Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0234 PM CDT Fri Mar 21 2025
Valid 212000Z - 221200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Severe thunderstorms are not forecast through tonight.
...20Z Update...
Prior forecast remains largely intact. Only change is to trim the
thunder area over southeast SD/far southwest MN in the wake/north of
the passing mid-level shortwave impulse in eastern NE.
..Grams.. 03/21/2025
.PREV DISCUSSION... /ISSUED 1124 AM CDT Fri Mar 21 2025/
...Iowa Vicinity...
An upper shortwave trough will move across the Midwest today and
tonight, with increasing deep-layer west/northwest flow associated
with this feature overspreading the region. Boundary layer moisture
will remain scant ahead of an east/southeast moving cold front
sweeping across the Lower MO/Mid-MS Valley this afternoon and
evening. Nevertheless, very cold temperatures aloft (near -25 C at
500 mb, as sampled by 12z regional balloon observations), will
support steep midlevel lapse rates. Additionally, surface heating
into the mid 50s to low 60s will support steepening low-level lapse
rates. These steep lapse rates amid cold temperatures aloft should
be sufficient for SBCAPE values up to 300 J/kg. As such, isolated
high-based, low-topped thunderstorms are expected this afternoon and
evening from the Mid-MO Valley into the Mid-MS Valley. Given the dry
boundary layer and near 30-40 kt flow between 850-700 mb, convection
may locally enhance already gusty surface winds, and a few stronger
gusts near 40-45 kt may occur, especially across southeast Iowa into
northwest IL. A couple instances of small hail/graupel also could
accompany this activity.
...Pacific Northwest/Northern Rockies...
An upper shortwave trough will move across the region tonight.
Cooling aloft will support steepening lapse rates and sufficient
destabilization to support isolated lightning flashes.
Read more CHECK UPDATE ZOOM GRAPHIC
http://dlvr.it/TJgnXy
