Post by SKYSUMMIT on Jun 6, 2019 11:59:35 GMT -6
Mesoscale Precipitation Discussion 0380
NWS Weather Prediction Center College Park MD
150 PM EDT Thu Jun 06 2019
Areas affected...Gulf Coast of Mississippi, Alabama, and the
Panhandle of Florida
Concerning...Heavy rainfall...Flash flooding possible
Valid 061749Z - 062249Z
Summary...Thunderstorms along a warm front and ahead of an area of
low pressure will continue to develop and move eastward along the
Gulf Coast through the evening. Rainfall rates of more than 2"/hr
are likely in the tropical airmass, with 1-3" of additional
rainfall possible. This rain will occur on top of pre-conditioned
soils from this mornings heavy rain to produce a flash flood
threat.
Discussion...Satellite and radar analysis this afternoon shows
increasing convection ahead of an area of low pressure currently
positioned near the elbow of Mississippi. Ahead of this low, a
warm front was analyzed draped eastward along the Gulf Coast into
the western Panhandle of Florida. A squall line of convection was
moving eastward from near Lake Pontchartrain into the northern
Gulf of Mexico, while new convection was developing just south of
the coast and lifting northward atop the warm front.
The environment will remain favorable through the afternoon for
continued thunderstorm development with heavy rain. Latest RAP
analyzed MUCape was near 1500 J/kg, with PWAT ranging from 2.0-2.2
inches, more than 2 standard deviations above the climo mean, in a
deeply saturated atmospheric column with low-level moist advection
continuing. Although the squall line is likely to weaken as it
moves eastward according to recent HRRR runs due to encountering a
more worked over and less unstable environment, it will remain a
heavy rain producer. Additionally, new development along and south
of the warm front in the more unstable regime will intensify as
cells lift northward into the frictional land-sea convergence
boundary, and in response to isentropic ascent atop the warm
front. The 0-6km mean wind is generally SW at 20-25 kts, fast
enough to preclude a widespread flash flood event even with rain
rates approaching 2"/hr. However, Corfidi vectors at a sharp angle
to the mean flow suggest that backbuilding and training of cells
is likely, especially along and south of the warm front/frictional
convergence boundary where the greatest instability gradient
resides. This is where the recent HREF neighborhood probabilities
show a high risk for rainfall of 3"/6hrs with rainfall rates over
1"/hr expected.
Despite high FFG of 4"/3hrs, soils have been pre-conditioned this
morning from rainfall already of 1-2", such that an additional
1-3" of rain could lead to flash flooding. The greatest potential
will be in the vicinity of poor drainage/urban areas and any
location that receives a backbuilding/nearly stationary cell.
However, the scattered nature of the heaviest rainfall will likely
preclude a more widespread flash flood threat into the evening.
Weiss
