703
FXUS63 KGLD 201106
AFDGLD

Area Forecast Discussion
National Weather Service Goodland KS
506 AM MDT Fri Sep 20 2024

.KEY MESSAGES...

- Briefly critical fire weather conditions are possible today
  in eastern Colorado.

- Showers and thunderstorms will develop over majority of the
  Tri-State area this weekend. Severe weather does not look
  likely, but there is a slight concern for flooding.

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

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 323 AM MDT Fri Sep 20 2024

This morning, a high pressure system over Texas is extending a
ridge over the Great Plains and Midwest. This will create mostly
clear skies for majority of the day, allowing temperatures to
warm into the low 90s. Winds will be south- southwesterly
throughout the day. In the far western CWA, around the Joes to
Flagler, CO area, the winds are expected to mix out surface
moisture and drop RH values to around 15% for a couple hours.
The winds will have picked up at this time and gusts around
25-30 kts are expected, briefly leading to localized critical
fire weather conditions. For more information, see the fire
weather section below.

Starting around 19-21Z this afternoon, a shortwave is forecast
to fire off some storms south of the CWA. Majority of this
precipitation will occur outside of the Goodland CWA, however,
Gove, Wichita, and Greeley counties could (~15% chance) see some
light showers late this afternoon. There is a low (~15%) chance
that lingering showers or sprinkles could last through the
night in the far eastern CWA. The best chance for showers over
there would be after 6Z Saturday.

Looking at isentropics, there is a well define moisture
boundary at 315K around the 19-23Z timeframe near the Tri-State
border. This feature could set off an isolated storm or two this
afternoon, but confidence is only around 10-15% this will
occur.

Overnight tonight, the pattern gets a bit more interesting as
the 850mb LLJ will kick up to around 30 kts, moving Gulf
moisture into the area. A shortwave ridge will move back over
the area, clearing out the skies by morning. A low pressure
system near the Four Corners will be moving northeast to stir up
the atmosphere throughout the day Saturday. Lows look to drop
into the low 50s in the northwestern CWA where the winds will be
weaker and skies will be clear, but in the southeast, mid 60s
are forecast where the cloud cover will linger most of the
night.

Saturday morning, the aforementioned low will be crossing over
the Rockies, but will extend a shortwave trough over the
southern CWA to cause some warm-front type showers. This
shortwave will push out the ridge from overnight, allowing
clouds to form across a large portion of the CWA. The shortwave
will also cause a broad cold front to move in from the
northwest, shifting winds as it move in. The new northerly winds
and additional cloud cover look to bisect the area, causing a
fairly strong thermal gradient to setup. In the northwestern
CWA, temperatures will be capped in the lower to mid 70s, but
southeast of the front, mid 80s are forecast.

Around 21Z Saturday, 500mb vorticity increases and begins
moving northward, indicating a start to the widespread forcing.
This forcing will cause showers and storms to form across
majority of the area with the precipitation lasting until Sunday
morning. Severe weather does not look likely (<5% chance) due
to a lack of instability, but deep shear and strong forcing
could cause a storm to over preform.

Saturday night, the low will move over the CWA causing
widespread precipitation. For more information about the rain,
see the hydrologic discussion below. Overnight lows will drop
into the 40s.

Sunday morning and into the mid-day, the low will be moving out
of the area to the east-northeast. The following pressure rises
will cause the rain to cease in the west around 15Z with
lingering showers in the east likely until around 18-21Z.
Northerly winds and clouds will keep temperatures capped to the
50s for the area. The skies are expected to clear in the
evening, allowing efficient overnight cooling.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Issued at 426 AM MDT Fri Sep 20 2024

Sunday night: Expect a west-east clearing trend as the upper
level wave responsible for inclement weather this weekend
progresses eastward into central-eastern portions of Kansas and
Nebraska. Guidance suggests that low temperatures on Monday
morning may bottom-out in the upper 30s over portions of eastern
Colorado.. where cloud cover will abate earlier. From a pattern
recognition standpoint, a few things stand out. A large, broad
mesoscale high -- in this case, a homogenous cool/saturated (or
near-saturated) low-level airmass -- will already be in place
over the region as the aforementioned upper wave exits from
west-east. Little or no horizontal thermal/moisture advection
will be present in the wake of the upper wave. In other words,
the airmass in place over the region Sunday evening -- an
airmass characterized by surface temperatures and dewpoints in
the 40s -- will remain in place overnight.. decreasing the
efficacy of radiational cooling. If this is the case, expect
atypically uniform lows in the lower-mid 40s.. and a potential
for fog. Higher elevation portions of Yuma, Kit Carson and
Cheyenne counties in CO could potentially see temperatures in
the upper 30s.. depending on precise airmass characteristics,
timing of the west-east clearing trend and duration of clear
skies prior to sunrise. Even so, the moist/saturated nature of
said airmass would likely preclude a potential for frost.

Monday: Guidance suggests that troughing /cyclonic flow/ aloft
will prevail over the Central Plains in this period.. on the
eastern periphery of an amplifying upper level ridge over the
Pacific Coast. Clear skies in the wake of the departing wave may
give way to increasing cloud cover late Mon- Mon night.. via
cyclonic shear vorticity on the eastern periphery of a strong
(~100-115 knot) northerly upper level jet extending southward
from Alberta and Saskatchewan to the central Rockies. Sunny
skies during the day will foster a warming trend. Expect
temperatures warmer than Sunday (albeit still cooler than
average).. ranging from the upper 60s (east) to mid 70s (west).

Tuesday-Friday: Below average forecast confidence. For clarity,
forecast confidence typically decreases with range -- `below
average` in this context is intended to communicate a further
reduction in confidence associated with /inherent to/ increased
pattern complexity -- e.g. patterns with cut-off waves,
multibranched wave interactions and potentially significant
forms of constructive/destructive interference or feedback.

Solutions from operational runs of the GFS/ECMWF noticeably
diverge on Tuesday. The 00Z GFS, for example, suggests that the
pronounced upper level ridge over the Pacific Coast will bodily
shift eastward across the Intermountain West (Tue), Rockies
(Wed) and Central/Northern Plains (Thu). The 00Z ECMWF suggests
a similar progression, with the exception that.. a closed low
progged (by both models) to develop invof the 4-Corners on Tue
becomes cut-off beneath.. and retrogrades within.. the
pronounced upper ridge as it progresses east across the Rockies
and Central-Northern Plains. At this time.. steering the
forecast toward climatology appears to be the most prudent
course of action.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 456 AM MDT Fri Sep 20 2024

VFR conditions are expected to prevail at both KGLD and KMCK
through the period, despite the spiders attempting to sabotage
the ASOS visibility sensors (the likely reason visibilities are
being observed less than 6SM across the region; there is no
meteorological reason). Winds will remain fairly docile this
morning until 15-17Z. At this time, winds will pick up with
gusts around 20 kts being expected. At KGLD, these winds will
continue throughout the period, but will become more westerly
after 6Z. KMCK will see the winds weaken around 0Z, but could
see northwesterly winds pick up around 12Z tomorrow morning as a
cold front starts moving into the area.

&&

.FIRE WEATHER...
Issued at 323 AM MDT Fri Sep 20 2024

This afternoon, in western Kit Carson and Yuma counties,
southwesterly winds are expected to pick up. Sustained winds around
15-20 kts with gusts up to 25-30 kts are expected. These winds will
work to mix in drier air, lowering RH values into the mid teens
across eastern Colorado. In the area mentioned above, local RH
values around 14% are expected for an hour or two. Widespread, long
duration critical fire weather conditions are not expected.

If the winds over perform and extremely dry air mixes down to the
surface, we could see some locations meet Red Flag criteria.
Confidence in the current forecast is moderate, around 60-70%,
meaning there is about a 30% chance three hours of critical fire
weather conditions could occur in the far western CWA.

&&

.HYDROLOGY...
Issued at 323 AM MDT Fri Sep 20 2024

An efficient 850mb LLJ is expected to set up around 21Z Friday-0Z
Saturday and continue until Sunday morning/mid-day. 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 early Saturday
morning, intensifying Saturday afternoon, and begin weakening Sunday
morning/mid-day before moving out of the area by Sunday evening.
Between 21Z Saturday and 18Z Sunday, nearly the entire Tri-State
area will see at least a few tenths of rain with the potential
(~25%) of seeing 1.25+ 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 or river flooding being slightly
higher at around 20%.

Throughout the entire event, locations along and southeast of a line
from Wallace, KS to Norton, KS can expect to see 0.9-1.6 inches of
rain, with pockets of 3+ inches being possible. Locations west and
north of that line will receive less precipitation, likely around
0.4-1 inch of rain, with some pockets up to 1.75 inches.

&&

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

&&

$$

SHORT TERM...CA
LONG TERM...Vincent
AVIATION...CA
FIRE WEATHER...CA
HYDROLOGY...CA