Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 201146

Area Forecast Discussion
National Weather Service Little Rock AR
646 AM CDT Wed Sep 20 2017

High pressure in control again through the TAF period with VFR
prevailing. A compact shortwave trough is progged to slide just
south of the forecast area, so highest confidence in TS should
remain south. Iso TS still possible but not confident enough to
include in TAFs this morning. Increasing pressure gradient will
boost southerly winds with gusts to 10-15 kts with winds subsiding
within a few hours of sunset. SCT cu aoa 5 kft through the day,
dissipating after sunset.


.PREV DISCUSSION...(ISSUED 402 AM CDT Wed Sep 20 2017)
SHORT TERM...Today Through Thursday Night
The large scale pattern remains fairly unchanged this morning with
upper ridging still firmly entrenched from the Gulf northeastward
to the Great Lakes. Under this regime, warmer than average
temperatures are expected through the period with most locations
reaching the upper 80s and low 90s this afternoon and again
Thursday afternoon. Expect overnight temps in the 70s with a
moist, muggy atmosphere in place.

Hi-res guidance shows a shortwave trough nosing in through the
larger upper ridge this afternoon. Considering the amount of
available energy...MUCAPE values exceeding 2000-3000
J/kg...isolated thunder is possible. However, larger scale
subsidence should act to limit areal coverage of convection if it
develops at all. Better upper energy associated with the
shortwave trough will pass to our south, so fairly confident
leaving very low end PoPs through the period. A tightening
pressure gradient will increase southerly flow with occasionally
gusty winds during the afternoons.

LONG TERM...Friday Through Tuesday Night
And the heat goes on. (Sorry, I couldn`t resist).

Evident in upper air analysis as well as satellite data this morning
is troughing starting to be carved out in the upper reaches of the
Ohio Valley to the west of Tropical Storm Jose. This will expand
southward into the Tennessee and lower Mississippi Valley, and
toward the Gulf by the end of the week. To the north of that,
persistent, irritating longwave ridge that will not seem to die
will remain for the time being.

So, while large-scale convection will be suppressed over much of
the region due to our not-so-friendly ridge, presence of the trough
near us will at least allow for isolated/widely scattered showers
and storms through the weekend. These will largely be diurnal, and
develop as daytime heating interacts with any mesoscale features.

As Jose eventually diminishes, and Maria moves northward, the ridge
will dampen out. Remaining upper low/trough will be absorbed into
Maria, with ridging building over the western Gulf.

What does this mean for us, you ask? Well, it will make the flow
over us a little more quasi-zonal, which will give momentum to a
frontal boundary that will be stalled in the plains. The boundary
will affect us just beyond the end of the period, with rain chances
increasing. Cooldown? Yes, it looks that way. Not as much as I would
like, mind you, but temperatures should get back closer to where we
would expect them this time of year. Oh well. It`s a start.


.LZK Watches/Warnings/Advisories...NONE.


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