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  Friday May 26, 2017

RSS Mesoscale Discussions from Storm Prediction Center

SPC - No watches are valid as of Fri May 26 07:24:02 UTC 2017

No watches are valid as of Fri May 26 07:24:02 UTC 2017.


No Mesoscale Discussions are in effect as of Fri May 26 07:24:02 UTC 2017.

SPC May 26, 2017 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
1246 AM CDT Fri May 26 2017

Valid 261200Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE HIGH
PLAINS FROM CO TO THE EASTERN OK PANHANDLE...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
SOUTHERN HIGH PLAINS TO IL/IN...

...SUMMARY...
Scattered severe thunderstorms are expected across the central
Plains with isolated activity into the eastern Texas Panhandle.  A
few strong storms may also be noted across parts of the middle
Mississippi Valley and Ohio Valley region.

...Plains...

Large-scale height rises are expected across most of the contiguous
US Friday, though large-scale troughing will hold across the Western
States.  Early-morning water-vapor imagery suggests a couple of weak
disturbances across the inter-mountain region and one notable
short-wave trough is observed over the northern Baja Peninsula.  In
the absence of significant large-scale forcing for ascent, it
appears diurnal heating and orographic influences will prove
instrumental in convective development across the High Plains.

Latest short-range model guidance suggests strong boundary-layer
heating will be observed across the High Plains such that surface
parcels should reach their convective temperatures near 22z. 
Scattered convection is expected to develop across eastern CO within
favorable southeasterly upslope flow.  Isolated storms are also
expected to evolve along the dryline into the eastern TX Panhandle,
possibly aided by aforementioned Baja short wave.  CINH should be
negligible across these regions by late afternoon and deep-layer
shear is more than adequate for supercell development.  Several
high-res models agree with this scenario and large hail and damaging
winds can be expected with these storms.  Organized severe threat
will struggle to reach central KS/south-central NE until after
midnight.  Even so, activity should be waning by this time.

...Mid MS Valley/OH Valley...

Early-morning radar data exhibits a long-lived convective cluster
moving into northeast KS.  Remnants of this convection may influence
daytime convection downstream across the mid MS and OH valley.  00z
model guidance is not particularly helpful regarding a convective
scenario later today across this region.  Significant capping is
observed across the southern Plains and this warm pocket of air at
700mb will spread across AR/southern MO by midday toward southern
IL.  Convection should struggle to develop at these lower latitudes
despite several model solutions suggesting otherwise.  With nebulous
forcing and broad height rising expected it appears diurnal heating
and weak warm advection atop the boundary layer could aid
thunderstorm risk.  Otherwise, remnant convective cluster over KS
could enhance storm development over IL/IN later in the day.

..Darrow/Dean.. 05/26/2017

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SPC May 26, 2017 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
0100 AM CDT Fri May 26 2017

Valid 271200Z - 281200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN AND CENTRAL PLAINS EAST-NORTHEASTWARD INTO THE MID
MISSISSIPPI VALLEY...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
ENHANCED RISK AREA ACROSS PARTS OF THE SOUTHERN AND CENTRAL PLAINS
EAST-NORTHEASTWARD INTO THE MID MISSISSIPPI VALLEY...CENTRAL
APPALACHIAN MOUNTAINS AND MID-ATLANTIC...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
SLIGHT RISK AREA FROM PARTS OF THE OUTSIDE OF THE ENHANCED RISK AREA
ACROSS PARTS OF THE SOUTHERN AND CENTRAL PLAINS EAST-NORTHEASTWARD
INTO THE MID MISSISSIPPI VALLEY...CENTRAL APPALACHIAN MOUNTAINS AND
MID-ATLANTIC...

...SUMMARY...
Widespread severe thunderstorms with wind damage, large hail and a
few tornadoes are expected Saturday and Saturday night from parts of
the southern and central Plains east-northeastward into the mid
Mississippi Valley and Mid-Atlantic.

...Southern and Central Plains/Mid Mississippi Valley...
An upper-level trough is forecast to move east-southeastward across
the northern Plains and central Rockies on Saturday as
west-southwesterly flow remains located across the southern and
central Plains east-northeastward into the mid Mississippi Valley.
At the surface, a cold front is forecast to advance southeastward
across the central Plains and southern High Plains. A very moist and
unstable airmass should be in place Saturday from eastern parts of
the southern Plains northeastward into the mid Mississippi Valley.
Surface dewpoints are forecast to be in the lower to mid 70s F
across much of this corridor contributing to moderate to strong
instability by afternoon. Deterministic and high-res solutions
suggest that a complex of thunderstorms will first develop across
the central Plains around midday with this complex growing in size
and moving east-southeastward into the mid Mississippi Valley during
the afternoon. The development of a linear MCS will be possible by
early evening across the enhanced risk area.

GFS forecast soundings on Saturday along the northern edge of the
strongest instability from southeast Kansas into southern Missouri
show a capping inversion in place for much of the day. This cap is
forecast to weaken by late afternoon. Forecast soundings also show
an impressive thermodynamic environment with MLCAPE values around
4000 J/kg across much of northeast Texas, eastern Oklahoma and
southern Missouri. In addition, 40 to 50 kt of 0-6 km shear is
forecast along this corridor suggesting thunderstorms will have no
problem organizing. The main question is what mode will be favored.
Some high-res solutions show two bowing line segments moving
east-southeastward across the enhanced risk area. This would be more
favorable for a wind-damage threat. If the storms can form into
clusters instead of lines, then supercells with large hail and
isolated wind damage will be favored. Hailstones of greater than 2
inches in diameter will be possible with supercells mainly from
southwest Missouri into northeast Texas. A tornado threat should
occur across parts of the region especially as low-level flow
strengthens across the region. The severe threat should be more
isolated with southwestward extent across parts of northeast and
central Texas.

...Ohio and Tennessee Valleys/Mid-Atlantic...
An upper-level ridge is forecast to move eastward across the Ohio
and Tennessee Valleys on Saturday as a warm front advances
northeastward into the southern Great Lakes and upper Ohio Valley. 
Thunderstorms are forecast to develop along the warm front with this
convection moving east-southeastward across the region during the
afternoon. Forecast soundings at 21Z on Saturday along and to the
south of the warm front in eastern Kentucky, southern Ohio and West
Virginia show moderate instability with MLCAPE values of 1000 to
2000 J/kg, 0-6 km shear values around 30 kts and steep low-level
lapse rates. This environment should support a wind-damage threat
with multicell line segments that can become organized. Hail will
also be possible with the stronger updrafts.

..Broyles.. 05/26/2017

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SPC May 26, 2017 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
0221 AM CDT Fri May 26 2017

Valid 281200Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN PLAINS...ARKLATEX...MID MISSISSIPPI VALLEY AND OHIO
VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
SLIGHT RISK ACROSS PARTS OF THE SOUTHERN PLAINS...ARKLATEX...MID
MISSISSIPPI VALLEY...OHIO VALLEY...GREAT LAKES...CENTRAL
APPALACHIANS AND CAROLINAS...

...SUMMARY...
Scattered severe thunderstorms with a threat for large hail, wind
damage and a few tornadoes will be possible on Sunday across parts
of the mid Mississippi and Ohio Valleys. Large hail and wind damage
will also be possible across parts of the southern Plains and
Arklatex.

...Mid Mississippi Valley/Ohio Valley...
An upper-level trough is forecast to move eastward into the mid to
upper Mississippi Valley on Sunday as a cold front advances
southeastward into the Ohio and mid Mississippi Valleys. A moist
airmass is forecast ahead of the front with surface dewpoints in the
mid to upper 60s F. This should be enough for the development of
moderate instability by afternoon across prats of western Tennessee,
Kentucky, southern Indiana and Ohio. Model forecasts along this
corridor generally develop scattered convection during the late
afternoon as the upper-level trough approaches. GFS forecast
soundings at 00Z/Monday from Memphis, Tennessee northeastward to
Louisville, Kentucky show MLCAPE values of 2000 to 2500 J/kg with
0-6 km shear values from 40 to 50 kt. If the convection can develop
into clusters with discrete cells, then the environment would
support supercells with large hail, wind damage and possibly a
tornado threat. If convection tends to organize into line segments,
wind damage could be the primary threat. A tendency to go linear may
be the more likely outcome due to unidirectional wind profiles and
the deep-layer shear vectors being somewhat parallel to the
boundary. The exact corridor with the highest severe threat will
likely depend upon the position of the cold front by late Sunday
afternoon.

...Southern Plains/Arklatex...
Westerly to west-southwesterly mid-level flow is forecast to be in
place across the Southern Plains and Arklatex on Sunday as a cold
front advances southeastward across the region. Ahead of the front,
surface dewpoints are forecast to be in the upper 60s and lower 70s
F with a corridor of moderate to strong instability in place by
afternoon. Model forecasts appear to develop convection along the
front and on the cool side of the front Sunday afternoon and
evening. GFS forecast soundings near the front at 00Z/Monday across
the Texas Hill Country and Arklatex show strong instability (MLCAPE
of 2500 to 4000 J/kg) with 0-6 km shear in the 30 to 40 kt range.
This combined with steep lapse rates in the 500-300 mb layer would
support supercell development with isolated large hail. Wind damage
would also be possible especially with storms that can persist and
develop mature downdrafts.

..Broyles.. 05/26/2017

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