1. IHOP Convection Initiation And Storm Evolution Studies
Jim Wilson & Rita Roberts
National Center for Atmospheric Research

2. Study Area
All 44 days plus 11 May

3. DATA
Satellite & 275
Surface Stations

4. DATA
Mosaic of NEXRAD
and S-pol

5. Enter
convergence
lines every
20 min

6. + identify storm initiation Identify storm initiation episodesb)
+ identify storm initiation
Identify storm initiation episodes
112 Episodes

7. Findings

8. 1. Afternoon and Nocturnal Initiation Maximum
112 Initiation Episodes
Afternoon peak 2.
Elevated
mostly night
Surface based
mostly day
Night max
Number

9. 3. Day – tendency for NE-SW orientation Night – no preferred
Solid – surface
Dashed – elevated
Red – 6-22 CST (day)
Blue – 22-6 CST (night)

10. 4. Surface forcing was primarily associated with
fronts and gust fronts; relatively few dry line 5 10 15 20
NUMBER
Front GF UNK COL TL DL Bore
Forcing Mechanism

11. 5. Elevated initiation not closely associated with low-level jet.
Large squall lines
Low-level jet
Elevated

12. 6.
66% elevated initiations associated with mid-level ( hPa) convergence features observed in RUC analysis

13. Was 2002 a Typical Year? Initiation episodes between 1800 and 0200 LST
a) b) 1999
Was 2002 a Typical Year?
a) 1998
b) 1999
e) 2002 (IHOP)
c) d) 2001
Initiation episodes
between 1800 and
0200 LST
Fig. 3) Thunderstorm initiation location from 12 – 20 LST for the period 15 May through 30 June.

14. Evolution of all
Initiation episodes
examined.

15. What episodes evolved to
Number
Length (km)

16. 7. Lifetime of storm complex dependent on development of a gust front.
Number
Lifetime (hr)

17. Analysis 15-16 June 2002 case L 8 hour loop Synoptic low and
trough line

18. High resolution convergence and stability analysis

19. 8. Convergence and CIN influence storm initiation more than CAPE.
AN IMPRESION -
high resolution
convergence and
CIN fields needed
to specify timing and
location 5
Cold Front
Outflow Boundary
max
min
4000
3000
b) CAPE
1000 15 65
115
c) CIN
d) Satellite

20. 9. After initiation CIN takes on less importance if convergence strong
a) Convergence 1 2 3
d) Convergence 3
1&2
9. After initiation
CIN takes on less
importance if
convergence strong
b) CIN
max
e) CIN 15
115
215
315
c) CAPE
1000
2000
3000
f) CAPE
1000
2000

21. 10. Gust front characteristics heavily influence storm evolution
Outflow Boundary
Cold Front
a) 2100 UTC 1 2 3 4
b) 0000 UTC
c) 0300 UTC

22. 11. Movement of storm complex greatly influenced by gust front motion
Steering Flow

23. Impressions & Implications
1. Elevated Initiation episodes more frequent (day and
night) then expected.
In Colorado and Florida elevated initiation rare, upper mid-west
more common than IHOP area. Why?
2. Elevated Initiation episodes many not as mysterious
as previously suspected - associated with mid-level
( mb) synoptic and mesoscale convergence
features visible in the RUC analysis.
3. Nocturnal precipitation maximum in the Great
Plains how much is due to advection of convective
systems from the west vs elevated initiation?

24. Impressions & Implications
4. Dry line initiation less than expected relative to
fronts and gust fronts. Is this typical?
5. Initiation along boundaries (time & space) was
very dependent on small scale variations in convergence
and CIN. Station spacing at least as dense as in OK
together with the WSR-88D is needed to specify
convergence on scale required.
Greater CIN resolution required (radar refractivity
promise) and observation of cap evolution.

25. Impressions & Implications
6. Gust fronts and their characteristics have major
influence on the evolution, lifetime and motion of
convective storm complexes.
Essential that accurate short period forecast systems
anticipate their emergence and characteristics. This is
a major research challenge.

26. THANK YOU @

27. Was 2002 a Typical Year? a) 1998 b) 1999 a) 1998 b) 1999 IHOP_2002
c) d) 2001
Fig. 3) Thunderstorm initiation location from 12 – 20 LST for the period 15 May through 30 June.