Scientific Forecaster Discussion
fxus63 klmk 191926
Area forecast discussion
National Weather Service Louisville Kentucky
326 PM EDT Sat Oct 19 2019
Short term...(this evening through sunday)
updated at 325 PM EDT Sat Oct 19 2019
A tale of two features...a shortwave disturbance embedded within
the longwave trough over the upper MS valley will converge upon
northward streaming moisture from ts Nestor, now located over the
coast of the Florida Panhandle. This interaction will produce increased
cloudiness over the Ohio Valley with a chance of overnight
showers as evident from meager isentropic lift at the 300k level.
Best chance of showers will be in the Lake Cumberland area and our
southwestern Indiana counties a little before midnight with a
ragged line of slight chance moving eastward across central Kentucky and
southern Indiana through the early morning hours. Model soundings
show ample dry air in the mid layers with most of this moisture
contained within the lower 5kft. Soundings also show basically no
cape to work with, so thunderstorms should not be an issue. With
the increase cloud cover, Sunday morning min temps will remain
mild in the low to mid 50s. Winds will be light and generally out
of the south, swinging between SW and southeast.
Low clouds will linger Sunday morning until early afternoon, which
could prompt a slow start to the warming trend. But with continued
southerly flow and an eventual break in clouds, expect to see Sunday
highs reach into the mid 70s.
Long term...(sunday night through saturday)
updated at 310 PM EDT Sat Oct 19 2019
..strong to severe storms with heavy rainfall possible on Monday...
..Gusty winds expected Monday and Tuesday...
Sunday night through Wednesday night...
Mid-level trough axis is forecast to push through the Central Plains
and towards the Ohio Valley on Sunday night. As it crosses the
plains the global models are suggestive that the trough may take on
a negative tilt as it gets toward the Mississippi River. As this
tilt occurs, we expect to see the surface low deepen as it moves
through the upper Midwest. Locally, we'll see clouds rapidly
increase Sunday night with some scattered convection reaching our
far western areas by dawn Monday. Gradient winds will increase
Sunday night as well with lows remaining in the upper 50s to around
Moving into the day on Monday, surface low pressure should continue
to deepen and move eastward across Minnesota and into Wisconsin as
the cold front sharply occludes southward through the Ohio Valley. A
look at proximity soundings across the Ohio Valley reveal that the
column should become rather moist quickly. Lapse rates still are
forecast to remain rather weak/marginal across the region likely due
to the colder mid-level air hanging back to the west/northwest.
Widespread precipitation production and cloud cover are also evident
which are limiting the cape values a bit (cape values generally are
in the 400-800 j/kg range for this event). Plenty of wind shear is
available here as the the 850 flow is likely to be in the 45-65kt
range with the mid-level tropospheric flow in the 70-90kt range.
This results in some low-level srh values that could support some
isolated spin ups in stronger convection. In general, the overall
kinematic and thermodynamic parameters are very much fit the typical
cool season Ohio Valley severe threat parameters.
Initial convection on Monday morning will likely be elevated above
the surface layer, based on the high resolution model soundings.
However, there remains a period of time from the late morning
through the afternoon where the above-mentioned surface based
instability could come into play. Based on previous setups, we're
most likely looking at a large swath of convection moving through
the region during the day with a stronger, perhaps pencil thin line
of convection along the actual frontal interface working its way
across the state in the afternoon. The area is outlined in a
marginal risk currently, but I suspect an upgrade to a slight risk
from I-65 eastward may be required in later outlooks.
As mentioned above, overall moisture quality and quantity look
rather good here. Precipitable water values in the 1.6-1.8 inch
range are well above average for this time of the year. So heavy
rainfall can be expected with the convection as it moves through. As
for quantitative precipitation forecast a solid 1-2 inches with localized higher amounts is
expected. The progressive nature of the system appears to be fast
enough to preclude widespread flooding concerns. However, localized
flooding of poor drainage areas can't be ruled out.
Lastly, gradient winds will be an issue with this system. Strong
southwest winds are expected to develop late Sunday night and
continue through the day on Monday. A Wind Advisory may be required
in subsequent forecasts.
The front is expected to push eastward Monday night with a
pronounced dry slot sliding into the region overnight and into
Tuesday morning. However, cooler mid-level temps look to overspread
the region on Tuesday which will steepen the lapse rates and a
stratocumulus deck is likely to develop. The gradient behind the
system will exceptionally strong as well with gusty northwest winds
expected. In fact, another Wind Advisory could be required for
Tuesday as well.
The upper trough will swing through the region Tuesday afternoon and
Tuesday night and high pressure will then build into the region for
Highs during the period will initially be warm with highs solidly in
the 70s on Monday and then dropping into the mid 40s by Tuesday
morning. Tuesday's highs may be overdone if a more significant
stratocu layer develops. For now have stuck with highs around 60.
Lows Tuesday night should get back down into the mid-upper 30s
before rebounding into the lower-mid 60s by Wednesday.
Thursday through Saturday...
By Thursday morning, surface high pressure is expected to be
anchored off the Carolina coast with the Ohio Valley in a broad
southwest flow. Another upper level trough is forecast to deepen
across plains during the day on Thursday and we'll see an increase
in clouds as the day wears on. Highs look to top out in the upper
60s to around 70, but could be slightly warmer if clouds hold off a
By Friday, the upper trough over the plains is expected to continue
to deepen and possibly become a cutoff low over Texas. The system
is then forecast to move to the northeast and will likely bring
another round of heavy rainfall with possible thunderstorms to the
Ohio Valley for late Friday and Saturday. Due to expected clouds
and precipitation, have kept temps on the cool side of the guidance
here with highs in the lower 60s and overnight lows in the 40s.
Aviation...(18z taf issuance)
issued at 140 PM EDT Sat Oct 19 2019
Current satellite shows mostly clear skies over all taf sites with a
layer of MVFR clouds moving northward through Tennessee. Expect VFR
conditions with south-southeast winds until after midnight, at which time the
aforementioned cloud deck should bring bwg down to MVFR and tempo
fuel alternate. MVFR cigs should overtake all taf sites by daybreak
and linger until early afternoon Sunday. Winds will be light and
generally out of the southeast to SW. VFR conditions will resume Sunday
afternoon with Lex being the last to improve.