Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 261953
SWODY1
SPC AC 261952

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0252 PM CDT Sat May 26 2018

Valid 262000Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS AND SOUTH FLORIDA...

...SUMMARY...
A severe threat with isolated large hail and wind damage will be
possible across parts of the northern high Plains late this
afternoon into the evening. A threat for tornadoes will also be
possible in parts of south Florida late tonight.

...DISCUSSION...
The only change to the outlook is to add a 5 percent tornado and
slight risk area to parts of south Florida. The HRRR suggests that
rotating storms will move inland across south Florida after
midnight. RAP forecast soundings increase low-level shear throughout
the night. Forecast hodographs suggest that a tornado threat will be
possible with semi-discrete rotating cells that move inland in the
06Z to 12Z timeframe.

..Broyles.. 05/26/2018

.PREV DISCUSSION... /ISSUED 1114 AM CDT Sat May 26 2018/

...ID/MT/ND...
A large upper low over CA continues to drift northeastward, with
strengthening mid level winds and large-scale ascent moving into the
northern Rockies.  Strong heating is occurring over much of ID/MT,
with thunderstorms expected to form over the higher terrain by
mid-afternoon.  These initial storms will pose a threat of locally
gusty winds and hail.  During the evening, more intense and
organized storms are expected to form over parts of central/eastern
MT, tracking into western ND tonight.  The combination of a deep,
mixed boundary-layer, sufficient CAPE, and relatively strong
vertical shear profiles support the risk of a few high-based
supercells capable of large hail and damaging winds.  The activity
may organize into bowing structures as they move east tonight.

...FL...
Low-level wind profiles around the northeast quadrant of Alberto are
slowly strengthening, with CAM guidance suggesting shear sufficient
for rotating cells by later this afternoon along and off the coast
of southwest FL.  Most model guidance keeps the bulk of the cellular
convection and stronger wind fields offshore, but there is a MRGL
chance of an isolated tornado in vicinity of the southwest coast
through tonight.

...WI/MI...
No changes to forecast have been made to this area.  Scattered
thunderstorms are expected to form this afternoon over parts of WI
and MI as an upper trough over MN approaches the region.  The
strongest cells will be capable of gusty winds and hail, but
coverage/organization is expected to be low.

...MO/IL...
Clusters of strong/severe afternoon thunderstorms may form today
over parts of northern MO and central IL.  Strong instability is
forecast for this area, with MLCAPE values over 3000 J/kg and steep
low-level lapse rates.  Shear will be relatively weak, promoting
multicell storm structures with occasional gusty/damaging winds and
hail.

...Central New England...
A weak surface front extends from northeast NY across parts of VT/NH
today.  Scattered thunderstorms are expected to form along this
boundary later today, tracking toward the coast by evening.
Instability is rather weak, but strong winds aloft, fast storm
motions, and steep low-level lapse rates will promote a risk of
gusty winds in the strongest cells.

$$



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