Flash flooding possible for southern Mississippi

Due to the constant heavy rainfall across the lower Mississippi Valley, the Weather Prediction Center is concerned about flash flooding.

From an earlier discussion, the WPC outlined this area.

Now, an updated discussion has been released. From the NOAA Weather Prediction Center:

SUMMARY…THUNDERSTORMS WILL TRAIN ACROSS SOME AREAS. A VERY MOIST ATMOSPHERE FOR DECEMBER COULD LOCALLY YIELD 1.5 INCHES IN AN HOUR AND MORE THAN 2 INCHES OVER THREE HOURS. FLASH FLOODING IS POSSIBLE.

DISCUSSION…THUNDERSTORM COVERAGE HAD INCREASED DIURNALLY…BUT ALSO WITH THE STRENGTHENING OF MID AND UPPER LEVEL SUPPORT FOR LIFT. THE LEADING EDGE OF GREATEST MOISTURE TRANSPORT WILL PUSH EAST THROUGH ALABAMA THIS EVENING…BUT THE THREAT OF HEAVY AND REPEATED RAINS IS INITIALLY GREATEST BACK TO THE WEST IN LA/MS…WHERE INSTABILITY IS SOMEWHAT GREATER NEAR A SLOWLY LIFTING WARM FRONT. THE EVENT AS A WHOLE IS ONLY LOOSELY FOCUSED…BUT A LARGER SCALE COLD POOL WAS ENTERING CENTRAL MS AT 2330Z. CONVECTION HERE AND CONVECTION OCCURRING OR FORECAST TO OCCUR IN BANDS FARTHER SOUTH ACROSS LA/MS MAY BECOME ALIGNED TO ALLOW TRAINING OF CELLS WITHIN DEEP UNIDIRECTIONAL FLOW ABOVE THE EFFECTIVE INFLOW LAYER.
THE RAP AND HRRR FORECAST A SEMI-FAVORABLE ENVIRONMENT FOR DEEP CONVECTION TO PERSIST INTO THE NIGHT…ALTHOUGH THE POOL OF 500-750 J/KG MUCAPE WILL ONLY INCH ITS WAY EAST ALONG THE GULF COAST…STRUGGLING TO COME NORTHWARD. SEVERAL HIGH RESOLUTION MODELS ALIGN WELL WITH THE HRRR CAPE FORECAST…RAP 925-850 MB MOISTURE CONVERGENCE FORECAST…AND THE WPC QPF FORECAST…PLACING THE AXIS OF GREATEST RAINS FROM SOUTH OF JACKSON MS TO WEST OF MONTGOMERY AL. RECENT RUNS OF THE HRRR…AS WELL AS THE NSSL WRF
AND CANADIAN GEM REGIONAL MODEL SUGGEST SWATHS OF 2 OR EVEN 3 INCHES OF RAIN LOCALLY THROUGH 05 TO 06Z. THIS MAY BE SUFFICIENT TO PRODUCE FLASH FLOODING IN MORE SUSCEPTIBLE LOCATIONS.

The “RAP” referenced is a computer weather model used in very short-term forecasts. It is only able to “see” the next 18 hours. Here is a graphical representation of what it suggests for rainfall totals: