2. CHECKLIST

The following severe weather checklist was developed for NWSO SGF, but can be used for the much of the Midwestern and southern United States. Local adaptations due to elevation, terrain and other local and regional factors must be made to fit a particular location. After a detailed surface and upper air analysis, one should proceed to this checklist (Table 1).
If six or more positive (or yes) parameters, proceed to the Miller/SPC checklist. In addition, calculate the wind index (WINDEX), and the height wet bulb zero (WBZ). If less than six positive parameters, there will probably not be organized severe weather in your area. One word of caution: Be vigilant for elevated convection above an elevated capping inversion. If your analysis reveals a stable atmosphere in the lower levels but has moisture above a fairly strong inversion, recalculate the indices above the inversion or check for steep mid level lapse rates. See section 8A for more information on elevated convection. One last word of caution: Beware of rapidly changing synoptic environments.

TABLE 1
NWSO Springfield Severe Weather Checklist

Severe
Weather
Parameter

Indicators (Circle Letter)

Favorable
Y/N
(Add remarks as necessary)

1.

Low Level Temperature and Moisture A. Depth of low level moisture now (or expected) to be greater than 3000 ft?
B. Surface dew point >60°F?
C. Distinct low level surface moisture axis present? Location/Time?
D. Low level moisture convergence expected? Location/Time?
E. Will the 850 mb max temperature ridge be over or west of the 850 mb moisture axis?
F. Will temperature exceed computed convective temperature?

 

Y/N
2. Low Level Jet A. Is a low level jet present or expected to develop? Location/Time?
B. Highest 850 mb jet speed expected over CWA.
C. 850mb moisture convergence expected? Location/Time?

 

Y/N
3. Upper Level Support A. Will there be a 300/250 mb jet >65 kts.
B. Ageostrophic circulation expected? Location?
C. Coupled jet expected? Location?

 

Y/N
4. Lifting Mechanisms A. Are any lifting mechanisms such as fronts or outflow boundaries present? List them along with their location.
B. Will any intersecting boundaries be present? Location?
C. Will lifting mechanisms be able to overcome capping inversion (generally if cap strength < 2°F and CIN <50 J/kg. Also note severe storms can develop regardless of CAP strength, "if" sufficient dynamic strength is available.)?

 

Y/N
5. Vertical Wind Shear A. Will winds show significant veering (0-3km shear values > 35kts)?
B. Is there (or will there be) speed shear >25kts and/or directional shear >30 degrees between 850 and 500 mb?

 

Y/N
6. Instability A. Is/will the Lifted Index be 0?
B. Is/will the K Index be >30? (Can be as low as 20-25 with elevated convection.)
C. Will CAPE >800 J/kg?
D. Will there be high mid level lapse rates (700-500 mb) > or = 6.5°C/km?
E. Will there be warm advection at 850 mb?
F. Will a significant capping inversion remain in place?

 

Y/N
7. 700 mb Dry Intrusion A. Is there or will there be a dry intrusion of air at or near the 700 mb level? (Dew point depression >6°C.)

 

Y/N
8. Upper Vertical Motion A. Is large scale forcing indicated by model Q vector and omega fields?
B. Will there be significant PIVA/Differential PVA?

 

Y/N
9. Satellite Imagery/Cloud Indicators A. Are there lines of cumulus or mid clouds (altocumulus castellanus-ACCAS) on the morning satellite imagery?
B. Does satellite imagery indicate a short wave moving into the area with corresponding significant height falls on upper air analysis?
C. Is there significant mid level drying present on water vapor imagery?

 

Y/N
10. Surface Pressure Falls A. Is there or will there be strong surface pressure falls
B. If 10A is yes, will there be a corresponding pressure rise moving toward the fall area? (The larger the absolute value of this rise-fall couplet, the larger the potential for severe weather in the pressure fall area.)

 

Y/N

TABLE 2
Severe Weather Checklist
(After SPC (1998) and Miller (1972))

PARAMETER

WEAK

MODERATE

STRONG

Surface Pressure >1010 mb 1010 to 1005 mb <1005 mb
Surface Dew Point <55°F 55-64°F >or = 65°F
12hr Surface Pres Change 0 to -3 - 4 to -7 < or = -8
850 mb Temp Axis East of Moist Axis Over Moist Axis West of Moist Axis
850 mb Jet <25 kts 25-35 kts >35 kts
850 mb Dew Point < or = 8°C 8 - 12°C >12°C
700 mb Dry Intrusion N/A or Weak 700 mb winds Winds from dry to moist intrude at <40° and are > or = 15 kts Winds intrude at an > or = 40° and are > or = 25 kts
700 mb Temp No Change Line Winds cross line< or = 20° Winds cross line >20° and < or = 40° Winds cross line >40°
500 mb Height Change < 30 m > or = 30 and < or = 59 m > or = 60 m
500 mb Wind Speed < or = 35 kts 36-49 kts > or = 50 kts
500 mb Vorticity Advection Neutral or NVA PVA-Contours Cross Vorticity Pattern < or = 30° PVA-Contours Cross Vorticity Pattern >30°

850-500 mb Wind Shear

a. Speed Shear
b.
Directional Shear

 

15-25 kts
20-30°

 

26-35 kts
30-60°

 

>35 kts
>60°

300-200 mb Jet < or = 65 kts 66-85 kts >85 kts
Mean R.H. 70-80% or 40-50% 50-70% 50-70%
TT <50 50-55 >55
LI >-2 -3 to -5 < or = -6
CAPE 800-1500 J/kg 1500-2500 J/kg >2500 J/kg
SWEAT <300 300-500 >500
WBZ >11000 ft
<5000 ft
9000-11000 ft
5000-7000 ft
7000-9000 ft
Helicity (0-3km) 150-300 m2/s2 300-450 m2/s2 >450 m2/s2
SSI -1 to +2 -1 to -3 <-3

The rest of this paper contains various weather checklists, rules of thumb, and other severe weather information. Forecasting large hail, strong winds, tornadoes, derechos, and pattern recognition are examined.

This paper will not address radar techniques applicable to severe weather. An excellent compendium of WSR-88D weather reference materials is by Falk (1997).

3. SURFACE, UPPER AIR, AND COMPOSITE CHARTS


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