Area Forecast Discussion
Issued by NWS Tulsa, OK

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FXUS64 KTSA 261159

Area Forecast Discussion
National Weather Service Tulsa OK
659 AM CDT Sun Mar 26 2017

Patchy fog has developed this morning as MVFR deck cleared the
terminals. Several terminals have had vsby bouncing around between
MVFR and LIFR/VLIFR. Fog should mix out by 14Z this morning. Focus
then turns towards an upper level system that will advance a line
of thunderstorms across Oklahoma this afternoon and evening. Hi-
res models have this convective line developing over central
Oklahoma between 21-22Z and moves the line eastward to impact the
terminals between a 00-04Z timeframe. Low-pressure center will
then slide across southern Kansas and northern Oklahoma and will
produce scattered showers and thunderstorms as it moves through.
Convective line should clear the area between 06-09Z according to
latest model runs.


.PREV DISCUSSION... /Issued 341 AM CDT Sun Mar 26 2017/


The main forecast concern will be severe weather potential late
this afternoon and into the evening. Other items of interest will
be heavy rainfall and severe potential with the next storm system
toward the middle of the week, and another round of possible rain
and storms by next weekend.

The active pattern over the southern tier of states is well
underway. The first system has lifted off to the northeast, and
all that remains of this system is some low cloud over the far
north and east. This low cloud should gradually erode with a
partly to mostly sunny and warmer day forthcoming with highs in
the 70s.

The next system of interest is moving across the southern Rockies
attm, and will be well timed as it emerges in the Plains during
peak heating this afternoon. At the surface, low pressure over
northeast NM should strengthen and slide east into western OK by
this afternoon. A dryline will arc to the south and east of the
low across central OK and down into central TX. Given favorable
upper support during peak heating, storms should fire along the OK
and north central TX portion of the dryline by mid afternoon.
Given more than sufficient deep layer shear and a more
perpendicular orientation of the shear vector to the dryline,
especially across the south central OK and north central TX
portion, discrete supercells look likely. This discrete cell mode
should last till about 27/03Z before a transition toward a more
multicellular mode occurs. The 26/03Z run of the HRRRX shows
several updraft helicity tracks across south central OK and north
central TX. The main question for our area of responsibility in
eastern OK will be how long into the evening that these discrete
cells can remain rooted close to the surface, and that hinges on
how far north the warm front lifts up into our area. After
perusing model sounding data from the NAM and GFS, as well as data
from the HRRRX, it appears a zone from around Okemah to McAlester
to Hugo stands the greatest chance for near surface based
supercells between 00Z and 03Z, and thus the greatest tornado
potential. Since the LLJ also picks up during this window of time,
a strong tornado can not be ruled out. Any supercell that remains
discrete into our area will have the potential to produce very
large hail as well. Once the transition towards more multicellular
clusters or lines occurs, the threat will trend more toward
damaging winds. Storms should weaken as they head into western AR
tonight, as they move east of the narrow theta-e axis. Other
storms are likely to form underneath the upper cold core as it
slides across southern KS and farther northern OK tonight. Since
instability will be less here than farther south, a marginally
severe hail and wind threat will accompany these storms. The
severe threat will likely be over sometime in the midnight to 3 AM

Yet another storm system is expected to affect our area toward the
middle of the week in this active pattern. The GFS and ECMWF both
develop a deep mid level closed low over the Southwest Tuesday,
and track it east across the central/southern Plains Wednesday and
Thursday. The rains should begin Tuesday night with the greatest
severe weather threat Wednesday afternoon and evening as the upper
low emerges into the Plains, much like yesterday`s system. Pockets
of heavy rainfall are possible as well.

What appears to be the last in a series of storm systems to affect
our area in this active pattern will arrive sometime next weekend.
Another round of rain, storms and severe weather potential can be
expected. However, the details with this system vary greatly
between the GFS and ECMWF at this time, thus I have gone with a
conservative PoP forecast for now.



TUL   73  55  69  46 /  40  70  10   0
FSM   77  59  72  49 /  10  80  30   0
MLC   77  58  72  49 /  30  70  10   0
BVO   71  52  67  43 /  30  80  10   0
FYV   71  56  62  46 /  10  80  50   0
BYV   70  57  64  47 /  10  80  60   0
MKO   75  57  69  48 /  20  70  10   0
MIO   70  54  64  46 /  10  80  30   0
F10   75  56  71  48 /  40  70  10   0
HHW   79  60  75  52 /  10  70  10   0




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