-- Discussion containing changed information from previous version are highlighted. --
400
FXUS63 KGLD 281116
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
516 AM MDT Tue May 28 2024

.KEY MESSAGES...

- Chance for severe weather and flooding throughout the week.
  Confidence in specific hazards change each day, but a very
  active pattern is expected.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 256 AM MDT Tue May 28 2024

Current observations continue to show a large upper ridge over the
Western CONUS while moisture continues to move in from the southeast in
the lowest kilometer or two. There have been a few echos on radar
trying to move in from the west, but the showers have not been able
to hold together with the drop in elevation and dry air over Eastern
Colorado.

For this morning, there could still be a few showers or storms just
before sunrise as the moisture advection continues along with some
mid level moisture already over the area. However, chances will
decrease after sunrise with a lack of instability or forcing
mechanisms based on the current forecast. There are some outlier
solutions that erode the inversion faster and bring better
saturation in the low levels to counties along and south of US 40.
If this panned out, there could be a chance for severe storms with
hail as the main threat. Current chance of this scenario is around 5-
10%.

For the afternoon and evening hours, a mix of clouds and clear skies
are forecast with more intermittent chances for showers and storms.
As long as cloud cover does not persist over an area, temperatures
should warm into the low 80`s with 850mb temps in the low 20`s
celsius. There will be two possible rounds of storms. The first
would be during the early afternoon. With broad low pressure to the
west and broad high pressure to the east, winds are forecast to
generally remain from the southeast, but locales near the Colorado
border could become more southerly depending on how far and deep the
low stretches. If the southerly winds do develop, a an area of
surface convergence would set up likely just east of Highway 27 and
serve as a genesis for storms. Anything that develops north of I-70
would likely struggle as most guidance suggests the effective shear
would be below 20kts and just allow for pulse storms. South of I-70,
effective shear could be better and potentially reach 40-45 kts
which would allow for large hail as the primary severe threat.
However, if the lower flow remains more homogenous, storms will
struggle to form at all and would be limited to pulse storms. Going
into the evening, a shortwave is forecast to move through the area
and help spark some storms off the higher terrain in Colorado. These
storms would south of I-70 where moisture availability is higher.
These storms could also be severe, but torrential rainfall would
also be more likely. Flooding chances remain low though as the
favored area for storms has been dry of late and would likely be
able to take a few inches.

In short, there are multiple chances for storms this afternoon and
evening with a small chance of them being severe. Large hail would
be the main threat, but there would be a low chance for damaging
wind gusts and a tornado. Overall severe threat is limited by a lack
of forcing and shear which may keep storms more as pop up storms
with short life cycles.

The rest of the night and into tomorrow morning, a mix of cloud
cover and clear skies is forecast with lows dropping into the 50`s.
Storm chances are also forecast to lower, but the increase in
moisture availability will keep at least a 10% of showers through
the period. The increased moisture and light southeasterly winds
could also produce fog across the area, favoring NW Kansas and SW
Nebraska.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 256 AM MDT Tue May 28 2024

SPC has placed portions of the CWA under a Slight risk Wednesday and
Thursday. Through Saturday, there is concern of flooding across the
CWA. The Hydrology section below will go into more detail about this
risk.

Wednesday afternoon, the upper-level ridge axis looks to be moving
over the CWA and will exit to the east throughout the evening and
overnight hours. A 250 mb trough will be moving in from the
northwestern CONUS and push the ridge on to the east. A 500 mb
shortwave is showing on most prognostic models around 18Z Wednesday
and lasting through about 6Z Thursday. At the same time, a high
pressure system over the Gulf of Mexico will extend a ridge up into
the easter Great Plains, leading to a persistent LLJ that will move
copious amounts of moisture into the mid-CONUS. These features will
cause the first round of storms over the next few days. There is a
slight risk for severe weather to occur from these storms in eastern
Colorado and adjacent counties to the east. The main threats with
these storms will be 1-1.5 inch hail and wind gusts near 60 MPH. As
the evening progresses into the night, the severe potential will
drop significantly, but showers and storms are expected to continue
into the eastern portions of the CWA into Thursday morning.

Thursday, the upper-level trough works farther to the east, as does
the ridge. Model guidance is suggesting the trough will be much
weaker than previous believed and we will have nearly zonal flow in
the upper levels that mid-level shortwaves will propagate through.
The LLJ looks to remain consistent until Thursday night, mainly due
to the 850 mb ridge splitting off and becoming it`s own high
pressure system near the Great Lakes region. Thursday night, an 850
mb lee low is expected to move through the area around 6-12Z Friday.
While this will disrupt the LLJ moving moisture directly into the
for about 30 hours, the low will cause wrap around moisture to move
into the area. After the low clears the area, the LLJ returns to its
former stance. This moist conveyor belt will keep PWATS in the 1-
1.3+ inch range until Saturday night.

Thursday is looking to have the highest PWATS, ranging from 1.15-1.4
inches, EBWD shear around 25-35 kts, and the 0C line being around
14,000 feet. These parameters suggest storms that form will produce
heavy rain and potentially severe weather. Instability in the
environment could easily turn heavy rain storms into large hail
storms. MUCAPE from the GFS is around 3,000 J/kg. The most likely
hazards Thursday will be heavy rain leading to localized flooding,
hail, and strong winds, in that order.

Friday`s severe convective parameters have reduced over the past 24
hours, likely due to the 850 mb lee low moving out of the area
around this time. If there is a severe threat Friday, it will likely
be limited in scope and severity. Any precipitation that does form
would still have 1 inch PWATS and about 500-1,000 J/kg of MUCAPE to
tap into, so high precipitation cells may form.

Model guidance is showing Saturday could be a fairly active day with
potentially severe weather. Confidence drops tremendously with
Saturday`s forecast, but we are expecting the upper-level trough
axis to move through the area and a weak ridge to build in. This
would create enough forcing for another round of storms before the
extra moisture is forced out of the CWA. PWATS around an inch are
still expected which suggests potential for high precipitation
storms, yet again.

Temperatures will be in the mid 70s to low 80s Wednesday through
Friday. Saturday, could see temperatures in the mid 80s if the
moisture clears out early, otherwise another day in the 70s can be
expected. Low temperatures will remain fairly warm Wednesday night
through Saturday night due to generally southerly winds and cloud
cover, and will remain in the 50s to low 60s throughout the
period.

For Sunday and into the beginning of next week, there is a little
uncertainty in what the pattern will look like as current guidance
suggest almost a zonal flow over the area. There is some hints at a
low amplitude trough moving through late Sunday. With this,
temperatures could warm into the 90`s with storms ahead of the
trough. After that, zonal flow or some ridging looks to return which
would keep the area warm with temperatures near 90 and daily chances
for storms.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
-- Changed Discussion --
Issued at 513 AM MDT Tue May 28 2024

For KGLD & KMCK... VFR conditions are forecast through most of
the period, though will need to watch for IFR conditions towards
the end of the period with fog moving in potentially after 09Z.
The other conditions worth noting is the chance for
thunderstorms at both terminals this afternoon. Between 18 and
23Z, there is a chance for pop up thunderstorms at both
terminals. However, the chance is only around 15-20% so the
thunderstorms have been left off the TAF at this time. As for
the morning showers ongoing, these should end near the terminal
within the first hour or two and look to already be away from
the terminals as of 1115Z.
-- End Changed Discussion --

&&

.HYDROLOGY...
Issued at 256 AM MDT Tue May 28 2024

Highly efficient moisture return looks to begin late Tuesday night
and continue into the end of the workweek via the 850 mb LLJ. This
moist conveyor belt will cause PWATS to increase above 1 inch
starting Wednesday and potentially remain that way until Saturday.
The highest values will be in the eastern CWA, but the majority of
the Tri-State area will have a good chance (60%+) at seeing PWATS
above 1 inch. Throughout this active pattern, a high melting layer
is also expected, generally 11,000-15,000 feet agl.

Tuesday does have a very low concern for flooding (~5%) as clusters
of storms could produce multiple rounds of precipitation over the
same area. This precipitation is expected to remain more in the
southern CWA where conditions have been dry, so the ground will
likely soak it right up.

Wednesday and Thursday are currently the best days for storms to
create heavy rainfall that could lead to rate-driven flash flooding
and duration-driven areal flooding. Friday and Saturday are also at
risk for flooding potential due to a combination of efficient rain
producing storms and potentially multiple days of heavy rain
saturating the soil.

Current confidence in localized flooding occurring in the latter
half of the week is around 10-15%.

&&

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

&&

$$

SHORT TERM...KAK
LONG TERM...CA/KAK
AVIATION...KAK
HYDROLOGY...CA