Scientific Forecaster Discussion
fxus63 klmk 252236
Area forecast discussion
National Weather Service Louisville Kentucky
636 PM EDT Tue Apr 25 2017
..updated aviation discussion...
Short term (now through Wednesday night)...
issued at 230 PM EDT Tue Apr 25 2017
Surface analysis reveals region being influenced by two separate
areas of low pressure, with one over the Carolinas and another over
parts of the Southern Plains. Surface flow near eastern Kentucky has
generally been out of the north and east, while western Kentucky has
had southerly flow for much of the day. Visible satellite reveals
broad area of strato-cu over much of the region. Should see clouds
slowly subside this evening after the sun sets.
Unlike the past couple of days where clouds have plagued the area,
we should see mostly sunny skies and very warm temperatures for
Wednesday. Winds could be a bit breezy out of the south, with gusts
reaching as high as 25-30mph Wednesday afternoon.
A line of strong to severe thunderstorms will fire off ahead of a
cold front in MO/IL/AR Wednesday afternoon and evening and make its
way toward our region. While deep layer shear remains favorable for
organized convection, instability ahead of the line will drop off
sharply as it enters the Ohio River valley region. High-res cams
show the line of storms weakening considerably by the time it begins
to approach western portions of the County Warning Area between 04z-07z Thursday due
to the lack of instability. Can't rule out a strong wind gust or two
with the weakening storms given the presence of a low level jet and amount of
shear that will be available in the environment, but overall severe
impacts look to be very low.
Long term (thursday through tuesday)...
issued at 245 PM EDT Tue Apr 25 2017
By Thursday morning, a ragged line of showers and thunderstorms will
be across much of the region ahead of a cold front. Similar to
Wednesday evening, deep layer shear will be modest, but instability
will be lacking. The front will clear the region by about 18z, so
there will not be a lot of time for instability to build into the
region ahead of the front. Even some of the high-res cams aren't
very excited about the event and show very little in the way of
strong convective activity late Wednesday night through Thursday
morning. Still, with modest deep layer shear and the potential for
some instability to be present, can't rule out a strong thunderstorm
or two at some point Thursday morning. The day 3 Storm Prediction Center outlook covers
A warm front begins to lift north of the region on Friday, and will
pull in some warmer, humid air from the Gulf of Mexico. Atmosphere
will also begin to destabilize during the day Friday, especially
across south-central Kentucky where 1000-2000j/kg of cape could be
Warm front that lifted north of the region Friday begins to get
pushed back south toward southern Indiana and north-central Kentucky
Friday night into Saturday morning. Models develop copious amounts
of precipitation along the frontal boundary as well as parts of the
warm sector in central/southern Kentucky. Might have to keep an eye
on severe weather parameters Friday night, as the presence of
instability/shear could support some organized convection. By
Saturday morning, the frontal boundary will be located pretty close
to the Kentucky/in border, but is forecast to slowly lift northward as a
warm front through the day. Depending on how far and fast it lifts
northward will have a big impact on temperatures, as cooler air
resides north of the frontal boundary and clouds/precipitation
associated with the boundary will keep temperatures cooler.
Showers and storms could redevelop Saturday afternoon, but coverage
should remain isolated to scattered. Cold front approaches from the
west Saturday night into Sunday, and precipitation chances will
increase ahead of the front. Will have to watch severe weather
parameters again for the weekend as environment could support strong
to severe storms.
Cooler weather will prevail for the early part of next week behind
the cold front. Too early to say if it'll be dry as some models
develop precipitation around a substantial upper level low and have
parts of the region experiencing a cold, stratiform rain. For now
will take a blended forecast approach given model discrepancies.
Aviation (00z taf update)...
issued at 630 PM EDT Tue Apr 25 2017
Diurnal cu is in the process of dissipating as mixing weakens, and
we'll see light winds and cirrus overnight. Only question mark is
Lex where the ceiling is holding on and just barely VFR, but that
will be an issuance time decision.
By mid to late morning, we'll see winds pick up out of the south
with a solid 12-15 kt and prevailing gusts near 20 kt for the rest
of the afternoon. Forecast soundings look a bit drier than today, so
not expecting much in the way of convective clouds, but we could see
a short-lived deck late in the morning before the mixing taps into
some very dry air near 850mb.