SPC MD 1658


MD 1658 Image

Mesoscale Discussion 1658
NWS Storm Prediction Center Norman OK
0354 AM CST Sun Nov 25 2018

Areas affected...Central...north-central and northeast
KS...southeast NE...southwest IA...and northwest MO

Concerning...Heavy snow 

Valid 250954Z - 251600Z

SUMMARY...Snowfall rates up to 1-2 inches per hour will increase
from west to east during the late overnight through this morning. 
In addition to heavy snow, strengthening northerly winds through the
morning will produce a blizzard with reduced visibilities in
whiteout conditions.

DISCUSSION...Short-term guidance remains consistent with the
forecast for a vigorous shortwave trough, now located over eastern
CO, to emerge eastward across KS overnight, with deepening of this
system between 12-18Z as it reaches eastern KS/western MO by late
morning.  Trends in mosaic radar imagery showed a band of
precipitation had developed from north-central KS to southeast NE. 
This corridor in the northern part of the discussion area is
expected to be the first southwest-northeast oriented zone to change
to snow and increase in rates as surface temperatures fall through
the lower 30s to upper 20s F by 11-12Z.  This same trend with snow
developing across the rest of the discussion area after daybreak
from central to northeast KS and far northwest MO to southwest IA
will occur as the surface low shifts east-northeast into MO.  This
will allow low-level winds on its north-northwest periphery to back
to northerly and strengthen, ushering in colder temperatures, and
supporting a high likelihood for reduced visibilities in whiteout

Meanwhile, an increase in upward vertical motion through the
dendritic-growth zone per forecast soundings is expected as, 1) the
shortwave trough deepens with eastward progression and 2) within the
exit region of a strengthening 500-mb 100-kt jet spreading across
northeast KS/northwest MO this morning.  This factor which is
expected to become stronger by 15-18Z suggests snowfall rates could
be up to 2 inches per hour, generally north of a line from KSLN to
KSTJ to 25 S KLWD, while the initial aforementioned band of snow
could have rates up to 1 inch per hour.  Forecast soundings also
indicated weak elevated instability rooted around 600 mb, given the
likelihood of steepening midlevel lapse rates (around 8 C/km) in the
exit region of the midlevel jet.  This could enhance snowfall rates.

..Peters.. 11/25/2018

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


LAT...LON   41259537 41359315 41159252 40309380 39249539 38409689
            38239774 38379854 38699916 38909976 39289995 39479979
            40099877 40489775 40979632 41259537 

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