Precipitation Efficiency of Warm-Season Midwestern Mesoscale Convective Systems

Market, Patrick S.; Allen, Stacy N.; Scofield, Roderick A.; Kuligowski, Robert J.; Gruber, Arnold

doi:10.1175/1520-0434(2003)018<1273:peowmm>2.0.co;2

Cited by 45 publications

(58 citation statements)

References 29 publications

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“…It is apparent that the role of the TC is to provide deep tropical moisture that can be transported poleward to produce anomalously high moisture values in midlatitudes. This deep tropical moisture from TCs can increase precipitation efficiencies (e.g., Market et al 2003) and provide a sizeable supply of moisture to sustain deep convection, given adequate synoptic and mesoscale forcing. The nearly moist neutral atmospheric conditions accompanying these TC moisture plumes can allow for PRE formation even in the presence of only weak forcing for ascent.…”

Section: Discussionmentioning

confidence: 99%

Predecessor Rain Events ahead of Tropical Cyclones

Galarneau

Bosart

Schumacher

2010

Monthly Weather Review

138

108

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Twenty-eight predecessor rain events (PREs) that occurred over the United States east of the Rockies during 1995-2008 are examined from a synoptic climatology and case study perspective. PREs are coherent mesoscale regions of heavy rainfall, with rainfall rates $100 mm (24 h) 21 , that can occur approximately 1000 km poleward of recurving tropical cyclones (TCs). PREs occur most commonly in August and September, and approximately 36 h prior to the arrival of the main rain shield associated with the TC. A distinguishing feature of PREs is that they are sustained by deep tropical moisture that is transported poleward directly from the TC. PREs are high-impact weather events that can often result in significant inland flooding, either from the PRE itself or from the subsequent arrival of the main rain shield associated with the TC that falls onto soils already saturated by the PRE.The composite analysis shows that on the synoptic-scale, PREs form in the equatorward jet-entrance region of a 200-hPa jet on the western flank of a 925-hPa equivalent potential temperature ridge located east of a 700-hPa trough. On the mesoscale, PREs occur in conjunction with low-level frontogenetical forcing along a baroclinic zone where heavy rainfall is focused. A case study analysis was conducted of a PRE ahead of TC Erin (2007) that produced record-breaking rainfall (.250 mm) from southern Minnesota to Lake Michigan. This analysis highlighted the importance of frontogenetical forcing along a low-level baroclinic zone in the presence of deep tropical moisture from TC Erin in producing a long-lived, quasi-stationary mesoscale convective system.

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Section: Discussionmentioning

confidence: 99%

Predecessor Rain Events ahead of Tropical Cyclones

Galarneau

Bosart

Schumacher

2010

Monthly Weather Review

138

108

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“…Not all of the water vapor that enters a cloud falls out as precipitation. The precipitation efficiency (PE) of a storm may be defined in a number of ways (as described in Sui et al 2007), most commonly as the ratio of rainfall at the ground to condensation (Ferrier et al 1996), to water vapor convergence and surface evaporation rates (e.g., Auer and Marwitz 1968;Heymsfield and Schotz 1985;Doswell et al 1996), or to the precipitable water (Market et al 2003). In all cases, however, precipitation fallout and PE are directly proportional; that is, storms with greater PE produce more rainfall at the ground, all else held equal.…”

Section: Implications For Precipitationmentioning

confidence: 99%

Sensitivities of Simulated Convective Storms to Environmental CAPE

Kirkpatrick

McCaul

Cohen

2011

Monthly Weather Review

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A set of 225 idealized three-dimensional cloud-resolving simulations is used to explore convective storm behavior in environments with various values of CAPE (450, 800, 2000, and 3200 J kg 21 ). The simulations show that when CAPE 5 2000 J kg 21 or greater, numerous combinations of other environmental parameters can support updrafts of at least 10 m s 21 throughout an entire 2-h simulation. At CAPE 5 450 J kg 21 , it is very difficult to obtain strong storms, although one case featuring a supercell is found. For CAPE 5 800 J kg 21 , mature storm updraft speeds correlate positively with strong low-level lapse rates and reduced precipitable water. In some cases, updrafts at this CAPE value can reach speeds that rival predictions of parcel theory, but such efficient conversion of CAPE to kinetic energy does not extend to all storms at CAPE 5 800 J kg 21 , nor to any storms in simulations at lower or higher CAPE. In simulations with CAPE 5 2000 or 3200 J kg 21 , the strongest time-averaged mature updrafts, while supercellular in character, feature generally less than 60% of the speeds expected from parcel theory, and even the strongest updraft found at CAPE 5 450 J kg 21 fails to reach that relative strength. When CAPE 5 2000 J kg 21 or more, updrafts benefit from enhanced shear, higher levels of free convection, and reduced precipitable water.Strong low-level shear and a reduced height of the level of free convection correlate closely with low-level storm vertical vorticity when CAPE is at least 2000 J kg 21 , consistent with previous findings. However, at CAPE 5 800 J kg 21 , low-level vorticity shares the same correlations with the environment as updraft strength. With respect to storm precipitation, in simulations initiated with only 30 mm of precipitable water (PW), all of the storms that last for an entire 2-h simulation tend to produce liquid precipitation at roughly similar rates, regardless of their CAPE. In environments where PW is increased to 60 mm, storms tend to produce the most rainfall at CAPE 5 2000 J kg 21 , with somewhat lesser rainfall rates at lower and higher CAPE. Nevertheless, over the simulation domain, the ground area that receives at least 10 mm of rainfall tends to increase as CAPE increases, owing to a greater number and size of precipitating updrafts in the domain.

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“…Finally, although some studies have attempted to quantify precipitation efficiency in convective storms (e.g., Market et al 2003;McCaul et al 2005), this remains a difficult quantity to estimate or predict.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of Precipitation Accumulation in Elevated Convective Systems to Small Changes in Low-Level Moisture

Schumacher

2015

Journal of the Atmospheric Sciences

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Using a method for initiating a quasi-stationary, heavy-rain-producing elevated mesoscale convective system in an idealized numerical modeling framework, a series of experiments is conducted in which a shallow layer of drier air is introduced within the near-surface stable layer. The environment is still very moist in the experiments, with changes to the column-integrated water vapor of only 0.3%-1%. The timing and general evolution of the simulated convective systems are very similar, but rainfall accumulation at the surface is changed by a much larger fraction than the reduction in moisture, with point precipitation maxima reduced by up to 29% and domain-averaged precipitation accumulations reduced by up to 15%. The differences in precipitation are partially attributed to increases in the evaporation rate in the shallow subcloud layer, though this is found to be a secondary effect. More importantly, even though the near-surface layer has strong convective inhibition in all simulations and the convective available potential energy of the most unstable parcels is unchanged, convection is less intense in the experiments with drier subcloud layers because less air originating in that layer rises in convective updrafts. An additional experiment with a cooler near-surface layer corroborates these findings. The results from these experiments suggest that convective systems assumed to be elevated are, in fact, drawing air from near the surface unless the low levels are very stable. Considering that the moisture differences imposed here are comparable to observational uncertainties in lowlevel temperature and moisture, the strong sensitivity of accumulated precipitation to these quantities has implications for the predictability of extreme rainfall.

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Precipitation Efficiency of Warm-Season Midwestern Mesoscale Convective Systems

Cited by 45 publications

References 29 publications

Predecessor Rain Events ahead of Tropical Cyclones

Predecessor Rain Events ahead of Tropical Cyclones

Sensitivities of Simulated Convective Storms to Environmental CAPE

Sensitivity of Precipitation Accumulation in Elevated Convective Systems to Small Changes in Low-Level Moisture

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