scholarly journals Tornadoes with Cold Core 500-mb Lows

2006 ◽  
Vol 21 (6) ◽  
pp. 1051-1062 ◽  
Author(s):  
Jonathan M. Davies
Keyword(s):  
United States ◽  
Severe Weather ◽  
Surface Heating ◽  
Vertical Shear ◽  
Cold Temperatures ◽  
Low Level ◽  
Close Proximity ◽  
Central United States ◽  
Surface Patterns ◽  
Cold Core

Abstract Tornadoes that occur in close proximity to midlevel closed lows with a core of cold temperatures aloft are not uncommon, particularly in the central United States. Although several informal studies have shown that severe weather and tornadoes can occur with these midlevel lows, little in the way of formal work has been published documenting features and ingredients of such systems, especially those that produce what are sometimes called cold core tornadoes. Of particular concern is that these tornadoes can be associated with surface and low-level moisture that appears deceptively small or marginal regarding severe weather potential, yet on occasion tornadoes of F2 or greater intensity can develop. In other cases, vertical shear may appear relatively weak at locations close to the midlevel low, suggesting little potential for tornadoes. These “atypical” characteristics can result in poor anticipation by forecasters of tornado events associated with closed 500-mb lows. This note documents some synoptic and mesoscale features commonly associated with tornado events in close proximity to cold core 500-mb lows using four tornadic cases in Kansas as examples, including photographs to show the small nature of storms associated with such systems. Recognition of surface patterns with a particular organization of boundaries and surface heating positioned near midlevel lows, along with the presence of some amount of buoyancy, can help with the operational awareness of the potential for tornadoes in many 500-mb closed low settings.

scholarly journals Hydrodynamics of the Caribbean Low-Level Jet and Its Relationship to Precipitation

2010 ◽  
Vol 23 (6) ◽  
pp. 1477-1494 ◽  
Author(s):  
Kerry H. Cook ◽  
Edward K. Vizy
Keyword(s):  
United States ◽  
South America ◽  
The United States ◽  
Caribbean Basin ◽  
Low Level ◽  
The North ◽  
South Central ◽  
Central United States ◽  
Low Level Jet ◽  
The Caribbean

Abstract The easterly Caribbean low-level jet (CLLJ) is a prominent climate feature over the Intra-America Seas, and it is associated with much of the water vapor transport from the tropical Atlantic into the Caribbean Basin. In this study, the North American Regional Reanalysis (NARR) is analyzed to improve the understanding of the dynamics of the CLLJ and its relationship to regional rainfall variations. Horizontal momentum balances are examined to understand how jet variations on both diurnal and seasonal time scales are controlled. The jet is geostrophic to the first order. Its previously documented semidiurnal cycle (with minima at about 0400 and 1600 LT) is caused by semidiurnal cycling of the meridional geopotential height gradient in association with changes in the westward extension of the North Atlantic subtropical high (NASH). A diurnal cycle is superimposed, associated with a meridional land–sea breeze (solenoidal circulation) onto the north coast of South America, so that the weakest jet velocities occur at 1600 LT. The CLLJ is present throughout the year, and it is known to vary in strength semiannually. Peak magnitudes in July are related to the seasonal cycle of the NASH, and a second maximum in February is caused by heating over northern South America. From May through September, zonal geopotential gradients associated with summer heating over Central America and Mexico induce meridional flow. The CLLJ splits into two branches, including a southerly branch that connects with the Great Plains low-level jet (GPLLJ) bringing moisture into the central United States. During the rest of the year, the flow remains essentially zonal across the Caribbean Basin and into the Pacific. A strong (weak) CLLJ is associated with reduced (enhanced) rainfall over the Caribbean Sea throughout the year in the NARR. The relationship with precipitation over land depends on the season. Despite the fact that the southerly branch of the CLLJ feeds into the meridional GPLLJ in May through September, variations in the CLLJ strength during these months do not impact U.S. precipitation, because the CLLJ strength is varying in response to regional-scale forcing and not to changes in the large-scale circulation. During the cool season, there are statistically significant correlations between the CLLJ index and rainfall over the United States. When the CLLJ is strong, there is anomalous northward moisture transport across the Gulf of Mexico into the central United States and pronounced rainfall increases over Louisiana and Texas. A weak jet is associated with anomalous westerly flow across the southern Caribbean region and significantly reduced rainfall over the south-central United States. No connection between the intensity of the CLLJ and drought over the central United States is found. There are only three drought summers in the NARR period (1980, 1988, and 2006), and the CLLJ was extremely weak in 1988 but not in 1980 or 2006.

The Low-Level Structure and Evolution of a Dry Arctic Front over the Central United States. Part II: Comparison with Theory

1996 ◽  
Vol 124 (8) ◽  
pp. 1676-1692 ◽  
Author(s):  
William Blumen ◽  
Nimal Gamage ◽  
Robert L. Grossman ◽  
Margaret A. LeMone ◽  
L. Jay Miller
Keyword(s):  
United States ◽  
Level Structure ◽  
Low Level ◽  
Central United States ◽  
Arctic Front

scholarly journals Environment and Early Evolution of the 8 May 2009 Derecho-Producing Convective System

2011 ◽  
Vol 139 (4) ◽  
pp. 1083-1102 ◽  
Author(s):  
Michael C. Coniglio ◽  
Stephen F. Corfidi ◽  
John S. Kain
Keyword(s):  
United States ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Lower Troposphere ◽  
Early Evolution ◽  
Convective System ◽  
Similar Time ◽  
Low Level ◽  
Central United States ◽  
Lapse Rates

This study documents the complex environment and early evolution of the remarkable derecho that traversed portions of the central United States on 8 May 2009. Central to this study is the comparison of the 8 May 2009 derecho environment to that of other mesoscale convective systems (MCSs) that occurred in the central United States during a similar time of year. Synoptic-scale forcing was weak and thermodynamic instability was limited during the development of the initial convection, but several mesoscale features of the environment appeared to contribute to initiation and upscale growth, including a mountain wave, a midlevel jet streak, a weak midlevel vorticity maximum, a “Denver cyclone,” and a region of upper-tropospheric inertial instability. The subsequent MCS developed in an environment with an unusually strong and deep low-level jet (LLJ), which transported exceptionally high amounts of low-level moisture northward very rapidly, destabilized the lower troposphere, and enhanced frontogenetical circulations that appeared to aid convective development. The thermodynamic environment ahead of the developing MCS contained unusually high precipitable water (PW) and very large midtropospheric lapse rates, compared to other central plains MCSs. Values of downdraft convective available potential energy (DCAPE), mean winds, and 0–6-km vertical wind shear were not as anomalously large as the PW, lapse rates, and LLJ. In fact, the DCAPE values were lower than the mean values in the comparison dataset. These results suggest that the factors contributing to updraft strength over a relatively confined area played a significant role in generating the strong outflow winds at the surface, by providing a large volume of hydrometeors to drive the downdrafts.

scholarly journals The Cold Front of 15 April 1994 over the Central United States. Part I: Observations

2005 ◽  
Vol 133 (6) ◽  
pp. 1525-1543 ◽  
Author(s):  
B. B. Demoz ◽  
D. O’C. Starr ◽  
K. D. Evans ◽  
A. R. Lare ◽  
D. N. Whiteman ◽  
...  
Keyword(s):  
United States ◽  
Water Vapor ◽  
Cold Front ◽  
Mixing Ratio ◽  
Frontal Surface ◽  
Undular Bore ◽  
Low Level ◽  
Central United States ◽  
Water Vapor Mixing Ratio ◽  
Moist Layer

Abstract Detailed observations of the interactions of a cold front and a dryline over the central United States that led to dramatic undulations in the boundary layer, including an undular bore, are investigated using high-resolution water vapor mixing ratio profiles measured by Raman lidars. The lidar-derived water vapor mixing ratio profiles revealed the complex interaction between a dryline and a cold-frontal system. An elevated, well-mixed, and deep midtropospheric layer, as well as a sharp transition (between 5- and 6-km altitude) to a drier region aloft, was observed. The moisture oscillations due to the undular bore and the mixing of the prefrontal air mass with the cold air at the frontal surface are all well depicted. The enhanced precipitable water vapor and roll clouds, the undulations associated with the bore, the strong vertical circulation and mixing that led to the increase in the depth of the low-level moist layer, and the subsequent lifting of this moist layer by the cold-frontal surface, as well as the feeder flow behind the cold front, are clearly indicated. A synthesis of the Raman lidar–measured water vapor mixing ratio profiles, satellite, radiometer, tower, and Oklahoma Mesonet data indicated that the undular bore was triggered by the approaching cold front and propagated south-southeastward. The observed and calculated bore speeds were in reasonable agreement. Wave-ducting analysis showed that favorable wave-trapping mechanisms existed; a low-level stable layer capped by an inversion, a well-mixed midtropospheric layer, and wind curvature from a low-level jet were found.

A forum on infrastructure: Unique challenges for infrastructure in the central United States from low-level seismicity

2018 ◽  
Vol 37 (5) ◽  
pp. 386-387
Author(s):  
Dwain K. Butler ◽  
Priyank Jaiswal ◽  
Laurie Whitesell
Keyword(s):  
United States ◽  
Low Level ◽  
Central United States

scholarly journals Accuracy of 404-MHz Radar Profilers for Detection of Low-Level Jets over the Central United States

1999 ◽  
Vol 38 (9) ◽  
pp. 1391-1396 ◽  
Author(s):  
Chad J. Daniel ◽  
Raymond W. Arritt ◽  
Christopher J. Anderson
Keyword(s):  
United States ◽  
Low Level ◽  
Central United States ◽  
Low Level Jets

The Low-Level Structure and Evolution of a Dry Arctic Front over the Central United States. Part I: Mesoscale Observations

1996 ◽  
Vol 124 (8) ◽  
pp. 1648-1675 ◽  
Author(s):  
L. Jay Miller ◽  
Margaret A. LeMone ◽  
William Blumen ◽  
Robert L. Grossman ◽  
Nimal Gamage ◽  
...  
Keyword(s):  
United States ◽  
Level Structure ◽  
Low Level ◽  
Central United States ◽  
Arctic Front

A Long-Term Climatology of Southerly and Northerly Low-Level Jets for the Central United States

2008 ◽  
Vol 98 (3) ◽  
pp. 521-552 ◽  
Author(s):  
Claudia K. Walters ◽  
Julie A. Winkler ◽  
Ryan P. Shadbolt ◽  
Jenni van Ravensway ◽  
Gregory D. Bierly
Keyword(s):  
United States ◽  
Low Level ◽  
Central United States ◽  
Low Level Jets
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