Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 260020
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
620 PM MDT Thu Apr 25 2019

.UPDATE...
Issued at 619 PM MDT Thu Apr 25 2019

Made minor issues to timing of tomorrow`s showers/storms forming
over the higher terrain and pushing off over the plains. May need
to bump up windspeeds moving off the foothills tomorrow late
afternoon as the convection pushes over the urban corridor in the
dry environment. Current forecast has gusts in the 15-20 mph
range, however looking at the inverted-v forecast soundings and
the short range hi res modeled wind gusts, may see closer to 30-40
mph. Will monitor model consistency and confidence.

&&

.SHORT TERM...(This evening through Friday)
Issued at 119 PM MDT Thu Apr 25 2019

A strong frontal push early this morning brought morning clouds that
dissipated into mostly sunny skies across the region. Overall,
conditions remain too stable over the plains for any convection
today, however, satellite shows some Cu developing over the higher
terrain as LAPS cape values increase into the 200 to 500 J/kg range.
This will help to bring isolated afternoon showers and thunderstorms
to the mountains into the late afternoon hours. Main hazards will be
light rain and gusty winds. At lower elevations, some gusting will
continue over the far eastern plains through into the early evening
with gusts up to 25 mph. For this evening, temperatures will drop
into the lower to mid 40s across the plains and 20s to 30s over the
mountains and foothills.

For Friday, upper level flow will be from the WNW with a surface low
in place over the northern foothills. This surface low will track SE
across the northern plains through the afternoon hours pulling SW
winds over the plains. This initial NW flow at the surface will
introduce drying in the lower levels across the plains. Later into
the afternoon models are showing increased instability with CAPE
values ranging from 200 to 800 J/kg. This will be enough for
scattered thunderstorms, but with dry low levels expect some
light rain but mostly gusty winds to accompany the storms.
Coverage for storms will be higher over the mountains on Friday
with showers, gusty winds and some lightning possible.
Temperatures will rebound from the frontal passage today with
highs back into the 70s over the plains and 50s in the mountains.

.LONG TERM...(Friday night through Thursday)
Issued at 119 PM MDT Thu Apr 25 2019

Friday night, there will be weak mid level qg ascent over
the area in the evening then strong subsidence develops as a
storm system exits into the from Wyoming into Nebraska. The models
show a strong west/northwest wind component 50-60 kts Friday
night. Moisture depth will be decreasing after 06z under
increasing subsidence. Mountains should see some light snow
accumulations of 2 to 5 inches above timberline. Across the
northeast plains, isolated to scattered high based thunderstorms
in the evening, then just isolated showers. Strong outflow winds
would be the biggest threat from the storms.

Saturday and Saturday night, a drier but fairly brisk northwesterly
flow aloft will remain over the area. Gusty winds will continue in
the mountains with just some lingering showers in the morning.
Across the northeast plains, not as warm as Friday but still above
normal. The models show gusty south/southeast winds developing
late in the day. By 00z Sunday, there may be must enough CAPE
(200-400 j/kg) over the Palmer Divide to pop a brief thunderstorm
but that may be it.

Sunday and Sunday night, an increasing zonal flow aloft as a
system passes well to the north through Montana. Enough mid level
moisture around coupled with daytime heating for scattered showers
and thunderstorms in the mountains, with the snow level just
above 10 thousand feet, with isolated to scattered showers and
thunderstorms over the plains in the afternoon and evening. A cold
front does push into northeast Colorado from the north in the
evening, which will help act as a focusing mechanism for the
thunderstorms. In addition, the right entrance region of jet max
passing through Wyoming around 06z Sunday night, which would help
enhance the precipitation especially in the mountains, maybe
enough to produce a few inches of snow in the higher mountains.
By 12z Monday, a subtropical jet will spread from the Desert
Southwest into central Colorado ahead of the next system.

Monday and Tuesday will be cooler and more unsettled with a better
chance of precipitation across the cwa. Uncertainty still exists
in regards to the timing, with the GFS faster vs the ECMWF with
the next system. Overall, it appears to be fairly wet during this
period. The GFS is still generating higher QPF than the ECMWF. In
terms of precipitation type, snow showers in the mountains, more
of a mix in the foothills and Palmer Divide. Across the plains,
precipitation type may be more of a mix in the morning with rain
showers in the afternoon. Still not sure when the best period for
precipitation would be, but Monday afternoon into Tuesday morning
looks like best compromise at this point as the upper trough
lifts out of the Desert Southwest and across Colorado. Wednesday
will be a little warmer, but still unsettled with a chance of
showers and thunderstorms in the afternoon and evening.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday afternoon)
Issued at 619 PM MDT Thu Apr 25 2019

VFR conditions are expected through the period. Easterly winds
are expected to veer to drainage by late this evening with speeds
staying between 6 to 12 kts. Isolated to scattered afternoon
convection tomorrow afternoon to move east off the higher terrain
after 19z, with conditions more favorable after 21z at KDEN. With
a dry environment and strong winds aloft, the convection may be
accompanied with gusts in the 25 to 35 kt range.



&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Kriederman
SHORT TERM...Bowen
LONG TERM...Cooper
AVIATION...Kriederman


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