638
FXUS63 KSGF 201055
AFDSGF

Area Forecast Discussion
National Weather Service Springfield MO
555 AM CDT Fri Sep 20 2024

.KEY MESSAGES...

- Hot again today. Heat Index values will reach the 95 to 105 F
  range. Some record highs may be challenged.

- 10-30% chance for isolated showers and thunderstorms today in
  the eastern Ozarks and along the Missouri-Arkansas border. If
  storms develop, some may produce wind gusts up to 40-60 mph.

- Numerous rounds of widespread showers and thunderstorms
  through the weekend (40-90% chance). Precipitation amounts
  will be highly variable across the region, but generally expect
  the highest amounts to be north of I-44.

- A cold front will bring cooler temperatures next week with
  highs in the 70s and limited rain chances.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 400 AM CDT Fri Sep 20 2024

Current water vapor imagery depicts broad clockwise flow associated
with a mid- and upper-level ridge over the Southern Plains. West
of the ridge, a deep upper-level low is currently over
California. The amplifying wave pattern is increasing jet stream
wind speeds to 80-90 kts as they overspread the central Plains.
At the surface, a slow-moving cold front is analyzed from north
IA down through central KS and into north OK.


Hot again today. Some record highs may be challenged:

Yesterday was hot for mid-September standards. Observed highs
exceeded the forecast highs by 4 degrees in many places. This
led to Springfield having a high of 94 F and Joplin reaching a
high of 99 F which beat the previous record of 98! With the
ridge continuing to build into the region, the brunt of the cold
front largely staying out of our area, and 21-23 C 850 mb
temperatures advecting in, today is expected to be another hot
one. Highs are forecast to be in the upper 80s in the eastern
Ozarks, to the upper 90s along the MO/KS border. Given
yesterday`s over-achievement, records may be challenged again
today. Especially if skies remain mostly clear and deep vertical
mixing occurs, as evidenced by RAP forecast soundings. See the
Climate Section below for a summary of challenged records.

With upper 60s to lower 70s dewpoints, Heat Index values will
reach into the 95 to 105 F range with the higher values along
the MO/KS and MO/AR borders. While a Heat Advisory is not
anticipated, these Heat Index values are abnormal for mid-
September (>0.8 on the Extreme Forecast Index with 1 shift of
the statistical tail). This paired with the multiple day stretch
of above 90 F highs brings possible "Major" (3 of 4) heat-
related impacts to areas west of Hwy 65. Therefore, please make
sure to still follow heat safety by staying hydrated and cool.
If working outside, allow time for multiple breaks. This is
especially true as lows tonight will provide little heat relief.
Lows will be in the lower to middle 70s (76 F near Joplin!).
These will be near record high minimums.


10-30% chance for isolated showers and thunderstorms today:

A 25-35 kt W`ly low-level jet is currently overspreading the
area. Modest warm air advection associated with this, along with
convergence and uncapped 500-1000 J/kg MUCAPE at the nose of
the LLJ, will allow isolated elevated showers and thunderstorms
to develop across the eastern Ozarks (20-30% chance). These will
generally develop around 5-7 AM and move out of our CWA by 10-11
AM. Severe weather is not expected with this round of rain.

Later this afternoon, as the cold front becomes situated across
central MO, 1000-2000 J/kg of MLCAPE will develop south of the
boundary. Weak convergence along the boundary has a 10-20%
chance to force isolated showers and thunderstorms south of
I-44. The main uncertainty is the degree of capping. RAP
forecast soundings not only depict weak low-level capping, but
also a pronounced subsidence inversion associated with dry air
in the mid-levels. Forecast parcel paths are just warmer than
the environment at this level, however, model soundings usually
underestimate these types of inversions. Additionally, the dry
air aloft will effectively cool rising air more than parcel
theory allows. For that reason, it will be difficult for many
deep updrafts to develop, hence the 10-20% chance. Nevertheless,
if storms do form, 25-35 kts of background 0-6 km bulk shear
and inverted-V low-level profiles could support some downburst
gusts up to 40-60 mph, especially along and SE of a line from
Rolla to Branson where shear is higher and a Marginal (1 of 5)
Risk is in place.


First round of widespread rain chances late tonight (20-40%):

As the potent trough traverses the Four Corners region tonight
large-scale ascent on the downstream side of the wave--along
with warm air advection within a strengthening nocturnal LLJ--
will create a strong surface mass response. The cold front will
rapidly lift north as a warm front, spreading the warm and moist
airmass back over our area. Ascent from strong positive
vorticity advection and warm air advection looks to force
a thunderstorm complex over east KS. CAMs then hint at this
complex diving south into our region, bringing 20-40% chances
for showers and thunderstorms north of I-44 between 1-7 AM
Friday night into Saturday morning. Confidence is medium-high in
thunderstorms impacting areas north of I-44 during this time,
but chances are somewhat low due to disagreement in exact track
and timing. Severe weather is not expected with this round.
Widespread and more prolonged rain is more likely.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 400 AM CDT Fri Sep 20 2024

Numerous rounds of widespread showers and thunderstorms (40-90%):

Details in exact location, timing, and amounts of the next
rounds of precipitation become fuzzy through the weekend. Just
as one example, outflow from the thunderstorm complex expected
to drop through the area late Friday night will have an impact
on the location of storms during the day Saturday. What is
clear, though, is chances become high for multiple rounds of
widespread showers and thunderstorms Saturday through Monday
night as a widespread area of large-scale forcing from strong
height falls and positive vorticity advection aloft and
convergence from fronts and outflow boundaries near the surface
spreads over the region. This leads to 35-65% chances Saturday
and Saturday night with the greatest chances north of I-44 where
the warm front will be situated. Severe weather is not expected
Saturday and Saturday night.

The best chances arrive Sunday and Sunday night as the potent
shortwave lifts through the central Plains and the strong cold
front progresses through our region. Chances Sunday and Sunday
night increase to 40-90%. Once again, the greatest chances will
lie along the warm front north of I-44. There is a Marginal (1
of 5) risk for severe thunderstorms for much of our area Sunday
as strong cold front forcing pairs with 25-35 kts of 0-6 km bulk
shear as evidenced by the 03Z SREF mean. Damaging winds look to
be the main hazard, but confidence is low since instability
will likely be limited due to copious cloud debris and ongoing
thunderstorms through the weekend.

Of additional note, flooding may be a hazard for localized areas
north of I-44. Confidence is still low on this as well, since
QPF spreads are still very high due to uncertainty in location,
timing, and longevity of each round. For example, areas north of
I-44 have a spread of 0.3-0.5 inches at the 25th percentile, to
2-2.5 inches at the 75th percentile for 48-hour rainfall
(Saturday through Sunday). That being said, areas north of I-44
have the greatest chance of receiving at least an inch of rain
over the length of the weekend (50-70%). The flooding threat
will continue to be monitored and evaluated in the coming days.


Cooler temperatures next week with limited rain chances:

Ensemble cluster analysis is starting to come into more
agreement with the large-scale pattern next week. While details
about the location and intensity of shortwaves are still
uncertain, the longwave pattern looks to have a deep trough
settle over the eastern CONUS, allowing for a cooler and drier
air mass to settle into place. As expected, PoPs have also then
decreased next week as models hone in on this pattern.

Before the cold front moves through, highs Saturday and Sunday
range from the lower 80s to the middle 90s with lows around 70 F
Saturday night and ranging from the middle 50s to the upper 60s
Sunday night (cooler to the west). After the cold front clears
the region, highs next week will be in the 70s with lows in the
50s.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 555 AM CDT Fri Sep 20 2024

Medium-high confidence that VFR conditions remain through the
entire TAF period at all TAF sites. 8-12 kt winds will slowly
shift from S`ly to WSW`ly between 12-18Z as a cold front slowly
approaches the area from the N. This boundary will quickly
retreat after 00Z, bringing back southerly winds through the end
of the TAF period.

Additionally, some models are hinting at isolated showers and
thunderstorms developing near BBG sometime between 18-03Z.
Confidence on this is currently low (10-20%), so have not put in
the TAF for now.

&&

.CLIMATE...
Issued at 400 AM CDT Fri Sep 18 2024


Record High Temperatures (Springfield):

September 20:
97 (1954)Forecast: 94



Record High Temperatures (Joplin):

September 20:
99 (1954)       Forecast: 97

September 21:
99 (2022) Forecast: 94



Record Highest Minimum Temperatures (Springfield):

September 20:
74 (2018) Forecast: 72

September 21:
73 (1931) Forecast: 72

September 22:
70 (2017) Forecast: 71



Record Lowest Precipitation for Month of September:

Springfield: 0.05" (1928)
September 2024 Thusfar: 0.04"

Joplin: 0.2" (2013)
September 2024 Thusfar: T"

&&

.SGF WATCHES/WARNINGS/ADVISORIES...
KS...None.
MO...None.

&&

$$

SHORT TERM...Price
LONG TERM...Price
AVIATION...Price
CLIMATE...Price