Heat Advisory 31, NWS Tulsa, OK

Area Forecast Discussion
National Weather Service Tulsa OK
1232 PM CDT Sat Sep 4 2021

.AVIATION...
CONCERNING TAF SITES KTUL/KRVS/KBVO/KMLC/KXNA/KFYV/KFSM/KROG.
Expect to see showers and thunderstorms develop across NE OK in
the next few hours near an outflow boundary in the vicinity of
I-44. Coverage will continue to increase and spread into NW AR
and eventually SE OK this evening and overnight, with MVFR
conditions becoming prevalent. Precip expected to taper off from
the north late tonight into Sunday morning with improving flight
conditions across NE OK by the end of the period.

&&

.PREV DISCUSSION... /Issued 1048 AM CDT Sat Sep 4 2021/

DISCUSSION...
An outflow boundary resulting from overnight storms across
southern Kansas, was positioned near I-44 this morning. Still a
few elevated cells developing near the OK/KS border and will leave
the relatively high POPs for the morning, but would expect an
overall downward trend for the next few hours. By this afternoon
the position of the boundary will determine most likely location
for re-development in an unstable airmass, with a well mixed
boundary layer supportive of strong downdrafts in most intense
cells. POP forecast for today seems appropriate overall.

Other possible concern will be heat and humidity, with HI
approaching 105 in some areas near and south of boundary. Dew
points farther south should eventually mix out some, but higher
values pooling near the boundary could be a significant factor.
This will depend largely on exactly when storms redevelop, and for
the time being will continue to monitor trends closely.

PREV DISCUSSION... /Issued 617 AM CDT Sat Sep 4 2021/

AVIATION...
CONCERNING TAF SITES KTUL/KRVS/KBVO/KMLC/KXNA/KFYV/KFSM/KROG.
VFR conditions expected this morning with the bulk of convection
remaining north of the TAF sites. Scattered showers/storms will
become more likely this afternoon for the northeast OK and
northwest AR sites, with the activity developing farther south
during the evening and overnight. Will see lower cigs/vsbys in
the heavier rain areas through the day, with more widespread
MVFR/IFR conditions possible overnight.

PREV DISCUSSION... /Issued 304 AM CDT Sat Sep 4 2021/

DISCUSSION...
Showers and storms have largely stayed to the north of the area
tonight where the surface cold front is located. The front will
push into NE OK by mid morning with showers and storms likely
being triggered by late morning to early afternoon near I-44.
Forecast soundings for this afternoon show a well mixed boundary
layer (0-1km lapse rate a little over 9C/km) past 1km with a nice
inverted V profile. Another thing to note is the abundance of dry
air in the mid levels starting at around 700mb and the DCAPE
values in the 1500J/kg range. Shear is relatively weak based on
forecast soundings thus the main severe weather type for this
afternoon (if severe weather does occur) will be damaging wind
gusts most likely in the form of downbursts. This seems
reasonable given the highly saturated airmass with dew points well
into the 70s, PWAT values near or over 2”, and the
aforementioned inverted V sounding with dry air in the mid levels.
In addition to the threat for strong to severe storms, locally
heavy rainfall will be possible given the highly saturated
environment well into the 90 percentile for this time of year.
This may lead to localized flash flooding. This wave will slowly
push across the CWA before largely diminishing during the evening
hours.

Another wave is expected to develop during the overnight hours
with showers and storms likely developing in the vicinity of the
first wave or near I-44. Forecast soundings with overnight
activity is very tropical looking with deep moisture through at
least 500mb. This results in PWAT values well over 2 to near
2.5” in some instances. This is again well above the 90
percentile and is pushing record values for this time of year. As
a result, locally heavy rainfall will be the main concern
overnight with localized flash flooding very possible. Storm
motions appear to be slow overall, but the latest guidance is
showing that these storms will be more progressive than originally
expected 24 hours ago. With that said, brief extreme rainfall
rates will be possible and it will not take long for rain to pile
up thanks to efficient rainfall processes that will be in place.
Brief rainfall rates of 3” per hour will be possible for some
locations. Severe weather is not a huge concern with the overnight
activity though gusty winds with the strongest cores may be
possible. Overall, HREF is continuing to highlight an area for
locally heavy rainfall (generally 1 to 2” with isolated amounts
of 3”) from about I-44 southward to just north of I-40 across E
OK and NW AR between the 2 waves. The max QPF product from the
HREF (which is usually not too bad at forecasting what the extreme
values will be but not necessarily the location) suggests
isolated amounts up to 2.5” will be possible with the afternoon
activity. The max also paints isolated 3” amounts possible with
the overnight activity. When this activity largely diminishes by
tomorrow morning, isolated locations of 4” will be possible with
a general 1 to 2” expected from about I-44 southward to about
I-40 with lower values the further north or south you go from this
zone. Confidence in the higher amounts (3 to 4”) is low overall
thanks to the latest CAMs showing a more progressive pattern with
heavy rainfall generally moving through quickly, thus opted to
not issue a Flash Flood Watch at this time though one was
considered. This will need to be evaluated again in future
forecasts.

Sunday will see shower and storm activity exit the southern half
of the area through the day. Heavy downpours will be possible
though not to the degree we will experience this afternoon and
overnight. Sunday will also feature much cooler temperatures
thanks to the passage of the cold front and cloud cover/showers
lingering. This cooler weather will be short lived as temperatures
increase Monday and especially Tuesday. Another cold front
approaches the area Tuesday night into Wednesday morning. The GFS
is still painting some precipitation for parts of the area while
the ECMWF continues to offer a dry frontal passage. Opted to
continue go with the ECMWF for this forecast as the GFS appears to
be the outlier when compared to other ensembles. This front will
lead to cooler temperatures and is expected to really knock down
the dew points Wednesday with Wednesday’s overnight lows rather
cool with some locations across NW AR and NE OK dipping into the
upper 50s! Temperatures will then warm through the end of the week
as a mid level high/ridge builds into the area from the 4 corners
region. Highs by next Friday and Saturday will be back above
normal with temperatures generally in low to mid 90s but much
lower dew points will likely make this more bearable heat.

Snider

&&

.TSA WATCHES/WARNINGS/ADVISORIES...
OK...None.
AR...None.
&&

AVIATION.....14

Hazardous Weather Outlook
National Weather Service Tulsa OK
102 PM CDT Sat Sep 4 2021

ARZ001-002-010-011-019-020-029-OKZ049-053>076-051030-
Adair OK-Benton AR-Carroll AR-Cherokee OK-Choctaw OK-Craig OK-
Crawford AR-Creek OK-Delaware OK-Franklin AR-Haskell OK-Latimer OK-
Le Flore OK-Madison AR-Mayes OK-McIntosh OK-Muskogee OK-Nowata OK-
Okfuskee OK-Okmulgee OK-Osage OK-Ottawa OK-Pawnee OK-Pittsburg OK-
Pushmataha OK-Rogers OK-Sebastian AR-Sequoyah OK-Tulsa OK-Wagoner OK-
Washington OK-Washington AR-
102 PM CDT Sat Sep 4 2021

This Outlook is for Northwest and West Central Arkansas as well as
much of Eastern Oklahoma.

.DAY ONE...Today and Tonight.

SEVERE THUNDERSTORM.
	RISK...Limited.
	AREA...Northeast Oklahoma and Northwest Arkansas.
	ONSET...Mid Afternoon.

HEAVY RAIN.
	RISK...Limited.
	AREA...Northeast Oklahoma and Northwest Arkansas.
	ONSET...Late Afternoon.

DANGEROUS HEAT.
	RISK...Elevated.
	AREA...Much of eastern Oklahoma and west central Arkansas.
	ONSET...Ongoing.

DISCUSSION...
A cold front will push into the area today, triggering showers and
storms mainly this afternoon, evening and overnight. Storms this
afternoon will likely produce locally heavy rainfall given the
highly saturated environment and may produce locally heavy
rainfall in portions of northeast Oklahoma and northwest Arkansas.
Some storms may briefly become severe this afternoon across
northeast Oklahoma and far northwest Arkansas with damaging wind
gusts the main severe weather concern.

South of the boundary, locations in, near, and to the south of
Tulsa will see heat indices approach 105 degrees this afternoon.
These elevated heat indices may be short lived as showers and
storms develop or dew points lower as mixing occurs.

SPOTTER AND EMERGENCY MANAGEMENT ACTION STATEMENT...
Local Spotter Activation May Be Needed.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.
SUNDAY...Thunderstorm Potential.
MONDAY through FRIDAY...No Hazards.

EXTENDED DISCUSSION...
Showers and storms will linger across southeast portions of
Oklahoma Sunday morning and early afternoon before gradually
exiting by Sunday evening.

Monday through Friday will see dry weather with another cold front
expected to move through Tuesday night into Wednesday. This front
lower temperatures a little but, more importantly, it will knock
down the dew points. The heat will return to end the week as a
ridge builds into the area, but the humidity will be lacking.

weather.gov/tulsa contains additional information.