Scientific Forecaster Discussion
fxus63 klmk 161301
Area forecast discussion
National Weather Service Louisville Kentucky
901 am EDT Mon Sep 16 2019
issued at 855 am EDT Mon Sep 16 2019
A few rogue showers are still persisting this morning just north of
the County Warning Area in Carroll/Gallatin counties (ky). This activity should
weaken as it pushes southward into central Kentucky where drier air
resides and little to no instability exist, so plan to continue the
dry forecast for the morning hours. Rest of forecast remains on
Short term...(today and tonight)
updated at 320 am EDT Mon Sep 16 2019
Seeing a few showers/storms form along a Theta-E ridge axis over
central Indiana early this morning. The hrrr/rap both show this axis
well, keeping it north of the region through daybreak, while they
show the cells moving east southeast away from that ridge axis. Thus
expect them to fade before making it into our area...but will keep
an eye on how they progress and update as necessary.
As the morning GOES on, moisture pocket seen on GOES sounder data
now over central Illinois and entering southern in will move into our
region. Forecast soundings from GFS show a cap aloft that would
limit coverage...but do not believe those soundings are handling
temperatures well, given recent cool bias. Also, convergence, albeit
weak, along the frontal boundary should aid in lift. Would not be
surprised to see a stronger storm or two pop up in the mid to late
afternoon hours...starting in the I-64 corridor and then shifting
southward as the afternoon progresses.
Then tonight, we have a pretty good signal in guidance for some fog
to develop, mainly south of the parkways in Kentucky. Pressure
gradient near that weak boundary will keep light winds, and expect
dewpoints to remain pretty high for this time of year. In addition,
any early evening rains will aid in that fog development. For now,
will limit coverage to areas of fog, but mention the dense potential
in the hazardous weather outlook for tonight.
Long term...(tuesday night through sunday)
updated at 230 am EDT Mon Sep 16 2019
..above normal temps along with parched ground continues...
..Pattern change the week of Sep 23...
Well...the arlatx and southern Ozarks 591 dm ridge will be the
dominating synoptic weather feature. Obviously Bermuda will be
watching Humberto as their main weather feature. The upper level
ridge will deflect and impede any significant systems to the northwest of
our County Warning Area. Looks like the storm track takes all that rain into the
northern MS River Valley.
With only a few cocorahs reports having observed a few hundreths of
an inch since 8/27 The Grasses will continue to wither while the
ground becomes quite parched.
The upper ridge will hover over the Ohio/Tennessee valleys with 850 mb temps
of +17c. This combined with arid ground will keep the lmk County Warning Area
ensconced in above normal Mercury readings. The GFS MOS numbers are
too low with mid 80s! The ridge amplitude will increase during the
week as an upper trough digs out of the Cascades and Bitterroot mtns
Thu and into badlands np South Dakota by Friday evening.
This system is what the County Warning Area needs to lessen the drought. The ridge
will move to the East Coast. This opens the door for a break in the
hot & dry pattern. That aforementioned system on Sat evening with
547 dm low over International Falls Minnesota brings a sweeping cold front
along the MS river on Sat evening.
The GFS slides the ridge to the east while the ecm suppress it to
the south and then builds it up big time over Dixie.
Will be be increasing pops on Sunday to slgt chance category range.
Confidence on the exact timing of the ridge breakdown remains low,
but feel quite confident of a major pattern change. The ecm and GFS
also have a secondary, even more potent system, during the middle of
next week. For your information...the autumnal equinox is next Monday.
Back to temps...using the Massie rose 1997 1000-850 mb air mass paper,
high temps will be averaging about 10-13 degrees above normal. Since
late in the week most normal highs in the area start to drop below
80, that will put highs each day in the upper 80s to lower 90s.
The one saving Grace through the period is that Gulf of Mexico low level
flow is shut off, so surface dew points should remain relatively
low, in the low to mid 60s.
One last parting thought...models are showing a tropical low in northwest
Gulf of Mexico Wed and Thu and depending on this development and how it
phases into the Lone Star state it could be a fly in the ointment.
It bears at least a mention in this missive.
Aviation...(12z taf issuance)
updated at 650 am EDT Mon Sep 16 2019
Some moisture is moving into southern in this hour, and continuing
to see some mid-level cloud cover. A few showers have developed over
central in, but not expecting those to make it to our sites this
morning. They are associated with a weak frontal boundary that will
bring a wind shift to the terminals late this morning and early
afternoon. Our sdf/Lex/bwg could see an isolated shower/storm in the
mid to late afternoon hours along this front. Next up will be
potential for some denser fog toward daybreak Tuesday. For now will
hint at that with MVFR fog and a few lower clouds, but would not be
surprised to see later updates get worse.