![]() Directions are in degrees azimuth, and speeds are in knots. Forecast motions are depicted by heavy solid arrows, with the MCS centroid depicted by the cross symbol. (c) (top) Application of original and (bottom) downwind versions of the vector technique to the MCS, based on sounding data in (a). (b) Regional surface mesoanalysis, valid for the same time as in (a): thermodynamic data (☏), wind (kt), and pressure (hPa, with first two digits omitted) synoptic-scale boundaries are depicted with large pips, mesoalpha-scale gust front is shown with small pips, and center of the MCS mesohigh is indicated by the “B” (“bubble high”) over southeast Michigan. 5a, but for White Lake, MI (near Detroit), 1200 UTC. Vector lengths are proportional to wind speed MCS centroids are denoted by the cross symbol. Numbers on the hodograph in the upper-right-hand side depict the altitude above ground level in kilometers.Ĭomparison schematics of (top) original (upwind) and (bottom) downwind versions of the vector technique to forecast short-term motion of upwind-developing systems (MCS motion given by thick red arrows) and downwind-developing systems (MCS motion given by thick green arrow at bottom of figure), respectively. Wet-bulb zero line is shown as a dashed line between environmental temperature and dewpoint profiles. ![]() Lifted parcel ascent curve (large dashed line) is for most unstable parcel, including correction for virtual temperature (rightmost small dashed line). Skew T–log p plot of radiosonde observations for (a) Lincoln, IL (near Springfield), at 1800 UTC, and (b) Topeka, KS, at 1800 UTC. Hypothetical wind profiles at left are for illustrative purposes only.Ĭomposite Doppler radar depiction of reflectivity over (a) northern Illinois, 1700–2000 UTC and (b) northern Missouri, 0030–0200 UTC (right) Plan view of an elongating cold pool, with cross sections perpendicular to the gust front along (top) a quasi-stationary segment and (bottom) a progressive segment, showing direction of cell propagation. Indicated spatial scale is for illustrative purposes only Dashed lines indicate gust-front positions at earlier times. Motion of boundary relative to ground is depicted by conventional frontal symbols. Plan-view schematic depicting temporal elongation of a cold pool and gust front associated with the hypothetical quasi-unidirectional wind profile shown at right. MCS centroid is depicted by the cross symbol (after Corfidi et al. Schematic of the original vector technique, with MCS core motion (thick dotted arrow) expressed as the vector sum of 1) advection of cells by the mean cloud-layer wind (arrow pointing to upper right) and 2) cell propagation directed into the low-level jet (arrow pointing to bottom of page). Summary of Cold-Pool Factors that Affect MCS Propagation.Computation of mean wind/cold-pool motion and low-level inflow Influence of the background synoptic-scale environment MCSs containing supercells and mesoscale vortices ![]() Application of downwind technique to a cool-season derecho: 20–21 November 1989 Application of downwind technique to a derecho: 19–20 July 1983 Comparison application of the original and downwind techniques: 16 August 1997 Case applications of the downwind vector technique Development of a vector scheme for downwind-developing MCSs A vector technique for downwind-propagating MCSs Concurrent upwind and downwind propagation
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