National Weather Service
ABRFC - Tulsa, Okla.
156th Committee Meeting
Oct. 17-19, 2006
Eureka Springs, Arkansas
Webpage changes: The ABRFC webpage has taken on a new appearance similar to
the RIDGE radar layout used by the NWS weather forecast offices. A national
effort is underway to standardize the appearance and navigation layout of NWS
webpages.
Figure 1: New ABRFC home page image
Gridded flash-flood guidance: The ABRFC is now issuing 1, 3, and 6-hour
values for flash flood guidance based upon 4 x 4 kilometer gridded radar
rainfall. The rainfall is input to a distributed rainfall-runoff model of the
same scale. Soil type, land use, and land slope data is incorporated to
determine threshold runoff values that produce “bankfull” flows within each grid
cell. The distributed model is run every six hours with stored existing moisture
states of the model used to initialize the model run. The gridded flash flood
guidance model computes how much rain is needed over the next 1, 3, or 6 hours
to produce surface runoff that matches the threshold runoff that has been
calculated for each 4 x 4 kilometer grid cell.
This method of calculating flash flood guidance will prove itself of greater
value to weather forecast offices responsible for issuing flash flood warnings.
The high variability of rainfall amounts received over an area will be
continuously accounted for, enabling the weather forecast office to issue flash
flood warnings based upon rainfall that has not been “averaged” over a larger
area.
This new method of computing flash flood guidance will eventually be
incorporated throughout all of Southern Region, with the eventual goal of
national implementation.
Figure 2: Problems associated with scale: Black outline – ABRFC
basin scale
Red outline – WFO basin warning scale
Figure 3: 24-hr rainfall and variability over operational model
scale
Figure 4: Resultant 4 x 4 kilometer gridded flash flood guidance
values
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