Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 181834
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
234 PM EDT Thu May 18 2017

.Short Term...(This evening through Friday night)
Issued at 222 PM EDT Thu May 18 2017

Current surface analysis reveals broad southwesterly flow across the
region and relatively warm temperatures in the 80s. Upper air
analysis/satellite show a weak elevated boundary oriented from
northeast to southwest along the Indiana/Kentucky borders. Scattered
showers and thunderstorms have fired off along the boundary this
morning, though most have remained weak in nature. Could see some
more scattered showers and thunderstorms this afternoon, with the
greatest chances along the boundary.

Cold front associated with a low pressure system over southern
Quebec will begin pushing south over parts of the Ohio River Valley
region tonight and stall out near the I-64 corridor tomorrow
morning. Additionally, an MCS from convection overnight in the
Plains will weaken and approach the region from the west tomorrow
morning. The stalled cold front and remnant MCV/outflow boundaries
will provide lift for showers and thunderstorms during the day
Friday. Some strong to severe storms are certainly possible, as
environment will be characterized by moderate to high instability
(+2500 J/KG) and decent deep layer shear (~30kts 0-6km). Main
threats with storms should be strong winds and hail. Heavy rainfall
in storms is also a possibility, as PWATs will be near ~1.5". Don`t
think flash flooding will be too much of a concern as storm motions
should keep storms from settling over one area for an extended
period of time.

The stalled cold front will begin to lift northward as a warm front
Friday night into Saturday morning. While most areas will have the
chance to see showers and storms overnight Friday, best chances for
storms should be along and near the warm front as it lifts
northward. Environment parameters will support a couple strong to
severe storms during the overnight hours.

&&

.Long Term...(Saturday through Thursday)
Issued at 230 PM EDT Thu May 18 2017

By Saturday morning, warm front from Friday near the I-64 corridor
should be north of the CWA. This will place the region deep within
the warm sector in an environment characterized by moderate to high
instability and deep moisture, but marginal deep layer shear. Models
vary with QPF, as the NAM/Canadian keeps things mostly dry and
capped until late Saturday afternoon while most other medium to long
range models develop scattered convection all day long. Given how
things evolve Friday night, any leftover boundaries or outflow could
certainly serve as focal points for convection, so can`t rule out
storms during the morning and afternoon. As a result, will take a
blended forecast solution for now. A few storms that develop
Saturday could be strong to severe with wind/hail being the main
threats.

Strong cold front is progged to move through region late Saturday
night into Sunday. Models develop a line of showers and storms ahead
of a pre-frontal trough and cold front, and with marginal
shear/instability values, can`t rule out a few strong storms. Cooler
and drier air will begin filtering in from the west late Sunday
afternoon.

High pressure builds in to the region Monday and keeps things cool
and dry, though the dry weather may be short-lived. Long range
models prog another cold front to impact the region around the
Tuesday-Wednesday timeframe and develop a line of showers and
thunderstorms ahead of the front. Some timing/placement issues still
need to be worked out but overall pattern looks to be cool and
unsettled.

&&

.Aviation...(18Z TAF Issuance)
Issued at 100 PM EDT Thu May 18 2017

VFR conditions are expected to prevail at the TAF sites through much
of the period.  Plume of convection may develop later this afternoon
across western KY/southern IL/southern IN and that may pose a VCSH
threat at KSDF.  HRRR is most robust with convective potential,
though the 3KM NAM run was much drier.  For now, will maintain a
VCSH period at KSDF through 19/00Z.  Southwest winds of 12-15kt with
gusts to 20kts will be possible through the afternoon.  VFR
conditions are expected this evening and into the overnight.
However, some overnight convection is likely to develop after 19/09Z.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Short Term...DM
Long Term...DM
Aviation...MJ



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