Convective Outlook

SPC 0730Z Day 3 Outlook
Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
1140 PM CDT Tue Oct 17 2017

Valid 201200Z - 211200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorm potential will increase across the south-central US and
over the upper Mississippi Valley.

...Discussion...

Strong short-wave trough will spread across the northern
intermountain region Friday into the northern High Plains by 21/12z.
Height falls ahead of this feature should encourage short-wave
trough over the southern Plains to eject into the Arklatex region.
Thunder probabilities will increase ahead of these features from the
lower Sabine River into the upper MS Valley.

1) South-central US - Southern-stream short-wave trough will eject
across NM into the TX South Plains early in the period. This feature
is expected to aid northward transport of low-level moisture and a
notable increase in PW from the upper TX coast into central OK where
values should be on the order of 1.5". Forecast lapse rates are not
particularly steep ahead of this feature but buoyancy should be more
than adequate for convection in advance of the trough. Some
consideration has been given to introduce 5% severe probs due to the
marked increase in moisture as deep-layer shear will increase ahead
of the trough such that convection could become sustained in nature.
If later guidance is more aggressive with buoyancy then severe probs
may be warranted.

2) Upper MS Valley - Low-level warm advection will increase across
the upper MS Valley during the day3 period as LLJ strengthens from
KS into the Arrowhead of MN. Air mass is initially quite dry across
this region but sustained moistening should lead to adequate
instability for weak elevated convection after dark well ahead of a
sharp cold front that will surge into this region by the end of the
period.

..Darrow.. 10/18/2017

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Updated 17 October 2017 | 11:59 pm

SPC 0600Z Day 2 Outlook
Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1044 PM CDT Tue Oct 17 2017

Valid 191200Z - 201200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorm probabilities will be greatest across the southern
Rockies, along the Pacific Northwest Coast, and over parts of
Florida.

...Discussion...

Dry and stable conditions will exist across much of the contiguous
US Thursday though three distinct areas of the country will have
some threat for thunderstorms.

1) Southern Rockies region - Several low-latitude disturbances will
traverse the international border over the next few days. These
features should encourage higher PW air mass to spread across
northern Mexico into NM and the adjacent High Plains. As a result,
convection is expected to develop across this region as instability
increases ahead of short wave. Thunderstorms that form over NM will
spread toward the TX South Plains during the evening aided by
nocturnal increase in LLJ across this region after dark.

2) Pacific NW - Profiles are expected to cool significantly along
the Pacific NW coast as a strong trough moves inland around 20/03z.
Primary threat for lightning will be with post-frontal convection
influenced by relatively more buoyant onshore flow. 

3) FL - Upper trough will move off the FL coast early in the period
and heights will rise slowly as ridge builds toward the state.
Large-scale surface pattern will change little over the next few
days with deep easterly flow expected to continue due to dominant
surface ridge anchored over the southern Appalachians. Showers will
focus along the east coast and sufficient buoyancy should exist for
at least a threat for lightning with the strongest updrafts.

..Darrow.. 10/18/2017

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Updated 17 October 2017 | 11:58 pm

SPC 1200Z Day 1 Outlook
Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1153 PM CDT Tue Oct 17 2017

Valid 181200Z - 191200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorm potential today will focus across portions of the
Florida Peninsula as well as over parts of western New Mexico and
far west Texas. No severe storms are expected.

...Synopsis...
Predominately zonal upper pattern is expected across the CONUS for
the majority of the period. Some modest pattern amplification is
possible after 00Z west of the Rockies as a strong shortwave trough
approaches the Pacific Northwest. Shortwave trough currently moving
through Saskatchewan is expected to continue eastward into western
Ontario while maturing. Associated surface low will take a similar
path while an attendant cold front moves eastward/southeastward
across the central Plains and upper Midwest. By 00Z Thursday, this
cold front will likely extend from western upper MI southwestward
into western KS. Thereafter, frontolytic processes, encouraged by a
deepening lee trough across the northern High Plains, will lead to a
weakening of the portion of the front across the central Plains.

Dry and stable conditions are anticipated across much of the CONUS.
Isolated to scattered thunderstorms are possible across FL as modest
surface convergence occurs amidst a moist and unstable airmass. 

Farther west (across southwest NM), increased mid-level moisture
associated with a weak shortwave trough (currently moving across
Baja California) combined with modest low-level moisture and steep
low-level lapse rates will support 100-300 J/kg of MLCAPE during the
afternoon. Lift provided by the shortwave trough, in tandem with
favorable orographic circulations, will interact with this
instability to support isolated to widely scattered thunderstorms.

..Mosier/Elliott.. 10/18/2017

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Updated 17 October 2017 | 11:57 pm