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Office: BOU

FXUS65 KBOU 181526

Area Forecast Discussion
National Weather Service Denver/Boulder CO
926 AM MDT Sat Aug 18 2018

Issued at 856 AM MDT Sat Aug 18 2018

Water vapor imagery showing upper level trof moving across
northwest Colorado this morning with associated cold front now
approaching the Continental Divide. Local radar also showing a
band of rain showers moving into the mountains now. This line of
storm will progressively move east over the Urban corridor
between 11 am and noon and over the Eastern Plains this afternoon.
Expect storms to intensify as they move east of the Front Range
and encounter better low level moisture and more time for daytime
heating. Expect a few of these storms to become severe over the
plains with hail and damaging winds and expect the main impact
may be outflow driven winds up to 70 mph. Current forecast has the
earlier timing expected today so minimal changes needed to
current forecast.


.SHORT TERM...(Today and tonight)
Issued at 249 AM MDT Sat Aug 18 2018

An upper level trough centered over Idaho will move across
Wyoming today and by 12Z Sunday strengthen into a closed low over
the Nebraska panhandle. Ahead of the main trough/low, a short wave
trough will pass through Colorado today. Satellite and radar
showing a broken line of showers and thunderstorms with this
feature over western Wyoming and Utah. This trough and convection
will move into western Colorado early this morning. Showers and
storms shift into the north central mountains mid to late morning
and then onto the Urban corridor around or shortly after noon.
HRRR shows a good blast of wind (40 knots) coming down the
foothills with the convection. These downslope winds could limit
convection across the Urban corridor. As the trough moves onto the
eastern plains, it will encounter greater moisture and
instability with CAPE values of 1000- 2000 J/kg. A few severe
storms will be possible with wind gusts up to 70 mph and hail to
one inch in diameter. A solid line of showers and storms should
develop to the east of the Urban Corridor mid to late afternoon.
By early evening, this activity is expected to be east of the

The left exit region of the jet moves over north central Colorado
this evening. This may provide enough lift for additional showers
and thunderstorms mid to late evening and possibly continuing
after midnight.

.LONG TERM...(Sunday through Friday)
Issued at 249 AM MDT Sat Aug 18 2018

On Sunday morning, a closed upper low will be over the Nebraska
Panhandle. This feature will shift to the southeast with a
moderate to stronger northerly flow aloft Sunday afternoon. The
models generally show the best qpf in proximity to the upper low.
Overall the best chance of showers will be through 21z Sunday
along the eastern border. Only light and more isolated shower
coverage is expected further west. Temperatures will be cooler
with highs only in the lower 70s for Denver. In addition, a
stronger north to south surface pressure gradient, and decent
flow aloft will allow for gusty bora winds in the late
morning/afternoon period. Some gusts in the 40 to 45 mph range
will be possible over northeast plains. The upper level ridge will
build over the region Sunday night into Monday, with clearing
skies and cool overnight temperatures. Not much in store for
Monday with a dry northwesterly flow in place. Temperatures will
warm slightly, but remain below normal as they struggle to reach
80. A strong northwesterly flow will remain over the cwa on
Tuesday, with an embedded short wave trough dropping out of the
northern Rockies and clipping the northeast corner of the state
Tuesday night around 06z. Both the GFS20 and ECMWF are similar in
the timing and track of this system, with isolated to scattered
pops reflected in the grids at that time, highest in the mountains
north of I-70 and over the northeast corner of the state.
Wednesday through Saturday, temperatures will warm back to normals
with highs in the mid to upper 80s. The upper ridge will build
over the region a bit more with more of a westerly flow aloft over
Colorado. Still enough subtropical moisture around, with another
potential short wave trough brushing across the region on Thursday.
Will generally keep isolated pops in the grids each day with
isolated to scattered pops possible on Thursday with the passage
of the short wave.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 856 AM MDT Sat Aug 18 2018

Expect a line of showers and thunderstorms to move across the
terminals between 18-20z with brief heavy rain and winds. Appear
main impact will be the winds with this line of storms and
certainly could see gusts in the 30-40kt range. More isolated
coverage mid to late afternoon. The upper trof will deepen into a
closed circulation later tonight and result in additional storms
and showers this evening and over night. There is also indication
of low clouds developing later tonight and Sunday and will address
this for the 18z taf.




LONG TERM...Cooper

Office: PUB FXUS65 KPUB 181023 AFDPUB Area Forecast Discussion National Weather Service Pueblo CO 423 AM MDT Sat Aug 18 2018 .SHORT TERM...(Today and tonight) Issued at 420 AM MDT Sat Aug 18 2018 Still a few weak remnants of overnight convection drifting around the SE Plains this morning, and will retain some low pops through sunrise for the far sern corner of the area. Attention then turns northwestward, as strong short wave will ride over the upper ridge today and tonight, eventually closing off a mid level low over the Central Plains by early Sun morning. Well defined trough and associated convection already showing up nicely this morning in satellite imagery from ern WY south into wrn CO/ern UT, with occasional CG lightning pushing through wrn CO as of 10z. For today, enhanced upward motion with the upper wave spreads eastward through the mountains early this afternoon, then across the I-25 corridor and eastern plains from mid-afternoon into the evening. Should see fairly organized band of tsra develop over the mountains in the early afternoon, with storms intensifying as they move east into the more unstable air mass on the plains. Threat of strong/severe convection and potential for heavy rain then shifts across the plains toward the KS border during the evening and overnight hours. SPC SWODY1 marginal risk of severe over the plains looks reasonable today/tonight, as 0-6km shear increases to around 40 kts by 00z, while CAPE climbs into the 1-2k J/KG range. Although brief heavy rainfall will be possible over the mountains, heaviest rain potential will likely occur over the plains, as convection organizes into an MCS by evening. Convection then ends from west to east overnight, as bulk of tsra activity shifts east in KS/OK/TX. Max temps today will run just a couple degf cooler than Fri with more cloud cover across the region. .LONG TERM...(Sunday through Friday) Issued at 420 AM MDT Sat Aug 18 2018 Sunday and Monday...Forecast models are are in good agreement during this period leading to high confidence in the forecast. The long term forecast period begins with the exit of a potent shortwave trough east out of Colorado and ridge recovery over the southwest US. Height rises, Q-Vector divergence, and moisture-scouring deep northerly flow will lead to drier conditions across the forecast area Sunday and Monday. Residual energy on the backside of the system may spawn an isolated storm or two over the eastern mountains Sunday, while weak energy in the northwest flow will help to develop a few isolated thunderstorms across the high terrain on Monday. Surface winds out of the north will be quite breezy on Sunday, in the 20-35 mph sustained range, across the I-25 corridor and eastern plains. Temperatures will be cooler within the northerly flow regime, with highs in the low 80s across the plains and high valleys, and mid 70s in Colorado Springs. Tuesday and Wednesday...Forecast confidence remains moderate-high as models remain in good agreement, with some differences beginning to develop in the position of the mid-level ridge by late Wednesday. The ridge shifts east slightly south of Colorado causing mid- level flow over the state to become more west-northwest. The flow becomes disturbed over Colorado as an upper level jet sags south. At the same time, surface flow becomes southerly/southeasterly from the Texas Gulf Coast into southern Colorado, returning moisture to the region. Thunderstorms will have no problem developing each day over the high terrain under the influence of strong daytime heating, shortwave energy, and upper level jet dynamics and a return of above average TPW. Storms will be steered onto the I-25 corridor and eastern plains during each afternoon and evening. While shear will be favorable both days with the jet overhead, instability will be marginal at best on Wednesday, as surface dew points are still recovering. Still, with such favorable shear, could get a low-end severe storm or two. Instability will be better on Wedensday as surface dew points increase after another day of return flow. Therefore, Wednesday looks like there may be a better chance for storms to be severe. Temperatures will be warmer this period, with highs in the mid to upper 80s across the plains, and low 80s in Colorado Springs and the high valleys. Thursday and Friday...Model solutions diverge more during this period with the position of the high and progression of disturbances, leading to less confidence in the forecast compared to above. It appears as though less moisture will be in place with the exit of the Tues/Wed storm system. While the ECMWF maintains a shortwave off the west coast and into the northern Rockies on Thursday, the GFS weakens the shortwave by the time it makes it this far east. This leads to more widespread convective coverage in the ECMWF vs the GFS over the high terrain on Thursday, though both models keep the plains dry. The GEFS also shows considerable spread with the progression of the mid-level pattern by this time. Regardless, the ridge remains centered somewhere south of Colorado with westerly to northwest flow overhead leading to thunderstorm chances at least over the high terrain. && .AVIATION...(For the 12Z TAFS through 12Z Sunday morning) Issued at 420 AM MDT Sat Aug 18 2018 Patchy MVFR stratus will occasionally impact both KCOS and KPUB through 15z, with some IFR cigs possible just west and north of KCOS through sunrise. Conditions then become VFR at all terminals into early afternoon before convection begins to move off the mountains and approach taf sites 19z-20z. Will include VCTS at all terminals for the afternoon and early evening, with best chance for tsra at both KCOS and KPUB. Storms today could be strong, with hail and gusty winds possible at KCOS and KPUB late this afternoon. && .PUB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...PETERSEN LONG TERM...LINE AVIATION...PETERSEN
Office: GJT FXUS65 KGJT 180923 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 323 AM MDT Sat Aug 18 2018 .SHORT TERM...(Today through Sunday) Issued at 322 AM MDT Sat Aug 18 2018 There's no question as to where the trough is at this hour. Simply look at satellite and it can be seen stretching down from just east of Salt Lake City to near St. George, Utah. Ahead of the trough, a nice line of storms popped up this morning. Right now, they're moving through Rio Blanco county and the northern portions of Garfield County. Quite a bit of lightning can be seen and expect some gusty winds up to 40 MPH possible from the line...maybe a bit higher. So far, not much happening south of I-70 though some weak cells are popping near Moab and will probably fill in as the morning progresses. All the short range models are doing an 'ok' job this morning. Looks like they're a little bit slow picking up on the convection but all things considered...not bad. The NAMNEST is showing the front at the UT/CO border by daybreak and near 10am, it'll stretch from Craig down to Grand Junction and Gateway. Noonish, the front will have reached Vail down to Aspen, and Telluride. Near 3pm, the front will have moved out of the CWA...yes, it's moving pretty fast. In fact, most areas will see plenty of sun from noon onwards except areas along the Continental Divide. Once the front has moved away, some cooler air aloft will drop down from the north allowing some instability showers to form but they look to be confined to the northern mountains. Smoke will largely dissipate as mixing and precipitation will break it up. Temperatures should also be a bit cooler. High pressure will build back in on Sunday as drier air continues to move in thanks to northerly flow. The chance for a few light showers persists over the Park and Gore Ranges but they'll be very isolated in nature. The rest of the CWA will see plenty of sunshine with seasonal high temperatures. .LONG TERM...(Sunday night through Friday) Issued at 322 AM MDT Sat Aug 18 2018 High pressure will build over the southwestern U.S. and southern Great Basin producing dry northwest flow aloft over eastern UT and western CO Sunday night. The high will be prevented from building further north over the rest of the Great Basin by a strong trough moving into the Pacific Northwest. This trough will move east Monday and force the southern ridge to the east, becoming centered over the AZ and NM state line. This orientation will allow subtropical moisture to flow north over western AZ into UT then curve east over the forecast area by Tuesday. It's not a strong flow of monsoon moisture but it will still be wet enough to produce showers and thunderstorms across much of the area each day next week. && .AVIATION...(For the 12Z TAFS through 12Z Sunday morning) Issued at 322 AM MDT Sat Aug 18 2018 A weak cold front will move across the CWA this morning and the early afternoon hours. As it does so, some showers and brief thunderstorms will be possible. All TAF sites are under the gun for some showers and storms this morning except KDRO which looks to be too far south to see any convection. Brief MVFR will be possible as visibility briefly drops to between 3 to 5SM. Some gusty winds will also accompany the front The front will have moved out of the area after 21Z bringing a return to VFR conditions. VFR will continue through 12Z tomorrow. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...TGR LONG TERM...CC AVIATION...TGR