FXUS65 KPUB 212104

Area Forecast Discussion
National Weather Service Pueblo CO
304 PM MDT Mon Aug 21 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 303 PM MDT Mon Aug 21 2017

Scattered thunderstorms developing over the mountains as of 21z,
with greatest coverage so far near the Continental Divide from
Monarch Pass northward. Over the plains, surface cold front was
slowly moving southward, with boundary just north of the Arkansas
River at mid afternoon. For the rest of the afternoon and into the
evening, expect isolated to scattered storms to continue to develop
over the mountains, with very slow/erratic storm motions as steering
currents have a very weak ely component west of I-25. On the plains,
last few runs of the HRRR and NAM both suggest at least isolated
activity developing along the cold front as it continues to push
south, and expect most storms to end up south of the Arkansas River
by mid to late evening. Main threat from any storms will be heavy
rainfall, with 06z NAM hinting at higher QPF amounts over the San
Juans/La Garitas this afternoon, then potentially over the srn
Sangres/Raton Mesa later in the evening. Front continues to sink
south overnight, and will keep some low pops for at least showers
going into Tue morning over the srn mts and near the Raton Mesa,
where N-NE upslope is maximized and residual convection is slow to

Cold front will be well south of the area on Tue, with
cooler/moister air mass over the plains through the day. GFS and NAM
both break out convection in the morning across much of the region,
with convective focus shifting across the mountains in the
afternoon. NAM would suggest little/no precip over the plains after
18z despite reasonably unstable (CAPE around 1000 J/KG) air mass,
while GFS hints at enough wly steering flow to push mountain storms
onto the plains late in the day. Will keep pops fairly high in the
mountains, with a broadbrush of isolated to sct at lower elevations.
Heavy rain again the main storm threat with weak shear and slow
storm motions. Max temps will run several degf lower than Mon along
and east of the mountains, while areas farther west see readings
just slightly cooler.

.LONG TERM...(Tuesday night through Monday)
Issued at 303 PM MDT Mon Aug 21 2017

Relatively active weather is expected to continue, with daily
chances for showers/tstms, especially over and near the higher
terrain, as moisture remains over the area and occasional weather
disturbance move across the state Tue night through Sat night.

At this time, it looks like the southeast CO plains could see fairly
widespread pcpn chances Thu night as one of those disturbances moves
acrs the area. Sat night, another disturbance drops southward
through eastern CO and could again bring widespread pcpn.

On Sun and Mon an upper level ridge is expected to be centered over
UT and will cover the western U.S. Overall, southern CO looks drier
on these days but there will likely still be enough residual
moisture for afternoon and evening pcpn over some of the higher


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 303 PM MDT Mon Aug 21 2017

Thunderstorms will 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. Could see some isolated -shra Tue morning across the area,
then more widespread convection develops over the mountains after
18z. Expect a risk of tsra at all taf sites after about 20z as
storms drift away from the higher terrain.




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