Scientific Forecaster Discussion
fxus63 klmk 162327
Area forecast discussion
National Weather Service Louisville Kentucky
627 PM EST Sat Nov 16 2019
..updated aviation discussion...
Short term...(this evening through sunday)
updated at 315 PM EST Sat Nov 16 2019
Surface high pressure beneath flat upper level ridging over the
region continues to provide sunny skies and dry conditions across
the Ohio Valley. Current satellite shows some mid and high clouds
streaming across IL, which should provide a beautiful sunset for
many this evening. Clearing skies overnight may result in some
patchy fog early Sunday morning, mainly north of the parkways and
within river valleys. Sunday will start off cold with temps in the
mid 20s. Expect to see increased mid and high level clouds
throughout the day Sunday ahead of a cold front that will be
positioned north-S along the Mississippi Valley. Clouds will do little
toward impeding diurnal warming; therefore, expect to see Max temps
reach into the upper 40s to low 50s.
Long term...(sunday night through saturday)
updated at 340 PM EST Sat Nov 16 2019
Sunday night through Tuesday night...
Upper level pattern looks to remain in a ridge west, trough east
type pattern through this period. Our region will sit within a mean
trough axis with several weaker perturbations moving through the
region. Model proximity soundings are still rather meager with the
overall moisture over our region. However, there may be just enough
forcing to get some light precipitation at times. The first
perturbation will move through the region late Sunday night and
early Monday. With the system moving through overnight, model
soundings suggest that we could have a mix across southern Indiana
where near term surface temps very close to freezing. Highs on
Monday look to rebound thorugh into the upper 40s to around 50.
Another weak system looks to move through late Monday night and
early Tuesday. Again model soundings are suggestive that some mixed
precip could occur. However, morning lows Tuesday morning look to
be slightly warmer than Monday morning. Overall forcing with this
system looks a little weaker, so precipitation would be rather light
and very scattered. Highs again will rebound into the upper 40s and
lower 50s. Lows Tuesday night will drop back into the 33-35 degree
Wednesday through Saturday...
Global models are in good agreement with a period of ridging for
Wednesday. Given the good model agreement and rather consistent
signaling here, yields a higher confidence forecast of dry and
pleasant conditions for Wednesday. Afternoon highs look to top out
in the low-mid 50s over southern Indiana and far northern Kentucky.
Highs across the southern half of the state look to warm into the
upper 50s to around 60. Wednesday night lows look to cool back into
the upper 30s to the lower 40s.
For the Thursday through Saturday period, forecast confidence drops
to below normal for a few reasons. First, we will have a split flow
pattern setting up across the Continental U.S.. dynamical models struggle
highly in a split flow regime. Secondly, we will have to watch two
features within the pattern that could potentially impact US for the
late week period. First feature is a fairly potent mid-level trough
within the northern stream and the second feature is a cut off low
over the southwest US. Earlier in the week, the global models were
suggesting that these two features would eject out similarly and
phase as they headed across the country. Yesterday, there was ample
agreement that the northern stream system would dive down and dig
faster leaving the southern stream system behind. Today's Euro and
CMC models continue this line of thinking keeping the systems
unphased with ample ensemble agreement as well. Today's GFS/fv3
solution attempts to phase the streams, but have given more weight to
the Euro/CMC op/ens solutions here.
With that thinking, we'll swath of widespread rain showers move into
the region late Wednesday and continue through the day on Thursday.
Some colder air may get in on the back side of that system by Friday
morning allowing for a possibility of a change over to snow before
ending. As always, it will be a race to see if the cold air can
catch the back side of the precipitation shield.
Today's data suggest that a secondary northern stream wave is
forecast to dip out of Canada and into the plains. This secondary
wave may end up phasing with the slower southern stream system
bringing another storm system through the region on Saturday.
Depending on the evolution of the upper level features, the track of
this system is highly uncertain and will likely change a bit over
the next week.
Aviation...(00z taf issuance)
issued at 627 PM EST Sat Nov 16 2019
Overall, aviation concerns should be minimal over the next 24-30
hours. Some light fog could lower conditions to MVFR, especially
between 11-14z, at hnb/sdf/Lex. Otherwise, VFR conditions likely.
Mainly clear skies overnight with just brief scattered cirrus. Northeast
winds around 5 kts are forecast to diminish to nearly calm by 09-12z
Winds will remain light throughout Sunday with a baggy gradient in
between weather systems. We'll see a substantial increase in high
level cloud cover during the afternoon and evening hours.