943 
FXUS64 KTSA 302330
AFDTSA

Area Forecast Discussion
National Weather Service Tulsa OK
630 PM CDT Thu Sep 30 2021

.AVIATION...
CONCERNING TAF SITES KTUL/KRVS/KBVO/KMLC/KXNA/KFYV/KFSM/KROG.
Scattered thunderstorms will primarily affect NW AR TAF sites
through 02Z with a few lingering showers possible this evening. 
Lower stratus/fog will likely develop overnight with the potential
for dense fog, especially across NE OK, where low level winds 
will be the lightest. Fog will also be possible elsewhere, but may
be more low clouds. Otherwise, ceiling heights will begin rising 
during the morning hours with the chance for scattered thunderstorms
again Friday afternoon. 

&&

.PREV DISCUSSION... /Issued 307 PM CDT Thu Sep 30 2021/ 

DISCUSSION...
A line of showers and thunderstorms has now raced well ahead of 
the cold front which is lagging behind on our western CWA border. 
The latest data from the mesonet shows winds from the east behind 
this ongoing line of storms with winds from the northwest behind 
the cold front. The front is expected to remain nearly stationary 
over the next several hours before slowly pushing into northeast 
Oklahoma with time overnight. In the mean time, the current line 
of storms is generally tracking (albeit slowly for the most part) 
slowly to the east. A gust front can be easily seen on radar 
outpacing the line and as a result, there has been a noticeable 
decrease in the intensity of these storms overall. With that said,
storms that are keeping up with the gust front are exhibiting 
strong wind gust potential. The overall severe threat at this time
appears to be relatively low, though there continues to be a 
nonzero chance for a damaging wind gust or two through the early 
evening especially for storms that can develop ahead or in close 
proximity to the gust front. In addition to the strong storm 
potential, the higher threat for the next several hours may be in 
the form of heavy rainfall. Radar has estimated rates of 2 to 4”
per hour with some rates locally exceeding 5” per hour at 
times. This may lead to localized flash flooding concerns over the
next few hours, especially where storms are slow to clear an 
area. Rain amounts with this line have been spotty but beneficial 
nonetheless. Some locations have seen nearly 4” of rainfall 
(eastern Pawnee county) as estimated from radar over the last 6 
hours but there are locations that have only seen 0.25” Expect 
the spotty nature of locally heavy rainfall to continue through 
the remainder of the afternoon and early evening as this line 
passes. NW AR will likely see some additional activity late this 
afternoon and evening as the gust front and line of storms pushes 
eastward. There is some uncertainty with this as the current line 
of storms may lose steam and dissipate with the loss of peak 
heating. This aspect, will need to be watched but regardless, at 
least spotty activity is expected to continue across NW AR this 
afternoon and evening. 

By midnight, the vast majority of activity will have likely 
diminished. A lack of a decent low level jet will likely keep the 
majority of activity at bay. With that said, there appears to be 
marginal amounts of theta-e advection (closer to sunrise mainly) 
which may be enough to trigger some shower and storm activity. 
PWATs will remain elevated (in excess of 1.5” possibly closer to
2”) through the night. Any activity that does develop will 
still feature the threat for heavy to very heavy rainfall rates 
with some rates briefly approaching 3” per hour at times. 

Friday will see an upper low across the four corners region 
beginning its trek toward eject the central plains as it 
transitions to become a more open wave. As the wave approaches the
region, so will better lift. This wave will also help to 
(initially) slowly push the cold front further into NE OK where it
will stall once again. In terms of precipitation chances, that 
will likely depend on what happens with this afternoon’s storm 
complex. Subsidence in the wake of the MCS will likely prevail 
thus the reasoning for mostly dry weather or perhaps a lull may be
the better term for much of the overnight and into tomorrow 
morning. Expect scattered to numerous showers and thunderstorms 
tomorrow afternoon across mainly the eastern half of the area 
where richer moisture characterized by higher PWAT values will 
reside. Synoptic lift will also start moving into the area as the 
aforementioned wave pushes into the region. With elevated PWAT 
values, locally heavy to very heavy rainfall rates will again be 
possible mainly over the eastern half of the area. Rates near 3”
per hour will be possible. Some strong storms will be possible 
though the lack of upper level support will really preclude the 
strong to severe storm risk. With that said, some gusty winds will
be possible. 

Friday night into Saturday will see the area within the warm 
conveyor region ahead of the upper low/opening wave ejecting onto 
the plains. A surge in PWATs and theta-e are noted ahead of the 
cold front during the overnight Friday. This will likely lead to 
warm advection showers and storms along with development of 
activity along the cold front that will finally get a push from 
the upper wave. The afternoon bears watching with the possible 
development of a triple point. If storms can fire ahead of the 
dryline (somewhere over central to eastern OK by the afternoon), 
there is enough shear through the atmospheric column that a severe
weather threat would be supported. Showers and storms will 
continue to push eastward through Saturday evening and overnight 
along with the cold front and upper wave. 

Sunday will largely be a dry day for most as Nwly flow aloft 
moves into the area effectively drying the atmospheric column, 
though some diurnal showers and isolated storms will linger across
the far eastern part of the area, mainly across northwestern 
Arkansas where some slightly elevated PWAT values will continue 
though not nearly to the extent that has or will be seen. 

Monday through the end of the upcoming week will see the system 
that moves through move to our east before cutting off. This upper
low will become trapped under a mid level ridge with the polar 
jet well to north (highly unusual for this time of year) in Canada
and with the low likely meandering around the eastern half of the
country mainly within the southeastern US. All of the models are 
showing a retrograding aspect to the upper low but exactly how far
west it may move is still in question. The GFS is by far the most
aggressive with the low retrograding all the way back into our 
area which would bring much cooler and wetter weather than the 
current forecast suggests. The ECMWF and Canadian keep the low 
well to our east largely keeping the area dry with slightly above 
normal temperatures. This pattern leads to very high uncertainty 
thus the forecast confidence past Monday begins to really drop 
off. 

Snider

&&

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

$$


AVIATION.....12