770
FXUS63 KGLD 212035
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
235 PM MDT Fri Jun 21 2024

.KEY MESSAGES...

- Continued very windy today with 20%-40% chances for afternoon
  and evening thunderstorms, mainly along/north of I-70, some of
  which could become severe.

- Weekend looks to remain hot with highs in the 90s to low 100s.
  Could be a few thunderstorms Sunday afternoon/evening.

- Skeptical regarding how quickly the upper level ridge
  retrogrades west going into next week. Depending on where the
  ridge is will dictate where storms will move through.

- If ridge is delayed, the arrival of the hottest temperatures
  will be delayed too.

- Chances for storms each day next week.

&&

.UPDATE...
Issued at 232 PM MDT Fri Jun 21 2024

Storms are forming over the northern portions of the CWA along
the cold front and in the eastern CWA along the dryline. The
storms in the north are in a favorable environment for
explosive growth. Due to the potential for these storms to
become severe over the next several hours, a Severe Thunderstorm
Watch has been issued until 10 PM MDT or 11 PM CDT.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 150 PM MDT Fri Jun 21 2024

We currently have a 250mb high pressure system over Texas and a low
pressure system north of Montana. These two features are creating a
jet streak from the southwest over the Colorado Rockies and into the
northern High Plains. Starting this afternoon and continuing over
the weekend, the high stays in place while the low moves on to the
east. This afternoon and overnight, the jet streak will strengthen,
while staying northwest of the CWA, giving us some upper level
support for convection. In the lower levels, a lee low will eject
off the Rockies in northern Colorado. Looking at current
observations, the low and associated cold front have already formed
and has nearly stalled out in eastern Colorado. A weak surface ridge
from Texas up into central Kansas is working to stall the low, but
this ridge will erode throughout the day. Around 22-1Z, the ridge is
mostly gone and the low is expected to start moving again. As the
cold front starts gathering speed, it is expected to trigger
convection. This will be our main round of storms for the evening.

However, before we talk more about the main event this evening, CAMs
are showing a line of convection forming around 21Z between Goodland
and McCook. This looks to be convective temperature initiated and
will quickly move out of the area to the east. Probability of these
storms forming are low, about 20%.

Back to the main event; severe weather is possible with the storms,
mainly between 0-4Z, but confidence is only about 10-20% severe
weather will occur. The biggest threat this evening will be wind
gusts. The storms will be fairly quick, about 40 kts of downshear
speed, about 2,000 J/kg of CAPE, 1,000 J/kg of DCAPE, with PWATS
ranging from 1.2-1.6. This is leading to the potential of a wet
microburst set up with quick moving storms. Gusts up to 60-65 MPH
are possible with the storms if they are able to vertically load a
heavy amount of precipitation. Hail will also be possible, but with
the 0C line being about 16,000 ft AGL, a fairly moist melting layer,
and effective shear only about 30 kts, large hail seems unlikely. We
could see a few stones around 1-1.5 inches if a storm lasts long
enough for hail to grow that large. Otherwise, SPLASHie (Storm
Producing Large Amount of Small Hail) storms or extremely heavy
downpours are expected from majority of the storms.

The storms are expected to form in our Colorado counties and move
east-northeast, generally staying north of a line of Sharon Springs
to Ludell. A small cluster or two of storms, or isolated cells are
forecast for this event, so widespread heavy rain is NOT
anticipated. The storms look to start decaying around 4-6Z with some
light showers possible afterwards until maybe 9Z at the latest.
Northwesterly dry air will then move in and end any remaining
precipitation.

Overnight, the cloud ceilings will continually ascend, even into
tomorrow afternoon, making skies mostly clear by then. Winds will
follow a similar trend and weaken gradually overnight and into
tomorrow, becoming northwesterly then northeasterly as time goes by.
Lows tonight in the east will be kept a bit warmer due to the cloud
cover, but temperatures will cool into the lower 60s to mid 70s.

Back up at 250mb, tomorrow sees the high stay in position over Texas
as the low continues on east, giving us mostly zonal flow. This
perpetuates through Sunday night, giving us a fairly stable upper-
level. At 500mb, the high pressure system retrogrades from the
southeastern US to the Southern Mississippi River Valley, continuing
to reduce the potential of organized convection through the weekend.
In the lower levels, we can expect southwesterly flow to continue
which will have little moisture content through the period. This
will also contribute to low PoPs. There are some near 30 PoPs in the
western CWA due to orographically forced showers and storms moving
into our area and decaying.

Temperatures will be a bit cooler tomorrow, due to the cold front
this evening, with highs in the upper 80s to mid 90s. Tomorrow night
will see mostly clear skies that allow the area to cool into the
lower to mid 60s. Sunday will start a warming trend and highs will
be in the upper 90s to lower 100s. This will be a very hot day and
precautions should be taken to stay cool Sunday!

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 1252 PM MDT Fri Jun 21 2024

This part of the forecast will be greatly influenced by the
upper level ridge. Models have the ridge entrenched over the
Southern Plains, centered over TX. With the ridge south of the
forecast area, models have zonal flow over us. Within the zonal
flow, upper level short wave troughs move overhead almost daily.
This may lead to precipitation chances for us.

However am skeptical of the ridge being centered over TX before next
week starts.  Models have been moving the ridge west too fast, which
is to be expected when the ridge is a blocking high pressure.  For
this reason am doubtful the ridge will scoot west as quickly as
currently forecast.  A delay in the ridge moving west should cause
the upper level flow over the forecast area to be more from the
southwest than the west.  This would influence where storms will
track across the forecast area, and affect how hot the forecast area
becomes.  If the ridge does end up being slower to move west, the
hot air under it will stay more to the east.

Even though models have upper level short wave troughs moving
through the flow over the forecast area, am thinking the storm
coverage should be on the low side.  This is more reflective of a
summertime pattern in which storms are isolated to scattered at
best.

If the current forecast is on track, there may be a brief
respite from heat midweek as a weak cold front moves through.
However high temperatures rebound by the end of the workweek.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1117 AM MDT Fri Jun 21 2024

Generally VFR conditions will be observed at both KGLD and KMCK,
but strong winds, made worse with storms this afternoon and
evening, will make for some tricky conditions. Models are
having a difficult time figuring out exactly what is going to
happen over the next 8 hours, but we are currently expecting two
waves of storms. The first will form around 21Z and move away
from the TAF sites by 0Z. The second wave, the wave with higher
confidence, will impact KGLD around 1Z and should stay south of
KMCK. This second wave is expected to produce strong winds as it
progresses eastward. If any of the stronger cells moves overhead
of either TAF site, heavy rainfall will reduce visibility
significantly. The heavy rain is the only concern for IMC
throughout the period. Later in the period, winds will weaken
and become northwesterly.

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...None.
CO...None.
NE...None.

&&

$$

UPDATE...CA
SHORT TERM...CA
LONG TERM...JTL
AVIATION...CA