Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 210526

Area Forecast Discussion
National Weather Service Pueblo CO
1126 PM MDT Sun May 20 2018

.SHORT TERM...(This evening through Monday)
Issued at 251 PM MDT Sun May 20 2018

Upper disturbance moving through the 4 corners region is helping to
spark thunderstorms across the mountains this afternoon.  As these
encounter sufficient low level moisture which has penetrated
westward into the valleys due to deep upslope flow from last night,
they have been tapping around 500 to a little under 1000 j/kg of
CAPE.  This has allowed a few to strengthen as they hit these
pockets of higher instability.  However, shear has been the limiting
factor today and this has kept storms more on the pulsey side of
things. Thus not anticipating much in the way of a severe threat.
But could see some small hail, local wind gusts to 40 mph and brief
heavy rainfall. Will have to monitor the burn scars closely,
particularly the Hayden Pass burn scar,  where there has been more
sun today to destabilize the atmosphere.

Meanwhile, persistent low clouds have remained banked up along the I-
25 corridor much of the day and expect this will continue into the
mid-late afternoon.  This has delayed heating, resulting in a more
stable atmosphere across the plains.  As storms develop and move
eastward, suspect they will decrease in intensity as they encounter
this cooler airmass.  The exception to this will be along the Raton
Mesa region where latest HRRR runs continue to indicate the
possibility of a thunderstorm developing and moving eastward through
the evening hours.  This could be forced by a developing low level
jet, so can`t discount it and have spread some isolated pops across
Las Animas and Baca counties for now.

Elsewhere, expect convection to decrease diurnally with pops
diminishing quickly towards midnight.  Should be another relatively
cool night across the area, though with increasing southwest flow
aloft, do not think we will see a repeat of widespread stratus
redevelopment across the southeast plains.  -KT

.LONG TERM...(Monday night through Sunday)
Issued at 251 PM MDT Sun May 20 2018

Upper level low remains over the swrn U.S. Mon night into Tues,
with rather deep sly flow ahead of the system bringing a modest
amount of moisture northward into CO through the period. As a
result, expected isolated to scattered -shra/-tsra over the
region Mon night/Tue/Tue night, as weak upper level energy
occasionally ejects from the swrn low. 0-6km wind shear remains on
the low side (30 kts or less) through the period, as wind profiles
are rather unidirectional and speeds rather light, so threat of
severe storms looks rather low. Best chance for a stronger storm
would be along the NM border Tue afternoon/evening, where
instability/shear will be greatest. Max temps Tue should drift
upward another couple degf versus Mon as sly flow continues.

Swrn low then lifts northward through the Great Basin into the nrn
Rockies Wed/Thu, with upper level ridging developing over the
western U.S. as deep low develops offshore of the Pacific Coast.
As pattern shifts, drier swly flow develops across srn CO,
shunting most moisture eastward both days. Still some low level
moisture/instability near the KS border ahead of the surface
trough/dryline, so will keep some low pops in place each afternoon
to account for this possibility. Could see some marginal critical
fire weather conditions in a few spots both days as well, though
given mix of fuels greening up and at least spotty precip, tough
to pinpoint any particular area at this point. Max temps will push
back into the 80s/90s at many lower elevations, as heights rise
and mixing deepens.

Upper wave then crests the ridge and drops into the Midwest from
Fri into next weekend, pushing a cold front south through CO Fri,
followed by surface high pressure dropping south through the
central plains. Should see at least a modest upturn in convective
chances increase through the period over the eastern mountains
and adjacent plains, as low level upslope winds develop and
transport moisture back westward into the area.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1123 PM MDT Sun May 20 2018

Winds will generally be light until the late morning or early
afternoon hours on Mon, then winds become southerly with speeds of
10-15 kts and higher gusts at times. Showers and tstms will be
possible Mon afternoon and evening, but it is difficult to know if
they will move into the vicinity of the terminal forecast sites.




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