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Storm Prediction Center Forecast


RSS Mesoscale Discussions from Storm Prediction Center

SPC - No watches are valid as of Mon Aug 10 07:32:01 UTC 2020

No watches are valid as of Mon Aug 10 07:32:01 UTC 2020.


SPC MD 1444

MD 1444 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR SOUTHEAST MN...WESTERN WI
MD 1444 Image


Mesoscale Discussion 1444
NWS Storm Prediction Center Norman OK
0230 AM CDT Mon Aug 10 2020

Areas affected...Southeast MN...western WI

Concerning...Severe potential...Watch possible 

Valid 100730Z - 100900Z

Probability of Watch Issuance...40 percent

SUMMARY...Isolated severe storms continue to affect the MSP local
area.  Small area of concern and uncertainty of longevity continue
to weigh against watch issuance, but we continue to monitor.

DISCUSSION...A small cluster of intense thunderstorms has been
affecting the greater MSP region for several hours, producing
isolated large hail and damaging wind gusts.  These storms formed
along/ahead of a cold front moving into the region, but have
remained quite isolated in nature.  Larger-scale steering flow would
tend to move these storms into western WI, where the air mass is
slightly less unstable.  A more likely scenario is for storms to
slowly develop southeastward along instability gradient along the MS
River toward southwest WI, although time-of-day and poor CAM
performance decrease confidence how much longer the storms can
maintain severe intensity.

We continue to monitor storms for upscale growth or a more
widespread risk of severe storms through the overnight hours.

..Hart.. 08/10/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...ARX...MPX...

LAT...LON   44699423 45309384 45299235 44609078 43509052 43479171
            43759299 44079373 44699423 

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SPC Aug 10, 2020 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
1229 AM CDT Mon Aug 10 2020

Valid 101200Z - 111200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM KANSAS TO
ILLINOIS...

...SUMMARY...
Scattered strong to severe thunderstorms will be possible later
today from Kansas to Illinois.  Severe gusts will be the primary
hazard.

...Kansas to Illinois...

Weak upper ridge remains elongated east-west about 32N across the
southern US. Latest model guidance continues to suggest several weak
disturbances will rotate around this ridge, just south of stronger
westerlies that should sag across the northern third of the country.
While the stronger westerly flow, and associated mid-level height
falls, will contribute to scattered thunderstorm development
along/ahead of a surface front across the Great Lakes/Midwest, a few
notable disturbances should migrate across the Four Corners, through
CO into KS by late afternoon.

Latest model guidance suggests scattered convection will be ongoing
from portions of the mid MO Valley, northeast into the upper Great
Lakes in response to height falls ahead of the northern stream
short-wave trough. This activity will likely not dissipate before
boundary-layer warming contributes to destabilization such that
renewed robust updrafts take advantage of diurnally-enhanced
buoyancy. Forecast wind profiles suggest much of this activity
should be multi-cellular in nature, possibly maturing into several
clusters, or an MCS as convection spreads/develops southeast toward
central IL. Severe wind gusts are the main threat with this
activity.

Farther west along the frontal zone across the central Plains,
strong boundary-layer heating will be noted across the high Plains
from west TX into central KS. This strong heating should result in
surface parcels reaching their convective temperatures by 22z. Aided
by frontal convergence, and approaching weak disturbances from CO,
it appears an elongated corridor of scattered convection should
develop along the wind shift. Weak vertical shear favors multi-cell
updrafts and severe wind gusts will be the main concern.

..Darrow/Squitieri.. 08/10/2020

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SPC Aug 10, 2020 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
1248 AM CDT Mon Aug 10 2020

Valid 111200Z - 121200Z

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

...SUMMARY...
Marginally severe thunderstorms will be possible on Tuesday in parts
of the Arkansas River Valley and High Plains.

...Arkansas Valley...
A shortwave trough will move from the southern Plains into the
Arkansas River Valley on Tuesday. At the surface, a corridor of
maximized low-level moisture is forecast from northeastern Oklahoma
extending eastward into the Tennessee Valley. Convection is forecast
to initiate along the western part of this corridor during the
morning in north-central Oklahoma with thunderstorms moving eastward
into the Arkansas River Valley during the day. Surface dewpoints in
north-central Arkansas should be in the upper 60s to near 70 F,
resulting in moderate instability by afternoon. Forecast soundings
at Little Rock Tuesday afternoon show weak deep-layer shear. In
spite of this, MLCAPE in the 2000 to 3000 J/kg range combined with
0-3 km lapse rates near 8.0 C/km may be enough for a marginal
wind-damage threat. Hail could also accompany the stronger updrafts,
mainly across the western part of the marginal risk area where
mid-level lapse rates will be a bit steeper.

...Central High Plains...
A subtle shortwave ridge is forecast to move eastward across the
central and northern Plains on Tuesday. At the surface, a moist
airmass will be located in the central Plains. The western edge of
this moist airmass should be in eastern Colorado where moderate
instability appears likely to develop by afternoon. As surface
temperatures warm during the day, convection should initiate in the
higher terrain. Although warm air aloft could be problematic for
vigorous convective growth, a few storms could move eastward into
the lower elevations during the mid to late afternoon. The
combination of instability and deep-layer shear may be strong enough
for an isolated severe threat near peak heating. Marginally severe
wind gusts and hail will be the primary threats. Any severe threat
should diminish by early evening as warm air aloft and capping
inhibits convective development across the region.

..Broyles.. 08/10/2020

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SPC Aug 10, 2020 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook
      
Day 3 Outlook Image
Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0215 AM CDT Mon Aug 10 2020

Valid 121200Z - 131200Z

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

...SUMMARY...
Isolated marginally severe thunderstorms will be possible Wednesday
afternoon and evening across parts of the central and northern
Plains.

...Central and Northern Plains...
An upper-level trough is forecast to move through the northwestern
U.S. as southwest mid-level flow becomes established across much of
the northern Plains. A shortwave ridge is forecast to move eastward
across the central Plains. Beneath the ridge, a moist and very
unstable airmass will be in place from central South Dakota into
central and eastern Nebraska. The upper-level ridge will impede
convective development across much of the central and northern
Plains through much of the day on Wednesday. However, isolated
thunderstorms could develop near or after peak heating in areas
where the cap weakens. Convective development would be most likely
during the early evening as a 30 to 40 kt low-level jet strengthens.
Although deep-layer shear across the central and northern Plains is
forecast to be in the 20 to 30 kt range, low to mid-level lapse
rates will be very steep. This would be enough for a marginal wind
damage and hail threat with isolated thunderstorms that can overcome
the cap. At this point, there appears to be a broad area where
isolated convective initiation could take place. But most of the
area will remain capped. Have introduced a marginal risk area that
spans most of the instability corridor where convective initiation
will be conditional.

..Broyles.. 08/10/2020

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SPC Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook
          
Day 1 Fire Weather Outlook Image
Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0108 AM CDT Mon Aug 10 2020

Valid 101200Z - 111200Z

...Synopsis...
Mainly zonal mid-level flow will prevail across the northwest CONUS
through the period as a trough aloft ejects into south-central
Canada from the northern Plains. Despite the zonal flow pattern, the
latest model guidance continues to depict isolated thunderstorm
development along a west-east oriented band of mid-level moisture,
positioned across northern Nevada into central Wyoming. Dry and
windy conditions, conducive for supporting wildfire spread, are
expected to remain relatively localized and brief given the lack of
discernible upper level support. 

...Northern Nevada into Central Wyoming - Dry Thunderstorms...
By mid to late afternoon, adequate buoyancy, driven by the
aforementioned mid-level moisture band and diurnal heating, will
encourage isolated high-based thunderstorm development atop a deep,
well mixed boundary layer. Storm motions are expected to be slow
overall. However, given the depth of the dry boundary layer and
precipitable water values barely exceeding 0.5 inches, any lightning
that can occur with these storms will most likely be dry. In
addition, fuels across the northern Great Basin into the central
Rockies have become very to critically dry in several locales,
suggesting that any strikes that can occur may ignite new fires.
Isolated dry thunderstorm areas were added where the greatest
coverage in dry strikes are expected. Adjustments or potential
expansions of these delineations may be needed based on the latest
high-resolution model guidance.

...West-central to southwest CONUS - Dry/Windy conditions...
Many terrain favoring locations, including the Snake River Plain in
southern Idaho, Great Divide Basin in southern Wyoming, and much of
the southwest CONUS, may experience locally elevated conditions (15
mph sustained surface winds overlapping with 10-20% RH) by afternoon
peak heating. The lack of upper support suggests that Elevated
conditions will be too spatially constrained and brief to warrant
delineations at this time.

..Squitieri.. 08/10/2020

...Please see www.spc.noaa.gov/fire for graphic product...

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SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook
          
Day 2 Fire Weather Outlook Image
Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0214 AM CDT Mon Aug 10 2020

Valid 111200Z - 121200Z

...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF CENTRAL INTO SOUTHEAST
WASHINGTON AND FAR NORTHERN OREGON...

...Synopsis...
A mid-level trough will amplify as it impinges on the West Coast
through the Day 2/Tuesday period. With the passing of the trough,
dry and breezy conditions along the lee of the Cascades will promote
conditions conducive to wildfire spread. Similarly, wildfire spread
potential from overlapping dry and windy conditions will also be
possible across portions of the lower Great Basin into the Four
Corners area. In addition, deep-layer ascent will promote
thunderstorm development across portions of the northern Great
Basin. With storms occurring atop a deep and mixed boundary layer,
dry strikes are also expected.

...Pacific Northwest into the northern Rockies...
Downward momentum transport of the stronger flow aloft, along with
downslope flow along the lee of the Cascades, will promote 20 mph
sustained westerly flow overlapping with 15-25% RH. High-resolution
model guidance depicts the strongest/driest downslope flow across
central and southern Washington into far northern Oregon in the
Columbia Basin, where a critical delineation has been added.
Downslope flow to the lee of higher terrain, combined with boundary
layer mixing, will also promote Elevated conditions by afternoon
peak heating across portions of the Harney Basin in southeast
Oregon, as well as the Snake River Plain in southern Oregon, where
Elevated areas were also added. 

...Northern Great Basin into the central Rockies...
Deep-layer ascent along a mid-level moisture axis will promote
isolated to potentially scattered thunderstorm development across
northern Nevada into south-central Wyoming during the afternoon
hours on Day 2. These storms will likely occur over a deep, dry
sub-cloud layer, with dry strikes expected. At the moment, training
storms in close proximity along with slow storm speeds are the
primary caveats for adding a scattered dry thunderstorm area across
central and northern Nevada at this time. Nonetheless, the northern
Great Basin appears to be the area where the relatively highest
thunderstorm density, including dry strikes, is expected.

...Southwest U.S...
Though the strongest flow aloft is expected to remain well north
into the northern Great Basin and Pacific Northwest, at least
locally Elevated fire weather conditions are possible across the
southwestern CONUS. At the moment, the greatest chance for a more
widespread overlap of 15 mph sustained winds and 10-20% RH is
expected to be over southwest portions of the Colorado Plateau,
where an Elevated delineation has been added.

..Squitieri.. 08/10/2020

...Please see www.spc.noaa.gov/fire for graphic product...

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