Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS11 KWNS 290904
SPC MCD 290904
Mesoscale Discussion 0589
NWS Storm Prediction Center Norman OK
0404 AM CDT Sat Apr 29 2017
Areas affected...Portions of southeast CO...extreme southwest
KS...the western OK Panhandle...the extreme northwest TX
Panhandle...extreme northeast NM
Valid 290904Z - 291500Z
SUMMARY...A long-duration period of heavy snow will affect portions
of the central/southern High Plains through the day, with peak
snowfall rates (up to 2 inches per hour) through 15Z. Snowfall rates
around 1 inch per hour will likely persist into the afternoon.
DISCUSSION...Recent water vapor imagery suggests a midlevel
deformation zone becoming increasingly defined from the central High
Plains to the CO Rockies Front Range. Related mid-level
frontogenesis is enhancing precipitation rates from southeast CO to
southwest KS, where deep subfreezing profiles, and ample ascent
through saturated dendritic growth zones, are supporting moderate to
locally heavy snow. Through 15Z, convectively generated
precipitation within an extensive warm conveyor, from the southern
Rockies to the central Great Plains, will likely glance the area.
This should support an increase in snowfall rates -- reaching 1-2
inches per hour. The highest of these snowfall rates is expected to
affect the CO Front Range and immediately adjacent High Plains,
where some upslope-flow component will exist.
Farther south, rain will transition to snow from north to south, in
response to cold advection. Likewise, the area of heavy snow will
also have a tendency of extending southward into portions of the
western OK Panhandle, the northwestern TX Panhandle, and northeast
NM through the morning. This will occur as a steady plume of
mid-level isentropic ascent enhances precipitation generation atop
the low-level cold advection. Snowfall rates around 1.0 inch to
locally 1.5 inches per hour will be likely in these areas through
the morning hours.
By early to mid afternoon, there will be an overall tendency for
snowfall rates to lessen, as stronger frontogenetic ascent advances
east of the area. Snowfall rates locally reaching 1 inch per hour
will likely continue, however, as elevated warm advection coincides
with saturated dendritic growth zones. Needless to say, this will be
a long-duration heavy snow event, with the potential for embedded
mesoscale, terrain-driven enhanced ascent to bolster snow rates
through the afternoon.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 37420518 38430499 38300250 37550146 36720166 36280306
36360406 36750477 37420518