Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 241957
SWODY1
SPC AC 241955

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0255 PM CDT Thu May 24 2018

Valid 242000Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE GREAT PLAINS AND UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Isolated to scattered strong to severe thunderstorms are expected
across the Great Plains and upper Mississippi Valley this afternoon
and evening.

...DISCUSSION...
Several changes have been made to the outlook for this issuance. The
first change is to extend the slight risk westward into eastern
Colorado where thunderstorms are currently developing. This
convection is expected to have a severe threat as it moves eastward
into increasing instability later this afternoon. The second change
to the outlook is to expand the slight risk area westward across
parts of northern Nebraska and east-central South Dakota. A maximum
of instability is analyzed by the Rap to the southeast of Pierre, SD
where a severe threat would be possible if storms can develop. The
third change to the outlook is to adjust the thunder line further
north across the mid Mississippi Valley where convection is ongoing
in northeast Arkansas.

..Broyles.. 05/24/2018

.PREV DISCUSSION... /ISSUED 1142 AM CDT Thu May 24 2018/

Models are rather inconsistent today regarding location/timing and
intensity of convection later today.  This leads to a relatively
low-confidence outlook.  Nevertheless, a few changes have been made
to the MRGL/SLGT areas based on 12z CAM consensus.

...ND/SD/MN this afternoon/evening...
Water vapor loop shows a strong upper trough rotating northward
across MT/ND into Manitoba.  Most of the lift associated with this
system will move into Canada by this afternoon, but some potential
for organized severe storms will be present across parts of
northern/northeastern ND and eastern SD.  Those storms that form
along a weak surface boundary/dryline will be in an environment of
at least moderate CAPE and sufficient vertical shear for
bow/supercell structures.  Large hail and damaging winds will be
possible in the strongest cells.  This activity should spread
eastward across MN through the evening.

...NE/KS...
Strong heating will yield steep lapse rates and minimal cap this
afternoon over parts of central NE into central KS.  Forecast
soundings suggest a very unstable air mass is also likely, with
sufficient mid/upper level flow for some convective organization.
The main forecast uncertainty is the extent of convective
development.  About half of the morning CAM solutions suggest storms
will form over north-central NE.  If this occurs, damaging winds and
hail would be possible.  A more consistent convective signal is
apparent over far eastern CO into western KS, where parameters
appear favorable for damaging wind gusts.

...West TX/Southeast NM...
Once again today, a few thunderstorms are expected to form in the
hot/unstable air mass in place across southeast NM and west TX.
Shear profiles are a little weaker than yesterday and upper forcing
is minimal.  Nevertheless, a few storms could produce hail and gusty
winds.

...NV...
A large upper trough is digging into CA, with height falls expected
to commence along the Sierra later today.  A cluster of
thunderstorms is forecast to develop over northwest NV, spreading
northward into southern OR tonight.  Forecast soundings show
inverted-v profiles and sufficient steering flow for some risk of
gusty/damaging wind.

...MN/northern WI/western Upper MI...
A decaying cluster of thunderstorms over northern WI will leave a
remnant outflow boundary, possibly focusing redevelopment of storms
later today.  If so, the strongest cells could produce hail and
gusty winds.

$$



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