Area Forecast Discussion
Issued by NWS Shreveport, LA

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FXUS64 KSHV 241603
AFDSHV

Area Forecast Discussion
National Weather Service Shreveport LA
1103 AM CDT Thu May 24 2018

.UPDATE...
Have lowered rain chances this aftn to 20 percent ne to 40 percent
sw given both current trends past couple of days and low MOS
values once again as overall pattern has experienced little
change. Also, raised temps slightly this aftn for much of area,
also given current trends of majority of cwa reaching at least 90
degrees. For the time being, convection development south of I-10
with stgr activity offshore./07/

&&

.PREV DISCUSSION... /issued 506 AM CDT Thu May 24 2018/

AVIATION...
Another day of atmospheric moisture content, a weakness aloft and
once convective temperatures are reached near the noon hour, we
should see scattered showers and thunderstorms once again across
most of our airspace. Will continue the trend of mentioning VCTS
in the 12z terminal package beginning around the 17-18z timeframe
and continuing that wording through the afternoon and early
evening hours when we should finally see a downtrend in convective
activity after sunset. Did leave VCTS out of the TYR terminal
however. Will continue to hit terminals with amendments if
necessary for any TSRA inside VCTS range.

Cannot rule out patchy fog once again at the TXK/LFK/MLU and ELD
terminals but that should not last beyond the 13-14z timeframe
this morning if at all. Look for light and variable winds today
except much stronger and gusty with outflow boundaries produced
by thunderstorms this afternoon/early evening.

13

PREV DISCUSSION... /issued 336 AM CDT Thu May 24 2018/

Short Term.../Today Through Friday/

Still dealing with some scattered showers and isolated thunderstorms
this morning across portions of Central Louisiana, but this
activity should continue to diminish in coverage and intensity the
closer we get to sunrise. Otherwise, our region of the country
continues to remain under the influence of an elevated inverted
trough of low pressure that now extends across the SE TX/SW LA
Coast northward into NW LA and SE OK/SW AR. If this trough has
moved any over the last 48 hours, its been slightly eastward and
it does appear this trend will continue through at least Friday.
We continue to see elevated PWAT values across our Northern and
Eastern zones with values near or just above 1.7 inches with
minimum values across our southwest zones still near or in excess
of 1.5 inches. All this to say that when you combine this kind of
atmospheric moisture content, the lift in association with the
trough axis and daytime heating, you have the perfect ingredients
for scattered showers and thunderstorms, something our area has
been under the influence of the last several days and today and
Friday will be no different. The only trend may be for our western
third to see slightly drier conditions, especially by Friday as
the inverted trough axis slowly inches eastward. Otherwise, this
forecast will remain hedged on persistence with the highest pops
warranted across our eastern half through the short term.

MOS continues to struggle with diurnal temperatures and the 00z
models are no different. Will continue the trend of going above
MOS Max Temps today and Friday and slightly below MOS Min Temps at
night as this has worked well given the last several days.

13

Long Term.../Friday Night through Wednesday Night/

For much of the extended periods, the flow aloft will generally be
dominated by a building upper ridge centered over Northern Mexico.
The axis of the ridge, extending from Mexico into Canada, will
gradually migrate eastward across the Central CONUS. By the middle
of next week, the Mexican ridge will become quite broad and expand
far enough to keep the main branch of the westerlies far removed to
the north.

For Friday night and into Saturday, the most noteworthy feature is
that the GFS and NAM suggest the potential for a convective complex
to develop across Oklahoma and move south into the area early
Saturday morning. This scenario is quite possible as convection
develops along a dryline over the Plains and steered toward the Four
State Region by northwest flow aloft. While this is a pattern more
typically associated with early to mid June, the last week or two
should sufficiently indicate that summer is arriving a bit ahead of
schedule this year. Best chances for any rain Friday night and early
Saturday will generally be north of Interstate 20.

Our attention now turns to the well-advertised subtropical or
tropical system that will move north from the Caribbean and into the
Gulf of Mexico during the weekend. Medium range model guidance is
starting to show better agreement through late Monday. Landfall is
still expected to be either very late Sunday or early Monday along
the northeast Gulf coast. After landfall, the weak and unorganized
flow aloft will likely cause the weakening trough to become quasi-
stationary or perhaps drift very slowly northeast before the
expanding Mexican ridge pushes it into the westerlies during the
latter half of the week.

The new model guidance suggests an even lower impact for our area
due to the upper ridge axis moving across our area around the same
time as landfall. This should keep the trough farther east, which
should reduce our rain chances. Diurnally driven convection will
still be possible, but PoPs were lowered significantly compared to
the previous forecast package for all periods from Saturday and
beyond. Only slight chance to low-end chance PoPs were maintained,
and those may even be too high.

With the lower rain chances and the building ridge, there won`t be
much to stop temperatures from climbing. Daytime high temperatures
may be pushing the mid to upper 90s by next Wednesday. For a quick-
and-dirty comparison at Shreveport Regional Airport, the last time
we were this warm this early was 2011. However, Winter 2010-2011 and
Spring 2011 were much drier compared to this last year. Thus, the
higher moisture this year may help to keep air temperatures lower
than in 2011, but the increased humidity will keep heat index values
elevated. Just some food for thought as the building heat appears to
be the highest impact weather in the long-term.

CN

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  93  69  92  72 /  30  30  40  30
MLU  89  70  91  70 /  20  30  50  40
DEQ  89  66  90  67 /  30  30  30  20
TXK  91  68  90  70 /  30  30  40  30
ELD  88  67  90  70 /  20  30  40  30
TYR  93  70  92  72 /  30  20  30  20
GGG  92  68  93  70 /  30  20  30  20
LFK  91  69  92  71 /  40  30  30  20

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&

$$


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