724
FXUS63 KEAX 111123
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
623 AM CDT Tue Mar 11 2025

...Updated 12z Aviation...

.KEY MESSAGES...

- Slightly Cooler Today, But Still Warm

- Above Normal Temperatures Through Friday

- Strong System Moves Through Friday and Saturday

- Conditional Severe Thunderstorm Threat Friday; Potential For Dry
  Air To Quickly Erode Thunderstorm Chances With This System

&&

.DISCUSSION...
Issued at 350 AM CDT Tue Mar 11 2025

Split flow regime still ongoing across North America with polar jet
streak across the Canadian Prairie Provinces and Northern Great
Lakes Region, with stronger subtropical jet streak over the Gulf
into the eastern Pacific. Subtle H5 height falls over the past 12
hours have moved southward with the northern system, but no
substantial forcing has made it close to our area. In general
perspective, the mid-level flow while brisk is still mostly zonal.
Strong PV anomaly off the southwest coast of the CONUS will provide
a few troughs and strong vorticity maxima over the next couple of
days through this mostly zonal flow regime. For today though, the
system in the Northern Great Lakes region is dragging a cold front
across much of the upper Midwest, and this is slowly moving
southward across Iowa. This is expected to provide a few hours of
northerly flow, especially for our northern Missouri Counties. Areas
south of Interstate 70 may still hold onto a southerly wind
component. Surface anticyclone over the Gulf continues to prevent
any notable moisture transport into our region, so despite the cool
thermal boundary, cloud development will be very limited if anything
develops at all. Temperatures across northern Missouri today will be
in the lower 60s as this boundary moves southward, with a gradual
increase into the mid and upper 70s for areas south of Interstate
70. NBM inner-quartile spread for any particular location is only
about 4F, therefore indicating higher confidence in the placement of
this boundary. Greatest variability is between Hwy. 36 and
Interstate 70, but in general most points are expected be in the
upper 60s to perhaps lower 70s. With clear skies allowing for
insolation most of the afternoon, expecting another day of strong
boundary layer mixing, which will again reduce dewpoints into the
lower and mid 30s across the area. This yields relative humidity
values in the lower 30s through the afternoon. Winds today will not
be as gusty as Monday, therefore fire weather related concerns are
not as high as they were yesterday. Fuels are still dry though, so
there is still some limited fire weather risks for this afternoon.
Through the evening, first localized vorticity maxima moves through
the flow, and provides weaker dCVA across the Central Plains that
will prompt some lift to lower surface pressure. The mid-level
support is not broad enough to develop a robust surface cyclone, but
it should be enough to prompt a flow response to southwesterly,
enhancing a WAA regime heading into the evening and prevents further
southward movement of the thermal boundary that will keep Northern
Missouri cooler this afternoon. Expecting some nighttime cooling
with clear skies, but not expecting temperatures to drop much below
45 degrees given the change to WAA.

Wednesday and Thursday, more notable H5 trough is progged to eject
across the Central Plains ahead of the strong PV anomaly moving
closer to the southwest California coast. The dCVA into the Plains
will deepen the weak surface cyclone and strengthen southwesterly
flow across our area, as well as creating modest mid-level ridge
axis that passes across the lower Missouri River Valley. This is
expected to boost temperatures back into the 70s for most of the
area. During this time, the flow remains more southwesterly than
southerly, meaning we are still missing out on stronger moisture
transport from the Gulf. As this system progresses, the better CVA
tracks toward the eastern portions of the southern Plains into the
lower Mississippi River Valley. The H5 height falls and enhanced
kinematics only make it as far north as the Ozarks region, not
climbing much further north than Interstate 44. Eventually by
Thursday, modest H5 height falls start, but again the better forcing
and moisture supply remains well south of the area. Therefore, will
maintain a dry forecast for our area. GEFS and other ensemble suites
limit probabilities for any measurable precipitation in our
southeast to under 15 percent. Given the dry boundary layer and very
dry antecedent conditions over the several days, hard to see any
activity developing unless this short-wave makes a dramatic shift
northward.

Attention than turns to Friday and Saturday, as the main PV anomaly
finally moves into the CONUS and brings a deep trough across the
Intermountain West. Over the past several days, had noted output
from NAEFS and other systems that provide context to extreme values
of various parameters were showing higher potential for extreme H5
height minima as well MSLP with this system, and current medium
range deterministic guidance still depicts an overall synoptic
pattern that supports this. During the very early Friday morning
period, 100+kt H5 jet streak starts to move around the trough axis,
allowing this deep trough to acquire a negative tilt. This setup
will favor robust dCVA into the Front Range, providing plenty of
lift for surface cyclogenesis. Surface pressure falls will quickly
spread eastward across the Plains into the lower Missouri River
Valley with this setup, increasing southerly flow across the area,
and begins to increase theta-e advection. Pressure gradient
drastically increases, and this will provide very gusty winds
throughout much Friday, even in periods without precipitation.
Depending on how much moisture transport we realize, there will
likely be a period of elevated fire weather concerns with this
system. Would imagine that at some point there should be some degree
of isentropic ascent. Overall, expecting an expansive warm-sector
across the area with respect to temperatures. Inner-quartile spread
amongst various ensemble suites are between 78F and 82F degrees for
most points in our forecast area. With this highly dynamic system,
the backside of this will start to pull in drier air, but with
daytime heating, should weaken the thermal gradient as it progresses
across the Plains. Current guidance is suggesting this airmass
behind the boundary to characterized by dewpoint depressions of over
30F, and in some ensemble members over 40F from the surface up to
around 700mb. This will be more a Pacific Cold front type of feature
or a psuedo dryline of sorts, given the amount of mixing that
appears that could be going on with the robust momentum that is
present. This feature is the reason why both the overall
thunderstorm threat and severe weather threat remains very
conditional. If the dry air wins out, we may just end up with strong
winds and a few light showers or sprinkles. As this system gains
speed, this boundary is likely to surge east very quickly throughout
the day. And as it does, will quickly erode boundary layer moisture,
as well as quickly reduce any type of SBCAPE or MLCAPE. Current
deterministic GFS and ECMWF depict around 500-700 J/kg of MLCAPE in
the warm sector after 18z on Friday. That may not seem like much,
but given the strong mid-level support and forcing along the
boundary, that will be all you need to get a thunderstorm if we are
able to realize it. However, respective ensemble guidance though
remains split on how fast this moisture discontinuity boundary
pushes through, with some members clearing this before peak heating
on Friday, resulting in no destabilization ahead of the most
favorable forcing for our CWA. Therefore, ensemble probabilities for
CAPE above 1000 J/kg remains very low, while a threshold of 500 J/kg
is around 50 to 60 percent, concentrated mainly east of Interstate
35. Areas east of Highway 63 hold onto higher probabilities for
severe weather, especially toward the Ohio River Valley as the
window for destabilization is much longer. Based on that, if this
system does not surge too quickly, deep layer shear of 55+ kts will
be capable of organizing storms Friday late afternoon into the early
evening if the moisture is there for it. Throughout the open warm
sector, could support a period of supercell development, but as the
cool/dry boundary moves eastward, deep layer shear becomes more
parallel to the overall forcing, which would favor some type of MCS,
could even be enough organization for a QLCS. Therefore, all severe
weather hazard types right now look to be possible if thunderstorms
are realized at all, we will see starting Thursday morning how the
CAMs handle the evolution of this system, might there be any kind of
differential heating boundary present if cloud cover develops in
isentropic upglide. This will make is easier to pinpoint potential
mesoscale outcomes. If we do not see enough instability, but
moisture transport with isentropic ascent occurs before this
moisture discontinuity boundary moves through, could see non-
thunderstorm rain shower activity early Friday. Current ensemble
members paint about at 30-40 percent chance for rain measurable
across most of the area, with above 60 percent closer to Hwy. 63.
For a threshold of 0.10 inches of QPF or greater, about 30-40
percent along and east of Hwy. 63, but rapidly decreases as you move
westward. A lot of ensemble members keep the KC metro dry with this
system. As mentioned in the beginning of this section, gusty non-
thunderstorms winds are still expected given how strong this system
is. If this dry surge occurs during daylight, we could also see fire
weather issues for a few hours, especially with wind gusts above 40
MPH. Finally, there will be a lot of cold air on the northwest side
of the system. As for right now, all the stronger lifting mechanisms
are progged from northern Nebraska into the northern Plains, and
this is where the highest wintry precipitation probabilities are at.
Our far northern Missouri Counties may become cold enough Saturday
morning to support frozen precipitation, but QPF remains very light
by the time temperatures drop below freezing. Thus, not overly
concerned about wintry precipitation impacts for our area at this
time.

Secondary trough axis moves through Sunday into Monday, and could
provide some light precipitation activity but moisture content may
not be there to actually produce it. Stronger ridge then develops
across the Central CONUS through the start of next week and should
send temperatures back into the 60s, perhaps 70s across our
area.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 621 AM CDT Tue Mar 11 2025

Clear skies will lead to VFR conditions across the area for
most of the day. Winds out of the southwest between 5 and 10
kts. Winds may be more northeasterly in northern Missouri. VFR
cloud bases may move in early Wednesday morning.

&&

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

&&

$$

DISCUSSION...Krull
AVIATION...Krull