Scientific Forecaster Discussion
fxus63 keax 191704
Area forecast discussion
National Weather Service Kansas City/Pleasant Hill MO
1204 PM CDT Thu Sep 19 2019
issued at 325 am CDT Thursday Sep 19 2019
Main concern with this forecast continues to be the potential for
heavy rain and flash flooding this weekend.
Thursday - friday: an area of slow moving thunderstorms in
eastern NE and western Iowa was nearly stationary as of 08z this
morning. New convection develops a little southward with time and
then lifts northward into the main convective system. This
southward development is likely aided by either an outflow
boundary or cold air reinforcing the main front. Regardless,
models are in decent agreement pushing this southward to get into
far northern MO later this morning. Have maintained the chance
pops along the Iowa/NE/MO tri-state area and eastward along the
Iowa/MO state line. Moving to this afternoon, forecast soundings
continue to show an uncapped or nearly uncapped atmosphere. With
potential of an outflow boundary moving into the area, it seems
like there is at least a slight chance for showers/storms to
develop in the vicinity of the MO river and then into central MO.
So have added slight chance pops to much of the forecast area for
this afternoon to account for this. For Friday, moisture return
starts to get deeper due to the remnants of Imelda being pulled
into the area. As such, think there is a decent chance for showers
and storms throughout the forecast area and have increased pops
accordingly. The best chances will be in our south, but the entire
forecast area has some potential during the afternoon.
Saturday - sunday: the forecast continues to look very wet with the
potential for heavy rain and flash flooding. Very strong moisture
transport is expected in the lowest portions of the atmosphere. In
fact, trajectories in the lower levels are straight from the
tropical Atlantic, through the warm Gulf, and right through the
middle of North America to the Hudson Bay. In the upper levels,
there is a contribution showing up from a decaying Pacific
tropical system that gets pulled into the middle of the country by
the upper jet associated with the deepening trough to our west.
The rich and deep moisture leads to precipitable water values
around 2 inches. As mentioned in yesterday's discussion, this is
above the Max value for the 12z top sounding climatology for the
date and around half an inch above the 90th percentile. This is
very anomalous moisture for this time of year. At the surface, a
slow- moving boundary will work its way into northern MO and
northeastern Kansas. With broad ascent associated with the upper
trough, and more focused ascent along the boundary, it looks like
widespread rainfall, with heavy rainfall along the front, can be
expected Saturday and Saturday night. Saturday night, when the low
level jet strengthens, maximizing moisture transport and
convergence along the front, is when the heaviest rain is likely.
Monday - wednesday: there should be a reprieve from the rainfall on
Monday. However, the front will not be pushed very far south as the
upper trough lifts northeastward with no strong push behind it.
Short-wave ridging builds back into the area but with another trough
moving into the southwest, low-level flow will quickly return to the
south. This will bring back the moisture and precipitation chances
through the middle of next week.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1201 PM CDT Thursday Sep 19 2019
A few lingering surface boundaries moving south near the terminal
sites will maintain the chances for isolated thunderstorms across
the area through the afternoon hours, though spatial coverage will
be relatively sparse. Otherwise, VFR conditions will persist while
light surface winds remain south to southeasterly.