jason elliott nws baltimore/washington media workshop march 29, 2013 pictured: gunpowder falls near...
TRANSCRIPT
NWS Flooding 101
Jason ElliottNWS Baltimore/Washington
Media WorkshopMarch 29, 2013Pictured: Gunpowder Falls near Parkton, MD
2012 – Year in Review
It was a quiet year… Drought over much of
the country No real spring flood…until Sandy… Conditions have turned
wetter both locally andin other parts of the countrysince late October 2012
2012 Year in Review 2012 had the fewest flood-related fatalities in
50 years! (28…only 3 east of the Mississippi)
19931995
19971999
20012003
20052007
20092011
0
20
40
60
80
100
120
140
160
0
10
20
30
40
50
Flood Fatalities & Damage
FatalitiesDamage
Annu
al F
atal
ities
Floo
d Da
mag
e ($
billi
ons)
Data Source:NWS HydrologicInformationCenter
Note: These datado not includesurge-relatedflooding, likeSandy or Katrina.
Year in Review Flash Flood Event:◦Baltimore County 8/26/12
L
H
Year in Review Flash Flood Event:◦Berkeley Springs WV 9/1/12
Photo: WHAG-TV Viewer Submission
Year in Review Flash Flood Event:◦ Frederick MD 9/18/12
Photo: Frederick News-Post
Year in Review – Goose Creek in “Sandy”
Major Flooding (worst since 1996)◦US 15 – primary north/south route – flooded
Photo: Loudoun Co. Sheriff
Year in Review – “Superstorm Sandy” 29 stream gauges with established flood levels
exceeded their flood stages in Sandy.Forecast Points in Flood (12)Potomac River at Brookmont (Little Falls), MDWills Creek near Cumberland, MDSeneca Creek near Dawsonville, MDConococheague Creek at Fairview, MDMonocacy River near Frederick, MDCacapon River near Great Cacapon, WVGoose Creek near Evergreen Mills (Leesburg), VAOpequon Creek near Martinsburg, WVShenandoah River near Millville, WVPotomac River at Point of Rocks, MDRappahannock River at Remington, VAAntietam Creek at Sharpsburg, MD
Non-Forecast Points in Flood (17)Monocacy River at Bridgeport, MD
NF Shenandoah River at Burnshire Dam, VA
Cedar Run near Catlett, VA
NW Branch Anacostia River near Colesville, MD
Patterson Creek near Headsville, WV
Broad Run at Sterling, VA
Battle Run at Laurel Mills, VA
Beaverdam Creek near Mountville, VA
NF Goose Creek near Lincoln, VA
Licking Creek at Pecktonville, MD
Rock Creek at Sherrill Drive, Washington, DC
Hazel River at Rixeyville, VA
Catoctin Creek (VA) at Taylorstown, VA
Antietam Creek near Waynesboro, PA
SF & NF Catoctin Creek (VA) near Waterford, VA
Georges Creek near Westernport, MD
How did we know?
“River Assessment Group” formed in 2011
Goal to determine floodrisk & levels at non-forecastlocations
Over 150 sites visited to date
Where we’ve been…
Results
More sites with flood stages Better anticipation of, and
(especially) knowledge oflength of flood
Longer (but increasinglytargeted) flood warnings
Beaverdam Creek / Loudoun County, VA Moderate Flooding◦ Stranded utility truck
Photo: Leesburg Today
Monocacy River / Frederick, MD Major Flooding◦MD 26 flooded near river; Gambrill Mill (NPS)
flooded. (at peak, water was up to seat of bench)
Photo: NPS
Antietam Creek / Leitersburg, MD “Minor” Flooding◦Water surrounded a house and covered Leiters Mill
Road enough to strand this car.◦ Flood stage here was revised downward.
Western Branch Patuxent / Upper Marlboro, MD Minor flooding…but significant impact!◦ Many nearby tributaries that we do not yet have a handle on
Photo: WTOP
River Flooding Freshwater flooding is handled by polygon-
based warnings, except for river forecast points◦ This will change!
The polygons will still belarger than the affected areabut more targeted◦ (example: the polygon won’t
include Middleburg for a Potomac flood)
Just a first step…◦Ultimately we would like to warn based on dynamic
inundation areas – but we’re not there yet
Determining a range of possibilities In the mid-Atlantic region, our flood forecasts
are usually 90-100% predicated on rain which has not yet occurred.
This means both the forecast rainfall and the river forecast can change significantly before the event is ongoing.
We give you our “most likely” forecast, but what if you want to know a range of possibilities?
River Forecast Ensembles http://www.erh.noaa.gov/mmefs Ensembles
offer ranges of possibilities based on different computer model changes
The officialforecast isnot depictedon this graph!
River Forecast Ensembles Important Note: The ensembles utilize the
GEFS, NAEFS, and SREF. (i.e., no ECMWF). So if we are favoring the Euro, so the official forecast could be outside the range of any of the ensembles.
Training on use of the ensembles is available:http://www.erh.noaa.gov/mmefs/RecordedTraining/
Once the rain is falling, you should use the official forecast instead of an ensemble range.
Flash Flooding We utilize the Flash Flood
Monitoring & Prediction System (FFMP) to monitor estimated precipitation vs. Flash Flood Guidance.
Flash Flooding Zooming in on a county helps us to know
which basins / parts of counties are affectedand which will not be.
Notes about dual-pol precip DP precip estimates are bad outside the bright
band in the winter.◦ Consistently too high
Notes about dual-pol precip On the plus side, the DP precip products are
higher-resolution so the beam blockages are not as pronounced…