SPC MD 1692


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Mesoscale Discussion 1692
NWS Storm Prediction Center Norman OK
0314 PM CDT Fri Oct 06 2017

Areas affected...Portions of southeast Nebraska...southwest
Iowa...and far north central Kansas

Concerning...Severe potential...Watch possible 

Valid 062014Z - 062145Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms are expected to develop in the next 60-90
minutes in the vicinity of the frontal zone.  Severe hail and brief
gusty winds are the main threat.  A watch may be needed by 21-22z.

DISCUSSION...A mostly stationary frontal zone stretching from
northwest Kansas into west-central Iowa will be the focus for
thunderstorm development in the next 60-90 minutes.  The most likely
area for first initiation will be along the intersection of a weak
surface trough and a differential heating boundary stretching
between Concordia and Russell where GOES-16 1-min imagery shows
cumulus steadily deepening. Shortly after the first CI in
north-central Kansas, thunderstorms are expected to rapidly develop
along the front into southeast Nebraska and southwest Iowa.  

Although extensive cloud cover south of the front has persisted, a
very moist boundary layer and temperatures in the low 70s is still
contributing to MLCAPE values of 500-1000 J/kg over southwest Iowa,
and 1000-1500 J/kg over Nebraska and north-central Kansas. These
values could increase somewhat as a steady northeastward advancement
of the clearing should continue through the period. Deep-layer shear
profiles are favorable for organized storms, including a few line
segments and supercells capable of severe hail and brief severe wind
gusts. While the low clouds have limited the magnitude of the
low-level lapse rates -- and thus the potential for low-level
stretching and a brief tornado -- wind speeds in the 500-1000 m
layer are forecast to increase with time to produce fairly large
low-level hodograph curvature in the unstable air. Based on RAP/HRRR
model soundings, temperatures that warm into the upper 70s to near
80F could produce low-level lapse rates steep enough to increase the
tornado threat.  Otherwise, the severe threat will be mainly severe
hail and brief severe wind gusts with any of the organized storms. 
Given the above expected evolution of storms, a severe weather watch
may be needed in the next hour or two.

..Coniglio/Grams.. 10/06/2017

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   41159475 40469559 40209605 40039644 39679700 39439747
            39209795 39129822 39099840 39159851 39349850 39839836
            40329825 40879787 41229730 41569684 41869629 42119576
            42339517 42429455 42209436 41889441 41159475 

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