SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0255 PM CDT Wed Apr 20 2022
Valid 202000Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
EASTERN OKLAHOMA AND FAR SOUTHEASTERN KANSAS...
...SUMMARY...
The greatest severe-weather threat for today and this evening
appears to be over portions of central/eastern Oklahoma into the
western Ozarks region, where up to a few supercells with hail,
isolated severe gusts and a tornado are possible.
...20z update Central/Southern Plains...
Considerable uncertainty still remains on the potential for discrete
convective initiation along the dryline across portions of
central/eastern OK into southeastern KS this afternoon/evening.
Regional water vapor imagery shows a well-defined, compact vort max
moving across the southern Plains. Lift from this feature along with
strong heating along the dryline may support a few supercells late
this afternoon into this evening.
Deeper mixing has allowed the dryline to move slightly farther
eastward than depicted by most morning hi-res guidance. Visible
imagery trends and veering surface flow around the OKC metro suggest
the greater severe threat may develop across eastern OK. Area
RAP/HRRR soundings continue to show a favorable environment for
supercells, particularly along the triple point/warm front
stretching from far southeastern KS to eastern OK. Mid-level lapse
rates of 7-8 C/km and large hodographs will support a risk for large
to very large hail with any supercells able to become established.
Backed surface flow sheltered from stronger mixing beneath the
lingering stratus deck slowly eroding across eastern OK may also
support low-level mesocyclones capable of a tornado or two with the
more dominant storms should they develop this evening.
Th previous forecast remains valid with no changes for portions of
the Pacific Northwest.
..Lyons/Mosier.. 04/20/2022
.PREV DISCUSSION... /ISSUED 1117 AM CDT Wed Apr 20 2022/
...Eastern OK and Vicinity...
Water vapor imagery shows a shortwave trough moving into western KS.
Ahead of this trough, strong heating is occurring west of the
surface dryline over OK, helping to mix it eastward. By mid/late
afternoon, the dryline will extend from a low in southeast KS into
east-central OK, with a very moist/unstable air mass present in the
warm sector. A capping inversion is also evident in forecast
soundings and in the numerous wave clouds present in visible
satellite imagery.
The confidence/coverage of convective initiation remains the main
forecast problem today. 12z model guidance continues to show a
diversity of solutions, ranging from several storms along the
dryline from southeast KS into southern OK, to virtually no storms.
Forecast soundings along the dryline show considerable low-level and
deep-layer shear that would be favorable for discrete supercell
development capable of very large hail, damaging winds, and a
tornado or two. Soundings also show a persistent but weak cap.
Therefore, will maintain the ongoing MRGL/SLGT areas with no
changes. However, will add a 5% tornado risk area given the
conditional risk if a storm or two can form. The primary risk
should be in the 22-03z window, before diurnal cooling strengthens
inhibition again.
...Western OR...
A shortwave trough off the coast of southwest OR will rotate
northeastward later today and affect the Cascades and coastal areas.
12z CAM solutions suggest a rather compact system with a focused
low-level jet tracking northward across the region late this
afternoon and evening. Enhanced low-level shear/forcing may be
sufficient for a few rotating showers or thunderstorms capable of
gusty winds or a brief tornado spin-up. Instability will be quite
weak, and it is uncertain whether updrafts will be strong enough to
take advantage of the low-level wind fields.
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