RSS Mesoscale Discussions from Storm Prediction Center

SPC May 14, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1228 AM CDT Fri May 14 2021

Valid 141200Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE CENTRAL AND SOUTHERN HIGH PLAINS...

...SUMMARY...
Scattered severe thunderstorms are expected across portions of the
central and southern High Plains late this afternoon through this
evening. Very strong wind gusts and hail up to 2 inches are possible
from extreme northeast Colorado into northwestern Kansas.

...Central and southern High Plains...

Latest water-vapor imagery depicts a weak but notable short-wave
trough over northern NV. This feature will translate across UT into
northern CO by peak heating, then track southeast toward northern KS
during the evening. While height falls will be minimal with this
feature, it should force a lee surface low to settle into southeast
CO which will become more favorable for boundary-layer moistening
across the central High Plains into northeast CO. Intense surface
heating will allow surface temperatures to warm into the lower 80s
as far north as the latitude of the lee low. While convective
temperatures should easily be breached along the lee trough/dry
line, convection should develop as far north as southeast WY ahead
of the short wave. Forecast soundings suggest this activity should
spread southeast towards a moistening boundary layer where
intensification is expected. Very steep lapse rates and favorable
large-scale support at mid levels would seem to support supercell
clusters growing upscale into a possible linear MCS with bow
structures. Latest HREF guidance supports this and have increased
both severe probabilities and hail/wind magnitudes for this possible
development.

Farther south, high-based convection should spread across northeast
NM/southeast CO toward the OK/TX Panhandle region by late afternoon.
Hail and damaging winds appear possible with this activity as well.

...Eastern Dakotas/Western Minnesota...

Weak mid-level troughing and cold temperatures aloft will spread
across the eastern Dakotas during the day. As surface temperatures
warm and lapse rates steepen, scattered thunderstorms will likely
develop north of a 500mb speed max. With 500mb temperatures on the
order of -20C it would seem likely that at least marginally severe
hail could accompany the strongest updrafts. This activity will be
strongly influenced by diurnal heating and should weaken after
sunset.

..Darrow/Dean.. 05/14/2021

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SPC May 14, 2021 0600 UTC Day 2 Convective Outlook

SPC 0600Z Day 2 Outlook
      
Day 2 Outlook Image
Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1253 AM CDT Fri May 14 2021

Valid 151200Z - 161200Z

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

...SUMMARY...
Severe thunderstorms associated with large hail and wind damage will
be possible across parts of the southern and central High Plains
Saturday afternoon and evening.

...Southern and Central High Plains...
A shortwave ridge will move eastward across the central Rockies on
Saturday as west-southwesterly mid-level flow remains in place
across much of the southern Plains. At the surface, a cold front is
forecast to move slowly southward reaching the northern Texas
Panhandle during the late afternoon. Moisture advection will take
place to the south of the front across the southern High Plains.
Surface dewpoints should reach the upper 50s and lower 60s F to the
east of a west Texas dryline. An axis of moderate instability should
be in place to the east of the dryline by afternoon, with scattered
thunderstorms developing from the dryline eastward across much of
the southern High Plains.

Deep-layer shear is not forecast to be that strong across the
southern High Plains on Saturday. NAM forecast soundings around
Lubbock increase 0-6 km shear from 25 kt at 21Z/Saturday to near 35
kt by 00Z/Sunday. However, low to mid-level lapse rates will be very
steep, with 850 to 500 mb lapse rates near 8.5 C/km. Low-level lapse
rates will be even steeper, suggesting that a damaging wind threat
will be possible late Saturday afternoon and early evening. The wind
damage threat could be greater if a line of storms can organize.
Isolated supercells with large hail will also be possible in areas
where the combination of instability and deep-layer shear is
maximized.

...Eastern Colorado/Western Kansas...
An upper-level ridge will move eastward across the central Rockies
on Saturday. West-northwesterly mid-level flow will be in place
across much of the central Plains. At the surface, a cold front will
move slowly southward as upslope flow is reinforced across much of
the central Plains on Saturday. A thermal axis is forecast to
develop from southwest Kansas into southeast Colorado, where
moderate instability should be in place by the mid afternoon.
Thunderstorms will develop in the higher terrain and move eastward
into the lower elevations of eastern Colorado during the mid to late
afternoon. Additional thunderstorms may develop across parts of
southwest and south-central Kansas.

NAM forecast soundings Saturday afternoon across southeastern
Colorado show moderate deep-layer shear, owing mostly to directional
shear in the low to mid-levels. This combined with lapse rates near
8.0 C/km in the 700 to 500 mb layer will be favorable for supercells
with isolated large hail. In addition, 0-3 km lapse rates are
forecast to be very steep, which will likely enhance the stronger
downdrafts making wind damage a possibility. The severe threat
should move eastward into far easterly Colorado and southwest Kansas
by early to mid evening.  The greatest chance for severe should be
located in the Arkansas River Valley, where severe weather
parameters are forecast to be maximized early Saturday evening.

..Broyles.. 05/14/2021

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SPC May 14, 2021 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook
      
Day 3 Outlook Image
Day 3 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0224 AM CDT Fri May 14 2021

Valid 161200Z - 171200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN AND CENTRAL HIGH PLAINS...

CORRECTED FOR WORDING

...SUMMARY...
Thunderstorms associated with strong wind gusts and hail will be
possible across parts of the southern and central Plains on Sunday.

...Southern Plains...
A shortwave trough is forecast to move eastward across the southern
Plains on Sunday as a shortwave ridge moves across the southern
Rockies. At the surface, winds should be southerly across much of
the southern Plains, resulting in moisture advection during the day.
Surface dewpoints should reach the lower to mid 60s F to the east of
a west Texas dryline by afternoon, allowing moderate instability to
develop across much of west Texas. The presence of the upper-level
ridge in the southern High Plains should keep convective coverage
isolated on Sunday. However, low-level convergence may be strong
enough to allow for isolated thunderstorm development near the
dryline. This convection should move eastward across west Texas
during the late afternoon and early evening. Directional shear in
the low to mid-levels and steep low to mid-level lapse rates will
probably be sufficient for a marginal severe threat.

...Central High Plains...
A shortwave ridge will move eastward across the central Rockies on
Sunday. At the surface, upslope flow will remain in place across
much of the central Plains. Moderate instability is expected to
develop by afternoon from southwest Kansas into southeastern
Colorado. As surface temperatures warm, topographical forcing will
result in thunderstorm development in the higher terrain of eastern
Colorado. These storms are forecast to move eastward into the lower
elevations during the mid to late afternoon. In addition to the
instability, forecast soundings near Lamar at 21Z on Sunday have 0-6
km shear in the 25 to 30 kt range with very steep low to mid-level
lapse rates. This should be enough for an isolated severe threat.
The stronger multicells could have marginally severe wind gusts and
hail, especially if a line segment can organize during the early
evening.

..Broyles.. 05/14/2021

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SPC May 14, 2021 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook
      
Day 4-8 Outlook Image
Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0356 AM CDT Fri May 14 2021

Valid 171200Z - 221200Z

...DISCUSSION...
...Monday/Day 4 to Wednesday/Day 6...
The medium range models are in generally good agreement on Monday,
with an upper-level trough in the Desert Southwest and a shortwave
ridge in the southern Plains. An axis of moderate instability is
forecast to develop in the southern Plains Monday afternoon.
Isolated thunderstorms would be possible behind the shortwave ridge
from eastern Colorado southeastward into the Texas Panhandle during
the late afternoon and early evening. Although a severe threat could
develop, isolated convective coverage should keep any threat
localized.

On Tuesday, the upper-level trough is forecast to move into the
southern Plains. A moist and unstable airmass is forecast across
much of the southern Plains. As surface temperatures heat up across
the southern Plains, thunderstorms could develop ahead of the
upper-level trough and move eastward across parts of central and
northern Texas Tuesday afternoon and evening. The models are in
fairly good agreement concerning this scenario. If this happens,
then a severe threat would be possible across parts of central and
north Texas Tuesday afternoon and evening. At this point, will wait
for run-to-run consistency before adding a threat area.

On Wednesday, the models remain in decent agreement, with the
upper-level trough remaining in place across the southern Plains. A
moist and unstable airmass is forecast in the trough's wake over
much of west-central Texas and western Oklahoma. However, subsidence
will likely exist across much of the southern Plains in the wake of
the upper-level trough. This will probably keep convective coverage
isolated, lessening the severe potential.

...Thursday/Day 7 and Friday/Day 8
On Thursday and Friday, the models generally show southwest
mid-level flow in the Great Plains. However, there is considerably
more spread among the model solutions. A moist and unstable airmass
is forecast across much of the Great Plains. Isolated thunderstorm
development will be possible both Thursday afternoon and Friday
afternoon across parts of the Great Plains. A severe threat may
develop in areas where mesoscale conditions become favorable. At
this forecast range, predictability is low concerning any specific
scenario.

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