Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 201816 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
216 PM EDT Mon Mar 20 2017

.UPDATE...
Issued at 216 PM EDT MON MAR 20 2017

Thunder has ended across the area early this afternoon, with
showers on the demise quickly. Surface winds have turned gusty on
the backside of the MCS, with a good pressure gradient set up
between northeast Kentucky and southern Ohio. New convection is
firing up across central Indiana, closer to a surface low and
approaching short wave trough. This convection will skirt by to
our northeast this evening and into the overnight as the cold
front drops southeast across our area. Temperatures continue to
flounder along and north of the Hal Rogers Parkway and Highway 80
corridors. Will have to retard the warm up even more so, resulting
in cooler highs still. Updates will be forthcoming.

UPDATE Issued at 1221 PM EDT MON MAR 20 2017

Showers and isolated thunderstorms continue to gradually weaken
overall; however, the coverage has expanded further south, so
increase POPs to match the radar trends better. Reduced the high
temperatures in the northeast somewhat with the lingering cloud
cover, but still think that a quick comeback may occur late
today, as readings have already warmed into the upper 50s in our
far southwest. Updates have been sent.

UPDATE Issued at 1029 AM EDT MON MAR 20 2017

Weakening MCS is makings its way into eastern Kentucky, with even
some minor development occurring all the way to the Tennessee
border. A continued diminishment is expected into early this
afternoon, as the forcing remains weak across the area. Did update
POPs to represent radar trends a bit better over the next few
hours. Also slowed the diurnal rise a bit more in the north
through early this afternoon, with the precipitation and heavier
cloud cover in place. Will reassess the highs in the next few
hours.

UPDATE Issued at 805 AM EDT MON MAR 20 2017

Hourly pops have been updated to account for radar and convective
allowing model trends for the convective complex moving across
parts of IL, IN and OH. This led to an increase in pops across the
northern portion of the CWA. The few HRRR runs bring this or what
is left of the complex across the area toward midday to early
afternoon period. This timing might be an hour or two slow per
radar trends and up to chance pops have been used accordingly to
account for this. Also, temperature, dewpoint, sky and wind grids
have been adjusted based on these and observation trends.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 430 AM EDT MON MAR 20 2017

Early this morning, an upper level ridge was centered over
northern Mexico and the Southern Plains with an axis of this ridge
extending northeast into the eastern Great Lakes with another
axis extending toward the Four Corners and Intermountain West.
Several rather weak shortwave were embedded in the westerly flow
from the Rockies to the Great Lakes and MS Valley between the
ridge and an upper level low over Central Canada. At the surface,
a deep area of low pressure was moving across Hudson Bay with a
cold front that is becoming more ill defined with time extending
south from this system to an area of low pressure that is nearing
the mid MS Valley. A warm front extended south southeast form the
low to the Gulf Coast states. Meanwhile in advance of the axis of
the mid and upper level ridge and sfc high pressure generally
dominating, a rather steep nocturnal inversion is in place with
deeper valleys generally in the mid to upper 20s at this time
while ridges other than the highest ridges were in the mid to
upper 30s. Preliminary non operational/test GOES 16 WV imagery at
the low, mid, and upper level channel indicate an increase in WV
is dropping south and east of the OH River at this time. Regional
observations indicate a mixture of mid generally mid and high
clouds with this. Meanwhile rather deep convection has developed
over northern IL, northwest IN, and portions of MI in advance of
the front.

The model consensus is for a shortwave trough moving around the
central Canada upper level low to move toward the Maritimes today
which should help push the weakening cold front into the eastern
Great Lakes to Lower Oh Valley region by this evening while the
warm front should lift across the TN and into the lower OH Valley
through this evening while the surface low nears the lower OH
Valley by sunset. Moisture will increase as the upper ridge axis
moves east today, initially in the mid to upper levels.
Convective allowing models take the weakening convection now to
the northwest of the area toward northern KY and southern after
sunrise and weaken it further as it moves into northeastern KY and
the Huntington WV metro area around midday. With dry low levels
in place, this will probably not be much more than light showers
or sprinkles when or if it reaches the northern sections of the
forecast area. Slight chance pops were used for much of the area
north of the Mtn Parkway for this with some chance pops generally
I 64 and north with a buffer of sprinkle chances just south and
east of these areas. The southwestern part of the area appears to
be poised to experience the least cloud cover today with a general
increase in clouds area wide by the mid to late afternoon hours.
Clouds and potentially some precipitation in the far north should
set the stage for about a 10 degree north to south temperature
gradient in highs for today from Fleming County to Wayne County.

Somewhat better chances for precipitation are expected by late
evening into tonight as the weak surface wave moves across the
area and the frontal/baroclinic zone sags into the Commonwealth
accompanied by some modest height falls. Some limited elevated
instability continues to be indicated in the models mainly late
this evening and tonight, so we have maintained some isolated
thunder in the weather grids. The northern and east locations
appear to have some better forcing this evening and tonight so
chances for measurable rain appear better. Uncertainty exists
though as the 0Z NAM had less convection across the area compared
to some of the other guidance, but the 06Z runs appears to be in a
bit better agreement with the guidance. Along and in advance of
the front, temperatures will be mild tonight and min T should have
at least a 10 degree range from north to south with locations in
advance of the boundary remaining in the low to mid 50s tonight.
Winds will increase ahead of the boundary, particularly aloft and
some of this stronger sustained winds and gusts should be realized
at elevations of 2500 feet and above where gusts of 30 mph or
higher are anticipated from around midnight through 5 AM tonight.

The next round of higher rain chances areawide may hold off until
early in the long term period on Tue night. Convection some
possibly strong is currently expected to develop near or just
south of the sagging boundary possibly near the confluence of the
OH and MS River. This convection should move east southeast and
track near or a bit south of the boundary that may reside just
south of the KY/TN border for much of Tuesday while more scattered
weaker convection is possible across most of East KY. Chances for
convection appear best across the Lake Cumberland/KY and TN
border region on Tuesday afternoon. If thunderstorms do affect
that area, the strongest storms could produce some small hail with
relatively low WBZ heights in place. Another wave and secondary
boundary will approach late, but convection from this should hold
off until after the period. The north to south temperature
gradient should persist for Tuesday Max T.

Overall, it increasingly appears that some locations may get
missed by the convection over the next couple of days completely or
only experience very light qpf.

.LONG TERM...(Tuesday night through Sunday)
Issued at 332 AM EDT MON MAR 20 2017

There will be three periods of note in the extended. First will be
the Tuesday night and Wednesday time frame. A large trough of low
pressure aloft is progged to move across the northern CONUS and
into New England through mid week. The surface cold front
associated with the trough will be our primary weather maker to
begin the period. Widespread rain showers are expected across the
area to start things off. We may even see a few thunderstorms
along and south of the Hal Rogers Parkway through 2 or 3Z
Wednesday, as the cold front sags southward across the area. Once
the front moves into Tennessee, general rain showers should be all
that remain behind the front. The rain will quickly taper off
during the night, with only scattered showers in place by 9 or 10Z
Wednesday. Cold air intruding from the north may be enough to
cause some snow to mix with the rain across the northern and
northeastern portions of the forecast area early Wednesday
morning. Any remaining precipitation should be out of the area by
around 17Z on Wednesday.

A ridge of cold high pressure is expected to settle over the
region from Wednesday through Friday, and will likely bring
unseasonably cool weather to eastern Kentucky Wednesday night
through Thursday morning. In fact, the deeper and more sheltered
valleys in the eastern portions of the forecast area may see areas
of frost on Thursday morning, as temperatures fall to below
freezing in those locations. Wednesday should also see below
normal temperatures, due to the lingering cloud cover and
precipitation.

A second period of wet weather is expected this weekend, as a more
vigorous area of low pressure is forecast to eject out of the
Plains across the Ohio and Tennessee valley regions. The onset of
rain looks to be some time Saturday morning, as a cold front
approaches from the west. The best chance for rain at this time
looks to be from Saturday afternoon through Sunday afternoon, as
the front moves across the area, and then the parent low tracks
eastward just to our north. Isolated thunderstorms will again be
possible Saturday and early Saturday night, as the front moves
through. The latest forecast soundings were showing enough
instability aloft to support some thunder. The rain will linger
through Sunday evening, as the parent low strengthens to our
north and slows down. The rain should steadily taper off Sunday
night into Monday morning, and should be out of the area by late
Monday morning.

A nice warm up should commence on Thursday, as high pressure takes
hold. The warmest period should be from Friday through Sunday, as
persistent southerly flow sets up across the region. Highs from
Friday through the weekend are expected to average in the 60s
across the area. A few locations may even reach or slightly exceed
70 degrees on Saturday. Nightly lows should also be plenty warm,
with minimum values in the 40s and 50s expected.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 216 PM EDT MON MAR 20 2017

Generally VFR conditions will hang on through this evening, as a
weakening complex of showers and isolated thunderstorms exits off
to our east. Additional showers and a few thunderstorms will move
into the area this evening and into the overnight as a cold front
drop southeast across the area. Better coverage will generally
occur along a line from KSYM to KSJS, with more scattered activity
expected west of I-75. Ceilings will drop down to MVFR and
eventually IFR towards dawn, as south to southwest winds of 5 to
10 kts become northerly behind the cold front, and low level
stratus sets in across the area. Additionally, some marginal
wind shear will set up across LOZ and SME tonight, as a low level
jet ramps up across the Ohio Valley.

&&

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

$$

UPDATE...GEOGERIAN
SHORT TERM...JP
LONG TERM...AR
AVIATION...GEOGERIAN



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