From Synoptic to Microscale:
A Case Study of a Frontal Passage using
Multiple OLYMPEX Observations
Hannah C. Barnes
University of Washington
Pacific Northwest Weather Workshop
4th March 2016
NOAA Western Regional Center, Seattle, WA
Funded by NASA grants NNX13AG71G, NNX15AL38G, and NNX16AD75G and NSF grant AGS-1503155.
Occluded Front
Synoptic Conditions
1800 UTC 12 December
IR Satellite
500 hPa temperature, height, wind
2 m temperature
10 m wind speed
Sea-level pressure
What happened during
the passage of the
occluded front?
12 December 2015 Timeline
12
13
14
15
16
17
Pre-Frontal
18
20
19
Frontal
Post-Frontal
Weather Events
KHI Waves
DOW Radar
NPOL Radar
D3R Radar
Env. Can. Radar
Quillayute Soundings
Env. Can. Soundings
NPOL Soundings
ER-2 Aircraft
DC-8 Aircraft
Citation Aircraft
Ground Instruments
21 UTC
NPOL Soundings
12 December
1516 UTC
1914 UTC
2123 UTC
Pre-Frontal
Frontal
Post-Frontal
• Increase winds
• Melting level rise
NPOL Reflectivity and Flight Tracks
1519 UTC
1719 UTC
Frontal
Pre-Frontal
1919 UTC
Post-Frontal
Frontal
2119 UTC
Post-Frontal
D3R Radar
Ku-Band Reflectivity
1926 UTC
Height (km)
Height (km)
2002 UTC
Melting Level
Melting Level
Frontal
Post-Frontal
dBZ
Melting level rose rapidly.
12
11
NPOL S-Band Radar
1842 UTC
Differential Reflectivity (ZDR)
10
9
8
7
6
5
4
3
2
1
• Melting level rose abruptly
• Nature of convection changes
Melting
Level
0
12
11
Reflectivity
10
9
8
7
6
5
4
Convective
3
2
1
0
Stratiform
Ground Observations: Particle Size Distribution
Diameter (mm)
Beach House
Time (UTC)
Pre-Frontal and Frontal
Post-Frontal
• Stratiform
• Broad distribution
• Convective
• Lots small
Occluded Front
Microscale Dynamical Features
DC8 Aircraft Data - Dropsondes
Dropsondes Toward Front
Farthest
Flight Track
1707 UTC
46°N 128°W
1711 UTC
46°N 127°W
Closest
1713 UTC
46°N 126°W
Flight Track
DC8 Aircraft Data Ka-Band Reflectivity
128°W
127°W
126°W
East
FRONT
West
More upper-level clouds and shallow precipitation as approach front.
DOW X-Band Radar
2102 UTC
Shear induced Kelvin-Helmholtz waves
Reflectivity
Radial Velocity
Spectrum Width
Strong
Shear
Kelvin-Helmholtz Waves
Conclusions
• OLYMPEX observations allow analysis from synoptic to microscale
• 12 December 2015
• Synoptic: Occluded front
• Mesoscale:
• Abrupt rise in melting level
• Stratiform -> convective
• Microscale:
• Drop size changes
• Midlevel drying behind front
• Kelvin-Helmholtz waves
• Similar analyses available for all days during OLYMPEX available at
http://olympex.atmos.washington.edu/index.html?x=Science_Summaries
Satellite Loop
12 December 2015 Occluded Front
NPOL S-Band Reflectivity
Quillayute Sounding Data
1200 UTC 12 Dec.
0000 UTC 13 Dec.
Pre-Frontal
Post-Frontal
•
•
•
•
Mid-upper troposphere dries
Destabilize
Melting level rise
Winds increase
Quillayute Surface Obs. - 12 Dec. 2015
Temperature (°C)
Temperature rise
Average wind speed and
gusts (mph)
Change in wind
direction
Wind direction
Accumulated
precipitation (mm)
Mean sea-level
pressure (hPa)
Most precipitation
before front
Broad pressure trough
Occluded Frontc