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FXUS63 KSGF 192014 AFDSGF

Area Forecast Discussion National Weather Service Springfield MO 314 PM CDT Sun May 19 2024

KEY MESSAGES

- High confidence in above average temperatures today into early this week (mid to upper 80s).

- Chance for two rounds of showers and thunderstorms through Monday. First is late tonight into early Monday morning along and west of Highway 65 (20-50% chances). Second is Monday afternoon/evening along and north of Highway 32/I-44 (15-30% chances). Small hail and isolated wind gusts up to 60 mph possible with these storms (5% chance).

- Slight (2 of 5) risk to Enhanced (3 of 5) risk for severe weather Tuesday evening through Tuesday night. Damaging wind gusts are the primary concern (15-30% chances) with large hail (15% chance) and a few spin-up tornadoes (2-5% chances) being a lower-end threat.

- Potential for another round of severe weather Wednesday toward south-central Missouri (15% risk/confidence).

- Unsettled weather may persist through the end of this week and into Memorial Day Weekend (daily 30-50% chances for showers and thunderstorms).

SHORT TERM /THROUGH MONDAY NIGHT/
Issued at 1231 PM CDT Sun May 19 2024

Large-scale mid- and upper-level ridging is currently very slowly exiting our area as broad W'ly flow moves in from the west. A longwave trough associated with the polar jet is situated over the Pacific NW, as seen on current water vapor imagery. A shortwave associated with a subtropical jet max is currently exiting NM/CO. This shortwave will be responsible for the short-term weather threat as it moves overtop a dryline in W TX and an E-W oriented stationary boundary across central KS/MO. An upper- level low associated with the subtropical jet over the east- central Pacific ocean will be responsible for the longer term weather threat.

Above average temperatures today into early this week:

The aforementioned ridging along with clear skies and light 8-12 mph S'ly winds will allow high temperatures to reach into the upper 80s today. Current observations are already in the mid-80s, suggesting that some places may break 90 F.

Even though a shortwave will move through the region tonight, the largewave pattern will remain with the WSW'ly flow of the polar jet remaining over the northern states, allowing ridging to persist. This, along with 850mb in the 16-18C range will continue to keep temperatures in the mid and upper 80s Monday.
Lows will also be quite mild as thunderstorms out over the central Plains will generate cloud cover over our region at night. This will keep lows in the upper 60s tonight and Monday night, with areas near the MO/KS border in the lower 70s which is near the record low maximum.

20-50% chances of thunderstorms late tonight into Monday morning:

A robust thunderstorm complex is forecast to traverse KS today through tonight. This complex will begin to dissipate in east KS as it escapes upper-level support and enters more stable air from the nocturnal boundary layer. The 12Z HRRR run depicts the complex falling apart right along the MO/KS border after 10 PM.
However, most CAMs are known to poorly handle convective cold pools. With a substantial cold pool expected to develop with this system in KS, the complex has a 20-50% chance to reach further east than model guidance. Indeed, mean MUCAPE across our region will be >1000 J/kg with 0-6 km bulk shear at 15-25 kts which would support this scenario. The MPAS models--which use a refined microphysics scheme--seem to handle the MCS progression better than others and brings the MCS to Hwy 65. As such, there is a 20-50% chance of leftover stratiform rain and embedded thunderstorms along and west of Hwy 65 with the highest chances along the MO/KS border. These storms would be at the I-49 corridor between 10PM-2AM timeframe and the Hwy 65 corridor by the 2-7 AM timeframe. Additionally, small hail and isolated 60 mph wind gusts are possible along the MO/KS border before the leading line of the MCS completely breaks apart.
Nevertheless, even if thunderstorms do not make it across the border, at least light isolated to scattered showers should persist until 7-9 AM at the latest.

15-30% chances of thunderstorms Monday afternoon/evening:

Given the robust convection expected across the Plains, an MCV is likely to develop along with the thunderstorm complex and migrate somewhere through central/northern MO. Additionally, surface outflow from the overnight storms could also be in the vicinity. Whereever these features set up could be the focus for new thunderstorm development Monday afternoon into the evening.
This threat is quite conditional, however, as lift from surface outflow and mid-level support from vorticity advection associated with the MCV will need to overcome upper-level subsidence due to rising heights ahead of another shortwave.
Capping may also develop across the area (20-30% chance of -50 J/kg according to the HRRR), especially if a sufficient cold pool persists across the area. These conditionalities lead to a 15-30% chance of scattered thunderstorm redevelopment along and north of the Hwy 32 to I-44 corridor during the afternoon hours. If storms do form, the environment will be characterized by 1000-2000 J/kg MLCAPE and 20-30 kts of 0-6 km bulk shear which could support a few marginally severe multicells.
Inverted-V low-level soundings suggest a few 60 mph damaging wind gusts as the main threat, but 7.5-8.5 C/km mid-level lapse rates would also support small to marginally severe (quarter- size) hail.



LONG TERM /TUESDAY THROUGH SATURDAY/
Issued at 1231 PM CDT Sun May 19 2024

Potential for severe storms Tuesday evening into Tuesday night:

Our greatest potential for severe weather comes Tuesday evening through Tuesday night as the SPC has an Enhanced (3 of 5) risk NW of a line from Pittsburg, KS to Osage Beach and a Slight (2 of 5) risk elsewhere. The aforementioned upper-level low over the east-central Pacific will lift NE through the four corners region. Additionally, a shortwave associated with the polar jet will drop SE from the Pacfic NW. The two waves will somewhat phase together, creating a unified SW'ly jet across the Plains.
This will force a greater surface mass response across the Plains. The stronger S'ly low-level flow will advect lower 70s dewpoints across the western area of our CWA and 19-22C 850mb temps across the area. This will bring a hot and muggy airmass across our area with highs in the upper 80s, potentially above 90. A surface cold front associated with the surface cyclogenesis will drop SE from the NE/IA region into east KS and central MO. This will force thunderstorms Tuesday evening, with some potentially severe, within this region. These will drop SE ahead of the front through the overnight hours.

Without a doubt, the environment will be ripe for severe weather, especially in the Enhanced risk where mean NBM CAPE values exceed 2000 J/kg, 0-6 km bulk shear values generally lying within the 40-50 kt range with forecast hodographs supporting supercells, and lapse rates in the 7.5-8.5 C/km range. There are questions, however, in the level of forcing, degree of capping, and evolution of convection. The greatest upper-level forcing will be displaced to N MO/IA where the most vigorous shortwave PVA is located. The surface cold front could be enough lift to overcome the lack of upper-level forcing, however, the 700 mb wave is looking to be somewhat positively-tilted which is placing warmer temperatures the further south you go from the mid-level shortwave. This could create a robust capping inversion, especially across our slight risk areas, which could shunt any convection along the cold front.

Nevertheless, if storms are to initiate along the front in east KS/west-central MO, supercells are likely to be the initial storm mode. This would be in the Tuesday late afternoon hours. With a SE cold front moving at approximately 3-5 m/s and the forecast bunkers right motion expected to be only 5 m/s faster than the front, these storms will likely stay on the boundary.
This paired with shear vectors largely parallel to the front will promote quick upscale growth. A line of storms is then the most likely mode as the storms progress further into our CWA
This means that initially, all hazard will be possible (generally just outside our CWA, but potentially reaching into our extreme NW counties. Then, damaging winds will be the main threat as the line organizes and moves through our CWA However, there is still the potential large hail given the thermodynamic profiles, and a spinup tornado or two given the kinematic profiles. They are just lesser threats. A better idea of exact hazards and intensities will be evaluated in future forecasts.

The line is expected to move through our CWA during the evening and into the overnight hours. The cold front will slowly sag SE, so by the morning hours, storms may not completely be out of our CWA The exact evolution is still in question, but latest trends have been slower and slower making the severe threat an overnight threat for areas east of I-49.

Potential for another round of severe storms Wednesday:

With the sagging nature of the surface cold front and the later trend of its progression, it is forecast to be somewhere across the I-44 corridor by midday Wednesday. This will promote highs in the mid 70s NW of I-44, and in the lower 80s SE of I-44.
Storms may be ongoing at midday, which brings up uncertainties in the evolution and potential redevelopment of storms ahead of the front. Nevertheless, a very unstable airmass is expected to be in place SE of the front (SE of I-44). The NBM mean is around 3000 J/kg with the 90th percentile pushing 5000 J/kg.
Additionally, 45-55 kts of 0-6 km bulk shear will be present thanks to the SW'ly mid- level speed max overhead. This will be more than enough to support organized severe thunderstorms SE of I-44, if they can redevelop amid ongoing convection and upper- level support being displaced well off to the north. With mean flow being SW'ly, parallel to the surface cold front, convection will likely be linear along the front with the potential for training storms. This would also promote a flooding threat. The WPC does have a Slight (2 of 4 level) risk for excessive rainfall across south- central MO. While more details are needed to advertise specific locations/timing/hazards, given cold frontal forcing and parallel flow, the main hazards will likely be damagaing winds and large hail. This will continue to be evaluated in future forecast updates.

Unsettled weather may persist through the end of this week:

Daily max precipitation chances of 30-50% persist through the weekend as ensembles agree on the longwave pattern producing a trough over the west coast with a suptropical jet pumping into the Southern Plains. This will allow multiple rounds of showers/thunderstorms through the weekend. CSU machine learning guidance also does place portions of our area in a 15% risk for severe weather each day through Sunday. This guidance, however, is based on the GEFS ensemble, which at this range is unable to resolve shortwave features. So while the synoptic pattern exists for showers/thunderstorms and the potential for severe weather each day, exact timing and locations of each round will depend on where and when ejecting shortwaves move through the area. At this point, ensemble agreement is too low to try and pinpoint any specific areas at any specific time.



AVIATION /18Z TAFS THROUGH 18Z MONDAY/
Issued at 1230 PM CDT Sun May 19 2024

VFR conditions will prevail for all sites until at least 06-08Z.
A cumulus field at 4500 ft will develop this afternoon and will dissipate by 02Z. Winds will generally be S'ly at 5-10 kts, though some deviations are possible later tonight (after 06Z)
as remnants of a thunderstorm complex approach. There is still uncertainty in how far this decaying complex will reach, but the highest confidence is that JLN may see some rain and embedded thunder between 07-13Z. Around this time, low-level shear will be near the 40 kt threshold at JLN. Leftover stratiform rain may then reach SGF and BBG by 10Z. All leftover rain should then dissipate by 13-15Z.

CLIMATE
Issued at 100 PM CDT Wed May 15 2024

Record High Temperatures:

May 20: KSGF: 90/1964 KJLN: 92/1956 KUNO: 89/1964

May 21: KSGF: 91/1987 KJLN: 91/1987

Record High Minimum Temperatures:

May 20: KSGF: 71/1902

May 21: KSGF: 70/1902

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

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