Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 181128 AAA
AFDLZK

Area Forecast Discussion...UPDATED
National Weather Service Little Rock AR
628 AM CDT Tue Jul 18 2017

.UPDATE...
Updated for 12z Aviation cycle
&&

.AVIATION...

VFR conditions will prevail for all terminals through the TAF
period. The only exception may be ADF, which has fog forming off
the adjacent swamp. Elsewhere, some very patchy/isolated fog has
formed, but kept VFR in TAFS due to the thin and transient nature
of the fog. Winds winds will be light and variable throughout the
day, with some fair weather cumulus developing in the afternoon.

&&

.PREV DISCUSSION...(ISSUED 353 AM CDT Tue Jul 18 2017)

SHORT TERM...Today Through Wednesday Night

Some patchy fog is beginning to form once again as of 08z across
the CWA. Have mention of fog beginning at 09z in the grids. In
general, any fog should be even more isolated than yesterday
morning, with dissipation expected soon after sunrise.

GOES16 7.3 micron imagery currently shows significant and
abnormally dry air in place over Arkansas as the region currently
sits in North/Northeast flow underneath a strengthening ridge of
high pressure. Models are currently advertising PWATS of just
around an inch this morning... which would place it near the 10th
percentile for July 18th.

With plenty of insolation expected today and fairly dry air in the
boundary layer, temperatures will rise to the mid 90s for much of
the state. I`m rather dubious of the GFS solution once again for
today and the next few days. The model places somewhat drier in
the boundary layer compared with most other models, and allows
for more efficient heating at the surface and with a resultant
rather substantial near-surface superadiabatic layer. This is
especially true in the heavily forested areas of the state... so
wonder if there is a parameterization issue. As a result, have
chosen to go closer to the NAM/Euro/SREF solutions for maximum
temperatures.

With temperatures expected to be in the mid 90s for much of the
state, and dew points in the upper 60s, heat indices will approach
100- which is fairly typical this time of year. Even if the GFS
happens to be right with temps closer to 100, the significant
surface mixing of the dew point will probably still keep heat
indices just below heat advisory criteria.

As far as rainfall in the short term... there will not be any.

LONG TERM...Thursday Through Monday Night

The upper level ridge in place across the region will be near it`s
peak strength at the start of the long term period...with 500 mb
heights around 596/597 dm over the AR. As a result...Thu and
potentially Fri should be the hottest days of this heat wave and
this forecast. Expect highs in the 90s for most areas...with the
exception likely being the higher terrain of the Ozarks and
Ouachitas where some upper 80s may be seen. Some locations may
approach the 100 deg mark...mainly across WRN and SWRN portions of
the CWA...though current forecast keeps temps just shy of the triple
digit mark in these regions.

As for heat index values during these hottest days...do think the
afternoon dewpts will mix out some with the lack of any
precip...with dewpts potentially dropping a few deg during the
hottest part of the day. So...even with the mid and upper 90s
temps...heat index values should remain just below the 105 deg heat
adv threshold for most areas. However...will need to monitor this
setup closely over the next few days.

By the weekend...the upper level ridge will slowly weaken...with a
resulting slight decrease in forecast highs expected. Even
so...expecting highs in the mid 80s to mid 90s for Sat and Sun. By
Sun...the ridge may be weak enough to start to see some diurnal
convection develop during the afternoon hrs that day.

Looks like the upper ridge will continue to slowly break down by
early next week...especially as a weak upper disturbance drops SE
towards the state. This will result in better rain chances and
cooler temps by the end of the forecast.

&&

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

$$

Aviation...Brown
Short Term...Brown / Long Term...62



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