RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Sat Sep 23 08:32:01 UTC 2017.
No Mesoscale Discussions are in effect as of Sat Sep 23 08:32:01 UTC 2017.
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1230 AM CDT Sat Sep 23 2017
Valid 231200Z - 241200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER MIDWEST INTO THE CENTRAL/SOUTHERN PLAINS...
...SUMMARY...
Isolated strong to locally damaging wind gusts and perhaps some
large hail will be possible mainly this afternoon from parts of the
Upper Midwest into the central and southern Plains.
...Synopsis...
An upper trough/low centered over the Great Basin will develop
slowly eastward today across the western CONUS, while an upper ridge
over the OH Valley/Great Lakes region moves little. Strong
south-southwesterly mid-level flow present over much of the
Southwest into the central/southern Rockies will overspread the High
Plains and Upper Midwest by this afternoon.
At the surface, a low will develop eastward across Ontario, with a
trailing front becoming nearly stationary across MN into the central
Plains. A moist low-level airmass will reside south of this front
across much of the Upper Midwest and Plains. Another surface low
over eastern CO will move little through the period as a
trough/dryline extends southward from this low across the southern
High Plains.
...Upper Midwest into the Central/Southern Plains...
Scattered thunderstorms will likely develop this afternoon from the
surface low over eastern CO northeastward along the length of the
nearly stationary front across the central Plains and Upper Midwest
as a weak mid-level impulse embedded within the large-scale trough
moves across these regions. Some of this convection may occur behind
the front, and would likely be elevated. Even so, a residual plume
of modestly steep mid-level lapse rates present mostly on the cool
side of the front will encourage weak to locally moderate MUCAPE
through peak diurnal heating this afternoon. Isolated instances of
large hail may occur with this mainly elevated convection across
parts of the central Plains into the Upper Midwest given forecast
effective bulk shear values of 30-40 kt supporting updraft
rotation/organization. Some strong to locally damaging winds may
also occur with any surface-based convection along/just south of the
front.
Mid-level flow is expected to be more meridional with southward
extent into the southern High Plains. Regardless, a strengthening
wind profile through mid/upper levels will support generally 25-40
kt of effective bulk shear across this region, and at least some
updraft organization appears likely to occur with afternoon
convection that develops along/east of the surface trough/dryline.
Scattered thunderstorms may be ongoing at the start of the period
across parts of eastern NM, which would delay diurnal
destabilization. Still, even though mid-level lapse rates will
remain modest, diurnal heating to the east of any morning activity
should allow for 500-1000 J/kg of MLCAPE to develop across the
southern High Plains. This weak instability coupled with sufficient
bulk shear and meridional flow suggest mainly a multicell/cluster
mode will develop and pose a marginal/isolated wind threat. This
threat should peak through maximum diurnal heating this afternoon
before diminishing quickly in the evening as instability weakens.
..Gleason/Dial.. 09/23/2017
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SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1236 AM CDT Sat Sep 23 2017
Valid 241200Z - 251200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Scattered showers and storms are expected in the southern and
central High Plains, although any severe threat should be sparse.
...Synopsis...
A persistent longwave trough in the West will make very slow
eastward progress throughout the day as a ridge - initially centered
over the Northeast - moves slowly eastward toward northwestern
Atlantic waters late in the period. Between these two large-scale
features, meridionally oriented mid-level flow will persist from the
southern Rockies/High Plains north-northeastward to Minnesota.
At the surface, a cold front will migrate southward across the
central Plains, extending from far southeastern Colorado
northeastward to eastern Minnesota at around sunset. An expansive
anticyclone across the East, combined with weak low pressure in the
lee of the Rockies, will foster a broad area of southerly low-level
flow that should maintain a modified maritime airmass (characterized
by 60s F dewpoints) across much of the center of the country ahead
of the front.
...Eastern NM/western TX north to eastern Nebraska...
Models suggest that an arc of showers and thunderstorms should be
ongoing at the start of the forecast period across this region, with
some expansion/intensification of this activity during peak heating
hours. Despite warming surface temperatures and sufficient deep
shear for loosely organized clusters/linear segments, meager
mid-level lapse rates and expansive cloudiness/precipitation should
limit overall destabilization in most areas. This will result in a
limited damaging wind threat that will likely be too sparse for
severe probabilities. Any existing threat should also wane with the
loss of surface heating.
..Cook.. 09/23/2017
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SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0141 AM CDT Sat Sep 23 2017
Valid 251200Z - 261200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Scattered showers and storms are expected in portions of the
southern Great Plains. The severe risk with this activity is
expected to be minimal.
...Synopsis...
A longwave trough will continue to remain nearly stationary near the
Four Corners region, while a ridge persists across the Northeast.
Southwesterly flow aloft will persist across from the base of the
trough across the southern Rockies northeastward to the western
Great Lakes region, although this flow should be comparatively
weaker compared to previous days.
At the surface, a cold front will continue to migrate slowly
southward across the central Plains and Mississippi Valley, and
should be located from the Texas South Plains northeastward to
western Wisconsin by early evening. Ahead of this front, 60s F
dewpoints will be common, with somewhat higher boundary layer
moisture (i.e., 70s F dewpoints) across south Texas and the Gulf
Coast.
Continued convergence along the surface front and daytime heating
will foster several areas of convection throughout the day -
especially from southwest Texas into central Kansas. Mid-level
lapse rates remain a limiting factor for a more widespread severe
threat. Shear will also be limited due to relatively weak low- and
mid-level flow. The overall risk for damaging wind gusts appears to
be too sparse to include severe probabilities at this time.
..Cook.. 09/23/2017
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Day 4-8 Outlook
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0328 AM CDT Sat Sep 23 2017
Valid 261200Z - 011200Z
...DISCUSSION...
Models generally eject the persistent longwave trough out onto the
northern Plains and into Ontario through D6/Thursday, while
lingering troughiness evolves into a closed low over the Desert
Southwest. Upper ridging will persist along the northwestern Gulf
of Mexico during this period as well. Meanwhile, a surface ridge
will build into much of the Plains and adjacent Rockies, resulting
in a cooler/drier airmass in much of those areas and deeper boundary
layer moisture being shunted southward toward the Gulf Coast. After
D6/Thursday, models are consistent in depicting another mid-level
shortwave trough that will migrate southeastward across the Great
Lakes and Ohio Valley as surface ridging becomes even more dominant
over a large part of the country. The net result of this pattern is
a decreasing severe risk as buoyant air is displaced well to the
south of areas of enhanced mid-level flow.
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SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0148 AM CDT Sat Sep 23 2017
Valid 231200Z - 241200Z
...Synopsis...
A large-scale upper trough/low centered over the Great Basin will
continue to move slowly eastward across the western CONUS today. An
upper ridge will persist over much of the eastern CONUS. While
enhanced mid-level southwesterly winds will remain present over
portions of the Southwest into the High Plains this afternoon, RH
values behind a surface cold front are generally expected to remain
above critical levels across these areas.
...Portions of the Sacramento Valley and Adjacent Coastal Ranges of
Northern CA...
On the back side of the upper trough/low described above, enhanced
northerly winds will persist over much of CA today. As diurnal
mixing of the boundary layer occurs, some increase in low-level
winds appears likely across parts of the Sacramento Valley and
adjacent Coastal Ranges of northern CA. Consensus of recent
short-term guidance indicates sustained northerly winds around 15
mph should occur in conjunction with RH values becoming lowered
generally into the 15-20% range for a few hours this afternoon. Fuel
guidance suggests most fuels remain receptive to large fire starts,
and therefore a small elevated area has been introduced across this
region.
...Portions of the Southwest...
Locally elevated fire weather conditions may briefly occur across
parts of northern AZ and southeastern UT this afternoon where RH
values will become lowered to around 15-20% in conjunction with
strong/gusty surface winds of 15-25 mph. However, only marginally
receptive to unreceptive fuels across this region and cooler
temperatures behind the surface cold front preclude the introduction
of an elevated area.
..Gleason.. 09/23/2017
...Please see www.spc.noaa.gov/fire for graphic product...
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SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0150 AM CDT Sat Sep 23 2017
Valid 241200Z - 251200Z
...Synopsis...
The upper trough/low centered over UT on Day 2/Sunday will make only
very slow eastward progress across the western CONUS as an upper
ridge remains across much of the eastern states. Enhanced mid-level
winds on the western half of the upper trough should slowly decrease
through the period. Subsidence on the back side of the upper trough
will promote strengthening surface high pressure across the Great
Basin by early Monday morning.
...Portions of the Sacramento Valley and Adjacent Coastal Ranges of
Northern CA...
Sustained northerly winds up to 15 mph may occur once again Sunday
afternoon across portions of the Sacramento Valley and adjacent
Coastal Ranges of northern CA. RH values should become lowered into
the 10-20% range, and with dry/receptive fuels expected to remain in
place, an elevated area has been introduced across this region.
...Portions of Coastal Southern CA...
A slowly strengthening surface pressure gradient across parts of
southern CA may result in weak to locally moderate offshore
northerly/northeasterly winds late Sunday night into early Monday
morning. Latest high-resolution guidance suggests sustained winds of
15-20 mph may occur in combination with poor overnight RH recovery
and drying fuels to support elevated fire weather conditions across
a small part of coastal southern CA late Sunday night into early
Monday morning when the surface pressure gradient will be maximized.
..Gleason.. 09/23/2017
...Please see www.spc.noaa.gov/fire for graphic product...
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