Scientific Forecaster Discussion
fxus63 kpah 261955
Area forecast discussion
National Weather Service Paducah Kentucky
255 PM CDT Wed Jun 26 2019
Short term...(tonight through Friday night)
issued at 255 PM CDT Wed Jun 26 2019
So much for our nice quiet week. Convection is already firing in
southeast Missouri, ahead of an mesoscale convective vortex northeast of ksgf. Cape of
3000j/kg or more has developed over the region, but the wind
fields are incredibly weak. While there may be a few strong
updrafts, they should be pulsy for the most part. The storms will
move very slowly eastward, and are not expected to make it to our
eastern counties before dying off around sunset.
The Fly in the ointment is the potential for some enhanced low
and mid-level flow south of the approaching mesoscale convective vortex. If it shows up,
slightly better storm organization is possible, leading to greater
coverage of severe weather and some possibility of a severe watch.
Storm Prediction Center is monitoring the situation. However, for now we are expecting
a few pulsy severe storms with damaging winds and large hail both
Torrential rain is expected with any thunderstorms this afternoon.
The extreme instability and very slow motion of the storms
currently, will result in some minor flood potential, but the
storms should not last long enough in any one place to result in
major flash flooding. However, given the terrain, some isolated
flash flooding cannot be ruled out.
Most of the 12z guidance, both cams and larger-scale models,
indicate that the mesoscale convective vortex will linger over southeast Missouri tonight
through Thursday, resulting in persistent convection with a heavy
rainfall threat. This is quite a change from the previous
forecast, so have jacked up pops to likely levels over portions of
southeast Missouri tonight into Thursday, and have leaned closely
to the wpc quantitative precipitation forecast.
Storm total quantitative precipitation forecast from this afternoon through Thursday evening has
3-4" of rain over Carter and Ripley counties with just under an
inch along the Mississippi River. Considered a Flash Flood Watch,
but it is a small area and a rather new development in the
guidance, so will settle for a strong mention in the severe weather potential statement for now.
If more widespread heavy rain falls this afternoon, it may
increase confidence for a Flash Flood Watch issuance this evening.
As the mesoscale convective vortex slips south of the area later Thursday and Thursday
night, the ridge aloft will build overhead resulting in dry
conditions late Thursday night through Friday night.
High temperatures Thursday will be dependent on the coverage and
persistence of convection. Wouldn't be surprised to see portions
of southeast Missouri stay in the lower 80s, but most of the area
will see highs near 90 with heat indices in the middle 90s.
Similar heat and humidity is expected throughout the region Friday
afternoon. However, a few locations in southeast Missouri may
reach triple digits, especially where the heavy rains fall through
Long term...(saturday through wednesday)
issued at 255 PM CDT Wed Jun 26 2019
Main forecast challenges for the extended forecast period will be
the placement of diurnal convection (if any) and any impact that may
have on heat index values approaching 100 degrees at some locations
late in the weekend and early next week.
The mvc (mesoscale vorticity center/circulation) over southwest
Missouri this morning may play a factor in reinforcing the weak
troughing over the southeast U.S. In the near term. However, the
medium range deterministic guidance suggests a range of influence
for convective development in the weather forecast office pah forecast area, with or
without the the existence of the aforementioned mesoscale convective vortex.
The CMC (canadian) guidance is very robust in developing a closed
low and retrograding this low westward along the Gulf Coast. The GFS
suggests an inverted trough will develop and also slowly move west
along the Gulf Coast. Finally, the European model (ecmwf) (european) shows little
deepening or translation of the southeast U.S. Trough. All of the
deterministic guidance does build the middle/upper level ridge axis
from the Desert Southwest into the Central Plains and middle
Mississippi Valley, with some low to middle level ridge intrusion
from the southeast Atlantic Basin.
The main uncertainty will be the location of the middle/upper level
shear axis on the ridge through the weather forecast office pah forecast area. If it is
further north (e.G. Interstate 64 corridor of southeast Illinois and
southwest Indiana ), most of the weather forecast office pah forecast area could see
diurnal (mainly afternoon and early evening) convective activity.
However, any convective activity would be scattered in coverage at
best, focused in mesoscale/microscale pools of high Theta-E air and
pockets of surface differential heating/boundary. Most storms would
be outflow-dominated, with the best potential of gusty winds near
drier air aloft, mainly along the mid/upper level ridge shear axis.
Precipitable water values of 1.2 to 1.6 inches are not overly
impressive in the extended time period, but could yield an hourly
rainfall rate in excess of three-quarters of an inch, which could
lead to extremely isolated water issues.
With all that said, strongly prefer the influence of the ECMWF,
leading to a drier, more hot and humid, forecast solution. This is
in line with the National blend of models (nbm) initialization.
Given the weak upper level wind fields, the Canadian and GFS appears
a little over done with respect to convection coverage and quantitative precipitation forecast.
The ridge appears to weaken toward the end of the forecast period,
so left a better chance for shower and thunderstorm development in
place from late Tuesday through next Wednesday.
Raised Max temperatures 1-2 degrees to account for the better
coverage/duration of sunshine (insolation) over the weather forecast office pah forecast
area early next this will likely lead to a rise in heat index
values into the 95 to 100 degree range over part of the weather forecast office pah
forecast area Sunday into Monday.
issued at 1213 PM CDT Wed Jun 26 2019
An upper-level disturbance will touch off scattered to numerous
showers and thunderstorms over the western half of the region this
afternoon. They will not be terribly well organized, so will just
go with thunderstorms in the vicinity at kcgi and kpah, and vcsh at kmvn. Will amend to add
prevailing ts when and where necessary. The disturbance will
linger over southeast Missouri tonight, and there is a decent
signal for convection straddling 12z, mainly over kcgi and kpah.