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Severe WX Severe Weather Threat 5/16-5/19, 2017

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Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Wed May 17 2017



...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM NORTHWEST
OK INTO SOUTHWEST KS...

Severe thunderstorms are expected across portions of the southern
and central Plains on Thursday and Thursday night. Very large hail,
damaging winds and tornadoes, some strong, will all be possible.

...Synopsis...
The western upper low will pivot eastward on Thursday, swinging a
negatively tilted trough into the Plains by evening. Strong
south/southeasterly low-level flow will bring rich boundary layer
moisture westward across the TX/OK/KS, where dewpoints in the mid to
upper 60s are likely along a sharpening dryline from southwest KS
into the TX Panhandle and west-central TX. Additionally, a warm
front will advance northward across KS as a surface low develops in
the vicinity of the OK/TX Panhandle. Strong heating along the
dryline/surface low vicinity will result in vigorous thunderstorm
development as upper forcing for ascent increases after 21z. During
the late evening into the overnight hours, upscale growth is
expected and bowing segments will surge east across KS/OK.
..Southern/Central Plains...

Rich Gulf moisture will surge westward in strong warm advection
regime on 30-40 kt southeasterly 850mb flow. Surface dewpoints are
forecast to range from around 64-69 F across the warm sector. As the
surface low develops in the vicinity of the OK/TX Panhandles, the
dryline will sharpen and strong heating will result in SBCAPE
exceeding 3000 J/kg. This strong instability, coupled with very
steep lapse rates around 8 deg C/km will result in vigorous
thunderstorm development in the vicinity of southwest KS to
southwest OK. Impressive deep shear profiles will favor discrete,
possibly long-lived supercells capable of very large hail.
Additionally, strong, vertically veering low-level winds will result
in large, curved hodographs indicative of strong tornado potential,
especially across the moderate risk area. By late evening into the
overnight hours, upscale growth is expected and one or more bows are
expected to track east across KS/OK, with an attendant strong wind
threat.
 


Text is messed up due an issue we are having with our theme. Here is what it says.

"DOW8s view of the Elk City tornado courtesy Tim Marshall/Karen Kosiba yesterday. Incredible data!""
 
 
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Strong long-track tornadoes will be likely from parts of central and southern Kansas southward into western Oklahoma.
...Tornado Outbreak Likely Across Parts of the Southern and Central
Plains Today and Tonight...
...Southern and Central Plains...
An upper-level low will move eastward across the Four Corners region
and central Rockies today as a lead shortwave rotates around the
southeastern side of the system into the southern and central
Plains. At the surface, a very moist airmass will advect northward
across Oklahoma into southern and central Kansas with surface
dewpoints reaching the mid 60s to lower 70s by afternoon. Strong
instability should be in place to the east of a well-developed
dryline situated from just east of Dodge City southward across far
western Oklahoma by mid-afternoon. Thunderstorms are forecast to
initiate rapidly during the mid to late afternoon along the dryline
with numerous severe thunderstorms moving east-northeastward across
the southern and central Plains during the late afternoon and early
evening. A very moist airmass, strongly unstable warm sector,
favorable deep-layer shear and impressive low-level shear appears
likely for a tornado outbreak from central and southern Kansas
southward across western Oklahoma.

At this time, surface maps show a very moist airmass across the
eastern third of Texas with lower to mid 70s F dewpoints at most
observation sites. This airmass is advecting northward quickly and
appears certain to overspread the moderate and high risk areas by
this afternoon. Deterministic and hi-res solutions suggest that a
strongly unstable airmass will be in place by afternoon with MLCAPE
values reaching the 3000 to 4000 J/kg range. In addition, the exit
region of a 45 to 60 kt mid-level jet is forecast to be located
across northwest Oklahoma and south-central Kansas by late afternoon
which will create strong deep-layer shear profiles over the top of a
pristine airmass. NAM forecast soundings late this afternoon show
0-6 km shear in the 50 to 60 kt range to the east of the dryline
with gradually veering winds with height in the low to mid-levels.
This wind profile will support discrete supercell formation. Backed
surface winds to the southeast, strong speed shear in the boundary
layer and a strengthening 40 to 50 kt low-level jet will be very
favorable for tornadoes. Low-level shear is forecast to increase
during the early evening with 0-3 km storm-relative helicities
reaching the 350 to 450 m2/s2 range across the moderate and high
risk areas. This will be favorable for strong tornadoes with several
long track tornadoes moving across the high risk and moderate risk
areas. High-end tornadoes will also be possible across the high risk
area. Forecast soundings also show very steep 700 to 500 mb lapse
rates of 8.0 C/km. This combined with the strong deep-layer shear
will make large hail likely with supercells. The more intense
supercells will likely produce hailstones of greater than 2 inches
in diameter. By late evening, MCS formation should take place as
several severe storm clusters move eastward across northern Oklahoma
and eastern Kansas. Some tornadoes along with large hail and wind
damage should be associated with this MCS.
 
Yeah, I don't see any real obvious potential hangups with this one like there have been with the others this year. Worried this is gonna verify.
 
12Z HRRR really makes the storms seem a lot more clustered, although it's very inconsistent from run-to-run. If there is a Forecasted Convective Amplification Deficiency factor today, it's the storm coverage and mode.
 
warneagle said:
Yeah, I don't see any real obvious potential hangups with this one like there have been with the others this year. Worried this is gonna verify.
Click to expand...
Well, I take that back. My concern would be that it might get messy quickly rather than staying discrete. We'll see.
 
The SPC is maintaining a small voice of caution with this setup. In their latest SWODY1 they state,
"Initiation of too many cells in early/middle afternoon (before warm-sector hodographs and
CAPE each are biggest), and/or too close to each other at once, is possible in some parts of the current moderate/high risks."

So, there are concerns re convection timing. But notice they say, "in some parts" of the watch area, & it is a relatively large coverage area for possible severe weather today. From a chaser's perspective it will be a hit or miss gamble. As it often is.
 
Brett doesn't seem happy... I think he has a case.
 
Brett absolutely has a case.
 
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