Convective Outlook

SPC 2000Z Day 1 Outlook
Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0300 PM CDT Mon Jun 26 2017

Valid 262000Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PART OF
NORTHERN AND CENTRAL KANSAS INTO A SMALL PART OF EASTERN COLORADO...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA IN THE CENTRAL TO SOUTHERN PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
PACIFIC NORTHWEST AND NORTHERN ROCKIES...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN
FL AND SOUTHEAST GA...

...SUMMARY...
Thunderstorms with severe hail and strong wind gusts are possible
late this afternoon into evening across the Pacific Northwest and
Northern Rockies in addition to parts of the Great Plains.  Other
strong storms may occur along the coastal southeast States.

...Eastern CO/southwest NE/northern and central KS...
Trends in visible satellite imagery and mosaic radar imagery showed
some increase in thunderstorm development across far southern NE
into northern KS and eastern CO.  Given the presence of moderate
instability and effective bulk shear of 30-40 kt, additional
organized storms appear a concern through the afternoon into the
evening.  Last several runs of the HRRR suggest a greater clustering
of storms may occur from northern KS to the south-southeast reaching
the Wichita, KS area this evening.  This outlook has increased the
severe hail and damaging wind probabilities resulting in a Slight
risk area in parts of KS to eastern CO.  For additional short-term
guidance, refer to mesoscale discussion 1152.

...Part of south-central WA...
Given ongoing convection and some thunderstorms developing in lee of
the southern WA Cascades, steep low-level lapse rates and DCAPE
exceeding 1000 J/kg suggest locally strong wind gusts will be
possible.  This outlook has expanded the marginal severe wind threat
westward some to include more of south-central WA.

..Peters.. 06/26/2017

.PREV DISCUSSION... /ISSUED 1144 AM CDT Mon Jun 26 2017/

...Pacific Northwest/northern Rockies...
Gradually strengthening westerlies aloft are expected over the
region today. This will be as an upper low just off the coast of
northern CA continues east-northeastward and a trough amplifies over
British Columbia, while a convectively related disturbance also
shifts eastward from southeast WA/northern ID into MT. It seems
likely that thunderstorms will increase this afternoon especially
east of the Cascades across central/eastern OR into adjacent
ID/southeast WA, in addition to parts of west-central MT.
Strengthening winds aloft/vertical shear will help support some
sustained east/northeastward-moving storms. Isolated instances of
locally damaging winds will be possible with the strongest storms
along with some hail, particularly across parts of OR into ID where
somewhat greater moisture/destabilization is expected. 

...Central Plains/southern High Plains...
Under the glancing influence of the Upper Midwest/Great Lakes
upper-level trough, isolated to widely scattered thunderstorms are
likely to develop by mid/late afternoon within a corridor from
southern NE southward into KS. Although mid-level lapse rates are
not particularly steep by late-June standards, gradually returning
moisture, moderate buoyancy, and supercell-favorable wind profiles
(in the presence of strong northwesterly flow aloft) should allow
for isolated severe thunderstorms capable of severe hail/locally
damaging winds as these storms spread southeastward through the late
afternoon and evening hours.

Elsewhere, as a moist upslope flow regime persists, other storms are
likely to develop/intensify across along the southeast CO/northeast
NM Raton Mesa vicinity and higher terrain of interior NM. In the
presence of moderate buoyancy and 30-35 kt of effective shear, some
of the stronger storms will be capable of hail.

Farther south, one or more remnant MCVs may refocus afternoon
redevelopment, including the possibility of a few stronger storms,
across parts of the TX Edwards Plateau and nearby Transpecos
vicinity.

...North FL/coastal GA...
As weak height falls spread toward the region today, a moist
environment and sea breeze circulations in vicinity of a
stalled/slow-moving front may allow for a few stronger storms this
afternoon capable of downbursts.

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Updated 26 June 2017 | 3:04 pm

SPC 1730Z Day 2 Outlook
Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1251 PM CDT Mon Jun 26 2017

Valid 271200Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND
SOUTHERN SOUTH DAKOTA THROUGH NEBRASKA TO FAR NORTHEAST COLORADO...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM YELLOWSTONE
N.P. AREA EASTWARD INTO THE NORTHERN PLAINS AND INTO PARTS OF THE
CENTRAL HIGH PLAINS...

...SUMMARY...
Areas of severe thunderstorms capable of large hail and damaging
winds are expected over much of central and western Nebraska as well
as South Dakota during the late afternoon and evening on Tuesday.
Isolated severe storms are also possible from eastern Colorado into
central Kansas, and from Yellowstone National Park into North
Dakota.

...Synopsis...
The northern branch of the western U.S. upper ridge will remain
progressive from today through Tuesday, as it shifts east through
the northern Great Plains and the Upper Midwest.  However, its
amplitude is expected to undergo further dampening, as phasing day-1
midlevel troughs (southern extent of the British Columbia system and
one moving through the Pacific Northwest) advance east of the
northern Rockies to the northern Plains.

A surface cyclone will develop over the western Dakotas Tuesday by
late Tuesday afternoon, and move east across SD/ND Tuesday night. 
Southerly low-level jet will translate east through the northern
Plains this forecast period, and strengthen Tuesday afternoon from
the central Plains into the central/eastern Dakotas.  Further
strengthening of this low-level jet is expected Tuesday night from
the central Plains through the mid MO Valley to MN, as heights fall
with the approach of the northern Rockies/High Plains phased
shortwave troughs.  These southerly winds will result in moisture
return through the central and northern Plains.

...Portions of central and northern Plains...
Surface dew points in the lower 60s are expected to spread poleward
across western and central parts of KS/NE and far eastern CO into
the central Dakotas by late Tuesday afternoon, beneath steepening
midlevel lapse rates.  This combined with diabatic heating will
result in moderate instability.  Storms are expected to form by 21Z
across the central and southern High Plains near the low pressure
area and southward in vicinity of the lee trough/wind shift.  Storms
will move into a slightly capped, but more unstable air mass with
eastward extent, where wind profiles will support supercells, with
very large hail and damaging winds possible. Storms are expected to
merge into one or more MCSs during the evening, with damaging winds
and some hail being the primary threats.  Capping will eventually
become a concern, given the lack of cooling midlevel temperatures
limiting the eastward progression of the stronger storms into the
Upper Midwest early Wednesday morning.

...ND/northeast SD into northwest MN...
Strong low-level warm-air advection developing later Tuesday
afternoon and evening within the nose of the strengthening Plains
low-level jet should support elevated strong to severe storms across
this region as heights fall with the approach of the upstream
shortwave troughs.  Coverage of the severe-weather threat (mainly
hail) is expected to remain as marginal.

...Yellowstone National Park area eastward to the Black Hills...
A shortwave trough will move over western areas during the day, with
cooling aloft and daytime heating resulting in sufficient
instability (despite scant moisture) for a few strong to severe
storms.  Storms are expected to form relatively early, between
18-21Z around the Yellowstone National Park area, and then continue
eastward across southern MT and northern WY during the evening. 
Locally severe hail or damaging winds will be possible.

...Central and eastern NY into New England...
A progressive shortwave trough, currently moving through WI per
water-vapor imagery, is expected to track northeast from in lee of
the lower Great Lakes through NY and northern New England.  Although
bulk shear of 30-40 kt will be sufficient for organized storms,
uncertainty in the amount of destabilization should preclude the
inclusion of a marginal severe-weather threat area across this
region.

..Peters.. 06/26/2017

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Updated 26 June 2017 | 12:52 pm

SPC 1630Z Day 1 Outlook
Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1144 AM CDT Mon Jun 26 2017

Valid 261630Z - 271200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
PACIFIC NORTHWEST AND NORTHERN ROCKIES...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
CENTRAL/SOUTHERN PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN
FL AND SOUTHEAST GA...

...SUMMARY...
Thunderstorms with severe hail and strong wind gusts are possible
late this afternoon into evening across the Pacific Northwest and
Northern Rockies in addition to parts of the Great Plains. Other
strong storms may occur along the coastal southeast States.

...Pacific Northwest/northern Rockies...
Gradually strengthening westerlies aloft are expected over the
region today. This will be as an upper low just off the coast of
northern CA continues east-northeastward and a trough amplifies over
British Columbia, while a convectively related disturbance also
shifts eastward from southeast WA/northern ID into MT. It seems
likely that thunderstorms will increase this afternoon especially
east of the Cascades across central/eastern OR into adjacent
ID/southeast WA, in addition to parts of west-central MT.
Strengthening winds aloft/vertical shear will help support some
sustained east/northeastward-moving storms. Isolated instances of
locally damaging winds will be possible with the strongest storms
along with some hail, particularly across parts of OR into ID where
somewhat greater moisture/destabilization is expected. 

...Central Plains/southern High Plains...
Under the glancing influence of the Upper Midwest/Great Lakes
upper-level trough, isolated to widely scattered thunderstorms are
likely to develop by mid/late afternoon within a corridor from
southern NE southward into KS. Although mid-level lapse rates are
not particularly steep by late-June standards, gradually returning
moisture, moderate buoyancy, and supercell-favorable wind profiles
(in the presence of strong northwesterly flow aloft) should allow
for isolated severe thunderstorms capable of severe hail/locally
damaging winds as these storms spread southeastward through the late
afternoon and evening hours.

Elsewhere, as a moist upslope flow regime persists, other storms are
likely to develop/intensify across along the southeast CO/northeast
NM Raton Mesa vicinity and higher terrain of interior NM. In the
presence of moderate buoyancy and 30-35 kt of effective shear, some
of the stronger storms will be capable of hail.

Farther south, one or more remnant MCVs may refocus afternoon
redevelopment, including the possibility of a few stronger storms,
across parts of the TX Edwards Plateau and nearby Transpecos
vicinity.

...North FL/coastal GA...
As weak height falls spread toward the region today, a moist
environment and sea breeze circulations in vicinity of a
stalled/slow-moving front may allow for a few stronger storms this
afternoon capable of downbursts.

..Guyer/Gleason.. 06/26/2017

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Updated 26 June 2017 | 11:48 am