Severe Thunderstorm Warning 207, NWS Goodland, KS

Area Forecast Discussion
National Weather Service Goodland KS
731 PM MDT Thu Aug 6 2020

.UPDATE...
Issued at 720 PM MDT Thu Aug 6 2020

Based on storm movement and activity, have adjusted the rainfall
chances to mainly be over the southern half of the forecast area.
Storms about to enter Cheyenne County CO will be encountering the
nose of a developing LLJ, which should cause them to increase, or
at least maintain, themselves. Question becomes how far east do
the storms move before fading. Based on latest data am thinking
the storms should decline in coverage as they move east of the CO
border. However, am concerned the close proximity of the LLJ nose
to the southern half of the forecast area will be enough to
continue to maintain the storms as they progress eastward.

As the evening draws on, confidence of severe weather occurring
with these storms is declining. Effective shear is on the low end
for severe thunderstorms, and this the time of day when
thunderstorm winds may not completely reach the ground with full
intensity compared to what is seen on radar. Due to the slow storm
movement, heavy rainfall is still a concern.

&&

.SHORT TERM...(This evening through Friday)
Issued at 235 PM MDT Thu Aug 6 2020

As of 3 pm CDT...2 pm MDT...skies across the Tri-State Region are
mostly clear although there are a few cumulus clouds and high clouds
out there. Temperatures have risen into the 80s areawide. Winds are
from the south to southeast at 10 to 15 mph with some gusts to 25
mph. At the surface, a lee trough is located just east of the
Colorado Front Range. Aloft, a shortwave trough is moving northeast
across central Colorado as seen from water vapor imagery. Latest
radar and satellite imagery show storms developing in the Denver
Metro and just east of Denver over the Colorado Plains. These storms
have bee slow to progress east so far and we likely remain a couple
hours from having storms in the NWS Goodland Forecast Area (Yuma,
Kit Carson, and Cheyenne Counties in Colorado).

For the rest of this afternoon through tonight, expecting the storms
in Colorado to begin progressing east, eventually approaching the
Colorado border by 6 pm MDT or so. Latest mesoanalysis indicates an
unstable environment (an axis of 2500-3500 j/kg of SBCape, little
CIN, lapse rates of 8 C/km or so) with some shear also present (0-6
km effective bulk shear of around 25-30 kts). In addition, DCAPE is
1000-1500 j/kg which suggests opportunity for downbursts/cold pool
formation. However, convective allowing models indicate that storms
may fall apart as they cross the Colorado border. This may be
because of a strengthening cap as suggested by model soundings. That
being said, similar to last night, if a cold pool is able to form
and the current storms gather some forward momentum, it's possible
the storms could advance much further than the models currently
suggest. Therefore, for tonight, have the best chances for storms
over eastern Colorado this evening (5-8 pm MDT or so), with chances
gradually trailing off as we go east into northwest Kansas and
southwest Nebraska. Will be interesting to see how it plays out, but
there is definitely a threat for storms for everyone across  the
area tonight. How far east that threat will make it is the question
reducing confidence this time around.

Once storms clear the area, attention then turns to the potential
for patchy fog tomorrow (Friday) morning. The best location for fog
will be east of Highway 25, ahead of an advancing surface low where
winds will go calm and low level moisture is highest. Did insert
patchy fog into the forecast as a result.

For tomorrow, anticipate much warmer temperatures across the area.
With a low pressure moving across the region, expect light and
variable winds throughout the High Plains. Dry air is widely
expected to move into eastern Colorado from the west...however, with
the light winds, don't think fire weather will be too much of a
concern, especially with recent rainfall over the area. Will still
mention a threat of elevated fire weather conditions due to the
longer-fused drought conditions being observed, but not sure it will
amount to much. Chances for precipitation tomorrow do not appear so
good, and have gone with a dry forecast.

.LONG TERM...(Saturday through Thursday)
Issued at 255 PM MDT Thu Aug 6 2020

At the beginning of the forecast period on Saturday, forecast
guidance shows the Tri-State region under the backside of an upper
air ridge giving a southwesterly flow aloft. Forecast models show an
upper air low over Saskatchewan continuing to move east across
Canada bringing an upper air trough reaching down into the Northern
Plains area and pushing the ridge eastward on Sunday. This pattern
will lead into a generally westerly zonal flow aloft going into
Tuesday. On Wednesday, an upper air ridge develops over the Rockies
and moves over the Tri-State area on Thursday.

At the surface, model guidance for Saturday evening shows a chance
for showers and thunderstorms across the CWA as an upper air
shortwave trough passes over the area. Monday also shows a chance
for showers and thunderstorms across the CWA as cold front
associated with Canadian surface low passes through the area. Models
show the eastern counties of the Tri-State area seeing a slight
chance of showers and thunderstorms on Tuesday evening as well
associated with an upper air shortwave trough passing through aloft.

High temperatures for the Tri-State area are expected to warm into
the middle to upper 90s through the weekend cooling to the upper 80s
on Monday due to the cold front with lower 90s for the remaining
days of the forecast period. Saturday may see heat indices in the
lower 100s in the eastern CWA counties. Low temperatures will remain
in the upper 50s to lower 60s range in areas west of Hwy 25 with the
eastern areas seeing lows in the lower to upper 60s during the
forecast period.

As the forecast period shows warmer temperatures during the weekend,
there is a chance for possible fire weather conditions for the
western portions of Kit Carson and Cheyenne counties as well as all
of Yuma, Kit Carson, and Cheyenne counties on Sunday. Minimum RH
values for these areas on these day are expected to be near or below
20%. However, forecasted wind gust values on both days do not
support elevated fire weather conditions.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 536 PM MDT Thu Aug 6 2020

VFR to MVFR conditions forecast for the TAFs. Current storm
activity over Eastern CO may move near KGLD between 1z and 5z. At
this time am not confident enough of storm activity to be near the
KGLD to put a mention in the TAF. At KMCK the storms should be
well south of the site. The main impact will be the slight
reduction in visibility and the low clouds moving up from the
south after 10z.

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

UPDATE...JTL
SHORT TERM...RRH
LONG TERM...076
AVIATION...JTL

Hazardous Weather Outlook
National Weather Service Goodland KS
734 PM MDT Thu Aug 6 2020

COZ090>092-KSZ001>004-013>016-027>029-041-042-NEZ079>081-080145-
Yuma County-Kit Carson County-Cheyenne County-Cheyenne-Rawlins-
Decatur-Norton-Sherman-Thomas-Sheridan-Graham-Wallace-Logan-Gove-
Greeley-Wichita-Dundy-Hitchcock-Red Willow-
734 PM MDT Thu Aug 6 2020 /834 PM CDT Thu Aug 6 2020/

This hazardous weather outlook is for extreme southwest Nebraska...
northwest Kansas and east central Colorado.

.DAY ONE...TODAY...

Strong to severe thunderstorms may occur south of I-70 this evening.
The main threats will be hail up to quarter size, wind gusts up to
60 MPH, and heavy rainfall.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH THURSDAY...

Elevated fire weather conditions are possible over eastern Colorado
as minimum relative humidity values drop below 15 percent Friday
afternoon.

Isolated severe thunderstorms are possible north of Interstate 70
Saturday afternoon and evening.

Heat Index values in the lower 100s are also possible east of a line
from McCook, Nebraska to Gove, Kansas where ambient temperatures in
the upper 90s will combine with dewpoint temperatures in the middle
60s.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed. Any weather reports by phone or
social media are appreciated.

JTL

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Special Weather Statement
National Weather Service Goodland KS
808 PM MDT Thu Aug 6 2020

COZ092-070245-
Cheyenne County CO-
808 PM MDT Thu Aug 6 2020

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN CHEYENNE COUNTY IN
EAST CENTRAL COLORADO UNTIL 845 PM MDT...

At 808 PM MDT, Doppler radar was tracking a strong thunderstorm 10
miles south of Boyero, or 36 miles south of Flagler, moving southeast
at 25 mph.

Penny size hail and wind gusts up to 50 mph will be possible with
this storm.

Locations impacted include...
Kit Carson, Wild Horse and Aroya.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 3869 10317 3869 10316 3893 10316 3878 10276
      3861 10294 3861 10317
TIME...MOT...LOC 0208Z 305DEG 21KT 3879 10324

JRM