
Colorado, which will bring exceptionally hot high temperatures to
the region. The ridge of high pressure is expected to affect
southern Colorado through the Saturday evening into Sunday morning,
but will be replaced by another upper low on Sunday. At this point
in time, the track of the low will be too far north for severe
weather to be an issue, but weak daytime thunderstorms over the
mountains, with a few storms making it over the plains, is expected.

Thursday:

Overnight showers and thunderstorms should dissipate in the early
morning hours. During the day, a ridge of high pressure develops
over the region with the 586 dam isopleth pushing further north as
the day progresses. The air mass associated with ridge will be a
particularly dry air mass, with minimum RH values ranging 10 to 15
percent over the SLV and adjacent plains and 15-20 percent across
the eastern plains.  The low RH values mean that fire conditions are
a concern, but will not be considered critical since the surface
winds will be too weak. The thunderstorm threat will remain over the
far eastern plains, but will be dependent on where the dry line sets
up. Variants of the NAM indicate that the dryline will set up over
the eastern plains, whereas the GFS puts the dryline east of the
region, so there is still plenty of uncertainty in the thunderstorm
forecast. The Euro, on the other hand, seems to be a steady
compromise of the NAM and the GFS, which puts the dryline near the
border of Colorado and Kansas.  Either way, the main issue with
thunderstorm development Thursday afternoon will be the lifting
mechanism, hence why model guidance is having difficulty picking up
on any thunderstorm initiation.

High temperatures across the plains will surpass the 90s in some
locations, the SLV and lower Upper Arkansas River Valley will span
the mid to upper 70s, and Lake County will experience the mid 60s.

Friday and Saturday:

The ridge will continue to affect southern Colorado on Friday and
Saturday. The most concerning weather element will be high
temperatures. On Friday, high temperatures will be in the low 90s
across the plains, low 80s over the SLV and lower upper Arkansas
River Valley, and the low 70s over Lake County. Saturday will be the
warmest day of the week, with the ridge axis oriented over southern
Colorado. Expect temps near 100F over the plains, lower 80s over teh
SLV and lower Upper Arkansas River Valley, and lower 70s in Lake
County.  The thunderstorm threat will be minimal across the region,
with the exception of an isolated storm over the mountains. Since
the air mass will be so dry there are fire weather concerns for
Friday and Saturday. Both Friday and Saturday will likely not meet
Red Flag Warning criteria, but the arid air will still cause rapid
fire starts. The limiting factor on Friday is the weak surface
winds. Saturday, however, will likely hit critical fire weather
conditions, but will miss Red Flag Warning conditions due to the
temporal constraints not being met.

Sunday through Tuesday:

An upper level low returns to the intermountain west, currently
tracking to travel over Nevada, Utah, then northeasterly over
Wyoming. The previously mentioned track isn`t conducive for
particularly strong thunderstorm, but daily thunderstorms are
expected to form over the mountains, with an isolated storm that
will travel over the plains. Starting Sunday, the high temperatures
will begin declining, but the temperatures will remain well above
normal for this time of year.

Emphasizing on Sunday now... Critical fire conditions are in the
forecast, a may warrant a Fire Weather Watch as the event
approaches. Currently, there are minimum RH values in the single
digits with sustained wind speeds greater than 20 kts in certain
locations.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1135 AM MDT Wed May 23 2018

VFR conditions expected at the TAF sites over the next 24 hours.
Winds will increase from the south to southwest with gusts up to
30 kts possible during the afternoon. Winds will decrease this
evening and become light overnight.

Isolated thunderstorms will be possible this afternoon, mainly
east of a line from KTAD to KLHX. These could become briefly
strong producing hail, erratic gusty winds up to 45 kts and MVFR
cigs/vis. Most should diminish or move out of southeast CO after
02-03z. -KT

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for COZ224.

&&

$$

SHORT TERM...LW
LONG TERM...SKELLY
AVIATION...KT



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