SPC MD 1684


MD 1684 Image

Mesoscale Discussion 1684
NWS Storm Prediction Center Norman OK
0148 PM CST Sat Dec 01 2018

Areas affected...Western Illinois into southern and central Illinois

Concerning...Severe potential...Watch possible 

Valid 011948Z - 012145Z

Probability of Watch Issuance...60 percent

SUMMARY...The severe threat is increasing through the afternoon with
a threat for hail, damaging winds, and a few tornadoes. A watch is
being considered.

DISCUSSION...A cluster of cumulus in far eastern Missouri has
deepened over the past hour. Radar trends and latest HRRR guidance
suggest this is the start of surface based convection that is
expected to track across the western 2/3rds of Illinois this
afternoon/evening. The atmosphere will likely need a bit more
surface heating/moisture advection before a greater severe weather
threat materializes. Therefore, expect convection to become more
widespread with higher severe weather potential after 21Z.
Currently, MLCAPE values are around 500 J/kg and are expected to
increase to around 1000 J/kg in the next hour or two. Given this
instability with deep layer shear around 35 to 40 knots, expect
supercells to be the primary storm mode. Surface winds will likely
remain backed across this area as a weak surface low, currently
analyzed in northeast Missouri tracks east northeastward along the
warm front. Therefore, given the storm mode and the low-level shear
profile (0-1 SRH ~ 150-200 J/kg), there will be a tornado threat
with the strongest storms. Therefore, a watch is being considered.

..Bentley/Hart.. 12/01/2018

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


LAT...LON   39799164 40229139 40499091 40809024 40848961 40608911
            40198889 39568870 39008861 38818862 38528877 38338920
            38168966 38189009 39299115 39799164 

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