Scientific Forecaster Discussion
fxus63 klmk 160048
Area forecast discussion
National Weather Service Louisville Kentucky
848 PM EDT Sat Jun 15 2019
issued at 847 PM EDT Sat Jun 15 2019
The overall threat of severe weather continues to decrease across
the region this evening. Mesoscale convective vortex is currently pushing into central in
with widespread convection remaining just north of the lmk County Warning Area. With
the threat staying north of our area, have coordinated with Storm Prediction Center to
Second remnant mesoscale convective vortex is moving through central Kentucky. This feature did
produce area of showers but this activity has been moving into a
more stable environment and will continue to diminish as it heads
toward the I-75 corridor.
With the diminishing trend and based on observations, will update
the forecast to decrease pops markedly for the remainder of the
evening hours. Upstream convection over northwest MO is just
getting underway. This activity will likely develop further as the
night wears on and send an outflow southeastward to our region. Also
some scattered showers and storms within a warm air advection scheme
with a nocturnal low-level jet axis are expected to develop later on
tonight. So pop chances will be allowed to increase late tonight
and into Sunday morning.
Issued at 750 PM EDT Sat Jun 15 2019
Watching two mcvs move through the region this evening. The first
is near Terre Haute and is producing widespread severe weather up
over weather forecast office ind's area. A second mesoscale convective vortex was moving through west-central
Kentucky near the Beaver Dam area. This is producing a small area of
showers that is pushing through Hardin County. A quick tenth of an
inch or two can be expected as this moves eastward.
Mesoanalysis across the region shows MLCAPE values around 500-1000
j/kg mainly west of I-65 with higher values well to our west near
St. Louis. Bulk shear values are higher to our north near
Indianapolis where effective srh values of nearly 400 m2/s2 were
noted just east of the mesoscale convective vortex heading toward the Indianapolis area.
This area of effective srh has been producing tornadic storms just
to the north of our area.
Based on latest observational and short term guidance suggests that
severe weather is less likely across the lmk area over the next few
hours. Have been in contact with Storm Prediction Center on ww360. We're going to wait
another 45 minutes or so to see if we have any additional convection
fire near our northern row of southern Indiana counties. If not,
then we will probably drop ww360 around 830 PM EDT.
Short term...(this evening through sunday)
issued at 324 PM EDT Sat Jun 15 2019
..severe weather threat this afternoon and evening...
Overall, a complex weather scenario during the short term with
mesoscale details this evening and overnight likely to play a big
role in Sunday convection. First and foremost, a well-defined mesoscale convective vortex
continues to churn east-northeast across Illinois this afternoon. Broader
cyclonic flow features enhanced west-southwest mid-level flow of 45-50+ kts
spreading over the northern County Warning Area. The mesoscale convective vortex will continue to the east-northeast
through central Indiana, and backed sfc flow near and to the
immediate south of that feature will result in enhanced low level
shear. 0-1 km shear will be on the order of 30+ kts in our southern
Indiana counties, enhancing the rotation/tornado risk somewhat.
Strong convection has developed along a leading convergence band in
SW Indiana and will push through our southern Indiana counties. The
thermodynamic environment was muddied somewhat in the far north by
the morning Indiana convection and associated cloud cover. However,
sfc dewpoints have risen into the upper 60s at hnb and mid 60s
further east. Just enough destabilization appears to have occurred
to support a severe risk of damaging winds and perhaps a tornado or
two. Thus, a Tornado Watch is in effect for our northern most row of
counties in Indiana closest to the circulation. Strong winds and
perhaps isolated severe weather will remain possible this afternoon
further south into far northern Kentucky.
It still appears showers and storms could become more numerous after
00z tonight along and north of I-64. An outflow boundary may try to
lay out west to east in the vicinity of the Ohio River. And the
broader warm conveyor belt/moisture transport axis will sag south.
Upper level flow overnight looks fairly zonal, with the 35-40 kt low level jet
veering west-southwest a bit. So will need to watch for any training convection
and localized flooding issues.
Yet another shortwave impulse will ride over top of the quasi-
stationary boundary on Sunday. Convection may be ongoing over the
northern half of the area to start the day but should weaken with
time. Then it will be a question of how fast the atmosphere recovers
during the afternoon. Sfc dewpoints will have surged into the lower
70s on the warm side of the boundary. Storm Prediction Center href still showing
substantial destabilization is possible in southern Indiana and
central Kentucky. However, effective bulk shear will be more
marginal around 25-30 kts. Mesoscale details for Sunday afternoon
and evening remain quite uncertain at this time.
Long term...(sunday night through saturday)
issued at 310 PM EDT Sat Jun 15 2019
..unsettled weather expected for much of the upcoming week...
..Localized flooding possible in some areas...
Sunday night through Wednesday night...
Stalled out frontal boundary will continue to serve as a focus for
renewed convective development for the first half of the week. The
boundary looks to reside just to our north through the period and
multiple perturbations within the upper level confluent flow
combined with daytime heating will yield rounds of showers and
storms across the region. Some strong storms are possible during
the period, but the temporal and spatial aspects of that will limit
predictability quite a bit. On the other hand, we will continue to
run persistent high rain chances through the period. With
precipitable water values up near 2 inches, the heavy rainfall
signal is certainly here. While we're likely to see clusters of
storms rolling through the region, the precipitation amounts on a
basin-wide scale will likely be in the 2-4 inch range. However,
areas that pick up repeated episodes of heavy rainfall could see
isolated higher amounts of 4-7+ inches. The highest threat area
seeing that 4-6+ inches of rainfall looks to be in areas north of
the Ohio River.
A look at the latest river forecast runs from the ensembles shows
that we can handle this rainfall as flash flood guidance has really
trended upward since the last period of heavy rainfall. However,
dropping 2-4 inch amounts with locally heavier amounts will likely
lead to localized flooding in some areas.
Highs during the period will average well below normal for mid June
with highs in the upper 70s to the very low 80s. Overnight lows
will generally be in the upper 60s to around 70.
Thursday through Saturday...
Upper trough axis looks to push through the region Thursday bringing
a final round of showers and storms to the region. After that,
there is a trend in the recent Euro runs of developing more
significant troughing out across the inter-mountain west. This
would promote downstream ridging over the MS valley and points
eastward. So Friday and Saturday may end up being a bit more drier
than forecast. We'll just continue to monitor those trends in
future forecasts. Highs during the period will run below normal
though with readings generally in the low to middle 80s with
overnight lows in the middle to upper 60s.
Aviation...(00z taf issuance)
updated at 700 PM EDT Sat Jun 15 2019
High resolution models are generally struggling with the overall
convective evolution this evening. Two mcv's are moving through the
region at the moment. The first is centered up near khuf and is
spawning severe convection along the I-70 corridor. A second mesoscale convective vortex
was moving through western Kentucky (north of khop) and was producing some
scattered showers and few rumbles of thunder. In general, the
terminals look to remain VFR this evening with only a slight chance
of a shower or storm. Main aviation concern will be surface winds
which will remain gusty out of the southwest through the evening
Convection evolution overnight is uncertain as well given the recent
model performance. In general, the models suggest an outflow
boundary from upstream convection over the Midwest will surge
southeastward and generate convection toward dawn over southern in
and into portions of central Kentucky. For this reason, have left vcsh in
the tafs with prob30 thunder in there between roughly 16/10-15z.
Outside of storms, conditions look to remain VFR, but temp drops to
IFR in storms toward dawn Sunday are possible.