MD 0519 CONCERNING SEVERE POTENTIAL…WATCH LIKELY FOR PARTS OF SERN NE…SWRN IA…NWRN MO…N CNTRL/NERN KS
Mesoscale Discussion 0519
NWS Storm Prediction Center Norman OK
0229 PM CDT Wed Apr 19 2017
Areas affected...Parts of sern NE...swrn IA...nwrn MO...n cntrl/nern
KS
Concerning...Severe potential...Watch likely
Valid 191929Z - 192200Z
Probability of Watch Issuance...95 percent
SUMMARY...Thunderstorm development with increasing severe weather
potential is expected by late afternoon. At least a couple of
severe weather watches are likely to be issued across the region by
21Z.
DISCUSSION...A cyclonic mid/upper jet streak (including 50+ kt at
500 mb) is in the process of nosing through the central Plains and
mid Missouri Valley region. Strongest forcing for ascent in the
exit region of this feature likely will remain focused well to the
cool side of a fairly sharp surface frontal zone, along which a
modest surface cyclone is now beginning to migrate east northeast of
the central Nebraska/Kansas border area. At the same time, the nose
of a plume of warm and capping elevated mixed layer air is wrapping
into the mid Missouri Valley region, across much of the warm/moist
sector of the surface low, and northward to the cool side of the
front ahead of the low.
However, latest model output, including the Rapid Refresh, suggests
that the leading edge of lower/mid tropospheric cooling is now
roughly near/east of the Grand Island NE through Russell KS. As
this continues to spread east northeastward this afternoon, guidance
indicates that it may provide the focus for increasing thunderstorm
development by 21-23Z, from near the surface low southward along the
dryline (as it is overtaken by the southward advancing cold front)
into parts of central Kansas.
In the presence of thermodynamic profiles characterized by very
steep mid-level lapse rates and mixed layer CAPE on the order of
1500-2000 J/kg, deep layer shear appears more than sufficient for
supercells. Near a 40 kt southerly 850 mb jet, sizable clockwise
curved low-level hodographs will contribute to a risk for tornadoes.
The extent of the tornado threat remains a bit uncertain due to an
expected tendency for fairly deep boundary layer mixing and some
drying within the warm sector, and rather cool/stable air to the
north of the front. Any tornadic potential may tend to be maximized
within a rather narrow corridor along and to the north of the warm
front, just ahead of the surface low, across parts of southeastern
Nebraska into southwestern Iowa.
..Kerr/Thompson.. 04/19/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...DMX...EAX...FSD...OAX...TOP...ICT...GID...
LAT...LON 40649785 41199747 41869727 42439643 42439552 42159522
40939509 39139671 38679899 39309897 39779839 40649785
from SPC Mesoscale Discussions http://bit.ly/1IhsOfu
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