Flash Flood Warning 12, NWS Denver/Boulder, CO

739 
WGUS75 KBOU 072255
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
455 PM MDT Wed Jun 7 2023

COC049-072305-
/O.EXP.KBOU.FF.W.0012.000000T0000Z-230607T2300Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Grand CO-
455 PM MDT Wed Jun 7 2023

...FLASH FLOOD WARNING FOR THE EAST TROUBLESOME BURN SCAR WILL 
EXPIRE AT 5 PM MDT THIS AFTERNOON FOR NORTH CENTRAL GRAND COUNTY...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat. Please continue to heed any road closures.

A Flash Flood Watch remains in effect until 900 PM MDT for portions 
of central and north central Colorado.

LAT...LON 4035 10595 4028 10593 4020 10604 4009 10607
      4010 10615 4014 10622 4020 10628 4027 10627
      4033 10621 4033 10619 4034 10617 4033 10614
      4035 10610 4035 10608 4037 10603

$$

Hiris

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1154 AM MDT Wed Jun 7 2023

.UPDATE...
Issued at 1009 AM MDT Wed Jun 7 2023

Sunny and quiet start to the day today. Minimal cloud cover has
allowed temperatures to warm in to the upper 60s across the plains
this morning. Heating has begun to help develop cumulus over the
mountains. Expect highs in the mid to upper 70s for most of the
plains/urban corridor this afternoon and 50s/60s for much of the
high country. Water vapor imagery shows plentiful moisture getting
transported into Colorado ahead of a closed low over the southwest
US. Only minor updates to the forecast for today to bump highs up
a degree or two and adjust precipitation chances to latest high-
res guidance. It still looks favorable for a Flash Flood threat
for portions of the north and central mountains this
afternoon/evening, mainly west of the divide. The biggest concern
will be our burn areas, especially East Troublesome, Williams
Fork, and Mullen.Cameron Peak and Calwood will also face a threat
for flash flooding; however, perhaps a bit less than the others
previous mentioned given slightly less storm coverage.

&&

.SHORT TERM...(Today and tonight)
Issued at 246 AM MDT Wed Jun 7 2023

...Heavy rainfall possibly leading to flash flooding and debris
flow for mountain burn areas today...

Large closed low over southern California will slowly drift
eastward into Nevada over the next 24 hours. This low will eject a
wave northward across the Central Rockies today. In addition to
this, flow aloft will be somewhat diffluent. Unlike the past two
days, there will be synoptic lift to help produce showers and
thunderstorms. However, most of the lift will be over the
mountains. For the plains, best thunderstorm development is
expected to be due to convergence along outflow boundaries.
Biggest uncertainty in the forecast will be how far east will
storms form? The air will be slightly drier over the plains and
there will be a lack of large scale forcing.

The airmass over the area will contain a little more moisture
today. Precipitable water values over the mountains climb to
0.50-0.75(in) today, which is 150-180 percent of normal. Across
the lower elevations, precipitable water values will range from an
inch along the Urban Corridor to three-quarters of an inch over
the northeast plains. Plenty of moisture will be available to fuel
showers and storms. Surface based CAPE reaches 1000 J/kg along
the Front Range. However, over the mountains CAPE will be under
400 J/kg, and could end up a fair amount less if it quickly clouds
up this morning. Thus, rainfall in the mountains could be
widespread showers with embedded thunderstorms. Decided to issue a
Flash Flood Watch for the burns areas west of the Front Range
mountains. This includes the East Troublesome, Williams Fork, and
Mullen burn areas. See Hydro section for details.

.LONG TERM...(Thursday through Tuesday)
Issued at 400 AM MDT Wed Jun 7 2023

There will be a broad trough over the western US on Thursday with
a thin band of vorticity centered mainly over the northeast part
of our CWA. There will be abnormally high moisture still in place
in Colorado and sunshine in the morning will allow weak
instability to build in. The moisture and instability will create
scattered showers and storms in the afternoon and evening.
Coverage of these showers and storms will on the lower side due to
subsident flow over the western part of our CWA and the lack of
orographic lift across the eastern part of our CWA. Nonetheless,
storms will develop with heavy rain, small hail, and gusty winds
possible. There does not appear to be much of a severe storm
threat due to weak shear but instability will be moderate so a
couple storms could approach severe limits. There will be a
limited threat of flash flooding in the burn areas.

Weak ridging will build in over our forecast area on Friday with a
more westerly component of the upper level winds. The weak ridging
aloft will help create subsident flow which will result in Friday
having the lowest coverage of showers and storms of the long term
period. There will be isolated showers and storms with a limited
threat for burn area flash flooding. The storms should remain
below severe criteria due to a lack of shear but small hail and
gusty winds are possible.

This weekend still appears that it will be very wet. A trough
moves southward out of Canada towards the central Great Plains
clipping Colorado in the process. There did appear to be more
disagreement about this trough in the models tonight than last
night which does increase uncertainty during this period. The main
lifting mechanism will be a cold front that moves across our
forecast area late on Saturday and into Sunday. This will provide
low level lift which continues through the day on Sunday as
upslope northeasterly winds develop. Healthy moisture levels that
are well above normal will be in place so any storm that occurs
will have the potential to produce heavy rainfall. Flash flooding
will be a concern with the burn areas seeing the highest chances.
WPC has already outlined the mountains, foothills, and I-25
corridor for a slight risk of flash flooding on Sunday so this
period will need to be watched.

A trough will move from the Las Vegas area towards Colorado late
on Monday and into Tuesday. This trough will have better
southwesterly flow aloft than we have seen for a couple of weeks.
This could provide enough deep layer shear for a severe storm
threat to exist. Monday and Tuesday will continue to be wet and
cool with scattered storms expected to develop. Conditions may
finally dry out in Colorado by the end of next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1140 AM MDT Wed Jun 7 2023

Light and variable winds become light easterly this afternoon.
Thunderstorms remain possible this afternoon. Some uncertainty in
the best timeframe, but likely looking like 22-03z for storms to
be at least be in the vicinity, with potential for some to push
over the terminals. Brief heavy rain, small hail, and brief gusty
winds up to 35 kts are possible. Nearby activity could still
produce the threat of outflow gusts which may produce a wind shift
or two. Winds return to light drainage overnight. Light and
variable winds for a good portion of Thursday with a chance for
scattered storms in the mid/late afternoon.

&&

.HYDROLOGY...
Issued at 246 AM MDT Wed Jun 7 2023

Widespread rain showers with scattered to numerous thunderstorms are
expected over the mountains today. Best chance will for heavy rain
will be over Park, Summit, Grand, and Jackson counties. Airmass will
be very moist today with precipitable water values of 150-180
percent over the mountains. Due to weak winds aloft, the showers and
storms will be slowly moving. Putting it all together, heavy rain is
expected from the slow moving showers and storms. This will elevate
the flash flood threat, especially for the burn areas. Will issue a
Flash Flood Watch for the East Troublesome, Williams Fork, and
Mullen burn areas. To the east for the Cameron Peak burn area, some
uncertainty how many showers and storms will occur. Southeast winds
may usher in slightly drier air from the plains. Most of the models
show much more activity on the west side of the mountains than over
the Cameron Peak area. Therefore, will keep the Cameron Peak area
out of the Flash Flood Watch.

With weak ridging aloft resulting in subsident flow, storm
coverage will be lower than previous days on Thursday and Friday.
The storms that do occur could produce heavy rainfall so a
limited threat of flash flooding will exist in the burn areas both
days.

Higher moisture values along with better forcing will increase the
chance of flooding this weekend. By late Saturday and through much
of the day Sunday, there will be scattered to widespread coverage
of showers and storms. An elevated threat for flash flooding will
exist over the burn areas with Cameron Peak potentially needing a
Flash Flood Watch as the event gets closer. The plains could see
flash flooding as well with storms potentially producing very
heavy rainfall rates.

The threat of burn area flash flooding will continue into next
week.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 9 PM MDT this evening for COZ030-032>034.

&&

UPDATE...Mensch
SHORT TERM...Meier
LONG TERM...Danielson
AVIATION...Mensch
HYDROLOGY...Danielson/Meier

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1011 AM MDT Wed Jun 7 2023

COZ030>051-081615-
Jackson County Below 9000 Feet-
West Jackson and West Grand Counties Above 9000 Feet-
Grand and Summit Counties Below 9000 Feet-
South and East Jackson/Larimer/North and Northeast Grand/
Northwest Boulder Counties Above 9000 Feet-
South and Southeast Grand/West Central and Southwest Boulder/
Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet-
Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear
Creek/Northeast Park Counties Below 9000 Feet-
Central and Southeast Park County-
Larimer County Below 6000 Feet/Northwest Weld County-
Boulder And Jefferson Counties Below 6000 Feet/West Broomfield
County-
North Douglas County Below 6000 Feet/Denver/West Adams and
Arapahoe Counties/East Broomfield County-
Elbert/Central and East Douglas Counties Above 6000 Feet-
Northeast Weld County-Central and South Weld County-Morgan County-
Central and East Adams and Arapahoe Counties-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County-
Southeast Elbert County Below 6000 Feet/South Lincoln County-
Logan County-Washington County-Sedgwick County-Phillips County-
1011 AM MDT Wed Jun 7 2023

This hazardous weather outlook is for northeast and north central
Colorado.

.DAY ONE...Today and Tonight

Showers and thunderstorms will develop again today, most numerous
over the central and north central mountains. Heavy rainfall and
small hail will accompany the stronger storms. There is an
elevated risk for flash flooding on the East Troublesome, Williams
Fork, and Mullen burn areas where a Flash Flood Watch is effect
for this afternoon and evening. There is a slightly lower risk for
Cameron Peak and Calwood burns due to lesser storm coverage. Storms
across the foothills, Urban Corridor, and eastern plains will
more scattered, but also capable of producing heavy rain, small
hail, gusty winds.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

There will be no change to the wet and cool pattern in the long
term period. Scattered showers and storms will develop every day
with the higher terrain usually seeing the bulk of the storms.
The primary concern will be flooding, particularly flash flooding
in the recent burn areas. The days with the highest chance of burn
area flash flooding will be Saturday and Sunday. Gusty winds,
small hail, and lightning will also be threats.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today or tonight. However,
any significant rainfall and flooding reports will be
appreciated.