Severe Thunderstorm Warning 42, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
127 PM MDT Sat Jun 6 2020

.UPDATE...
Issued at 127 PM MDT Sat Jun 6 2020

Sufficient heating for mixing of that higher momentume air into
the Denver area. We upgraded to a High Wind Warning for east of
I-25, and north to Greeley and Fort Morgan as they should start to
blow as well with further mixing.

UPDATE Issued at 1025 AM MDT Sat Jun 6 2020

...THUNDERSTORMS WITH DAMAGING WINDS THIS AFTERNOON...

Anomalously strong wind field in place today, as we're seeing
standardized anomalies in the 3-4 range. That's already indicated
on the regional 12Z soundings and KFTG vad wind profiler, with 50
knot south/southwest flow down close to 8000 feet, at least with
the passing showers.  The winds aloft will continue to increase
this afternoon, with the upper level jet rounding the base of the
ejecting trough axis. We see a core of 60-70 knot winds down to
600 mb, and widespread 50+ knot winds at and under 700 mb.

There is abundant cloud cover which is limiting daytime heating
and mixing, which is a wildcard regarding wind/storm development.
However, as the gradient strengthens and deeper convection in
western CO/eastern UT moves in this afternoon, we believe more
and more places will see high wind criteria met, not just those
under the current High Wind Warning, but locations along the I-25
corridor and even over the mountains. We will have to be fairly
generous with severe thunderstorm warnings to account for the
potential damaging thunderstorm winds. If we see just enough
breaks in the clouds, MLCAPE should increase to around 500-800
J/kg with DCAPE near 1000 J/kg. Momentum transport of the stronger
winds aloft and enhanced thunderstorm outflow would support
damaging wind gusts up to 80 mph possible from the stronger
storms. Hodograph lengths are long, and mean 0-6 km wind is close
to 60 knots so storms will be absolutely flying in this
environment. Despite the curved hodographs and favorable shear
profile, we think most storms on the plains will be outflow
dominated with relatively high LCL levels of 7000-9000 feet,
limiting the tornado threat but still not ruling one out given
0-1km helicity near 100-150 m2/s2 and 0-3km upwards of 300 m2/s2.
If we were to see a tornado, this would be likely be the day to
see one in the mountains or western Colorado where LCLs are lower
and shear/updraft helicity profiles are even stronger.

Other concern for this afternoon is blowing dust and hazardous
travel conditions with strong crosswinds. Visibility near open
fields could be reduced to near zero.

Red Flag Warning and High Wind Warnings remain in place.

&&

.SHORT TERM...(Today and tonight)
Issued at 339 AM MDT Sat Jun 6 2020

The positively tilted upper level trough is currently sitting over
southern CA with increasing Gulf moisture pushing into the four
corners region and into Colorado. Associated with this feature is a
100+ jet that will circumvent the base of the trough and push into
Colorado through the day today. QG analysis shows modest lift ahead
of the trough combined with the increased PW moisture values to
bring enough instability for storms to continue across western
portions of the state and move across the Central Rockies through
the morning hours. With model PW values projected to be between 0.75
to over an inch storms that move over the higher terrain through the
morning could be capable of moderate to heavy showers.

For storm projections later this afternoon models show a decent
enough shear profile to support rotating updrafts along with CAMs
indicating a few long track helicity swaths across portions of the
high country and northern foothills. There will be some initial
cloud cover over the plains that could hinder mixing of the boundary
layer, however it is expected that lapse rates will be strong enough
at around 9.0-9.7 C/km with DCAPES above 1000 j/kg to support strong
winds across the plains by the late afternoon. Storms will push east
off the higher terrain and move across the plains during the late
afternoon hours and continue into the early evening. Some of these
storms will be able to produce severe winds with outflows possibly
bringing gusts of 60 to 80 mph along with large hail and dangerous
lightning.

Temperatures today will once again reach well above normal with
highs projected to be in the 90s across the plains and 60s to 70s in
the high country. With the increased moisture provided by the upper
trough, RH values will see a slight boost with values in the upper
teens to lower 20s across the plains. However, as conditions
deteriorate with severe winds projected across the eastern plains
counties fire danger will worsen. For this reason a Red Flag Warning
remains in effect for a portions of the eastern plains starting at
11 am today and continuing through Sunday. More information can be
found in the fire weather section below.

.LONG TERM...(Sunday through Friday)
Issued at 339 AM MDT Sat Jun 6 2020

For Sunday, Colorado will remain under a strong southwest flow
regime with low pressure over the northern Rockies. The state will
be much drier than Saturday with no convection expected during
the day. Precipitable water values drop to under .50 of an inch
for most areas. Main concern on Sunday will be critical fire
weather conditions with low humidities and strong southwest winds
(see fire weather section below for more details).

There is some good news for early next week with an expected cool
down on Monday and Tuesday with a better chance for showers and
storms late Monday and into Monday night. The next upper trof will
move across Colorado Monday night through early Tuesday with a
fairly healthy cold front and enough moisture to spawn a round of
showers and thunderstorms late in the day, especially over
northern sections bordering Wyoming and Nebraska.  Temperatures
will drop to a little below normal temperatures both days with
readings into the 70s.

By Tuesday and Wednesday Colorado will be replaced with a moderate
and dry northwest flow aloft. Temperatures will be quite cool on
Tuesday behind the trof then some moderation in temperatures on
Wednesday. The flow weakens some as high pressure ridge builds into
Colorado through Saturday. temperatures will warm back into the 80s
with just a slight chance of late day storms by Friday afternoon.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1025 AM MDT Sat Jun 6 2020

Winds will be the concern through the afternoon. There has been a
temporary lull behind the first batch of passing light showers,
but with more heating, mixing, and additional showers and storms
winds will become strong and gusty. Stronger winds are expected to
develop by 20Z with gusts 40-45 knots likely. Blowing dust may
reduce visibility to less than 5SM. It looks like stronger
convection (perhaps a couple rounds) will race across the Front
Range airports 20Z-24Z, with gusts around 55 knots possible.
Winds will gradually subside 00Z-03Z.

&&

.FIRE WEATHER...
Issued at 339 AM MDT Sat Jun 6 2020

Strong winds combined with warmer than average temperatures will
increase fire danger across the eastern plains later this afternoon.
Humidity values should drop to 15 to 20 percent, just above
criteria, but given the magnitude of winds any fire could spread
rapidly out of control. We should see higher coverage of rain in
Park County and southern foothills (Fire Zones 214 and 216), so we
won't be issuing there.

Continued critical fire weather conditons expected again on
Sunday afternoon. In the wake of Saturday's disturbance, Eastern
Colorado will be under a moderate to strong southwest flow aloft.
Good mixing will result in southwest wind gusts up to 40kt
expected in the afternoon while humidity levels dropping to around
10 percent. May need to add fire weather zone 216, 217, 244 but
will wait and see how much precipitation falls today before
adding more zones to the Sunday threat. Should be noted that since
the Saturday and Sunday red flag warning conditions have been
combine, the threat for early Sunday morning is lower.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 9 PM MDT this evening for COZ041-045>051.

Red Flag Warning until 9 PM MDT Sunday for COZ241-245>251.

High Wind Warning until 6 PM MDT this evening for COZ040-042>044.

&&

UPDATE...Barjenbruch
SHORT TERM...Bowen
LONG TERM...Entrekin
AVIATION...Barjenbruch
FIRE WEATHER...Bowen/Entrekin

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1055 AM MDT Sat Jun 6 2020

COZ030>051-071700-
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-
1055 AM MDT Sat Jun 6 2020

...HIGH WINDS...SEVERE STORMS WITH DAMAGING WINDS...AND HIGH FIRE
DANGER TODAY...

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

.DAY ONE...Today and Tonight

Scattered thunderstorms developing this afternoon will be capable
of producing damaging winds. Wind gusts as high as 80 mph can be
expected from the stronger severe storms, possibly resulting in
property damage and dangerous travel conditions. High profile
vehicles should not travel this afternoon, while others should
remain aware for very strong cross winds and areas of blowing
dust. Visibility may be suddenly reduced near open fields.

Outside of the thunderstorms, gusty winds of 45 to 60 mph will
develop in all areas this afternoon. The strongest of these more
persistent winds are expected to develop over the Palmer Divide
and just east of the I-25 Corridor.

Fire danger will also be very high over the eastern plains and
Palmer Divide as high winds combine with unseasonably warm
temperatures. Avoid burning or any outdoor activity that may
produce sparks, as rapid fire growth is possible.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

The plains will see very warm temperatures and gusty south winds
increasing by late Sunday morning which will raise fire danger
again to critical levels through early Sunday evening. Wind gusts
up to 50 mph are expected Sunday while humidity levels will be
under 15 percent. Conditons will be drier with no thunderstorms
expected.

On Monday, another upper level weather disturbance will be
passing over the northern half of Colorado with showers and
thunderstorms over the mountains moving out onto the plains in the
afternoon. Some thunderstorms may become severe Monday afternoon
over northern sections.

Cooler temperatures are expected through the middle part of next
week with a little less thunderstorm activity for Tuesday and
Wednesday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated today and tonight. However,
any reports of strong wind gusts or wind damage will be
appreciated.

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE DENVER CO
118 PM MDT SAT JUN 6 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0100 PM     NON-TSTM WND GST 3 E PARKER              39.51N 104.71W
06/06/2020  M71 MPH          DOUGLAS            CO   TRAINED SPOTTER

            MINOR TREE DAMAGE.

1247 PM     NON-TSTM WND GST 2 SE DENVER INTL AIRPOR 39.84N 104.65W
06/06/2020  M59 MPH          DENVER             CO   OFFICIAL NWS OBS

1234 PM     NON-TSTM WND GST 2 NE LONE TREE          39.56N 104.85W
06/06/2020  M62 MPH          DOUGLAS            CO   ASOS

            CENTENNIAL AIRPORT.

1130 AM     NON-TSTM WND GST 13 ENE KIOWA            39.41N 104.24W
06/06/2020  M59 MPH          ELBERT             CO   MESONET

            MESONET STATION AR864 KIOWA.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE DENVER CO
227 PM MDT SAT JUN 6 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0212 PM     TSTM WND GST     1 ENE BERTHOUD PASS     39.80N 105.77W
06/06/2020  M75 MPH          GRAND              CO   AWOS

            AWOS STATION K0CO BERTHOUD PASS.

0154 PM     TSTM WND GST     3 ESE COPPER MOUNTAIN   39.47N 106.10W
06/06/2020  M79 MPH          SUMMIT             CO   MESONET

0154 PM     TSTM WND GST     1 S COPPER MOUNTAIN     39.48N 106.15W
06/06/2020  M74 MPH          SUMMIT             CO   AWOS

            AWOS STATION KCCU RED CLIFF PASS.

0102 PM     NON-TSTM WND GST 2 SE DENVER INTL AIRPOR 39.85N 104.65W
06/06/2020  M60 MPH          DENVER             CO   ASOS

            ASOS STATION KDEN DENVER.

0100 PM     NON-TSTM WND GST 3 SSW CASTLE ROCK       39.34N 104.86W
06/06/2020  M64 MPH          DOUGLAS            CO   MESONET

            MESONET STATION DW6400 CASTLE ROCK.

0100 PM     NON-TSTM WND GST 3 E PARKER              39.51N 104.71W
06/06/2020  M71 MPH          DOUGLAS            CO   TRAINED SPOTTER

            MINOR TREE DAMAGE.

1247 PM     NON-TSTM WND GST 2 SE DENVER INTL AIRPOR 39.84N 104.65W
06/06/2020  M59 MPH          DENVER             CO   OFFICIAL NWS OBS

1245 PM     NON-TSTM WND GST 13 ENE KIOWA            39.41N 104.24W
06/06/2020  M71 MPH          ELBERT             CO   MESONET

            MESONET STATION AR864 KIOWA.

1234 PM     NON-TSTM WND GST 2 NE LONE TREE          39.56N 104.85W
06/06/2020  M62 MPH          DOUGLAS            CO   ASOS

            CENTENNIAL AIRPORT.

1125 AM     NON-TSTM WND GST 3 NNW LOUVIERS          39.51N 105.02W
06/06/2020  M67 MPH          DOUGLAS            CO   MESONET

            MESONET STATION AT112 LITTLETON.

&&