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SPC Day 3 Outlook
Day 1 Day 2 Day 3 Day 4-8
SPC Day 3 Outlook Categorical
Categorical
Probabilistic
000
ACUS03 KWNS 150728
SWODY3
SPC AC 150727

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0227 AM CDT Tue May 15 2018

Valid 171200Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THURSDAY
AFTERNOON AND EVENING ACROSS PARTS OF NORTHEASTERN
COLORADO...EASTERN WYOMING ...WESTERN AND CENTRAL SOUTH DAKOTA AND
NEBRASKA...

...SUMMARY...
Severe storms are possible Thursday afternoon and evening across
parts of Front Range of the Rockies and Black Hills into the
adjacent High Plains.

...Synopsis...
Westerlies emanating from the Pacific will remain split through this
period and beyond, as blocking persists near the Pacific coast.
This likely will include an increasingly prominent high centered
near the British Columbia coast.  Within the southern branch of this
regime, fairly broad, somewhat amplified troughing is generally
forecast to slowly progress through the Great Basin and Southwest.
Sharp downstream ridging likely will linger across the central and
southern Plains, although some suppression of this feature is
possible east of the Front Range of the Rockies and Black Hills.
Farther east, elongated troughing, in phase with troughing in the
subtropical westerlies, is expected to persist east of the lower
Mississippi Valley into the Caribbean.  Seasonably high moisture
content will generally remain focused within a broad plume east of
this latter feature, wrapping around the western periphery of
western Atlantic subtropical ridging, which may continue to build
northwestward into portions of the Mid Atlantic.  However, at least
modest moisture levels appear likely to be maintained in
southeasterly low-level flow across parts of the central Plains into
the Front Range of the Rockies and Black Hills region.

...Front Range/Black Hills and adjacent High Plains...
The maintenance of low-level moisture on southeasterly flow into lee
surface troughing appears likely to contribute to moderately large
CAPE (around/perhaps in excess of 2000 J/kg) by Thursday afternoon,
in the presence of steep lower/mid tropospheric lapse rates.  The
various models appear similar indicating that low-level convergence
will become focused across the plains of northeast Colorado into
southwestern South Dakota, as a short wave impulse emerges from the
upstream southern branch trough during the late afternoon and
evening.  Associated forcing for ascent may aid initiation of
discrete storms off the Front Range and Black Hills, before activity
becomes more numerous and perhaps consolidates while spreading into
the plains by Thursday evening.

It is possible that the short wave may be accompanied by a 30+ kt
lower/mid-level speed maximum, which probably will provide
sufficient shear, given veering of winds with height in
lower/mid-levels, to support a few supercells initially.  An upscale
growing and organizing mesoscale convective system may not be out of
the question during the evening hours, before activity weakens in
waning instability Thursday night.

..Kerr.. 05/15/2018

$$

The Thunderstorm Outlook is created by the Storm Prediction Center in Norman, OK.
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