Starting with NCDC cases

Using the NCDC storm events database, reports were sorted for "high wind" in the "Anchorage Muni to Bird Creek, Alaska" area. The time period was very limited; only including October 2006 through December 2011. However this still returned 41 events with wind reports of at least 50kts in the area. These 41 events were then sorted by magnitude, and split into strong (20) and weak (21) cases. The median was 72.5 which was used as the benchmark for evenly splitting the cases. From this point, the date and time of each report was rounded to the nearest 6-hour increment.

Date         Time     Wind   Class
--------------------------------------
20061003     1200     65     Weak
20061008     1800     71     Weak
20061208     1200     89     Strong
20070125     1800     83     Strong
20070129     1800     73     Strong
20070201     1200     76     Strong
20070407     0600     61     Weak
20070907     0600     67     Weak
20071025     1800     73     Strong
20071108     1800     74     Strong
20071122     1200     67     Weak
20071125     0600     64     Weak
20071208     0000     77     Strong
20080120     0600     65     Weak
20080121     1800     74     Strong
20080219     1800     74     Strong
20080305     1200     71     Weak
20080401     0600     63     Weak
20081009     1800     87     Strong
20090113     1800     91     Strong
20090115     1800     65     Weak
20090329     0600     64     Weak
20091111     1200     71     Weak
20091130     1800     72     Weak
20100305     0600     69     Weak
20100510     1800     71     Weak
20100816     1800     63     Weak
20100924     1200     51     Weak
20101203     1200     72     Weak
20110101     0600     75     Strong
20110407     0000     87     Strong
20111014     0600     68     Weak
20111024     1800     68     Weak
20111025     0600     62     Weak
20111103     1200     77     Strong
20111203     1200    103     Strong
20111207     1200     75     Strong
20111210     1200     78     Strong
20111211     1800     84     Strong
20111217     1800     90     Strong
20111220     1200     73     Strong

Two files containing the date and time of the cases were created for the strong set and the weak set. 6-hour composites were then created from the NCEP/NCAR reanalysis using ESRL. The following variables were examined at both the report time and 24 hours prior:

• 850hPa wind 
• Sea level pressure 
• 500hPa heights 
• SB Lifted index 

850hPa wind 0hr

850hPa wind -24hr

Sea level pressure 0hr

Sea level pressure -24hr

500hPa height 0hr

500hPa height -24hr

SB Lifted index 0hr

With regards to the time shift concern:
Averaging the difference between the actual time of the wind report and the rounded time yielded an average of a 29 minute lag for the strong class, and a 33 minute lead for the weak class. In the composites above, the strong class does appear to lag the weak class in a number of features, however the 62-minute difference is too small of a magnitude to consider the differences on a synoptic scale. Therefore, analysis of the results will assume that all of the cases are perfectly synchronized by the time of the wind event, and that any differences in the composites are significant to the differences between strong and weak events.