Severe Storm Outlook Narrative (AC)
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000
ACUS01 KWNS 251259
SWODY1
SPC AC 251257

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0757 AM CDT Thu May 25 2017

Valid 251300Z - 261200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL
HIGH PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
CENTRAL ROCKIES TO CENTRAL PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
MID-ATLANTIC STATES...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS SOUTH
FLORIDA...

...SUMMARY...
Severe thunderstorms will be possible this afternoon into tonight
across the central High Plains, while other isolated strong to
severe thunderstorms will be possible today across portions of the
mid-Atlantic region and south Florida.

...Central High Plains...
An upper low will continue to move eastward over the northern Plains
and nearby Canadian prairies while a trailing shortwave trough digs
southward over the northern intermountain region and parts of the
Great Basin. This scenario will lead to height falls and a general
strengthening of mid-level westerlies from the Rockies into the
north-central High Plains. While low-level moisture will be somewhat
lacking (surface dewpoints 40s to lower 50s F), lee-side
cyclogenesis and a sharpening lee trough will contribute to an
increase in low-level upslope flow and a gradual moistening through
the afternoon and evening into the central High Plains.

It is likely that initial storm development will occur this
afternoon across parts of northern CO/southern WY and subsequently
increase and spread east-southeastward into the high plains of
northeast CO/western NE. Adequate moisture and deep-layer shear in
the presence of steep lapse rates will support a few supercells
capable of large hail, with some severe-caliber winds a possibility
as well, particularly as storms potentially grow upscale as they
spread southeastward into far southwest NE and northwest KS (and
possibly even north-central KS) through the late afternoon and
evening hours.

...Mid-Atlantic States...
Relatively low-topped thunderstorms should redevelop across the
region by late morning into afternoon in close proximity to a
secondary vort max and upper cold pocket as low/mid-level lapse
rates gradually steepen. While overall buoyancy will be relatively
weak across the region, deep-layer/low-level shear will be adequate
to support some severe storms capable of hail, wind, and perhaps a
brief tornado. Any supercell/tornado risk would appear to be
semi-focused mainly across the Delmarva vicinity toward southeast
PA/southern NJ in vicinity of a surface low and warm front.

...Florida...
Thunderstorms have gradually redeveloped overnight into the early
morning hours across the southern FL peninsula to the south of a
southward moving cold front. Gradual subsidence including some level
warming will overspread the peninsula by afternoon. However, diurnal
destabilization within a residually most air mass (surface dewpoints
near 70), in the presence of strong unidirectional southwesterly
winds, could yield a few strong to locally severe storms capable of
stronger wind gusts and possibly even a waterspout/brief tornado
this morning into the afternoon. The 12Z observed sounding from
Miami was very much supportive of at least some severe risk,
featuring a very moist air mass with around a 2 inch precipitable
water value and mean mixing ratio near 17.6 g/kg, which contributed
to 2300+ J/kg MLCAPE in the presence of 45+ kt effective shear. For
additional short-term details, see Mesoscale Discussion 838.

..Guyer/Jewell.. 05/25/2017

$$



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