Scientific Forecaster Discussion
fxus63 klmk 161107
Area forecast discussion
National Weather Service Louisville Kentucky
607 am EST Mon Jan 16 2017
Issued at 607 am EST Mon Jan 16 2017
Dense fog has shown some staying power in Bowling Green and
visibility in Greenville recently fell to 0, so we went ahead and
expanded the dense fog advisory into Warren and Butler counties.
Short term (now through tuesday)...
issued at 257 am EST Mon Jan 16 2017
Fog, dense in spots, is widespread across the region early this
morning north of a warm front over the Tennessee Valley. Will hold
onto the fog for the first few hours of the forecast.
A weak lead shortwave trof ahead of a large plains storm system will
eject eastward across the Tennessee and Ohio valleys this afternoon
and evening, sparking scattered showers and possibly an isolated
thunderstorm after mid-afternoon. The warm front to our south will
surge northward, allowing temperatures to rise into the lower and
middle 60s south of the Ohio River, upper 50s north.
Tonight the plains storm system will send a surface cold front
toward US as low pressure crosses northern Illinois. Showers and
scattered rumbles of thunder are a good bet with this system,
dropping general amounts of a quarter to half inch of rain.
Temperatures won't fall any further than the 50s as we remain in the
warm sector all night.
The cold front will sweep through on Tuesday, with shower and
isolated thunder chances diminishing from west to east over the
course of the day. There's no cold air immediately following the
frontal passage so even though we'll be behind a cold front in
January, high temperatures will still be about 20 degrees warmer
than normal for the day. Temperatures may start to fall in the
afternoon in southern Indiana as cooler air gradually filters in.
Long term (tuesday night through sunday)...
issued at 309 am EST Mon Jan 16 2017
A Desert Southwest upper low on Wednesday will cross the plains
Thursday and get absorbed into an eastern lobe of a longwave npac
trof Friday. Another southwestern low will then develop out of the
larger trof and arrive in the middle Mississippi Valley by the end
of the weekend. General ridging will pump up over the eastern United
States, keeping US mild.
Tuesday night-Wednesday look mostly dry beneath local upper
shortwave ridging and behind the departing cold front described in
the short term section.
Thursday deep, moist flow will establish itself from the western
Gulf of Mexico into the Mississippi and Ohio valleys ahead of the
upper low crossing the plains. Thursday night soundings in central
Kentucky become nearly saturated and warm cloud depth will be just
over 9k'. Instability is weak so will keep thunder out of the
forecast for now, though a rumble or two isn't out of the question.
That system will then move off to the northeast, leading to dry
conditions Friday night - Saturday.
Saturday night and Sunday rain chances will return ahead of the next
upper low and its surface low moving from the Southern Plains to the
upper Mississippi Valley. Showers and scattered thunder will again
be the rule, with very warm temperatures continuing.
Aviation (12z taf update)...
updated at 550 am EST Mon Jan 16 2017
Stratus deck remains in place, keeping IFR or LIFR ceilings in sdf
and Lex. At bwg is has built down into dense fog, and the main
challenge this morning is the evolution of that stratus/fog and its
impacts. Hi-res models are very keen on moving that dense fog north
into sdf and Lex just after daybreak, and scouring out bwg. However,
that northward move has yet to begin as advertised, this forecast
will fall more in line with such guidance as the GFS lamp, which is
more persistent with the bwg fog, and does not hit visibility as
hard in sdf and Lex.
That said, we'll stay socked in until midday, or even early
afternoon, when the warm front lifts through. Look for a fairly
quick improvement to MVFR, and bwg/Lex may even break out into VFR
for a few hrs in the southerly flow. Improvement will be short-lived
as we quickly get into the isentropic lift ahead of the next system.
Showers move in this evening, with just enough elevated instability
to warrant thunderstorms in the vicinity. Deep saturation will cause ceilings to deteriorate
to IFR, and could even go into LIFR at times. Low-level jet will
crank up to around 40 kt, which could put low level wind shear in play for sdf and
Lex after midnight. Will not mention just yet given the lead time
and associated uncertainty. Look for precip to end by mid-morning
Tue, with improving cig/vis in the sdf planning period.
Kentucky...dense fog advisory until 9 am CST this morning for kyz061-