Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 072345
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
745 PM EDT Tue Jul 7 2015
Issued at 745 PM EDT Tue Jul 7 2015
...Flash Flood Watch in Effect through Wednesday Evening...
The main synoptic boundary is sinking nearer the Ohio River at this
hour and will stall out through the overnight hours. Meanwhile, main
focus of showers and scattered thunderstorms will be across central
and southern KY ahead of the front. This airmass will be
characterized by precipitable water values around and just above 2
inches through the column. Some instability will linger across south
central KY through the late evening hours as the region has yet to
be worked over. A few strong to severe storms will still be possible
with gusty wind and brief torrential rainfall as the main threats.
Precipitation rates are low enough and progression is fast enough
that flood concerns are low at this hour, however concern will
linger through the night as several more waves move along the
stalled frontal boundary. Flash Flood Watch still looks good.
.SHORT TERM (Now through Wednesday Night)...
Issued at 320 PM EDT Mon Jul 6 2015
...Flash Flood Watch through Wed Evening...
Issued a flash flood watch given the latest model guidance suggests
multiple rounds of showers/storms through Wed evening and we already
have very saturated grounds and a very moist airmass in place.
Mesoanalysis indicates an axis of 2+ inch precipitable water values
from the southern Plains into southern/central Indiana and points
northeastward ahead of a slow approaching sfc front. A few
different upper level shortwaves exist along this axis as well and
will continue to ride northeast producing multiple rounds of
showers/storms through Wed evening. H850 moisture transport is
strong and parallel running parallel to the boundary.
Because of these reasons and flash flooding in western KY/southern
MO/and southern IN this morning, believe that we will have several
more chances for flash flooding through Wed evening. The best
chances will come when convection strength peaks moving slowly ENE
or regenerating in the same areas leaving bands of intense rainfall
rates and amounts. Some areas this morning already received 2 to 4
inches of rainfall and expect that may be common with locally up to
5 by in these heavier rainfall bands that occur through Wed
evening. With 1 hr FFG running between 1.5 to 2.25 inches and 3 hr
FFG running between 1.9 to 3.9 inches, flash flooding will
certainly be possible.
The heaviest waves of precipitation look to be in a round of showers
and scattered storms this afternoon/evening and then another round
expected late tonight as the low level jet ramps up. Models are
having a difficult time with the individual waves, but feel this
might be the most reasonable soln with a general lull around
midnight and the early morning hours Wed. Also the early morning
round of showers and scattered storms should bring central KY the
heaviest rainfall as the sfc front sags further south closer to the
By late morning the frontal boundary will begin to lift north
shifting precip chances back northward. Also precip intensity will
weaken during the late morning/afternoon hrs Wed. For Wed night,
think that most of the area may see a dry period before a low
pressure system threatens the area toward sunrise.
Temps will be tricky depending on rainfall areas and exact frontal
boundary location tomorrow morning. With rain in the area in the
morning will stay on the warm side of guidance with lows in the mid
60s over southern IN to lower 70s over most of central KY. We
should see quite the range of high temps tomorrow again depending on
rain/cloud location and how quickly they move northward throughout
the day. Highs should be limited to the mid to upper 70s in rainy
areas with drier and partly cloudy locations reaching the low to mid
80s. Lows Wed night will be in the upper 60s/lower 70s.
.LONG TERM (Thursday through Tuesday)...
Issued at 250 PM EDT Tue Jul 7 2015
The long term will begin with quasi-zonal flow aloft. Ridging will
gradually build from the south as a southern ridge retrogrades. By
this weekend the forecast area will be on the periphery of this
upper level ridge.
For Thursday a weakening frontal boundary will slide in from the
north. This front will stall and continue to wash out across central
Kentucky Thursday. Scattered storms will develop near this boundary
on Thursday. These will mostly dissipate on Thursday night, but a few
showers or storms may hang around, so will not go completely dry
overnight. Friday continues to look wet in the models as a weak
upper level disturbance dive into the region. This combined with
residual boundaries from overnight convection to the north and
daytime heating will lead to renewed storm chances Friday afternoon.
Thus, have increased pops Friday afternoon.
Rain chances will decrease through the weekend as the ridge builds
in. Precipitation chances will somewhat depend on how strong this
ridge is. The best chance for any shower/storms over the weekend
will be across the northern Bluegrass and portions of southern
Indiana. Temperatures will be hotter through the weekend. Highs will
top out in the upper 80s to lower 90s with heat index values nearing
100 in the afternoons.
By Monday we will transition back to a more northwest flow pattern
with disturbances diving southeast through this flow. Thus, it looks
like we will see renewed rain chances early next week.
.AVIATION (00Z TAF Update)...
Issued at 707 PM EDT Tue Jul 7 2015
Complex situation over this TAF period as a frontal boundary slides
near the Ohio River later tonight, stalls through the pre-dawn hours,
and then begins to lift back north through Wednesday. Scattered to
numerous showers (and perhaps a rumble of thunder) are expected to
ride along and ahead of this boundary through the period. BWG will
have the best shot at a period of TSRA this evening, but will leave
mention out of SDF/LEX due to lack of instability.
Will generally keep visibilities VFR outside of the heavier rain
showers or storms, however will be able to drop into lower MVFR or
even brief IFR in the heaviest pockets. Tried to convey the best
timing for these occurrences in the TAFs.
Next concern will be whether ceilings go down as the frontal
boundary stalls near SDF/LEX and winds slacken in the pre-dawn
hours. Will include mention of ceilings below fuel alternate from
sunrise through midday at SDF, until the warm sector gets more
established over the area. Another round of showers and a few storms
will be possible during the day on Wednesday.
Overall, surface winds should stay steady out of the SW, gradually
veering around to WSW as the front nears. Once the boundary starts
to lift back north on Wednesday, expect a return to SW.
KY...FLASH FLOOD WATCH through Wednesday evening FOR KYZ023>043-
IN...FLASH FLOOD WATCH through Wednesday evening FOR INZ076>079-083-