U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 170610 
Storm Prediction Center ac 170608 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0108 am CDT Sat Mar 17 2018 

Valid 171200z - 181200z 

..there is a slight risk of severe thunderstorms across parts of 
central and northern Texas... 

..there is a marginal risk of severe thunderstorms surrounding the 
slight risk into the Arkansas-la-tex region... 

..there is a marginal risk of severe thunderstorms across eastern 
Kentucky and Tennessee into part of southern Virginia and western to northern NC... 

Scattered strong to severe storms will be possible across part of 
central and northern Texas this afternoon into The Ark-la-tex region 
tonight. Farther east, a marginal severe risk exists across eastern 
parts of Kentucky and Tennessee this afternoon into southern 
Virginia and part of North Carolina this evening. 

A progressive shortwave trough will track to the east-southeast 
through the Ohio Valley to the coast of the Carolinas and southeast 
Virginia this forecast period, while heights rise in the wake of this 
system across the eastern plains and Mississippi Valley. A 
large-scale trough will prevail across the western U.S. And deepen 
into the southwest states, as a shortwave trough digs south then 
southeast into Southern California by this evening and into western Arizona by 
12z Sunday. An ill-defined midlevel impulse/jet Max embedded within 
the southern stream is expected to track to the east-northeast 
reaching central/northern Texas by peak heating, and then progress into 
the lower Mississippi Valley tonight. 

At the surface, an area of low pressure and trailing cold front 
attendant to the progressive midlevel trough will track across Kentucky 
and Tennessee today, and through the Carolinas tonight. A warm front will 
shift a little northward through Kentucky and into southern WV, southwest 
Virginia and into northeast NC today. Meanwhile, the western extent of 
the cold front is expected to advance more slowly southward across 
the mid-south, AR, and North Texas as it becomes oriented parallel to 
the westerly flow aloft. 

..central and northern Texas into the arklatex... 
Moisture return will be underway into central Texas at the start of 
this forecast period and will persist south of the cold front today, 
with surface dew points in the middle 60s expected to reach 
locations in the slight risk area and eastward into the lower 
Mississippi Valley. Models suggest a weak surface wave/sub-synoptic 
low attendant to the southern-stream impulse should develop and move 
east along the cold front in TX, reaching central or north-central 
Texas between 21-00z near or north of bwd. A dryline will extend south 
from the surface low. Surface heating of the moistening environment 
combined with steep midlevel lapse rates should result in MUCAPE of 
at least 1500 j/kg. Thunderstorm development is likely during the 
afternoon as forcing for ascent increases attendant to the weak 
midlevel impulse and exit region of accompanying 50-60 kt 500-mb 
jet. Favorable thermodynamics and strong effective bulk shear will 
support organized storms, including supercells. Long, straight 
hodographs at convective initiation suggests hail will be the 
initial severe threat. This threat will persist as storms continue 
to develop and spread east into the early evening, with a greater 
potential for a tornado or two by early evening as low-level 
hodograph curvature increases with a strengthening of low-level 
southerly winds. 

Elevated strong to severe storms will remain possible into the 
evening and perhaps overnight into The Ark-la-tex region, as 
low-level warm advection increases along the track of the midlevel 

..eastern Kentucky and Tennessee into western Virginia and NC... 
Convection is expected to be ongoing at the start of day 1 across 
much of this marginal risk area, however models suggest 
destabilization should occur in the wake of this activity given some 
surface heating. New storm development is expected as the surface 
low and cold front advance into a marginally unstable environment 
across eastern KY/TN. Although strengthening deep-layer westerlies 
will favor organized lines/bowing segments, the weak instability 
should preclude the need for higher severe probabilities, with 
isolated damaging winds and hail the primary threats. 

Potential exists for a marginal severe risk to extend to the 
east-southeast across northern NC and southern Virginia this evening, as 
mainly elevated thunderstorms develop and advance through this 
region along the track of strongest forcing for ascent with the 
midlevel trough. Effective bulk shear will be sufficient for 
organized storms, with steep midlevel lapse rates aiding in a hail 
threat, though weak instability should limit the overall coverage of 
this risk. 

.Peters/Gleason.. 03/17/2018 


Mesoscale Discussion

acus11 kwns 170859 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 170859 

Mesoscale discussion 0125 
National Weather Service Storm Prediction Center Norman OK 
0359 am CDT Sat Mar 17 2018 

Areas affected...chicagoland...northern/east-central 
in...west-central/south-central Ohio 

Concerning...winter mixed precipitation 

Valid 170859z - 171300z 

Summary...mixed winter precipitation is possible over portions of 
the Ohio Valley this morning. 

Discussion...regional radar imagery shows a band of precipitation 
arcing from northern Illinois into southwest/south-central Ohio. This area 
of precipitation is expected to gradually shift eastward over the 
next several hours as the shortwave trough responsible for the 
ongoing warm-air advection progresses through the Ohio Valley. Surface 
observations show that mixed winter precipitation exists from 
chicagoland region into adjacent northwest in. A transition to 
freezing rain is also anticipated across central in soon. However, 
in these areas, precipitation will likely erode from southwest to 
northeast over the next hour or two as the dry slot associated with 
the shortwave trough continues to push into the region. 

Farther southwest (across east-central in and west-central/ 
south-central oh), precipitation rates are expected to increase over 
the next hour or so with a predominant precipitation type of 
freezing rain. This precipitation is generally expected to be light 
but freezing rain rates may briefly exceeded 0.05"/hr within the 
heavier cores. 

.Mosier.. 03/17/2018 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 40598689 41608896 42138920 42168811 41378597 40188291 
39868217 39228182 38948305 40598689