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Arnold, Missouri 7 Day Weather Forecast
Wx Forecast - Wx Discussion - Wx Aviation
NWS Forecast for Arnold MO
National Weather Service Forecast for: Arnold MO
Issued by: National Weather Service Saint Louis, MO
Updated: 8:37 pm CST Jan 1, 2025
 
Tonight

Tonight: Increasing clouds, with a low around 27. Calm wind.
Increasing
Clouds

Thursday

Thursday: A chance of sprinkles between 3pm and 5pm.  Mostly cloudy, with a high near 44. Calm wind becoming south 5 to 7 mph in the morning.
Chance
Sprinkles

Thursday
Night
Thursday Night: A chance of sprinkles and flurries before 10pm, then a slight chance of rain between 10pm and midnight.  Cloudy, then gradually becoming partly cloudy, with a low around 24. Light and variable wind becoming northwest 5 to 10 mph in the evening. Winds could gust as high as 20 mph.  Chance of precipitation is 20%.
Slight Chance
Rain/Flurries
then Mostly
Cloudy
Friday

Friday: Sunny, with a high near 35. Northwest wind 7 to 9 mph.
Sunny

Friday
Night
Friday Night: Partly cloudy, with a low around 20. Northwest wind 3 to 6 mph.
Partly Cloudy

Saturday

Saturday: Mostly sunny, with a high near 32.
Mostly Sunny

Saturday
Night
Saturday Night: A chance of snow and freezing rain before midnight, then snow and freezing rain likely, possibly mixed with sleet.  Mostly cloudy, with a low around 23. Chance of precipitation is 60%.
Chance Wintry
Mix then
Wintry Mix
Likely
Sunday

Sunday: Snow and freezing rain.  High near 30. Chance of precipitation is 90%.
Wintry Mix

Sunday
Night
Sunday Night: Snow likely, possibly mixed with freezing rain before midnight, then a chance of snow.  Mostly cloudy, with a low around 19. Chance of precipitation is 70%.
Wintry Mix
Likely then
Chance Snow
Lo 27 °F Hi 44 °F Lo 24 °F Hi 35 °F Lo 20 °F Hi 32 °F Lo 23 °F Hi 30 °F Lo 19 °F

 

Tonight
 
Increasing clouds, with a low around 27. Calm wind.
Thursday
 
A chance of sprinkles between 3pm and 5pm. Mostly cloudy, with a high near 44. Calm wind becoming south 5 to 7 mph in the morning.
Thursday Night
 
A chance of sprinkles and flurries before 10pm, then a slight chance of rain between 10pm and midnight. Cloudy, then gradually becoming partly cloudy, with a low around 24. Light and variable wind becoming northwest 5 to 10 mph in the evening. Winds could gust as high as 20 mph. Chance of precipitation is 20%.
Friday
 
Sunny, with a high near 35. Northwest wind 7 to 9 mph.
Friday Night
 
Partly cloudy, with a low around 20. Northwest wind 3 to 6 mph.
Saturday
 
Mostly sunny, with a high near 32.
Saturday Night
 
A chance of snow and freezing rain before midnight, then snow and freezing rain likely, possibly mixed with sleet. Mostly cloudy, with a low around 23. Chance of precipitation is 60%.
Sunday
 
Snow and freezing rain. High near 30. Chance of precipitation is 90%.
Sunday Night
 
Snow likely, possibly mixed with freezing rain before midnight, then a chance of snow. Mostly cloudy, with a low around 19. Chance of precipitation is 70%.
Monday
 
A 30 percent chance of snow, mainly before noon. Mostly cloudy, with a high near 27.
Monday Night
 
Mostly cloudy, with a low around 9.
Tuesday
 
Partly sunny, with a high near 23.
Tuesday Night
 
Mostly cloudy, with a low around 5.
Wednesday
 
Mostly sunny, with a high near 21.

 

Forecast from NOAA-NWS for Arnold MO.

Weather Forecast Discussion
894
FXUS63 KLSX 012326
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
526 PM CST Wed Jan 1 2025

.KEY MESSAGES...

- There`s a 40% chance of light snow across far northeast MO and
  west-central IL tomorrow afternoon and evening, little to no
  impacts are expected.

- An impactful winter storm will move through the mid-Mississippi
  Valley Sunday into Monday, bringing a mixture of winter
  precipitation to the area. Uncertainty remains in the specific
  details of this system.

- Temperatures will drop below normal by Friday and remain below
  normal through the end of next work week.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 231 PM CST Wed Jan 1 2025

A surface high is sliding into the mid-Mississippi Valley, and dry,
cold air advection along the associated northwesterly flow is
helping to erode the cloud cover from the previous few days. This
high will slide across the forecast area overnight, and by tomorrow
morning southerly winds will be in place. The associated warm air
advection will help warm temperatures a few degrees compared to
today.

In the mid-levels, disturbances will slide across the northwesterly
flow through the day. During the morning, a surface low will form
over Nebraska as a result of one of the disturbances. This pairing
will march eastward across Iowa and Illinois during the afternoon to
evening, and an associated cold front will slide through the
forecast area. A majority of the precipitation associated with this
small system is expected to remain north of the CWA. However, I
cannot rule out some light precipitation falling across far
northeast Missouri and west-central Illinois during the afternoon
and evening as the system pushes through. Further south,
probabilities of precipitation are much lower than the last forecast
package, now 20% or less. A few hundredths of precipitation is
possible, particularly closest to the Iowa border, and could result
in a few tenths of an inch of snowfall across the far northern CWA.
However, given the near to just above freezing air temperatures,
warm ground temperatures, and light snowfall rates, any snow
accumulation will be confined to grassy and elevated surfaces.
Little to no travel impacts are expected. Where precipitation falls
further south, rain will mix in with snow or dominate completely
thanks to air temperatures peaking in the upper 30s to low 40s
tomorrow afternoon. The cold front from this system will push
through the forecast area overnight and bring a renewed shot of cold
air advection to the region.

Delia

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 231 PM CST Wed Jan 1 2025

The mid-level flow becomes more amplified in the wake of the
Thursday shortwave and at the surface a strong high will build into
the Plains/Mississippi Valley region Friday, though the center will
stay to our northwest. Dry, cold air advection along deep
northwesterly to northerly flow will result in a precipitation free
day Friday with temperatures around 10 degrees cooler than Thursday.

At the same time our next system will be approaching the West Coast,
coming onshore Friday into Saturday as a deepening mid-level trough.
70-80% of ensemble guidance indicates the system will continue to
deepen and move eastward into the central CONUS by Sunday. This
guidance has been relatively consistent in pushing the 850 mb low
northeast along the I-44 corridor through St. Louis. This would keep
the highest snowfall to the northwest of the low across central and
northeast Missouri and west-central Illinois. A small minority of
guidance (20-30%) shows a significantly weaker trough moving across
the upper Mississippi Valley during the same timeframe. While this
solution is less dramatic, it is still possible and is an
illustration of the uncertainty that still exists with the strength
and track of this system. Despite these differences, confidence is
increasing (80%) that the system will push into the forecast area
Sunday morning and track across the CWA. There is less certainty
when it will exit, but precipitation should be exiting between late
Sunday night and early Monday morning (60% confidence).

Low-level temperatures will have an dramatic impact on this system.
We are confident that a warm nose will develop near the 850-750 mb
layer somewhere across the region from the low-level warm air
advection ahead of the system. What remains uncertain is how far
north that warm nose will extend and how quickly it is eroded by the
incoming system. As of the 00Z ensemble runs, this zone is just to
the south of the St. Louis metro, running from roughly Rolla to
Festus to Carbondale, but this will likely change over the coming
days as we hone in on the strength and track of the system. To the
north of this transition zone, snow will dominate, but to the south,
a wintry mix including sleet, freezing rain, and snow dominate for
most of the system. After two days of near to below freezing
temperatures, snow, sleet, and freezing rain will be able to
accumulate effectively on all untreated surfaces.

Ahead of this system precipitable water values will surge to
0.50- 0.75 inches according to the NAEFS situational awareness
table, near the 90th climatological percentile for this time of
year. The deeper and more wound up this system is, the more
moisture it will be able to pull into the system. Given that, if
the stronger system comes to fruition, I wouldn`t be surprised if
precipitable water values increase. Uncertainty in the system`s
movement and strength results in an interquartile precipitation
spread from near 0.25" (25th percentile) to up to 1.25" (75th
percentile). The difference in precipitation amounts could spell
the difference between a sub- advisory winter system to a
significant winter storm. To highlight this, the ECMWF Extreme
Forecast Index/Shift of Tails has highlighted northern Missouri
and central Illinois for both an unusual amount of snowfall for
this time of year and noted that a number of the members are
forecasting extreme values. Now this is just one ensemble, but
this is an upward trend compared to yesterday and gives us a heads
up that a significant winter storm is still on the table.

In the wake of this system, the cold weather will continue (which
could make storm clean up difficult). CPC and analog guidance
continue to point to well below normal temperatures lingering
through next week. Ensemble guidance indicates only a 20-50% chance
that high temperatures will exceed 32F Monday (1/6) through Saturday
(1/11), with the highest probabilities across southern Missouri and
Illinois.

Delia

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 515 PM CST Wed Jan 1 2025

Confidence is high in VFR flight conditions through much of the
forecast period at all local terminals. Late in the period
tomorrow afternoon and early evening, a quick-hitting weather
system will pass through the region. Given forecasted
temperatures, this system`s precipitation will be primarily snow
that will move northwest to southeast. Given this track and the
timing, KUIN is where confidence is highest in impacts before the
end of the forecast period.

Elmore

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX
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Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather






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