SNOWIE: Seeded and Natural Orographic Wintertime clouds - the Idaho Experiment Wyoming King Air Summary – IOP 3 Author: Jeff French Summary of Operations:

The UWKA flew one flight (RF03) during IOP3, approximately 3.5 hours. It operated along track 4a (directly W-E) between altitudes of 14 kft and 11.5 kft, starting high and stepping down through the flight and back up to 12 kft for the last couple of legs. (Fig. 1). It encountered LWCs up to about 0.4 g m-3 with low droplet concentrations (typically less than 40 cm-3). Mean droplet diameters ranged from about 20 to 30 µm, leading only to light icing conditions. An upper cloud extended up to 8 – 8.5 km on the WCR, with a lower cloud that had tops sloping upward downwind over the mountain. At flight level, the UWKA was often between cloud layers on the upwind side of the leg and the clouds merged (often) about halfway through the leg.

 Figure  1:  Plot  of  Flight  Track  of  UWKA  during  IOP  3

The UWKA flew 10 legs. The first leg started much further west to try to capture a broader length of the storm system. On the west end, legs were often shortened by a few nmi in instances when we were well clear of cloud. On the east end, a couple of the legs needed to be shortened for those instances when our clearance was down to 11000 ft (even if we were flying at higher altitudes) due to ATC requirements and minimum IFR altitudes in the area. Flight level winds were 27 – 30 m s-1 at 14 kft, and were 20 – 24 m

s-1 at 12 kft (the winds may have also been weakening through the flight. The UWKA flight track was directed along the wind direction at flight level.

Both the CIP and 2DS probes were having problems during the flight. Prior to takeoff, there was heavy rain on the ground at Boise. During the ~15 minutes that the probe covers were off prior to takeoff, the optics on both probes became heavily fogged. This became slightly better during flight, but its likely that data from these probes may be largely unusable for the entire flight.

The table below provides a brief summary of the observations from each track.

Leg #

Times (GMT) Dir. Alt. of

UWKA T °C Alt. of Seed AC**

Notable Observations

1 0247 – 0304 W 14 kft -14.5 NOT*

Line started well west to capture upwind character of system. Western1/2 to 2/3 of line in clear air, well below upper cloud and above lower cloud. By midway through line, both clouds have merged and 2DP is seeing ~5 L-1 of precip. CDP detects ~30 cm-3 of droplets, CLWC maxes at roughly 2 g m-3. Cloud water only on eastern most end of line and in regions where 2DP concentration is least.

2 0307 – 0324 E 14 -14.5 13??

Roughly same as last leg. CLWC is less (max of ~0.1 g m-3). 2DP at 5 – 10 L-1, in eastern half of leg only. Western have of leg is between layers.

3 0327 – 0334 W 14 à

12

-14.5 à

-10.5 13

Layers separating for almost entire leg, even on eastern end (Fig 2). Decided to have UWKA descend to 12 kft at very end of line an in turn prior to next leg. At lower altitudes, UWKA measured ~0.15 g m-3 on eastern end of leg.

4 0337 – 0352 E 12 -10.5 13

Layers remain separated, however, UWKA is now in lower cloud for nearly the entire leg. UWKA encounters CLWC of 0.4 g m-3 for eastern 2/3 of

leg, with little or no 2DP (precipitation) particles at flight level.

5 0354 – 0403 W 12 à

11.5 -10.5 à -9 13

Clouds still separated for much of leg except for eastern-most portion. UWKA clipping through tops at 11500 ft with CLWC up to 0.4 g m-3. CLWC and w trace suggest some regularly spaced positive vertical motions along the middle of the leg…waves at cloud top? (Fig 3) Precipitation shows up on eastern end of line with reflectivity approaching 20 dBZ at flight level. (Fig 4)

6 0406 – 0421 E 11.5 -9 13

Pretty much same story as last leg, CLWC up to 0.35 g m-3 throughout much of leg, most precipitation from 2 DP and WCR reflectivity on eastern end. Cloud layers remain separated on western side of line.

7 0424 – 0435 W 12 -10.5 13?

It appears that lower cloud is growing and ascending into upper cloud. CLWCs are larger, in excess of 0.45 g m-3. Streaks are definitely visible in WCR data.

8 0437 – 0458 E 12 -10.5 NOT??

Eastern half is now one large cloud mass, extending from surface up to 8 km. UWKA measures CLWC through eastern 2/3 of leg, only western-most portion are the two cloud layers still distinct.

9 0501 – 0513 W 12 -10.5 NOT

Similar to last leg, lower portion of upper cloud appears to be descending on western side of line. Throughout middle and eastern half, the two cloud layers have merged and there appears significant precipitation.

10 0516 – 0528 E 12 -10.5 NOT

Deep, solid cloud along entire line. Even significant precipitation on western end.

*Seeding Aircraft not yet on track **not very good notes on the seeding aircraft, should verify these times and altitudes

 Figure  2  WCR  vertical  profile  of  reflectivity  for  leg  3  (west  to  east)  and  first  half  of  leg  4  (east  to  west)  

 

Leg      3   Leg      4  

 Figure  3  trace  of  CLWC  (top),  cloud  Droplet  Concentration  (2nd  down),  vertical  wind  (3rd  down)  and  twoDP  concentration  (bottom)  from  Leg  5  (west  to  east  from  left  to  right).

 Figure  4  WCR  vertical  profile  of  reflectivity  for  leg  5  (west  to  east)  and  first  half  of  leg  4  (east  to  west).  Note  precip  and  higher  reflectivity  on  eastern  most  end  of  line.  

Leg      5   Leg      6  

Waves??