Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 241925
SWODY1
SPC AC 241923

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0223 PM CDT Mon Jul 24 2017

Valid 242000Z - 251200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
EASTERN PA...MD...SOUTHERN NJ AND VICINITY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FOR EASTERN SD AND NORTHERN NE...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON FOR WESTERN ND...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FOR A SMALL PART OF SOUTH CENTRAL MT...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FOR WESTERN NV INTO SOUTHERN OR...

...SUMMARY...
Isolated severe storms may occur across parts of the Northeast
States into this evening, the western Great Basin late afternoon
into early evening, and the northern Great Plains this evening into
tonight.

...Synopsis...
The forecast areas in the Northeast and the Great Basin remain
largely unchanged from the previous outlook, aside from minor
adjustments to the Northeast area for movement of ongoing
convection.

...Northern Plains areas...
A remnant shortwave trough/MCV will continue moving eastward along
the SD/ND border through this evening.  The stronger destabilization
is occurring along the southern flank of the MCV in SD, where
isolated strong thunderstorm development is more probable this
afternoon.  A separate area of convection is possible late this
afternoon across western ND along a surface cold front and
pre-frontal trough.  There will be a narrow window for marginally
severe hail/wind, before convective inhibition strengthens late this
evening.

..Thompson.. 07/24/2017

.PREV DISCUSSION... /ISSUED 1126 AM CDT Mon Jul 24 2017/

...Northeast...
Scattered showers along a cold front across western NY/PA will
intensify this afternoon with moderate downstream diabatic heating
amid broken cloud cover. Deep-layer speed shear with 30-40 kt
effective values will favor semi-elongated straight-line hodographs
and a few rotating/splitting updrafts. Area 12Z RAOBs sampled poor
700-500 mb lapse rates of 5.0-5.5 degree C/km which will limit
updraft acceleration. Primary hazard should be localized strong
winds producing tree damage. However, a brief tornado is also
possible, particularly in the vicinity of eastern PA and adjacent
states from 21-02Z as storms along the cold front impinge on a
quasi-stationary front.

...Western Great Basin...
A nearly stationary mid-level low will remain anchored along the
northern CA coast. A belt of enhanced upper-level southerlies will
be prevalent downstream over the Sierra Nevada mountains across the
western Great Basin. With inverted-v thermodynamic profiles at peak
heating, 20-25 kt effective shear could foster a couple multicell
clusters producing isolated severe wind gusts.

...Northern Great Plains...
Isolated severe storms appear most likely to occur within three
regimes. The first is along a cold front from southwest to
north-central ND around 23-02Z. Here, MLCIN should become minimized
at peak heating. In conjunction with the leading edge of weak
mid-level height falls and strengthening mid/upper-level westerlies,
isolated to widely scattered storms should form. A couple high-based
supercells may evolve with a risk for severe wind/hail. Inhibition
should rapidly increase after sunset and spatiotemporally confine
the risk.

The second regime may occur along a surface trough expected to lie
across central SD into western NE. Hot temperatures along it will be
necessary to minimize MLCIN and a couple storms may form within the
very steep lapse rate environment, yielding a risk for severe
wind/hail. Tonight, a strengthening low-level jet should foster an
area of elevated storms towards the west-central MN vicinity. While
mid-level lapse rates will be steep, modest cloud-bearing shear
should support a cluster mode and limit severe hail magnitudes.

A third regime may occur with widely scattered storms developing
over the Absaroka Range in southern MT. Inverted-v thermodynamic
profiles and moderate speed shear through the cloud-bearing layer
could yield a multicell cluster in the 23-03Z time frame, with a
risk for isolated severe wind gusts.

$$



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