U.S. Severe Weather Forecast (Konvektīvā prognoze)

Day Three

acus01 kwns 200528 
Storm Prediction Center ac 200527 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1127 PM CST Mon Feb 19 2018 

Valid 201200z - 211200z 

..no severe thunderstorm areas forecast... 

thunderstorms are expected from Texas to the Great Lakes today into 
tonight. While a stronger storm or two may occur from the arklatex 
to the Ozarks, organized severe weather is not currently expected. 

The large-scale mid/upper pattern will remain relatively unchanged 
today, as the center of a strong ridge persists offshore the 
southeast US and a deep trough encompasses much of the western US. 
Between the two, a broad corridor of strong mid-level 
southwesterlies will exist from the Desert Southwest northeastward 
to the upper Midwest. Within this regime, an elongated, diminishing 
vorticity maximum will advance across the Southern Plains, while 
multiple weak, convectively augmented impulses eject north/northeast 
in advance of this vorticity Max. At the surface, a cold front will 
accelerate southeastward across the Southern Plains and mid 
Mississippi Valley. 

..arklatex to the Ozarks... 
Weak mid/upper ascent will approach the region during the afternoon 
and evening hours. As it does so, a persistent low-level jet and 
related convergence near/ahead of the advancing front are forecast 
to Foster an increase in convection. Heating will be limited during 
the day, but northward moisture return should support upwards of 500 
j/kg of MLCAPE by late afternoon. Aided by this buoyancy, shallow 
thunderstorms should organize from northeast Texas to southern 
Missouri through the evening hours. Forecast soundings suggest 
low-level shear may be favorable for a localized wind/tornado threat 
with any cells/segments ahead of the front. However, convection may 
struggle to stay firmly rooted in the surface warm sector ahead of 
the front, considering south/southwesterly cloud-layer flow, weak 
buoyancy, and the southeastward push of the front. Therefore, have 
opted against introducing marginal probabilities at this time, 
although they could be added in later updates. 

.Picca/jirak.. 02/20/2018 


Mesoscale Discussion

acus11 kwns 200843 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 200843 

Mesoscale discussion 0073 
National Weather Service Storm Prediction Center Norman OK 
0243 am CST Tue Feb 20 2018 

Areas affected...portions of Iowa into southeast Minnesota and 
portions of western Wisconsin 

Concerning...freezing rain 

Valid 200843z - 201145z 

Summary...freezing rain/mixed wintry precipitation will continue 
spreading northeast across portions of Iowa and adjacent southeast 
Minnesota, and spreading into western/southwestern Wisconsin over 
the next 1-2 hours. 

Discussion...latest radar loop shows a band of heavier precipitation 
-- including occasional/embedded lightning -- continuing to shift 
northeast across central and eastern Iowa and adjacent southeast 
Minnesota at this time. The precipitation is occurring within a 
zone of warm advection, with qg ascent bolstered by a compact vort 
Max whose center of circulation is indicated in water vapor imagery 
to be shifting into southwest Iowa at this time. While the rather 
fast motion of the precipitation field is limiting duration of 
heavier amounts at any one locale, briefly moderate to heavy rain -- 
where surface temperatures are largely in the upper 20s to low 30s 
-- will continue to allow icing to occur. 

Latest model runs -- in particular several hi-res cams -- suggest 
steady or even diminishing precipitation intensity over the next few 
hours. In addition, an axis of above-freezing surface temperatures 
are apparent along the Mississippi Valley northward into southwest 
Wisconsin/northeast Iowa. Still, moderate to briefly heavy freezing 
rain will occur across portions of the area -- as highlighted by the 
mesoscale discussion graphic -- over the next few hours. 

.Goss.. 02/20/2018 

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


Latitude...Lon 44809034 44259005 43779037 43249161 42639213 41489252 
40849303 40969353 43099313 44089261 44859147 44809034