RSS Mesoscale Discussions from Storm Prediction Center

SPC Jun 25, 2019 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1102 AM CDT Tue Jun 25 2019

Valid 251630Z - 261200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
SOUTHEAST NEBRASKA...NORTHEAST KANSAS...NORTHERN MISSOURI...AND
SOUTHERN IOWA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
NORTHERN HIGH PLAINS...

...SUMMARY...
The greatest potential for severe thunderstorms today is over parts
of the central Plains to northern Missouri and southern Iowa, where
very large hail and sporadic severe gusts are possible.

...NE/KS/MO/IA...
Water vapor imagery shows relatively strong zonal midlevel winds
extending from the northern Great Basin across the northern Plains. 
The southern fringe of the stronger westerlies lies across CO/KS/MO,
where a weak E-W surface boundary is also present.  South of the
boundary, southerly low-level winds are helping to transport very
moist air northward, with dewpoints expected to approach 70F by late
afternoon along the border of eastern KS/NE.  Strong heating is also
occurring, which will yield an extremely unstable air mass. Present
indications are that isolated intense storms will form along the
boundary in the 19-21z period, with initial supercells capable of
very large hail and damaging wind gusts.  An isolated tornado or two
is also possible.  Activity is expected to build quickly eastward
during the late afternoon along the boundary into southern IA and
northern MO.  Activity may organize into one or more short bowing
segments with a risk of damaging wind gusts.

...Northern Plains...
The axis of strong midlevel winds extends across southern MT into
SD, with a few weak shortwave troughs embedded in the flow.  It
appears likely that widely scattered strong storms will develop over
the higher terrain of western and southern MT by late afternoon -
spreading eastward through the evening.  As this activity emerges
into western SD later today, slightly greater moisture/instability
profiles may result in sufficient intensification for a few
organized severe storms capable of large hail and damaging winds.

...IA/IL/WI into Lower MI and northern IN...
Morning visible satellite imagery shows a well-defined MCV over
eastern IA.  Strong heating is occurring ahead of this feature, and
some of the 12z CAM guidance suggests that a cluster of
thunderstorms will intensify this afternoon over southern
WI/northern IL.  If this occurs, strong westerly flow aloft, steep
low-level lapse rates, and sufficient CAPE would pose a risk of
damaging wind gusts.  Have expanded the risk areas slightly farther
east/south into Lower Michigan and northern Indiana, and will
monitor the region for further expansions of severe potential in
later updates.

..Hart/Goss.. 06/25/2019

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SPC Jun 25, 2019 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0252 PM CDT Tue Jun 25 2019

Valid 252000Z - 261200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR SOUTHEAST
NEBRASKA INTO SOUTHWEST IOWA AND NORTHWEST MISSOURI...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
WESTERN AND CENTRAL SOUTH DAKOTA...

...SUMMARY...
The greatest potential for severe thunderstorms this afternoon into
the evening is forecast from southeast Nebraska to northwest
Missouri and southern Iowa, where very large hail and sporadic
severe gusts are possible.

...Discussion...
The only substantial change this forecast update was to trend
towards the notion of greater storm coverage across parts of
southeast NE east along the MO/IA border.  Short-term guidance has
shown a tendency for lower storm coverage across parts of
east-central KS where 30-percent hail probabilities were located in
the previous outlook.  Have adjusted these probabilities to both
communicate this trend in model guidance but also to seemingly
reflect where convective potential appears highest across southeast
NE according to visible satellite imagery.  

Otherwise, the previous forecast thinking is on track.

..Smith.. 06/25/2019

.PREV DISCUSSION... /ISSUED 1102 AM CDT Tue Jun 25 2019/

...NE/KS/MO/IA...
Water vapor imagery shows relatively strong zonal midlevel winds
extending from the northern Great Basin across the northern Plains. 
The southern fringe of the stronger westerlies lies across CO/KS/MO,
where a weak E-W surface boundary is also present.  South of the
boundary, southerly low-level winds are helping to transport very
moist air northward, with dewpoints expected to approach 70F by late
afternoon along the border of eastern KS/NE.  Strong heating is also
occurring, which will yield an extremely unstable air mass. Present
indications are that isolated intense storms will form along the
boundary in the 19-21z period, with initial supercells capable of
very large hail and damaging wind gusts.  An isolated tornado or two
is also possible.  Activity is expected to build quickly eastward
during the late afternoon along the boundary into southern IA and
northern MO.  Activity may organize into one or more short bowing
segments with a risk of damaging wind gusts.

...Northern Plains...
The axis of strong midlevel winds extends across southern MT into
SD, with a few weak shortwave troughs embedded in the flow.  It
appears likely that widely scattered strong storms will develop over
the higher terrain of western and southern MT by late afternoon -
spreading eastward through the evening.  As this activity emerges
into western SD later today, slightly greater moisture/instability
profiles may result in sufficient intensification for a few
organized severe storms capable of large hail and damaging winds.

...IA/IL/WI into Lower MI and northern IN...
Morning visible satellite imagery shows a well-defined MCV over
eastern IA.  Strong heating is occurring ahead of this feature, and
some of the 12z CAM guidance suggests that a cluster of
thunderstorms will intensify this afternoon over southern
WI/northern IL.  If this occurs, strong westerly flow aloft, steep
low-level lapse rates, and sufficient CAPE would pose a risk of
damaging wind gusts.  Have expanded the risk areas slightly farther
east/south into Lower Michigan and northern Indiana, and will
monitor the region for further expansions of severe potential in
later updates.

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SPC Jun 25, 2019 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook
      
Day 2 Outlook Image
Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1155 AM CDT Tue Jun 25 2019

Valid 261200Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
NORTHEAST OREGON...SOUTHEAST WASHINGTON...AND NORTHERN IDAHO; PARTS
OF WESTERN AND CENTRAL MONTANA...

...SUMMARY...
Widely scattered severe storms capable of wind and hail are possible
on Wednesday across western and central Montana, and in a separate
area from northeast Oregon into northern Idaho.

...Synopsis...
A mid-level low will meander slowly east over the eastern Pacific
and reach the Oregon coast late Wednesday night.  Downstream over
the northern High Plains, a ridge will amplify.  A belt of
moderately strong flow will extend from the Upper Midwest east
through the northern Great Lakes and into parts of the Northeast.  A
mid-level anticyclone located over the lower MS Valley will result
in a largely mesoscale and diurnally driven pattern for thunderstorm
development for the Mid South.

...Northeast OR into southeast WA and northern ID...
A cyclonically curved jet streak will extend from south of the
eastern Pacific mid-level low through northern CA and arcing
northeastward into the Columbia Basin by late afternoon.  The exit
region of the upper jet and associated large-scale upper forcing for
ascent will favor isolated thunderstorm development during the
afternoon over central and eastern OR in a more deeply mixed
boundary layer.  As storms move into slightly richer moisture in the
area over northeast OR, storm intensity and coverage are forecast to
increase.  Steep low- to mid-level lapse rates and long hodographs
will favor storm organization.  Forecast soundings show effective
shear 40-50kt and SBCAPE 500-1000 J/kg which may result in a few
transient supercells.  Multicells capable of a risk for severe gusts
(60-70mph) and marginally severe hail are also possible.  During the
evening, storms will move into far eastern WA and northern ID and
the severe threat may continue primarily due to isolated to
scattered severe gusts.  

...Montana...
Strong heating and steep midlevel lapse rates will result in MLCAPE
values from around 500-1500 J/kg. A deeply mixed sub-cloud layer
(i.e. inverted-v thermodynamic profile) and strong midlevel flow
will support strong downdrafts capable of severe wind gusts much of
MT.  High-based supercells are possible given the elongated
hodographs coupled with 7.5-8.5 C/km midlevel lapse rates will
support the risk for large hail.  Storms will likely weaken by mid
evening due to diurnal cooling.

...Northern Plains to Central High Plains Vicinity...
Height rises are expected across the Plains but temperatures aloft
will remain cool, maintaining a large area of very steep lapse rates
atop a moderate EML in the 850-700 mb layer. Some guidance suggests
convection may be ongoing, but decaying, at the beginning of the
period in the vicinity of the mid-MO Valley. This activity could
pose a marginal severe threat, but more likely will result in
various outflow boundaries. Southerly low level flow will maintain
rich boundary-layer moisture, with dewpoints in the 60s to mid 70s F
across all but the western portions of the Plains states where a
surface trough and dryline will extend north to south from far
eastern WY/western NE through western KS and into the OK/TX
Panhandles.  Mid to upper level west/southwesterly flow across the
central/southern Rockies will be rather modest, but there is some
evidence of a weak impulse ejecting across the region during the
afternoon.  Strong heating/instability could lead to isolated storms
during the late afternoon/evening hours if forcing becomes strong
enough to overcome moderate capping.  Severe gusts and hail would be
possible with any storms that form. 

Some guidance suggests the as a southerly low level jet increases
during the evening/overnight, a complex of storms could emerge from
dryline convection perhaps in NE, or develop along outflow from
aforementioned morning convection. The overall conditional and
uncertain nature of the threat across the region will preclude
higher severe probabilities at this time. 

...Northeast OH into PA/NY/VT...
A couple of weak impulses associated with northern Ontario mid/upper
low will migrate through westerly flow in the Great Lakes vicinity
on Wednesday afternoon.  This will result in a moderate midlevel
flow around 30-40 kt downstream of Lake Michigan toward western
PA/NY.  Southwesterly low level flow will maintain 60s dewpoints and
strong heating will result in 1500-2500 J/kg MLCAPE.  As a result,
one or more bands of storms are expected to develop and shift
east/southeast across the region.  Strong wind gusts will be the
main threat but some near-1 inch hail is possible as well.

...MAXIMUM RISK BY HAZARD...
Tornado:   2%     - Marginal
Wind:     15%     - Slight
Hail:     15%     - Slight

..Smith.. 06/25/2019

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