Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 281205
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
805 AM EDT Fri Apr 28 2017

.UPDATE...
Issued at 805 AM EDT FRI APR 28 2017

Continue to see significant differences in short term, high
resolution model solutions this morning with a fairly consistent
and stubborn HRRR being a general outlier when compared to the
NAM/RAP/ARW/NMM. The ARW does lend a little support to the HRRR,
but the NMM much less so. Interestingly the ECMWF lends some
support to the HRRR as well. However, there continues to be what
can best be described as a general disconnect between synoptic
scale changes expected over the next 12 to 24 hours and the HRRR.
The HRRR has waffled a bit but still wants to bring the main
thrust of thunderstorm activity straight into the heart of the CWA
late this afternoon and evening. Depending on the evolution of
events over the next several hours, there could be some major
alterations to PoPs and sensible weather. For now can only monitor
and adjust the forecast as trends become more clearly defined.
Did make some minor tweaks to the grids for the latest hourly
trends. No update to the zone package at this time.

&&

.SHORT TERM...(Today through Saturday)
Issued at 508 AM EDT FRI APR 28 2017

Models are in good agreement with general mid and upper level
pattern through the period. Jet max will be digging into the
Intermountain West resulting in the development of a cutoff low
over the deep southwest by Saturday morning. This deepening
western system will induce rising heights across the southeastern
U.S. beginning as early as today with substantial height rises
occurring across the region. At the surface, ridging aloft will
drive a stalled out frontal boundary to our south quickly
northward today. We expect this frontal zone will push north of
the Ohio River Valley by this evening and become the focus of much
more active weather for the next 24 hours. The Storm Prediction
Center has focused on this baroclinic zone for the potential of
widespread severe weather later today and tonight.

Main forecast challenge for our area will be timing and location
of the potential for severe weather this evening. Ridging aloft
will help cap much of any activity across our area. Main questions
causing the greatest amount of uncertainty is exact location of
the surface boundary to our north and whether the cap over the
area will be strong enough to limit convection across the region.
At present thinking is that ridging will keep most of the activity
across our area limited to the far north, generally along and
north of I-64 and west of I-75. With the exception of the HRRR
CAMs seem to support this line of thought. However, trends in the
HRRR suggest the severe threat may extend further south than
originally expected.

Should the cap be weak enough, forecast soundings indicate more
than enough instability and ample shear for the potential of
severe thunderstorms with hail and damaging winds being the main
threat. Strong shear in the lowest 1-3 km of the column allow for
the potential of a few tornadoes as well. PWATs do not look
impressively high. However, CAMs also suggest the potential of
some training storms, would could increase the risk of some
flooding.

At this point, confidence in the described scenarios is quite
low. In general there seems to be a disconnect in the strength of
ridging developing across the region and the amount of convection
being offered up by the CAMs. There is also considerable
uncertainty in the location of the frontal boundary riding north
today and where it eventually sets up. These factors will
ultimately determine the location of greatest concern with respect
to any severe weather this evening. Bottom line is to remain
vigilant and aware of future updates in what may be a rapidly
changing situation.

.LONG TERM...(Saturday night through Thursday)
Issued at 400 AM EDT FRI APR 28 2017

Eastern Kentucky will remain in the warm sector through Sunday
with the unseasonable warmth continuing. Record highs on Sunday
are a bit higher (88 for Jackson, and 89 for London) and will
likely be approached, but may be hard to exceed those numbers.
Regardless, another warm day with highs in the mid to upper 80s.

Meanwhile, a low pressure system will become cut off over the
western great lakes with an occluded front surging east across the
Ohio river valley. Model guidance continues to slow down this
front and now looks like it should pass through the area late
Sunday night into Monday morning. Ahead of the front, winds could
turn quite gusty Sunday night. As the band of showers pushes on
through Monday morning we could see some gusty winds out of any
showers as well. The weather should dry out Monday afternoon with
much cooler conditions returning to the area to start the new
month. Dry weather will last through Tuesday. Weather looks like
it may turn more unsettled by the middle of next week as a
shortwave trough ejects out into the region. While some
uncertainty remains on the pattern, it does look like shower and
thunderstorms chances are warranted from Wednesday through
Thursday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 805 AM EDT FRI APR 28 2017

Valley fog was prevalent this morning but had only temporary
effects on area terminals. Expecting generally VFR conditions
across the area through the period. However, there is
considerable uncertainty in the forecast. A warm frontal boundary
should lift to the north today and showers and thunderstorms are
expected to develop along this feature. The main forecast
challenge has been to determine the position of the boundary by
the end of the day. Models have not been much help, even with
trends. For now only have storms affecting SYM by late this
afternoon. Winds will be light but pick up from the southwest
through the day at about 10 kts, and could become gusty for a few
hours during the late afternoon.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

UPDATE...RAY
SHORT TERM...RAY
LONG TERM...KAS
AVIATION...RAY



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