EWP Blog

A line of storms is north of St. Louis as of 630 pm CDT and is tracking southward toward an area of increased CAPE per All Sky LAP product.  This convection continues to trigger along the leading outflow.  The overall environment has limited shear so it is primarily cold pool driven.  ProbWind has consistently displayed around 65-78% since around 600 pm CDT.

SPC issued a meso discussion talking about the threat for severe wind gusts on cells bowing out towards St. Louis.  The cell in Pike county on the look above has the outflow boundary tied into it on this RGB (in blue) and the updraft still is stronger with waves radiating out from the overshooting top.  We decided to issue a large SVR for winds traveling southeast out of this storm.

Below is a comparison of two different TPW products (AllSkyLAP layer Precipitable water and Merged TPW Composite Sat Sfc Merged Total Precipitation Water) compared to RAP Analysis from the SPC Mesoanalyst page.

The AllSkyLAP product (below) seems to do a better job at “painting the picture,” however, it’s reliance on the GFS model often leads to a delay in PWAT drops in areas of convection. This is highlighted the best across central IL, where RAP Analysis shows PWATs in the 1 – 1.25 inch range while the AllSkyLAP product shows values closer to the 1.5 inch range straight from GFS output.

TPW (below) does a better job at accounting for this, at least across the central IL study area, resulting in more realistic 1.1 to 1.3 inch values.

The effective surface cold front remains well north of Illinois, draped west to east across central Wisconsin as of the 22z surface analysis. Further south across the state, two main forcing mechanisms continue to play host to strong to severe convection. The first (southernmost boundary) is nearly stationary acting as the area of primary convergence, while also service as the dividing line between 70 degree dewpoints (south) and mid to upper 60s (north). The second is an outflow boundary loosely associated with earlier day convection, which continues to race southward driven largely by cold pool propagation. This boundary is anticipated to overtake the primary boundary over the next few hours, ushering the majority of shower and storm activity south of the Lincoln IL CWA later this evening (Showcased well by NUCAPS forecasts). With ample CAPE (1500 – 2500 J/KG per the 22z AllSkyLAP product) remaining along and south of said boundaries, storms are expected to retain their intensities through the early evening hours. Primary threats will remain damaging wind gusts, large hail, and flash flooding primarily in areas that see repeat thunderstorm convection this afternoon and evening.

—————————————————————————————————–Mountain Bone

IR and RGB imagery showing outflow coming out of the storms in the eastern LSX area not firing up additional storms.  NUCAPS 400-200 mb RH product shows quite a bit of drier air that the line is pushing into.  More moisture is west of the MO/IL line, so that part of the line may have a better chance to maintain themselves/develop new cores ahead of the line along that outflow.

Charley

Band of storms dropping in from the north is moving into an environment favorable to at least maintain severe wind gusts as well as some hail potential.  AllSky CAPE parameter shows the line moving into airmass with 2500 J/kg, similar to values given by earlier ILX special sounding and recent modified NUCAPS sounding.  Latest RAP shows DCAPEs up to 1400 J/kg, indicating good potential for severe wind gusts. Had a couple of reports of blackout conditions from blowing field dirt along I-55 near Litchfield.

Charley

Total PW looks good from the operational version (minus the blacked out data, of course).  It is a little blotchy on the merged TPW (left).  A similar comparison below of the AllSky TPW and Operational product.

CAPE is a different story.

AllSky calculations are mostly in a clear airmass, as you can tell by the operational product not being blacked out.  Peak values on the right are in the 1700-1800 J/kg range, whereas points on the left peak at 2600-2800.

Charley

Similar to MPX area yesterday, the 0.9-0.7 sigma level LPW product had an area ahead of the line of storms that had increasing moisture.

Modified NUCAPS sounding near ILX is pretty similar to KILX special sounding taken at 17Z!  MUCAPES both around 3000 and LI -9.

Values similar to AllSky at 18Z.

Those CAPE values near 2500 J/kg…also similar.

This similarity gives us some confidence in new forecasts, especially in clear sky regions out ahead in the AllSky data.

The forecast NUCAPS CAPE does not show much to the south of our line…and based on clear skies and warm conditions to the south would tend to lean away from this forecast.

Charley