712
FXUS63 KGLD 191046
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
446 AM MDT Thu Sep 19 2024

.KEY MESSAGES...

- Thunderstorms confined to southeast CO and southwest KS may
  send robust outflow north toward the I-70 corridor late Friday
  afternoon, resulting in an abrupt wind shift (from SW at 15-25
  mph to S at 40-55 mph). Dangerous fire weather conditions and
  significant reductions in visibility assoc/w blowing dust
  would accompany such a wind shift, if present. Confidence is
  low that such a scenario will unfold.

- Showers and thunderstorms will develop over much, or all, of
  the Tri-State area this weekend as a potent upper level low
  tracks eastward across the Rockies and Central Plains. An
  instance of flash flooding or river flooding is possible,
  mainly Saturday afternoon through Sunday morning. Barring a
  significant change in the evolution of the upper wave, severe
  weather seems unlikely in the Goodland CWA.

- Low temperatures in the upper 30s are forecast for eastern
  Colorado Monday morning.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 440 AM MDT Thu Sep 19 2024

Overview: A modest upper level ridge over the Southern Plains
will amplify and extend northward over the Central Plains today
and Friday. A potent upper level low stalled along the central-
southern California coast today-tonight will begin to track E
toward the Desert Southwest (Fri) and ENE toward the 4-Corners
(Fri night).

Today: Clear skies and unimpeded insolation assoc/w the
amplifying upper ridge over the region will foster dry
conditions. Modest cold advection /15-25 mph N-NW winds/ in the
wake of a weak cold frontal passage early this morning will
temper highs to some degree. Expect light/variable winds and
temperatures ranging from ~80-88F this afternoon, coolest in
northeast CO.

Friday: A modest, baggy lee cyclone will develop in the lee of
the Rockies during the aft-eve.. as upper level flow backs to
the SW and strengthens in advance of the aforementioned upper
low. Recent /00-06Z/ guidance indicates low-mid level flow
(winds from the surface to 10 KFT AGL) on the order of ~15-20
knots Friday afternoon.. suggesting SW winds on the order of
15-25 mph. Near-critical to locally critical fire weather
conditions are possible in eastern CO and adjacent KS-NE border
counties (mainly along/west of Hwy 27).. where deep vertical
mixing may yield very dry conditions (minimum RH readings ~10
percent). While isolated high-based convection cannot entirely
be ruled in far southern portions of the area (Greeley, Wichita,
Gove counties) where meager high-based instability may be
present during the late afternoon.. guidance continues to
indicate that diurnal convection will likely be relegated south
and east of the Goodland CWA. While convection itself may be
relegated to southeast CO and southwest KS.. simulated
reflectivity forecasts via recent runs of the HRRR and NAM NEST
suggest that said convection may produce robust outflow that
surges north toward the I-70 corridor during the late afternoon.
If such a scenario were to play out -- i.e. an abrupt
convective wind shift (from SW @ 15-25 mph to S @ 40-55 mph) in
the 22-02Z time frame -- dangerous fire weather conditions and
significant reductions in visibility assoc/w blowing dust would
both be `on the table`, especially along/south of I-70. Given
that this scenario highly depends upon specific aspects of
upstream convective development/coverage (in a weak forcing
regime, no less).. confidence is quite low.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 236 AM MDT Thu Sep 19 2024

The long-term looks to start off active and become more docile
through early next week.

Saturday morning, a well organized low pressure system will be
near the Four Corners Region, rapidly moving northeast into the
High Plains. Throughout Friday night, a moderately strong 850 mb
LLJ will set up and move additional moisture into the region.
The additional moisture will keep temperatures from cooling off
too much Saturday morning, but will limit day time heating. High
temperatures are expected to be in the upper 70s to mid 80s
across the region, but if the clouds break, expect warmer
temperatures. The combination of warm, moist air with the low
pressure system (and associated fronts) will increase shower and
storm intensity in the late afternoon and evening hours
Saturday. Models are fairly consistent with widespread
precipitation being expected. Deep layer shear during this event
looks to increase the potential for severe weather (~5%), but
instability is fairly weak. The heaviest precipitation looks to
be focused between 21Z Saturday through 12Z Sunday, with lighter
rain linger through Sunday. There is a hydrology section below
which goes into more detail about the precipitation.

There is also a small (<10%) chance winds ahead of the storms
could gust around 35 kts in eastern Colorado producing blowing
dust. If there is a clearing of the clouds and the winds are
able to pick up, localized blowing dust could occur, otherwise
blowing dust is not expected to be a major hazard.

As the low moves farther into the CWA, winds will become
northwesterly and start cooling off the area. High temperatures
on Sunday look to remain largely in the upper 60s, and
potentially cooler depending on the efficiency of the CAA. The
low pressure system will take until Sunday night to move out of
the area, giving the area increased PoPs through Sunday evening.

Sunday night, as rising pressure clears out the sky, winds in
the southwestern CWA are expected to weaken. The clear skies and
weak winds will allow for very efficient cooling, potentially
dropping temperatures into the mid 30s by Monday morning. If
these ideal cooling conditions can start occurring at sunset,
there is about a 15% potential for light, patchy frost to form
in the extreme southwestern CWA. If the clouds linger or winds
are stronger than forecast, frost will not be an issue.
Throughout the CWA Sunday night, Colorado looks to cool below 40
while the rest of the CWA will be in the low to mid 40s; autumn
is starting to show up.

Once the low moves out, northwesterly flow is expected to
dominate the High Plains through the remainder of the period.
This will keep high temperatures in the 70s. Overnight, winds
look to hover around 5-10 kts, keeping the lows in the 40s to
low 50s for the rest of the period. As is typical in
northwesterly flow on the High Plains, shortwaves are bound to
occur and could bring isolated to scattered showers and storms
into the area. Monday through Thursday, no organized systems
seem likely, just the potential shortwave showers.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1053 PM MDT Wed Sep 18 2024

Not much change. VFR prevailing at both KGLD and KMCK
overnight. S winds shifting NW closer towards Thursday morning
becoming breezy towards midday with gusts up around 20 kts. Will
see those NW winds diminishing into the evening hours.

&&

.HYDROLOGY...
Issued at 236 AM MDT Thu Sep 19 2024

An efficient 850mb LLJ is expected to start setting up around
21Z Friday and continue until Sunday morning. This LLJ will
provide a moist conveyor belt from the Gulf of Mexico into the
High Plains. As mentioned above, an organized low pressure
system will move into the region Saturday, creating a moderately
strong forcing mechanism to start precipitation.

Precipitation looks to start in the eastern CWA Friday evening,
intensifying Saturday afternoon, and begin weakening Sunday
morning before moving out of the area by Sunday evening. Between
21Z Saturday and 12Z Sunday, nearly the entire Tri-State area
will see at least a couple tenths of rain with the potential
(~25%) of seeing 2+ inches in that timeframe. If the higher
amounts do occur, especially in the eastern CWA, there will be
increased flooding concerns. Concerns for flash flooding are low
(<10%) with the potential for areal flooding being slightly
high at around 20%.

Throughout the entire event, locations along and northeast of a
line from Oakley, KS to Yuma, CO can expect to see 0.75-1.5
inches of rain, with pockets of 3+ inches being possible.
Locations southwest of that line will receive less
precipitation, likely in the 0.3-0.75 inches of rain.

&&

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

&&

$$

SHORT TERM...Vincent
LONG TERM...CA
AVIATION...024/Sipprell
HYDROLOGY...CA