Transcript IHOP Convection Initiation and Storm Evolution Studies (Wilson)

IHOP Convection Initiation
And Storm Evolution Studies
Jim Wilson & Rita Roberts
National Center for Atmospheric Research
Study Area
All 44 days plus 11 May
DATA
Satellite & 275
Surface Stations
DATA
Mosaic of NEXRAD
and S-pol
Enter
convergence
lines every
20 min
+ identify storm initiation
Identify storm initiation episodes
a)
b)
112 Episodes
Findings
1. Afternoon and Nocturnal Initiation Maximum
112 Initiation Episodes
Afternoon peak
30
elevated
surface
Number
25
20
Night max
Surface based
mostly day
15
10
5
0
10 13 16 19 21 0
TIME (CST)
3
2.
Elevated
mostly night
6
3. Day – tendency
for NE-SW orientation
Night – no preferred
orientation
Solid – surface
Dashed – elevated
Red – 6-22 CST (day)
Blue – 22-6 CST (night)
4. Surface forcing was primarily associated with
fronts and gust fronts; relatively few dry line
20
NUMBER
15
10
5
0
Front
GF
UNK
COL
TL
DL
Forcing Mechanism
Bore
5. Elevated initiation not closely associated with
low-level jet.
Large squall lines
12
10
Low-level jet
8
Elevated
6
4
2
0
15
17
19
21
23
25
27
29
31
2
4
Date
7
6
5
4
3
2
1
0
6
8
10
12
14
16
Date
18
20
22
24
6.
66% elevated initiations associated with mid-level (900-600
hPa) convergence features observed in RUC analysis
Was 2002 a Typical Year?
a) 1998
b) 1999
c) 2000
d) 2001
e) 2002 (IHOP)
Initiation episodes
between 1800 and
0200 LST
Evolution of all
Initiation
episodes
examined.
What episodes evolved to
25
SQ
L
M
Number
20
15
10
5
0
0-199
200-399
Length (km)
>400
7. Lifetime of storm complex dependent on
development of a gust front.
30
GF
No GF
25
Number
20
15
10
5
0
0-2
>2-4
>4-6
>6-8
Lifetime (hr)
>8
Analysis 15-16 June 2002 case
8 hour loop
Synoptic low and
trough line
L
High resolution convergence and stability analysis
8. Convergence and
CIN influence storm
initiation more than
CAPE.
b) CAPE
5
Cold Front
max
min
AN IMPRESION high resolution
convergence and
CIN fields needed
to specify timing and
location
Outflow Boundary
d) Satellite
c) CIN
15
65
115
15
65
a) Convergence
9. After initiation
CIN takes on less
importance if
convergence strong
1
d) Convergence
2
1&2
3
3
b) CIN
e) CIN
315
215
15
15
c) CAPE
f) CAPE
1000
10. Gust front characteristics heavily influence
storm evolution
a) 2100 UTC
b) 0000 UTC
c) 0300 UTC
Cold Front
L
4
3
2
Outflow Boundary
1
11.
Movement of storm
complex greatly
influenced by
gust front motion
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
(900-600 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?
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.
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.
THANK YOU
@
Was 2002 a Typical Year?
a) 1998
b) 1999
IHOP_2002
c) 2000
d) 2001