Heat in Texas, August 26, 2019

Area Forecast Discussion
National Weather Service Shreveport LA
1043 AM CDT Mon Aug 26 2019

.UPDATE...

High pressure at sfc and main frontal boundary sinking into srn
cwa. Any isold convection near front expected to remain in se cwa
and be short lived as airmass a 12z kshv appears quite dry aloft,
despite dewpoints still elevated in mid to upper 70s./07/.

&&

.PREV DISCUSSION... /issued 700 AM CDT Mon Aug 26 2019/

AVIATION...

For the ArkLaTex, we are blanketed with mostly IFR/MVFR cigs and
these low clouds will slowly break, scatter and lift this mid
morning. Winds becoming S/SW 5-15KT on the SFC with SW winds now for
climb 10-20KT before veering to NW-NE flow aloft 20-30KT for high
up FLs. Any showers/isold TS should keep to our SE for today, but
overnight an MCS is modeled to move across I-30 down toward I-20
overnight to around and just past daybreak. Then boundary will
fire more in the aftn. A weak fropa is on approach for Wed. /24/

PREV DISCUSSION... /issued 500 AM CDT Mon Aug 26 2019/

SHORT TERM.../Today through Tuesday/

We have a blanket of low clouds just about areawide with a solid
range of air temps all in the 70s this morning. The clouds are
not raining, but they will help to keep the morning rise on temps
at a more reasonable pace. The low decks will scatter and lift by
around lunch time with sunshine boosting temps and the heat index
along with for the afternoon. The heat advisory for East Texas
has been expanded to include SW AR and NW/W LA from 1pm until 7pm
this evening.

Just a few showers on HRRR and most other models from Toledo Bend
up to near Monroe this morning, and then shifting SE into the
afternoon. The evening will be quiet as will the overnight for
many, but an MCS has been consistent in all the models coming
into our cwa after midnight for McCurtain Co and maybe more toward
daybreak into our I-30 corridor. Low to mid 70s with any rain,
otherwise mid to upper 70s can be expected.

The models all have also been consistent with the MCS activity
falling apart by mid morning with heating, but then some
additional development along the boundary as the afternoon unfolds
with more scattered elements. Meanwhile, our heat indices will be
cooler in the North, but may still be marginal South of I-20 for
Tuesday. Some highs will keep to the 80s North with low to mid 90s
most everywhere else on Tuesday. /24/

LONG TERM.../Tuesday Night through Sunday Night/

Longwave troughing swinging E across the Plains into the Upper
Midwest Tuesday evening, will sharpen a cool front from SW OK NE
into NE OK/NW AR/Srn MO, with convection expected to deepen near and
just ahead of this front through the overnight hours. Any residual
daytime convection Tuesday should diminish during the evening with
the loss of heating, with the convection upstream expected to
gradually build SSE into portions of NNE TX/SW AR/possibly extreme
Nrn La by daybreak Wednesday, where a convectively reinforced
outflow/mesoscale bndry will lie from earlier convection Tuesday.
The short term progs are in reasonable agreement with the greatest
low level convergence (via a 20-25kt SSErly low level flow) near the
sfc front over N TX/possibly far Srn OK, which may linger through at
least daybreak Wednesday before weakening. Thus, convection (and
more efficient rain producers within an already high PW environment
characteristic of PW's in excess of 2 inches) should be deepest over
this area, with large scale forcing spreading ESE atop the sfc
front/residual mesoscale bndry across portions of NE TX/SE OK/SW
AR/I-20 corridor of N LA. Given higher confidence in convection
development Tuesday night, have increased pops to likely across SE
OK/portions of NE TX, tapering this area with high and mid chance
pops elsewhere across E TX/SW AR/N LA. Even though the low level
convergence weakens along the front after 12Z Wednesday, the
existing convection should remain deep enough to continue producing
mesoscale bndrys which will initiate additional convection, and thus
have expanded likely pops Wednesday for much of E TX/N LA Wednesday
morning, before drier mid and upper level air begins to advect SE
with the upper trough passage Wednesday afternoon, which should act
to taper the convection off from NW to SE.

The convection Wednesday should reinforce the weak sfc front SSW
across the remainder of the area by evening, with sfc ridging
building ESE into the Mid MS Valley Wednesday night allowing for
drier sfc air to begin backdooring SW into the region Thursday.
There is still some uncertainty as to how quickly this bndry will
backdoor SW through the area Thursday, with the bndry placement
dependent on where isolated to widely sct convection will develop
especially for the afternoon during peak heating. The ECMWF has
backed off though with the extent of convection W of the bndry, with
the GFS/Canadian mostly dry especially given the lack of appreciable
forcing aloft. Have scaled back pops to slight chance over SE OK/E
TX, but did maintain low chance pops over Deep E TX per the ECMWF.
Drier air building WSW behind the front will yield lower RH's
despite the seasonal max temps in the lower 90s, with the front
expected to continue slowly mixing W into SE OK/Ecntrl TX Friday.
Did keep slight chance pops going for these areas Friday, with sfc
and low level ridging expected to be maintained through the upcoming
weekend.

A weak NW flow aloft will be maintained though the weekend, with the
Four Corners upper ridge expected to linger here and over the Srn
Rockies/into portions of Wrn OK/TX. The GFS/ECMWF/Canadian have all
backed off on isolated convection that may build SE into the I-30
corridor of extreme NE TX/SE OK/SW AR Saturday along weak troughing
aloft around the Ern periphery of the upper ridge, likely due to the
lack of forcing aloft, subsidence with the H850 ridge centered over
this area, as well as the drier air that will advect into this area
with the passage of the late week backdoor front. Have removed pops
from the forecast Saturday, although the air mass looks to begin
moistening up by Sunday as a weak inverted trough migrates W along
the Gulf Coast into portions of the Lower MS Valley. Thus, isolated
convection may affect the SE zones Sunday, while the gradually
moistening air mass may allow for isolated convection to affect the
far NW zones near the weak elevated troughing. While min temps will
be a few degrees below normal by late week/into the weekend, max
temps will remain near or slightly above normal in the lower to mid
90s, although lower RH's will result in lower heat indices. /15/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  96  78  94  75 /  10  40  30  40
MLU  92  76  93  74 /  20  20  30  40
DEQ  95  74  84  70 /  10  60  60  50
TXK  95  75  87  72 /  10  50  60  50
ELD  93  75  88  71 /  10  40  30  40
TYR  98  78  93  73 /  10  30  30  50
GGG  97  78  93  75 /  10  40  30  50
LFK  95  78  96  75 /  10  10  20  30

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...Heat Advisory until 7 PM CDT this evening for ARZ050-051-059>061-
     070>072.

LA...Heat Advisory until 7 PM CDT this evening for LAZ001>003-010-011-
     017-018.

OK...Heat Advisory until 7 PM CDT this evening for OKZ077.

TX...Heat Advisory until 7 PM CDT this evening for TXZ096-097-108>112-
     124>126-136>138-149>153-165>167.

&&

Hazardous Weather Outlook
National Weather Service Shreveport LA
546 AM CDT Mon Aug 26 2019

ARZ050-051-059>061-070>072-LAZ001>003-010-011-017-018-OKZ077-
TXZ096-097-108>112-124>126-136>138-149>153-165>167-271100-
Sevier-Howard-Little River-Hempstead-Nevada-Miller-Lafayette-
Columbia-Caddo-Bossier-Webster-De Soto-Red River-Sabine-
Natchitoches-McCurtain-Bowie-Franklin-Titus-Camp-Morris-Cass-Wood-
Upshur-Marion-Smith-Gregg-Harrison-Cherokee-Rusk-Panola-
Nacogdoches-Shelby-Angelina-San Augustine-
546 AM CDT Mon Aug 26 2019

This Hazardous Weather Outlook is for portions of southwest
Arkansas, northwest Louisiana, southeast Oklahoma, east Texas and
northeast Texas.

.DAY ONE...Today and Tonight...

An upper level ridge of high pressure will expand east across the
Southern Plains and into much of the Four State Region today,
allowing afternoon temperatures to climb into the mid and upper
90s across East Texas, Southeast Oklahoma, much of Southwest
Arkansas, and Western Louisiana. When combined with the high
humidity, afternoon heat indices will range from 105 to 110
degrees. Thus, a Heat Advisory is in effect this afternoon for
these areas. Those that must be outside today should wear
lightweight, loose fitting clothing, drink plenty of water, and
take frequent breaks in air conditioned facilities.

Showers and thunderstorms are expected to increase this evening
across Central and Eastern Oklahoma and Northwest Arkansas, near a
weak cold front and associated upper level disturbance. This
thunderstorm complex is expected to shift south southeast into
Southeast Oklahoma, Southwest Arkansas, extreme Northeast Texas,
and possibly Northwest Louisiana late tonight, but weaken as it
does so. However, some of the stronger storms will still be
capable of producing strong and possibly damaging winds and brief
heavy rainfall before weakening by daybreak Tuesday.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday...

Isolated to scattered showers and thunderstorms will remain
possible across the area Tuesday, but additional shower and
thunderstorm development is expected late Tuesday night over North
and Northeast Texas and Southeast Oklahoma, which will spread
east southeast across the remainder of the region Wednesday along
a weak surface front. Locally gusty winds and heavy rainfall will
be possible in the stronger storms Wednesday morning over portions
of Northeast Texas and North Louisiana, before diminishing from
northwest to southeast during the afternoon. The weak front will
drift west southwest into East Texas and Southeast Oklahoma
Thursday and Friday, which may allow for isolated to widely
scattered showers and thunderstorms each day over these areas.

.SPOTTER INFORMATION STATEMENT...

Activation of emergency managers, spotter networks, and amateur
radio operators, may be needed late tonight across portions of
Southeast Oklahoma, Southwest Arkansas, and extreme Northeast
Texas.

ARZ073-LAZ004>006-012>014-019>022-271100-
Union-Claiborne-Lincoln-Bienville-Jackson-Ouachita-Winn-Grant-
Caldwell-La Salle-
546 AM CDT Mon Aug 26 2019

This Hazardous Weather Outlook is for portions of south central
Arkansas, north central Louisiana and northwest Louisiana.

.DAY ONE...Today and Tonight...

An upper level ridge of high pressure will expand east across the
Southern Plains and into much of the Four State Region today,
allowing afternoon temperatures to climb into the lower and
possibly mid 90s across Southcentral Arkansas and Northcentral
Louisiana. When combined with the humidity, heat indices will
range from 100 to 105 degrees. Isolated showers and thunderstorms
will be possible today over the southeast sections of Northcentral
Louisiana, before diminishing by sunset.

A complex of showers and thunderstorms that will develop this
evening over Central and Eastern Oklahoma into Northwest Arkansas
near a weak cold front, will shift south across Arkansas, possibly
affecting portions of Southcentral Arkansas and the Interstate 20
corridor of Northcentral Louisiana late tonight. Locally gusty
winds and brief heavy rainfall will be possible from the stronger
storms before they weaken as they move into the area.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday...

Isolated to scattered showers and thunderstorms will remain
possible across the area Tuesday, but additional shower and
thunderstorm development is expected late Tuesday night over North
and Northeast Texas and Southeast Oklahoma, which will spread
east southeast across the remainder of the region Wednesday along
a weak surface front. Locally gusty winds and brief heavy
rainfall will be possible in the stronger storms Wednesday,
before diminishing from northwest to southeast during the
afternoon. The weak front will drift west southwest into East
Texas and Southeast Oklahoma Thursday, allowing for seasonal
temperatures, lower humidities, and thus dry conditions over the
region late this week through much of the weekend.

.SPOTTER INFORMATION STATEMENT...

Activation of emergency managers, spotter networks, and amateur
radio operators, should not be needed today or tonight.

15