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000
FXUS63 KLSX 141718
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1218 PM CDT Sun Apr 14 2024

.KEY MESSAGES...

- Daily high temperature records will be challenged today.
  Afternoon highs are forecast to reach the mid-80s areawide with
  some locations approaching 90 degrees.

- We are still confident in the potential for severe weather late
  Tuesday afternoon into Tuesday night with all hazards possible.
  Portions of northern and central Missouri have the highest
  potential at seeing severe weather. The strongest thunderstorms
  are expected to occur in these locations.

- Isolated to widely scattered thunderstorms are possible (20 -
  40%) late Monday afternoon into Monday evening. One or two of
  these thunderstorms could produce quarter sized hail.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 345 AM CDT Sun Apr 14 2024

Today and tomorrow will be the warmest days of the week with high
temperatures approaching daily high records. This is supported by
the continued advection of warm air into the region. By this
afternoon, 850 mb temperatures will be within the 14C to 16C range,
above the 90th climatological percentile. With mixing up to 850 mb
and full insolation this afternoon, this translates to highs in the
mid-80s. Some locations may approach 90 degrees, especially those
downwind of the Ozarks where warming from downsloping is possible.

A weak cold front will ooze into the northern to middle CWA from the
north today. We`re still expecting dry conditions today despite its
presence due to pronounced capping, weak moisture convergence along
the boundary, and mid-level subsidence. On Monday this boundary
will be lifted north by a deepening surface cyclone in the central
High Plains. Most global models and CAMs initiate isolated to
widely scattered convection along the boundary late Monday
afternoon into night due to more moisture convergence along the
front and weaker capping. Positive vorticity advection in the mid-
levels will also provide some lift. Thunderstorms that develop be
working with up to 1500 J/kg of SBCAPE and 25 to 35 kts of bulk
shear. Despite plentiful instability, low shear values dampen the
potential for organized convection. Marginally severe hail and
gusty winds will be possible with the most robust thunderstorms.

There is still some uncertainty regarding how exactly this round of
convection will impact the severe potential on Tuesday. More
abundant and continuous showers and cloud cover could keep the
region from destabilizing efficiently. However, we`ve recently
seen that we can get severe weather despite daytime cloudiness.
Mid-level troughing approaching the region will also help us cool
aloft, steepening mid-level lapse rates and destabilizing the
region to an extent regardless.

Jaja

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 345 AM CDT Sun Apr 14 2024

The mid-level trough will be pushing northeast through the central
Plains on Tuesday, cooling the region aloft and introducing a lobe
of vorticity to portions of western and northern Missouri Tuesday
afternoon. By 18z-21z the surface low will be centered in eastern
Nebraska with its dryline extending south through western Missouri
and central Iowa. As mentioned in the last paragraph of the short
term, the extent to which we destabilize is yet to be seen. Both
deterministic and ensemble guidance have a wide range of numbers,
fueled by differences in timing, moisture content, and the impact of
morning convection. What is consistent is that the most instability
will be centered in central Missouri into Iowa in the afternoon, and
that instability values decrease as the system moves east. SBCAPE
values have actually decreased from previous model runs with
ensembles keeping values under 750 J/kg within the CWA. MUCAPE
values are generally under 1000 J/kg as well, with the exception of
the ever robust NAM. This creates uncertainty in how far east/how
late the severe threat will last.

Though instability is in question, bulk shear values of 60 - 70 kts
have remained consistent over the past few days. Southeasterly bulk
shear vectors will cross the front at about a 45 degree angle,
supporting an initial supercell threat in north central Missouri.
Abundant lift within the hail growth zone will make large hail a
threat. SREF probabilities of >200 m2/s2 of 0-3 km helicity fall
between 50 and 70%, and curved hodographs in that region suggest a
real tornado threat in this area as well. How far east these threats
go will depend on instability, but it`ll also depend on how quickly
thunderstorms congeal into a QLCS. When this does occur, the primary
threat will transition to damaging winds.

The passing surface low will also bring high pressure gradient winds
on Tuesday with sustained winds of up to 30 mph and gusts of up to
45 mph. Although the strongest winds will occur Tuesday afternoon,
gusty conditions will persist until the system exits late Wednesday.
The next chance (30-50%) at rain will be Thursday with a second cold
front. This will take us back down to below average temperatures
through this weekend.

Jaja

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1214 PM CDT Sun Apr 14 2024

Dry, VFR conditions are forecast through the period along with a
mostly clear sky. A weak cold front will slowly move through parts
of northeast Missouri and west-central Illinois by early this
evening. Its southward progress will stall out somewhere near or
just south of the central Missouri and metro St. Louis terminals
late tonight into Monday morning. After the frontal passage, winds
should become more northeast/east with speeds below 10 knots.

Gosselin

&&

.CLIMATE...
Issued at 225 PM CDT Thu Apr 11 2024

DAILY HIGH TEMPERATURE RECORDS

          |=== 4/14 ==|=== 4/15 ==|
St. Louis | 92 (2006) | 89 (2002) |
Columbia  | 89 (2006) | 90 (1896) |
Quincy    | 86 (2006) | 88 (2002) |


&&

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

$$

WFO LSX