Event Summary
     National Weather Service, Raleigh NC

Tropical Storm Alberto, June 2006
Updated 2009/02/26


Satellite image of Tropical Storm Alberto - Click to enlarge
(Click on the image to enlarge.)


Event Headlines -
...The National Weather Service in Raleigh issued 45 Flash Flood Warnings on Wednesday, June 14, 2006...
...Raleigh-Durham International Airport (RDU) shattered the precipitation record for June 14 with 5.64 inches of rain and it also broke the all time daily precipitation record...
...Rainfall amounts ranged between 2 and 5 inches in a corridor from near Rockingham to Raleigh to Roanoke Rapids with some locations near Raleigh receiving between 6 and 8 inches of rain...
...Local media reports stated that the Raleigh-Wake 911 center received more than 1,076 calls for help...
...Police and fire fighters in Wake County performed 47 water rescues...



Event Overview -
Tropical Depression One developed at 700 CDT on Saturday, June 10, 2006 in the Yucatan Channel. The depression developed into Tropical Storm Alberto at 1100 AM EDT on Sunday, June 11 with maximum sustained winds of 45 MPH. Alberto reorganized and reached its maximum intensity with sustained winds of 70 MPH at 1100 AM EDT on Monday, June 12. The tropical storm maintained this intensity during the day on Monday before weakening slightly on Monday night. Alberto moved onshore just after 1200 PM EDT on Tuesday, June 13 near Keaton Beach Florida with maximum sustained winds of 50 MPH.

Alberto moved north across northern Florida and southeastern Georgia during the afternoon and evening hours on Tuesday, June 13. Alberto was still a tropical storm at midnight on Wednesday, June 14 while it was centered over eastern Georgia. At the same time widespread showers and thunderstorms were invading North Carolina from the south. As the storm moved from Georgia into South Carolina it began to interact with a stationary front that was draped across the Southeast.

Alberto was downgraded to a tropical depression at 500 AM EDT on Wednesday, June 14 while it was centered over South Carolina. Warm moist air associated with the tropical depression moved up and over a cooler and more stable airmass in central and western North Carolina where dewpoints were in the lower to mid 60s. At the same time, a shortwave trough located over the Ohio Valley dropped southeast and began to interact with the remnants of Alberto. Upward motion out ahead of the short wave trough enhanced the precipitation associated with the remnants of Alberto.

A shield of very heavy rain developed in an arc to the north and northwest of the storm as it moved into North Carolina. The orientation of the precipitation shield (a band stretching from northeast to southwest) and its northeast translation resulted in excessive rainfall totals.


Key Factors that Came Together to Enhance the Precipitation across Central North Carolina


Based on research conducted by Croke/NCSU (Tropical Cyclone Landfall and Precipitation), several key factors came together to enhance the precipitation across central North Carolina on June 14th.

  1. A Very Moist Airmass - Precipitable water values across the region were near to slightly above 2 inches ( GSO RAOB  |   MHX RAOB). Model moisture transport vectors indicated strong moisture advection into the region from coastal sections of Georgia and South Carolina.

  2. Low Level Focus - A weak surface cold front crossed the region Monday night then stalled across South Carolina on Tuesday, the 13th. Northeast flow behind the boundary advected cooler drier air into the region as dewpoints midday Tuesday were in the mid and upper 50s. As the remnants of Alberto moved north northeast across southern Georgia late Tuesday afternoon and Tuesday night, the winds just above surface veered to a more south southeast direction, pulling moisture over the surface cool dome. This caused patches of light rain to break out across central North Carolina Tuesday evening. This patchy precipitation helped to establish a limited area of cold air damming across most of the Piedmont. The development of the cold air damming aided in the formation of an inverted surface trough across the coastal plain of central North Carolina by 0600 UTC/14th with northeast winds across the Piedmont and east to southeast winds across the coastal region. The heavy rain axis coincided along and just north of this boundary. Finally, there was significant speed convergence over central North Carolina at 850 and 700 MB. Winds of 35-45 knots were across South Carolina and southeast North Carolina while winds across central North Carolina were 10-15 knots.

  3. Upper Level Support - In the upper levels, a distinct mid level trough was crossing the Ohio River valley, headed toward the central and northern Appalachians. This feature likely increased the potential vorticity over central North Carolina. At 250 MB, a jet maxima of 100-105 knots was positioned across New England, placing central North Carolina in the favorable right entrance region. The approaching mid level trough and the jet max produced strong upper level divergence over the area. Another feature, not well depicted by the models, but detected in the 500 and 300 MB upper air subjective analyses, 12Z on June 13, was a weak short wave diving south along the southern Mississippi River valley. It was hypothesized, though not documented in external discussions, that such a feature could possibly pull the tropical low slightly westward of the forecast track. It does appear that the surface low center did indeed move left of the 24 hour forecast track position for 12-21Z on June 14 across interior NC.

  4. Tropical Cyclone Precipitation Distribution - In the preliminary forecast mode using numerical model output and latest NHC/TPC forecast track positions for Alberto, product bundles from the Tropical Procedure on AWIPS were used to estimate the likely area of heaviest rainfall associated with the storm track. Deep layer shear, 850-300 MB, showed the dominant shear vector pattern along or in the direction of the path of the storm suggesting the heaviest rainfall would likely occur along the track of the low pressure center. Divergence aloft, 250 MB, showed a maximum of divergence to the north of the storm track. Given a predicted storm track running from near Dillon, SC at 12z/14 to just east of Virginia Beach, VA at 00z/15, it appeared the heaviest rain based on these parameters would occur just to the east of US 1 or from Laurinburg to Raleigh to Roanoke Rapids. It was also noted that heaviest rainfall within this zone would likely occur near the stalled front or boundary between cooler, drier air to the northwest and subtropical warm, humid air to the southeast. This was thought to most likely occur in the northeast Sandhills and central Coastal Plain, roughly from Fayetteville to Wilson.

    As shown in the HPC analysis below, the heaviest rain fell along and left of the storm track across North Carolina.

    Post storm precipitation analysis from HPC shows that the heaviest rain fell along and left of the storm track





Alberto's Track

Tropical Storm Alberto Track
Tropical Storm Alberto Track - Click to enlarge
(Click on the image to enlarge.)



Precipitation Totals from Tropical Storm Alberto


List of rainfall reports across central North Carolina from Tropical Storm Alberto

A list of some very impressive totals is available here.


Analyzed Precipitation Totals from Tropical Storm Alberto

The map below contains precipitation totals during the period in which Alberto impacted North Carolina

Precipitation Totals from Tropical Storm Alberto




Alberto Precipitation Data for GIS/ArcMap - GRID and Layer Files
Data courtesy of Ryan Boyles, State Climate Office of North Carolina

alberto2006
dblbnd.adf  |   hdr.adf  |   prj.adf  |   metadata.xml  |   sta.adf  |   w001001.adf  |   w001001x.adf

info
arc.dir  |   arc0000.dat  |   arc0000.nit  |   arc0001.dat  |   arc0001.nit


state IV precipitation data for Tropical Storm Alberto


Satellite

Visible satellite imagery from 1515Z (1115 AM EDT) on Wednesday, June 14, 2006

The visible satellite image below from 1515Z (1115 AM EDT) shows the remnants of Tropical Storm Alberto centered over North Carolina. The circulation center was located about 70 miles southwest of Raleigh at the time of this satellite image. The National Hurricane Center advisory from 1100 AM EDT notes that Alberto was losing its tropical characteristics at this time.

A Java Loop of Visible satellite imagery from 1045Z (645 AM EDT) through 2245Z (645 PM EDT) Wednesday, June 14, 2006 is also available.

Visible satellite imagery




Water Vapor satellite imagery from 1015Z (615 AM EDT) on Wednesday, June 14, 2006

The water vapor satellite image below from 1015Z (615 AM EDT) shows a short wave trough located over the Ohio Valley as it begins to interact with the remnants of Tropical Storm Alberto. Upward motion out ahead of the short wave trough enhanced the precipitation associated with the remnants of Alberto.

A Java Loop of Water Vapor satellite imagery from 0620Z (220 AM EDT) through 1550Z (1150 AM EDT) Wednesday, June 14, 2006 is also available.

Water Vapor satellite imagery



Surface Analysis

Analyzed surface map from 12Z (800 AM EDT) Wednesday, June 14, 2006

The surface analysis from 12Z (800 AM EDT) Wednesday, June 14, 2006 shows the remnants of Alberto centered in central South Carolina with a stationary from draping across the North Carolina.

A Java Loop of surface analysis imagery from 12Z Tuesday, June 13, 2006 through 06Z Thursday, June 15, 2006 shows Alberto moving onshore in Florida at around 15Z on Tuesday, June 13 and then moving northeast across Georgia and the Carolinas before moving offshore south of Virginia Beach at around 00Z on Thursday, June 15, 2006.

Surface analysis from 12Z (800 AM EDT) Wednesday, June 14, 2006



Radar Loops

Java Loop of regional radar reflectivity imagery from 05Z (100 AM EDT) Wednesday, June 14 through 19Z (300 PM EDT) Wednesday, June 14, 2006. Note - this loop includes only 14 frames.

Java Loop of every half hour of KRAX radar base reflectivity imagery from 0304Z (1104 PM EDT) Tuesday, June 13 through 2058Z (458 PM EDT) Wednesday, June 14, 2006. Note - this loop includes imagery from every half hour (includes 37 frames !)

Java Loop of all KRAX radar base reflectivity imagery from 0304Z (1104 PM EDT) Tuesday, June 13 through 2058Z (458 PM EDT) Wednesday, June 14, 2006. Note - this loop includes imagery from every radar scan (includes 215 frames !)

Java Loop of KRAX Storm Total Precipitation imagery from 0559Z (159 AM EDT) through 2200Z (600 PM EDT)Wednesday, June 14, 2006. Note - this loop includes 33 frames.


KRAX base reflectivity image from 1510Z on Wednesday, June 14, 2006 (1110 AM EDT)





Crabtree Creek at Glenwood Avenue

Details regarding the flooding in this important part of the city

Some of the most dramatic pictures and news associated with the flooding produced by the remnants of tropical storm Alberto occurred in the Crabtree Valley area of Raleigh ( map ). The Crabtree Creek has been frequented by flash flooding during the past several decades. The creek runs from its origin in the William B. Umstead State Park in the northwestern portion of Wake County and flows east across north Raleigh and into the Neuse River in eastern Raleigh. The Crabtree Creek collects a tremendous amount of runoff from urban and suburban locations in Raleigh and it is especially prone to flash flooding.

The Crabtree Creek at Glenwood Avenue (RLHN7) river gauge was reporting a stage of just less than 6 feet before daybreak on Wednesday, June 14. As heavy rains moved into the Crabtree Creek basin after sunrise, the creek began to rise very rapidly. Between 800 AM and 900 AM the creek rose nearly 4 feet and between 800 AM and noon the creek rose nearly 10 feet. The creek crested at 430 PM at a stage of 23.77 feet.

Hydrograph of Crabtree Creek at Glenwood Avenue in Raleigh showing the change in stage during the flooding on Wednesday, June 14.

Hydrograph of Crabtree Creek at Glenwood Avenue in Raleigh


The table below provides a list of the stage and CFS values at the Crabtree Creek at Glenwood Avenue on Wednesday, June 14.   7 days of tabular data in text format  |   7 days of tabular data in XML format

Date  Time (UTC)  (EDT)       Stage     CFS

06/14    12:00Z - 800 AM EDT  6.63 ft   0.287 kcfs 
06/14    13:00Z - 900 AM EDT  10.24 ft  1.24 kcfs  
06/14    14:00Z - 1000 AM EDT 13.35 ft  2.45 kcfs  
06/14    15:00Z - 1100 AM EDT 16.13 ft  3.81 kcfs  
06/14    16:00Z - 1200 PM EDT 19.27 ft  5.63 kcfs  
06/14    17:00Z - 100 PM EDT  21.77 ft  7.27 kcfs  
06/14    18:00Z - 200 PM EDT  22.93 ft  8.09 kcfs  
06/14    19:00Z - 300 PM EDT  23.45 ft  8.47 kcfs  
06/14    20:00Z - 400 PM EDT  23.76 ft  8.70 kcfs  
06/14    20:30Z - 430 PM EDT  23.77 ft  8.71 kcfs  
06/14    21:00Z - 500 PM EDT  23.71 ft  8.66 kcfs  
06/14    22:00Z - 600 PM EDT  23.41 ft  8.44 kcfs  
06/14    23:00Z - 700 PM EDT  22.87 ft  8.05 kcfs  
06/15    00:00Z - 800 PM EDT  22.2 ft   7.57 kcfs   

The table below includes impacts at various stages of the creek at Glenwood Ave and a few of the historical crests.

3 - 5 feet - Typical stages at low flows
14.00 feet - Water covers the lower parking lot at Crabtree Valley Mall
18.00 feet - Water enters the lower entrance to the Hecht's/Macy's Department Store
21.50 feet - Hurricane Floyd (September 16, 1999)
20.00 feet - Most parking lots at Crabtree Valley Mall flood, including the Shell gas station
22.00 feet - Glenwood Ave and the lower level Crabtree Valley Mall parking lot flood
23.00 feet - The Glenwood Ave (U.S. 70) bridge floods. Travel on Glenwood Ave and the area around Crabtree Valley Mall is severely hampered
23.00 feet - Hurricane Fran (September 6, 1996)
23.77 feet - Tropical Storm Alberto (June 14, 2006)
24.00 feet - Glenwood Ave (U.S. 70) becomes impassible
26.00 feet - Water reaches the top of the Glenwood Ave (U.S. 70) bridge railing
27.69 feet - All time record high (June 29, 19730



Selected photographs of the flooding from around Crabtree Valley

Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge

Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge

Photo of flooding around Crabtree Valley.  Photo courtesy of NCDOT traffic camera - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of NCDOT traffic camera - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of NCDOT traffic camera - Click to enlarge


Rainfall Rates at Holly Springs, NC
Data courtesy of Dr. Sandra Yuter, Cloud and Precipitation Processes and Patterns Group, North Carolina State University


The two images below provided some additional details about the incredible rainfall rates that were observed in Wake County on June 14, 2006. The data below is from instrumentation located in Holly Springs, NC which is located about 15 miles or about 25 kilometers southwest of Raleigh or 15 miles or about 25 kilometers south-southwest of the Raleigh-Durham International Airport (KRDU). The total precipitation for this event at Holly Springs was 7.02 inches or 178.4 mm.

This image provides a graph of the one-minute rainfall rates during the event. Keep in mind that 1 inch equals about 25 millimeters (1" = 25.4mm). Note that there were a few spikes in where rainfall rates exceeded 3 inches per hour (76 mm per hour) with a prolonged period of rainfall rates around or in excess of 2 inches per hour (51 mm per hour) between 1400 UTC (1000 AM EDT) and 1600 UTC (1200 PM EDT).

Graph of one-minute rainfall rates at Holly Springs, NC


The image below is a rain rate histogram that shows the frequency of specific rain rates at Holly Springs, NC. There were 897 minutes of rainfall during the event Minutes of Rainfall or nearly 15 hours. During this period there were almost 5 hours (288 minutes) of rainfall rates in excess of 10 mm per hour or 0.4 inches per hour.

Rain rate histogram at Holly Springs, NC



Video from the Flash Flood Event
Video courtesy of Brandon Locklear.


The video below was filmed by Brandon Locklear in Apex, NC on Wednesday, June 14 at approximately 1100 AM where the Beaver Creek flows under Kelly Road ( map ).
(click on the image to view video.)

still image from Fuquay-Varin hail video
Note - the video is 20 seconds in length and approximately 2.1 MB in size.



Selected Photographs of the Severe Weather Event

Photos courtesy of Jamie Wirth, NC DOT, and Jeremy Gilchrist.
(Click the image to enlarge.)


Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge

Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of Jamie Wirth - Click to enlarge

Photo of flooding around Crabtree Valley.  Photo courtesy of NCDOT traffic camera - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of NCDOT traffic camera - Click to enlarge           Photo of flooding around Crabtree Valley.  Photo courtesy of NCDOT traffic camera - Click to enlarge

Photo of flooding around Woodlake which  is around 5 mile east of Vass in Moore County.  Photo courtesy of Jeremy Gilchrist - Click to enlarge           Photo of flooding around Woodlake which is around 5 mile east of Vass in Moore County.  Photo courtesy of Jeremy Gilchrist - Click to enlarge           Photo of flooding around Woodlake which is around 5 mile east of Vass in Moore County.  Photo courtesy of Jeremy Gilchrist- Click to enlarge


Case study team -
Phil Badgett
Rod Gonski
Gail Hartfield
Brandon Locklear
Scott Sharp
Jamie Wirth
Jonathan Blaes

For questions regarding the web site, please contact Jonathan Blaes.


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