Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/03/24
Area Forecast Discussion
National Weather Service Louisville KY
847 PM EDT Tue Apr 2 2024
.KEY MESSAGES...
* Severe storms still possible this evening, but overall threat
is decreasing. Damaging winds, hail, and brief tornadoes are
possible.
* Rain on Wednesday could mix with or change to snow Wednesday night
into Thursday morning. A light accumulation of snow cannot be
ruled out, but significant impacts from snow are unlikely.
* Quiet weather expected Friday into next weekend with increasing
chances of below freezing temperatures Saturday morning.
&&
.MESOSCALE...
Issued at 844 PM EDT Tue Apr 2 2024
Current convective activity has slowed down substantially
compared to a couple of hours ago, as seen in the GLM FED.
Surface observations and SPC low-level frontogenesis analysis
locate the frontal boundary oriented southwest to northeast
across central Kentucky. Most of the storms are arranged along a
broken convective line with sporadic embedded supercells which
have exhibited some intermittent upticks in lightning and mid-
level rotation given plenty of effective bulk shear, sufficient
(100-200 j/kg) effective SRH, and some leftover instability. The
downside regarding updraft strength/maintenance for the coming
hours will be the decaying instability, increasing MLCIN, and
weakening mid-level lapse rates (as shown by the latest SDF/BNA
ACARS soundings) so chances of severe weather will continue to
diminish through the evening until the front moves out of the
forecast area. On the other hand, cool and stable airmass is
rushing in behind the frontal line allowing a quick transition
to dry but still cloudy and breeze conditions. As a result,
counties behind the front are being trimmed out of the Tornado
Watch while the Flood Watch was allowed to expire.
Issued at 624 PM EDT Tue Apr 2 2024
Squall line with embedded supercells has moved through southern
Indiana and now pushing across central Kentucky. QLCS tornadoes
continue to be the most impactful threat and Tornado Watch 78
remains in place until 2Z. Have cleared a few southern Indiana
counties behind the line.
Progress will be slow as storm motion is nearly parallel to the line.
So far we have not had any flash flooding but will continue to
monitor.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 407 PM EDT Tue Apr 2 2024
Severe weather threat is currently ramping up as storms try to
become more organized along/just ahead of a cold front in the Wabash
Valley. Morning and midday convection left behind quite a bit of
cloud cover, but that has scoured out and allowed temps to warm
quickly into the lower/mid 70s with several hours of daylight
remaining.
Storms struggled to get organized until the last 30-45 minutes, with
some of the storm motion keeping storms along or even behind the
effective boundary. Over the next several hours, the instability and
shear profiles will enable any storm that can stay on or ahead of
the front to easily go severe. All severe threats are on the table,
including damaging winds, large hail, and fast-moving, possibly
strong tornadoes. Boundaries left behind by earlier storms will
likely be the main focus for tornadoes. Tornado Watch 78 is in
effect until 10 PM EDT, though the threat will diminish earlier than
that for our northern and western counties as the front pushes
through.
Flood Watch until 00Z is a little tricky as most of the heavier rain
from the earlier storms fell just outside the watch area. Storms
this evening look progressive enough, and the heaviest rainfall is
not expected to repeat over the hardest hit areas from earlier, so
will not expand the watch at this time. However, with neighboring
counties still under a Flood Watch, will maintain status quo for
now.
Temps crash behind the front overnight as strong cold advection
takes hold. After morning lows in the lower 40s on Wednesday, we
will struggle to crack 50 degrees in the afternoon. Winds at a
solid 15-20 mph with gusts near 30 mph will make it feel closer
to 40 than 50 throughout the day. Deep cyclonic flow and a strong
cold pool will support widespread light rain showers, especially
Wednesday afternoon. Could even see some graupel or small hail given
the steep low-level lapse rates.
&&
.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
Issued at 407 PM EDT Tue Apr 2 2024
Synopsis...Large-scale mid-level pattern height will remain largely
amplified during the long term period. Initially, broad upper
low/longwave trough will be anchored in the East CONUS as bouts of
shortwave energy continue rotating around its axis. Further west,
weak upper ridging will exist across the Rockies with positive
height anomalies across the northern Plains/southern Canada and
another upper low carving its way into California coast. At the
surface, occluded low pressure system will slowly move eastward from
the Great Lakes to the Northeast US keeping the Ohio Valley under
cool, windy, and showery conditions for most of the second half of
the week. During the weekend, the height anomaly configuration will
resemble an Omega blocking pattern as the features at play slowly
progress to the east, although the strongest portion of the jet will
zonally extend across the southern half of the Lower 48. As a
result, the mid-level ridge will approach the forecast region with
surface ridging nosing in from southern Canada/Upper Great Lakes.
The pattern will be speed up Sunday into next week as West Coast
upper low moves inland while the mid/upper ridge and associated
surface high pressure get pushed to the eastern seaboard.
Model Confidence/Evaluation...Most of the long term period will be
characterized by above-average model agreement as most of the
deterministic guidance consulted has similar output solutions
regarding the Omega blocking pattern and the position of the
synoptic features. Forecast uncertainty starts decreasing Sunday
into next week as models handle differently the inland trajectory of
the West Coast upper low, possibly due to its interaction with
shortwave energy upstream, and to a lesser extent the strength of
the downstream East CONUS upper ridge. The trajectory of the upper
low will ultimately determine the position of the attendant surface
low pressure and attached fronts which will influence the amount of
cloudiness or any weather next Monday, April 8, when the solar
eclipse will occur. As mentioned in the previous discussion, the GFS
still hints at a upper low farther east (higher probability of
cloudiness and rain) while the position of the upper low in the
CMC/ECMWF solutions is more to the west (lower chances of cloudiness
and rain).
Wed Night - Thursday...Surface low pressure and attendant low- to
mid-level vorticity impulses will move down from Lake Michigan to
southern Ohio during this period keeping the lower Ohio Valley under
persistent cloudiness with intermittent showers and breezy WNW
winds. The main forecast reasoning has not changed much as prog
soundings still show a saturated column into the DGZ early Wednesday
evening with falling surface air temperatures, low freezing levels,
and steep low-level lapse rates. Therefore, anticipate in the first
few hours of Wednesday evening liquid-precipitating, shallow
convective cells to still pose a threat of sub-severe gusty winds,
lightning, and some small hail with a quick transition to brief
rain/snow showers (possible some graupel) overnight as mid-level dry
air entrainment takes over and surface air temperatures/freezing
levels keep falling. At this moment, there could be some dusting of
accumulation over elevated surfaces early Thursday morning with no
significant impacts otherwise. Clouds, intermittent light showers
(mostly liquid), and breezy winds will continue during the day on
Thursday; however, the track of the surface low argue for a heavier
showers over the Bluegrass area given the track of the surface low
and attendant forcing. GFS forecast soundings over the Bluegrass
during Thursday afternoon hint at a renewed chance of heavier showers
(compared to the rest of the forecast area), low lightning chances,
and possibly some hail and enhanced gusty winds as cooling mid-level
temps will steepen low-level lapse rates and forcing promotes deeper
saturation into the DGZ. If heavier showers do occur, there is a non-
zero chance of a brief period of frozen hydrometeors based on low
freezing levels and additional effect of dynamic cooling. Finally,
went a few degrees below guidance for highs on Thursday but still at
or above convective temperatures for that matter.
Friday - Sunday...Friday still looks quite cloudy and somewhat
breezy, although the wind will slow down compare to Wednesday and
Thursday values. Precipitation chances will also largely decreased
for most as increasing mid-level heights and subsidence aloft start
to erode the depth of the moisture layer. As a result, a few breaks
in the cloud cover could allow highs to climb around the 50 degree
mark, but still below average for this time of the year. Increased
presence of surface ridging will allow clearer skies and weaker
winds, so that lows Friday night are still on track to be or below
freezing levels (especially over southern Indiana). Therefore,
frost/freeze headlines could be needed for Friday night/Saturday
morning. A warming trend with dry weather is anticipated for
Saturday and Sunday. Last but not least, action stage or minor river
flooding across the Ohio cannot be ruled as HEFS/GEFS/NAEFS hint at
increasing probabilities of those categories.
Next Week...Big question will be chances of rain and any cloudiness
on Monday due to the solar eclipse. As mentioned above, there is at
least a low chance of light rain showers and clouds over the southern
Indiana and northern Kentucky as a warm front lifts through the
region. But again, there is enough variability and the forecast
windows is still so far out that confidence in the forecast is still
low. So, stay tuned for new updates during the next coming days.
&&
.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 734 PM EDT Tue Apr 2 2024
Showers and storms ahead of a cold front are slowly pushing off to
the east this evening. The front should clear the region by
midnight, with gusty westerly winds in its wake. MVFR stratus will
also build in behind the front and persist through early morning
before gradually lifting during the day tomorrow. Showers are
expected to develop by late morning or early afternoon across most
of the region.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
MESOSCALE...ALL/RAS
SHORT TERM...RAS
LONG TERM...ALL
AVIATION...DM
Area Forecast Discussion
National Weather Service Nashville TN
849 PM CDT Tue Apr 2 2024
...New UPDATE...
.UPDATE...
Issued at 849 PM CDT Tue Apr 2 2024
Tornado Watch will expire at top of hour. Regional radar imagery
showing line of convection pushing eastward, but with environment
along and ahead of it worked over and 03/00Z KOHX Sounding derived
indicies showing very marginal low to mid level lapse rates, which
has been one of the main players in putting a "Nail in The
Coffin" for robust strong to severe thunderstorm development
across our area as these early evening hours have progressed, not
expecting any more organized severe potential tonight. As Tornado
Watch expires at top of the hour, will updated gridded forecast
shortly afterwards and will do a more thorough examination of
forecasted weather conditions through remainder of tonight.
&&
.SHORT TERM...
(Rest of today through Wednesday)
Issued at 1104 AM CDT Tue Apr 2 2024
A dangerous setup is in place this morning for severe weather late
this morning through the evening hours. A wave of showers and storms
developed over eastern AR/western TN and has lifted northeast into
the western part of our CWA. The atmosphere ahead of that wave is
characterized by 500-1000 J/kg of mlCAPE. According to SPC
Mesoanalysis West Tennessee and the northwestern third of Middle
Tennessee are uncapped. So far, small hail and some strong winds
have been reported in West Tennessee. Closer to Nashville, the 12z
OHX raob and BNA ACARS soundings show a cap in place just above 700
mb. ACARS around 15z show that the cap has eroded away.
Additional storms are expected to develop just west of the area
early this afternoon as the leading edge of large scale ascent noses
closer to the area. The environment ahead of that second wave will
be dependent on this morning`s round. Ample shear will be in place
regardless, but the amount of recovery for instability is in
question over the northwestern part of the area. Further south and
east, the environment will be less questionable with mlCAPE
values between 1000-1500 J/kg. Storm modes could be a mix between
supercells and line segments. The more recent runs of the HRRR
have been holding onto the morning round a little longer which in
turn has made the afternoon round more linear in nature and less
cellular. This scenario would favor damaging winds and embedded
rotations instead of a scenario where we have discrete cells that
would favor potentially long track tornadoes, large hail, and
damaging winds. The severe threat will come to a close on the
plateau by 7 to 9pm. Some additional showers may continue through
the rest of the evening hours before coming to an end.
A trough ejecting out of Manitoba will phase with the southern
stream energy from today`s event developing into a large upper low
centered near Chicago Wednesday morning. A lobe of energy will
rotate around the base of the upper low on Wednesday sparking
showers over our area.
&&
.LONG TERM...
(Wednesday Night through next Tuesday)
Issued at 1104 AM CDT Tue Apr 2 2024
The upper level low will wobble eastward on Thursday with another
lobe of energy rounding the base of the trough leading to more
shower chances along the northern plateau For the rest of the area,
conditions will be cool and breezy once again. Temperatures Friday
morning will drop into the low to mid 30s but widespread frost is
not likely due to surface winds remaining 5-10 mph. By Friday, the
upper low will be centered over New England with northwest flow over
Middle Tennessee leading to another cool and breezy day, but it
should be dry. Temperatures Friday night will drop into the upper
20s to mid 30s. Winds will be a little lighter Saturday morning
leading to more widespread frost compared to the previous night.
Upper level ridging will start to build into the area late on
Saturday allowing temperatures to begin to rebound. By Sunday
afternoon temperatures will be back in the mid 60s to lower 70s. A
trough looks like it will move through the central plains late in
the weekend which may bring some rain chances to our area late
Sunday or on Monday.
&&
.AVIATION...
(00Z TAFS)
Issued at 653 PM CDT Tue Apr 2 2024
03/00Z TAFs focused primarily thru 03/06Z per potential
significant convective aviation impacts. Several admendments
probable per forecasted weather element fluctuations thru 03/06Z.
Current regional radar trends, addressed 1hr TEMPO groups,
BNA/MQY, & 2 hr TEMPO groups, SRB/CSV, for best convection time
window impacts with initial VFR ceilings/vsbys lowering to
MVFR/VFR ceilings/vsbys with sfc gust 40-50kts. Sfc backing winds
thru 03/06Z. Sustained sfc winds 10-20kts. VCSH thru 03/24Z.
&&
.PRELIMINARY POINT TEMPS/POPS...
Nashville 46 58 40 54 / 80 60 40 20
Clarksville 43 55 39 52 / 50 70 40 20
Crossville 40 52 34 45 / 100 60 50 50
Columbia 43 57 39 53 / 80 40 20 10
Cookeville 42 54 37 47 / 100 70 50 50
Jamestown 40 53 34 45 / 100 80 60 60
Lawrenceburg 44 57 40 53 / 90 40 20 10
Murfreesboro 43 57 38 53 / 90 60 40 20
Waverly 42 55 38 52 / 50 60 30 10
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE.......JB Wright
SHORT TERM...Reagan
LONG TERM....Reagan
AVIATION.....JB Wright