Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 240453
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1253 AM EDT Tue Mar 24 2015
...Updated Aviation Discussion...
Issued at 912 PM EDT Mon Mar 23 2015
Issued another update this evening to account for the latest
trends. Any light shower activity has pushed to the east of the
region this evening, as large-scale subsidence in the wake of the
passing PV anomaly builds into the region. Therefore, have removed
pops for tonight given the upstream trends and the latest HRRR
runs. Can`t completely rule out a stray shower given the proximity
of the front, but coverage should be below 20 percent. Otherwise,
going forecast looks on track.
Issued at 606 PM EDT Mon Mar 23 2015
Quick update this evening to account for the latest radar trends.
Impressive frontal boundary remains off to the north of the Ohio
River, with an impressive temperatures contrast across it.
Temperatures in Louisville were in the 60s as of 6PM EDT, with lower
40s in Cincinnati. The latest WV imagery shows the compact PV
anomaly scooting to the north across IN/OH. The forcing with this
will largely remain to the north, so expecting nothing more than a
few sprinkles/isolated showers tonight along/behind the front. Have
trimmed back pops a bit from the previous forecast to account for
this expected less coverage. Otherwise, everything looks on track.
.SHORT TERM (Now through Tuesday Night)...
Issued at 300 PM EDT Mon Mar 23 2015
Water vapor imagery this afternoon with 500 mb heights overlaid
shows broad northwest flow from the Upper Midwest through the
Mid-Atlantic. Embedded shortwave troughs are pivoting through, one
of which is located across Illinois into parts of central Indiana.
At the surface, low pressure is analyzed near St Louis, tracking
generally due east. Locally across the Ohio Valley, sunny skies but
seasonably cool temperatures have prevailed. Mid afternoon readings
range from the low 50s across southern Indiana to low to mid 60s
with light easterly to northeasterly winds.
For this evening, the aforementioned weather system across
Illinois/Indiana will weaken as it tracks just north of the forecast
area. It will be running into a much drier airmass and limited
forcing, however, mid level clouds will be on the increase, mainly
along and north of the KY parkways. An isolated sprinkle or rain
shower is not out of the question for southern Indiana, so will keep
slight rain chances for portions of this evening.
The frontal boundary stalls across northern Kentucky overnight with
a gradual moistening and saturation of the low/mid levels. Plan on
lows in the upper 30s to middle 40s. By Tuesday morning, upper level
energy and a developing surface low pressure coming out of the
central Plains will work to lift the stalled front back north during
the day. Shower chances will be mainly confined to along/north of
the KY parkways, with the highest chances across southern Indiana.
Rainfall amounts look to be light, generally 0.1 to 0.2 during the
course of the day.
A tight high temperature gradient is expected Tuesday with mid/upper
60s across southern Kentucky while north of the stationary/warm
front, cool easterly winds, clouds and rain showers should hold
highs down into the low 50s. By Tuesday night, the front should be
north of the area, setting the stage for a mild night with southerly
to southwesterly flow at the surface and aloft. Overnight readings
are expected to be in the mid 50s.
.LONG TERM (Wednesday through Monday)...
Issued at 305 PM EDT Mon Mar 23 2015
Limited forecast confidence heading into a fairly active period of
weather. Wednesday will start with an impulse exiting the area but
leaving a front draped somewhere across Kentucky. Subsidence behind
the precip shield could provide us with dry weather for much of the
day, but POPs will start to ramp up again by late in the day as
another wave lifts out of the southern Plains. Will carry high-end
chance (40-50) POPs with the expectation that the best chances will
be skewed either toward the beginning of the day or the end, but not
enough confidence to get specific with the timing. Max temp forecast
is fairly conservative at around 70 out of respect for extensive
cloud cover, but if we get more breaks in the cloud cover we could
push solidly into the 70s.
Best chances for precip will be Wednesday night into Thursday as a
50-60 kt low-level jet cranks up ahead of the surface wave. Rain is
pretty much a slam dunk at some point, but just enough uncertainty
in timing to limit each period to likely. The dynamics will support
embedded thunder, and we`ll mention gusty winds in the Hazardous
Weather Outlook, but SVR potential is limited by the nocturnal
timing and overall lack of instability.
Thursday night through the weekend will be marked by a deep eastern
CONUS trof in the upper levels, with Canadian high pressure at the
surface. Unseasonably cold temps are expected Friday through Sunday
morning, and NW flow impulses diving into the trof could make for an
interesting precip forecast. One impulse on Friday in tandem with
low-level cold air advection should create at least a shallow
saturated layer near 850mb, with temps at that level near -10C. If
this layer gets deep enough we could see snow showers out of it, but
ground and low-level air temps will be warm enough to limit any
impacts. Will just carry rain/snow mention Fri evening. Temps will
run 15 to possibly 20 degrees below normal into the first half of
the weekend, before they start to rebound in return flow on Sunday.
Will carry a slight chance POP Sunday into Monday as another NW flow
system could impact the Ohio Valley, but there remains plenty of
uncertainty in timing and availability of moisture. Temps near climo
Sunday night into Monday.
.AVIATION (06Z TAF Update)...
Issued at 1252 AM EDT Tue Mar 24 2015
In general, VFR conditions are expected at the terminals overnight.
A stalled out front currently lies across central KY early this
morning. Ceilings north of the front are around FL060-080 and
should hold there throughout the rest of the overnight hours. There
is a possibility that they could drop to around FL050 toward
morning. Winds north of the front will be out of the northeast at
5-8kts while KBWG generally will see light/variable winds.
Moisture will gradually work northward during the morning hours as a
weather system organizes out to the west. This should result in
ceiling lowering a bit more, but it still looks like we will stay
above MVFR levels at this time. Some scattered rain showers will be
possible by late morning into the afternoon hours at KLEX and KSDF
as the aforementioned cold front lifts back northward as a warm