Current Conditions at Sanborn Field

 

Friday Night: Partly Cloudy. Low: 60

 

 

Saturday: Overcast, chance for thunderstorms. High: 77

 

 

Saturday Night: Possible severe thunderstorms, heavy rain. Low: 42

Sunday: Light rain throughout the day. High: 50

 

Sunday Night: Rain ends, clouds decrease. Low: 38

 

 

Thanks to IconArchive.com for the icons!

====================================================================

Discussion:

Disruptive weather will present itself this weekend as a cold front makes its way though the area on Saturday. Two primary rounds of thunderstorms will move through the area this weekend. The first round will most likely arrive around 2-4pm Saturday. The second round of thunderstorms will arrive Saturday evening, with a greater possibility for severe events such as hail and damaging winds. A cold, light rain will remain Sunday morning after the primary thunderstorm exits, with light winds present. Conditions will clear Sunday evening into Monday morning.

-Sausen

 =================================================================

Forecasters: Thomas, Sausen, McGuire

Date Issued: 4/14/2023 4:20PM CDT

Technical Discussion:

As of right now, the cutoff low that came up from the Gulf continues to slowly migrate northeast, slowly becoming absorbed in the forward side of the large scale upper trough over the western third of the CONUS, which is currently deepening. While the center of this low is carrying some of its’ own moisture, its larger-scale influence is largely dry, except for a swath from Florida and the Pacific up into the Southeast. A secondary area of jet maxima over the Baja California looks to couple with the trough over the Plains.

Surface satellite analysis shows clouds wrapping around the cutoff low over MS/AL/TN, with associated convection to its’ southeast. A few streaks of upper level clouds are slowly advecting east, and a cumulus field has developed over eastern MO, though nothing will likely become of it with a lack of lift.

This forecast will be rather complicated, therefore I will be using a mixture of operational products (The HREF, the RAP and the GFS), particularly due to the potential for severe convection on Saturday.
By the evening, upper level divergence looks to emerge associates with strong convection over Kansas and Colorado as the upper level trough slowly makes its’ way east into the Plains, bringing with it 500mb vorticity maxima and mostly warm 850mb temperature advection. Sounding analysis from the RAP at 22z Saturday over Kansas shows a rather dry lower level but very high lapse rates especially at the surface. With a surface cold front to the south, a warm front stretching northeast from the center of the surface low, dewpoints in the 50’s by 22z over eastern Kansas as well as low level jet support should be enough to overcome limited surface moisture and high LCLs to start off convection. With convection in the forecast, I’ve switched to the HREF, RAP and HRRR for the forecast tonight into Saturday night.

HREF ensemble members mostly show a weakening of the convection that spawned in Kansas, but its’ associated outflow boundary’s influence is not lost, and CAMs generally place it over the forecast area by 10z. Although mean PWATs are close to 1.2 inches during the time the outflow boundary passes, the amount of convection that will reform as the sun rises is up in the air, with different members showing different outputs there. Will go with chance probs for the morning.
The most complex and difficult part of the forecast comes later. The large scale trough continues to slowly make its way east, and the 500mb jet max over OK/TX will strengthen over Missouri by the evening, but by then most of the convection will have shifted out of the forecast area, so we likely won’t see the most influence from the jet stream. Surface dews should moisten up around 16z to 60 degrees ahead of frontal passage. Shear will take its time to enter Missouri as well, with most CAMs pushing it back to 02-03z, though with rather high values pushing into the forecast area (~80kts of 0-6km bulk shear). While CAMs disagree with timing and intensity, they seem to divide the event into three separate areas. Initial convection should be semi-ongoing behind the decaying MCS in northeast Missouri/eastern KS with a northeastward motion. CAMs that develop this convection are showing a decent bit of discreteness with it, and if these cells were to advect south enough, we could see a more hail-oriented threat between 19 and 23z. The biggest threat for severe weather looms to be frontally-initiated, spawning over SW and W MO around 20z with a northeastward storm motion. The biggest problem with this convection will be northward extent, as the axis of greatest surface dewpoints barely extends beyond Boone County. The third potential for severe convection will be pre-frontal, should the front stall and take its’ time in comparison to current CAM outputs. If this were to occur, a few isolated discrete cells could form, with an all-hazards scenario in or near the forecast area. While the numerous potential outcomes for convection tomorrow cloud the forecast, HREF means do show total precip amounts totaling close to an inch. HREF thunder probabilities show one node between 11 and 16z and another between 21z Saturday and 01z Sunday. Therefore, have gone with showers and thunderstorms for the forecast area, and a high of 77 based on ensemble mean. Overall, a largely wind-based threat seems most likely given low SRH values and linear convection outputs from CAMs, but should convection become isolated we could see more of an all-hazards risk.

After the passage of the frontal system, temperatures should drop sharply into the overnight hours as the deepened trough progresses east, leaving us in the backside jet maxima for the duration of the rest of the forecast period. Wraparound moisture could push back into the forecast area, though GFS output values are rather dismal in terms of moisture, so widespread cloud cover with scattered stratiform rain seems most likely. Near the surface, a decently strong surface high centered over the Texas coast should keep the area in rather calm conditions to the end of the forecast period.