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 b) + identify storm initiation Identify storm initiation episodes 112 Episodes

Findings

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

3. Day – tendency for NE-SW orientation Night – no preferred 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 5 10 15 20 NUMBER Front GF UNK COL TL DL Bore Forcing Mechanism

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

6. 66% elevated initiations associated with mid-level (900-600 hPa) convergence features observed in RUC analysis

Was 2002 a Typical Year? Initiation episodes between 1800 and 0200 LST a) 1998 b) 1999 Was 2002 a Typical Year? a) 1998 b) 1999 e) 2002 (IHOP) c) 2000 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.

Evolution of all Initiation episodes examined.

What episodes evolved to Number Length (km)

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

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

High resolution convergence and stability analysis

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

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

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

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

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.

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Was 2002 a Typical Year? a) 1998 b) 1999 a) 1998 b) 1999 IHOP_2002 c) 2000 d) 2001 Fig. 3) Thunderstorm initiation location from 12 – 20 LST for the period 15 May through 30 June.