National Weather Service Raw Text Product

858 
FXUS64 KTSA 281924
AFDTSA

Area Forecast Discussion
National Weather Service Tulsa OK
224 PM CDT Tue Sep 28 2021

.DISCUSSION...
An upper low centered over the four corners region this morning 
is continuing to transition to be an open wave this afternoon. 
This wave will continue to migrate northeastward along the front 
range the next few days. A mid level ridge continues to develop 
and sharpen to our immediate east. This has allowed for gusty 
winds this afternoon up to 25mph and will continue to pump 
moisture into the area with the most noticeable increase expected 
during the overnight hours and into tomorrow morning. At the time 
of writing, upper 60s to low 70 dews were just crossing the Red 
River in far SE OK. Lows tonight will be rather warm across the 
area. A low of 70 tonight in Tulsa is much warmer than average 
(58) but not quite a record. The record high minimum temperature 
for 9/29 in Tulsa is 75 set not that long ago in 2019. In 2019, we
set 6 high minimum temperature records in a row from 9/27 through
10/2. As for the rest of today, borderline elevated fire weather 
concerns will continue given the lack of recent rainfall, 
relatively low RH values in the 30 to 40% range and gusty 
southerly winds up to 25mph at times. Fire weather concerns will 
drop off by mid evening as moisture continues to move in. 

As moisture increases overnight, so will our chances for showers 
and storms. Storms will tend to fire along a dry line well to our 
west and southwest in W OK and N TX. Latest CAMs show this 
activity largely diminishing before reaching E OK by early 
tomorrow morning with only isolated activity possible. As a 
result, opted to keep PoPs low for the overnight hours given a 
favorable environment for development but low uncertainty. The 
latest HRRR has shown an MCV develop with the activity late 
tonight into early tomorrow morning. This may be a focus for 
scattered thunderstorms toward early morning. 

Tomorrow afternoon will see greater chances for showers and 
storms across E OK and NW AR with the best chances generally along
and east of US 75 thanks to peak afternoon heating, a zone of 
enhanced moisture return, and synoptic scale ascent along a subtle
short wave moving over the region. Bulk shear continues to be not
overly impressive at 15 to 25kts during the afternoon. The best 
low level dynamics will likely be just to our west and northwest 
though still very marginal for strong to severe storms. With that 
said, forecast soundings do support the possibility of some strong
to marginally severe downbursts with some hints of drying in the 
mid levels along with some small hail. If the sun can peek out, 
looks pretty cloudy for much of the day for most locations at the 
moment, mid and low level lapse rates could steepen allowing for a
slightly higher risk for strong to severe storms with marginally 
severe hail as well tomorrow afternoon. The coverage of showers 
and storms will likely decrease during the evening and overnight 
though isolated to scattered showers and storms will continue to 
be possible. One thing to note will be the potential for locally 
heavy rainfall, PWAT values Wednesday afternoon will be on the 
increase with values exceeding 1.5” for most and locally 
approaching 2” for some. These values easily exceed the 90th 
percentile and will be close to if not exceeding record values for
this time of year. Any storm that develops will see very heavy 
downpours with rainfall rates likely exceeding 2 or even briefly 
3” per hour at times. Luckily, these storms should be fairly 
progressive which will help to mitigate the flash flooding risk. 
With that said, low lying areas easily prone to flooding will need
to be watched as it will not take long for rainfall to 
accumulate.

Thursday morning, according to the latest CAMS, may start off 
with storms firing at sunrise across parts of central and eastern 
OK given enhanced instability/moisture with dew points in the 
upper 60s to lower 70s and a modest low level jet ahead of a 
rapidly approaching cold front that will likely quickly stall to 
the west and northwest of the area by late Thursday morning as the
synoptic push stops. There may be a lingering MCV from the 
previous day’s activity as well, as hinted in the 12Z HRRR, 
across NE OK which may help to fire off some activity as well. 
Storms that fire ahead of the front will likely congeal into a 
line thanks to unidirectional flow above the lowest 1km. Some 
bowing in the segments will be possible with cold pool pushes 
which may yield strong to briefly severe wind gusts late Thursday 
morning into the early afternoon across parts of E OK with a 
lesser threat for NW AR where shear and instability will be lower.
Again, another thing to note will be the threat for locally heavy
rainfall. PWAT values will once again be in the 1.5 to 2” range
which will translate to very heavy rainfall rates (again 2 to
possibly 3" per hour at times) with these storms. Luckily, these 
storms will be progressive which will help to mitigate any 
widespread flash flooding issues but low lying areas prone to 
flooding will need to be watched, especially if they receive a 
dose of heavy rainfall the day before. 

Friday into Saturday will see another upper low over the four 
corners region eject as an open wave onto the central and southern
plains which will continue to bring unsettled weather to the 
region. This will also help to slowly push the cold front into 
northeast Oklahoma potentially by Friday before slowly and 
stalling once again. Showers and storms appear to be likely both 
days for most with multiple rounds expected. Some of these round 
may be strong to marginally severe, mainly Saturday as the best 
combination of low level dynamics from the short wave trough 
passing over the region and thermodynamics meet and thanks to the 
presence of the cold/stationary front. It is still a little too 
early to get into exact timing or the specific risks for Saturday 
as there are still some factors that need to be ironed out. Again,
elevated PWATs for Friday and Saturday will yield a threat for 
locally heavy rainfall across E OK and NW AR. Thankfully, the 
rounds of showers and storms will be progressive which should 
again mitigate flash flooding concerns. I know, I sound like a 
broken record at this point. 

The cold front finally pushes and begins to clear the area 
through late Saturday night into Sunday as the upper short wave 
passes through the region. This will lead to decreased dew points 
and gradually decreasing shower and storm chances though some 
activity may linger through the day Sunday with some afternoon pop
ups possible Monday likely initiated within the higher terrain of
NW AR. The models differ as we progress into the early to middle 
part of next week in terms of the chances for precipitation and 
the evolution of a large upper low over the midwest. Uncertainty, 
as a result past Tuesday, is relatively high at this time. Though 
not specifically highlighted in this forecast package, very 
isolated showers and storms will be possible Tuesday and Wednesday
as well.

So how much rainfall are we expecting? The GEFS ensembles are
still painting widespread amounts greater than 1” with
approximately 85% of the runs going this direction with 40 to 50%
suggesting a majority of the area seeing 2” or more from tonight
through Sunday evening with the best chances for these higher
amounts along and south of I-40. The GEFS mean suggests 1.5 to
2.5” area-wide with the highest amounts located across SE OK
into west-central AR. This also lines up well with the
deterministic GFS and ECMWF. Overall, this isn’t much change
compared to the ensembles 24 hours ago, though the chances for
2” or greater have marginally increased, thus is leading to
higher confidence in the forecast totals. The HREF along with
other CAM solutions over the next 48 hours paint isolated pockets
of locally heavy to very heavy rainfall across parts of the area
which seems reasonable given the highly saturated environment and
isolated to scattered convection expected through at least early
Wednesday afternoon. Where these pockets of rainfall ultimately
establish themselves will need to be watched closely as additional
rounds of showers and thunderstorms pass through the area.
Hopefully, the Tulsa mesonet site along with much of the area
receives beneficial amounts of rainfall through Sunday which seems
like a fairly safe bet given the latest available data with a
widespread 1” to 2.5” expected through Sunday evening with
locally higher amounts possible. If my yard could talk, it would
probably be low key excited for this forecast. 

Snider


&&

.PRELIMINARY POINT TEMPS/POPS...
TUL   70  85  68  83 /  20  60  30  70 
FSM   70  86  69  83 /  20  80  50  70 
MLC   68  83  66  82 /  20  70  30  70 
BVO   65  85  65  82 /  20  50  40  70 
FYV   64  83  63  80 /  20  60  50  70 
BYV   65  83  65  79 /  10  60  50  70 
MKO   68  82  66  81 /  20  60  30  70 
MIO   68  84  66  80 /  20  50  40  70 
F10   68  84  66  83 /  20  60  30  70 
HHW   68  81  67  81 /  20  70  30  70 

&&

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

$$


LONG TERM....21