Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 292217
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
617 PM EDT Mon Jun 29 2015
Issued at 617 PM EDT Mon Jun 29 2015
Thunderstorms continue to move eastward across the region. Most
storms have cleared the I-65 corridor. However, more upscale growth,
most likely related to approaching short wave impulse coming up out
of AR is helping fuel convection across southern KY. Coordination
with SPC had us expand Tornado Watch #369 southward to cover this
activity. An isolated spinup is possible down across southern KY
for the next few hours, but feel wind damage and large hail will be
the primary severe weather threats.
Elsewhere, some additional convection has fired behind the main
convective line. This activity extends from Cincinnati
southwestward to near Bardstown. This will move east and affect the
Bluegrass region over the next few hours. Rainfall amounts have
been impressive with 1-2 inch reports in the southern Bluegrass and
down toward the Lake Cumberland region. This has resulted in some
minor flood issues and a number of flood advisories are in effect
As convection pushes south and eastward out of the region, we will
be dropping the watch from NW to SE.
.SHORT TERM (Now through Wednesday)...
Issued at 325 PM EDT Mon Jun 29 2015
The synoptic pattern this afternoon features northwesterly cyclonic
flow aloft over the Ohio Valley, with an upstream ridge across the
western CONUS. This will set the stage for PV anomalies to dive
southeast through the flow aloft, bringing a couple of chances for
thunderstorms in the short term period.
The first round of storms has already developed this afternoon.
They have formed mainly along confluence bands and along the main
synoptic cold front which is now pushing across the Ohio River.
Dewpoints pooling in the upper 60s along the front coupled with some
diurnal heating has pushed MLCAPEs to 1000-2000 J/kg. However,
latest WV imagery shows the main shortwave and kinematics aloft have
pushed to the east of the area. This has led to rather meager
effective shear values of only 20-30 knots. This marginal
deep-layer shear coupled with only weak convergence along the
boundaries will likely limit storm severity quite a bit, with only
an isolated storm or two likely to reach severe limits. There
appears to be a very marginal tornado risk, but that will be mainly
northeast of the LMK CWA where winds remain locally backed. Latest
observations show winds have veered substantially from SDF to FFT,
so think any tornado threat will be limited to the northern
Bluegrass where winds remain the most backed helping to enlarge
low-level hodographs. The main threat in the strong to locally
severe storms will be damaging winds to 60mph and hail to the size
of quarters. Another threat will be very heavy rainfall. Bowman
Field in Louisville saw an inch of rain in about 20 minutes when a
storm passed through there, which may lead to some localized minor
Convection should quickly dissipate as it pushes east this evening.
The night will be mainly dry, with just some passing mid/high
clouds. There could be some fog especially where rain falls today,
but the passing clouds coupled with at least some light surface flow
should keep the fog from becoming too dense.
Tuesday will be a very similar setup to today. The only difference
is there appears to be a better trough axis swinging through, which
may help to add a bit more vigor to updrafts. Therefore, once again
expecting strong to marginally severe storms to fire in the
afternoon hours, capable of locally damaging winds and hail to the
size of quarters. Expect the best coverage across the northeastern
CWA where the better forcing will coexist with more favorable
diurnal timing. Highs Tuesday will be similar to today, with
readings expected in the low to mid 80s. Tuesday night will dry
out, with lows in the mid to upper 60s.
.LONG TERM (Wednesday Night through Monday)...
Issued at 329 PM EDT Mon Jun 29 2015
Overall hemispheric pattern is characterized by a 6 wave pattern
aloft. Three anchor lows, one out over the Aleutians, one over
Hudson Bay, and one out near Iceland will continue to drive the
pattern. The overall pattern is very much an -AO/+PNA pattern which
looks to result in the ridge west, trough east pattern across NOAM
to continue. With our region in the northwest flow, we will have to
watch for several pressure perturbations move through within the
flow. The global models are in good synoptic agreement here and
generally are tracking the perturbations well. The first looks to
arrive Wednesday and into Thursday, with yet another coming in
Friday/Saturday. The models do have some placement issues with the
actual tracks, as the GFS is a little north with the Euro being a
bit more south. In any case, rounds of showers and thunderstorms
are pretty much a given throughout the upcoming week. Precipitable
water values will start off rather low early in the period and then
rapidly increase from mid-week onward with values well over 2
inches. Thus, repeated rounds of thunderstorms are likely to result
in hydrologic/flooding issues as we close out the week. Storms
could be strong at times...especially in the afternoon during peak
heating and peak instability. Damaging winds, torrential rains and
marginal hail would be the main threats with any strong storm.
As for the upcoming holiday weekend, the pattern is not expected to
change all that much. The models do forecast another wave in the
train to come through the region. However, timing issues are going
to be key as to whether or not we`ll see a washout for the weekend.
For now, plan on staying above climatologically PoPs for the weekend
until timing issues can be resolved. This should occur by the
Thursday/Friday time frame...so stay tuned. By late in the weekend
and into early next week, there is a bit of a signal suggesting that
some height rises may develop and move in from the west. Overall,
we`re not totally buying into this signal just yet, given the
configuration of the hemispheric pattern which would continue to
support the NW flow aloft pattern over the Ohio Valley. Thus,
climatologically PoPs will be featured in the upcoming forecast at
As for temperatures, the stormy pattern and upper level flow will
likely keep afternoon highs below climatologically values. Latest
blend of consensus model guidance keeps highs in the upper 70s to
the lower 80s for much of the week. As a broadbrush, yeah, that may
work out fine, though I do think some pockets of higher temps may be
realized at times. This would be especially true across southern
KY. Overnight lows will remain mild too, with lows in the upper 60s
to around 70. Some moderation in temperatures may occur late this
weekend and into early next week with highs returning to the upper
80s to around 90.
.AVIATION (18Z TAF Update)...
Issued at 112 PM EDT Mon Jun 29 2015
The TAF period will be characterized by generally VFR conditions,
with brief restrictions possible in thunderstorms this afternoon.
Thunderstorms have already begun to form near the Ohio River, with
coverage expected to increase this afternoon across southern and
east-central KY, mainly affecting KLEX and KBWG. Brief restrictions
are possible in any storm with gusty winds.
Otherwise, skies will go partly cloudy overnight. Some light fog
will be possible at KBWG where winds will be the lightest, but
confidence in fog occurrence is not very high. Confidence will
increase if KBWG receives rain this afternoon/evening. Tuesday will
begin as VFR with additional scattered storms possible, but
most will be after this valid TAF period and into the SDF planning