Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 200818
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
318 AM CDT Mon Mar 20 2017

.SHORT TERM...(Today through Wednesday night)
Issued at 253 AM CDT Mon Mar 20 2017

We inherit a warm sectoring lower troposphere in the near term
Today, with active convection already initiating to our north.
That`s where some energy aloft is shooting out/overtop the actual
boundary, which looks poised to sag southward toward the FA today.
The difficulty comes with the modeling. All suggest a
destabilizing atmosphere with thunder supportive indices, with
0-1KM MU Capes from several hundred J/KG2 upwards to near 2000
J/KG2, depending upon the model. At the same time, models are
warming mid levels from the southwest, which may compete against
the otherwise favorable parameters and inhibit free parcel uplift.
If so, it`ll take the boundary`s entry into play, to make for more
active convective chances. That`ll come later in the day, into
tonight. Therefore, we`ll start with a small Pop north, and expand
that Pop southward and westward with time, as this occurs. Another
shot of energy shoots overtop the boundary during the Tuesday-
Tuesday night time period. This will markedly spike Pops, upwards
into the likely/categorical range. 00Z models displace the
boundary further south, but elevated instability still supports
overrunning convection, for about the south half of the FA, so
we`ll modify the (thunder) grids accordingly. During the
pm/evening hours, differential heating on modified sounding data
indicates surface based CAPEs upwards to 1500 J/KG in the peak
axis near the front, with incoming jet streak topping off 0-6KM
shear at the same time. This instabilty/jet enhancement
intersection with the boundary results in a Marginal Risk of Svr
Storms during the pm/evening hours, for far SEMO/SWKY, but
probably, is best pointed toward the peak axis in West-Central TN
and southeastward from there. Alot will just depend upon
convection initiation and actual boundary location at the time of
peak heating. Damaging winds/large hail will both be svr storm
possible hazards.

Canadian CP airmass settles overtop the Great Lakes during the mid
week under surface High pressure, and this air gradually invades
the lower Ohio valley with cooler/drier filtration Wed-Wed night.
Blended models still suggest rimfire convection, but we`ll seek to
minimize that, pending our neighbors` collab agreement.

.LONG TERM...(Thursday through Sunday)
Issued at 253 AM CDT Mon Mar 20 2017

Confidence continues to improve with timing and even strength of the
systems in the extended.

High pressure will still be in control of the weather pattern
beginning the long term, but will slowly be shifting to the east
toward the end of the week. However upper level ridging builds
into the region Thursday. This should keep most areas dry. In
contrast at the surface a warm front will lift north of the region
placing the quad state in the warm sector late Thursday into
Friday. This could set off some WAA showers but the ridging should
negate most any rainfall. In addition the available moisture is
rather shallow for that time frame. Overnight Friday we finally
have a deep column of available moisture with mild instability
starting to develop ahead of the next system. The vertically
stacked cut off low will still be fairly progressive in its
eastward track. Also since it is vertically stacked would expect
it to start to fill and lose some of its intensity as it moves
east of the region. PW do get up to 1.25" but instability is low
to moderate with the deep moisture with LI`s negative one and
CAPEs under 500 j/kg2. Low level winds are 50 knots plus as low as
925 mb but remain unidirectional. So the main threat would be
wind and heavy rain. During the day Saturday instability increases
but available moisture decreases. By Sunday most of the precip
should be moving out if not already east of the area. Friday
should be the warmest day with temps well above normal as the warm
front lifts north of the region. Monday appears to warm above
normal as well when upper level ridging builds back into the area.
Other days will be near seasonal temperatures.

&&

.AVIATION...
Issued at 253 AM CDT Mon Mar 20 2017

Warm air advection clouds already developing in the northeast FA
will expand southward and westward and offer potential MVFR to low
VFR bases temporarily early Today. Upstream energy aloft will
activate scattered convection that may ultimately produce vicinity
mentionables for our terminals, but at this writing, expect just
an increase or expansion in MVFR to lower VFR bases. South winds
will prevail thru the bulk of the forecast, though a
developing/approaching front will ultimately bring a shift to
northerlies late tonight-Tuesday as it makes northward to
southward passage across the Heartland. Further/more aggressive
flight restrictions to both CIGS/VSBYS will be possible then.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$



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