U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 301249 
Storm Prediction Center ac 301247 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0747 am CDT Sat may 30 2015 

Valid 301300z - 311200z 

..there is a slight risk of severe thunderstorms over northern ME... 

..There is a slight risk of severe thunderstorms over parts of the lower Ohio and Tennessee 

..there is a marginal risk of severe thunderstorms from southern and eastern Texas northeastward into 
the lower Great Lakes/New England... 

..there is a marginal risk of severe thunderstorms over parts of the northern rockies and 
northern High Plains... 

Scattered thunderstorms...some with strong to possibly severe winds 
and hail...will develop near and ahead of a cold front from parts of 
the northeast and Ohio Valley southwest into Texas. A few strong to 
possibly severe storms also are expected over parts of New 
Mexico...and central and eastern Montana this afternoon and evening. 

..synoptic setup... 
A multi-stream trough will progress slowly east from the plains into the 
Great Lakes...Ohio Valley...and lower MS valley this period as a ridge persists 
over the western Atlantic and heights rise across the Great Basin. Within 
the trough...southern stream vorticity now over western Arkansas should continue NE into 
western Kentucky by this evening while upstream impulse now over western Nebraska/Kansas moves 
east into Iowa. At the same time...stronger northern stream disturbance now 
over western ont should track east into northern/central Quebec by early 
sun...strengthening existing west-southwest flow across the lower Great Lakes/New 
England. A series of weak disturbances will top building ridge over 
the interior west...and an mesoscale convective vortex may evolve from mesoscale convective system now over north central 

At the surface...a cold front at this time extending from eastern Quebec southwestward through 
the lower Great Lakes and lower Ohio Valley into west central Texas should progress 
steadily east/southeast through the period. This boundary...bands of 
confluence ahead of it...and surface low along the front over the lower Ohio 
Valley...will serve as the primary low-level sources of lift for 
thunderstorms...especially this afternoon and evening. 

..upstate New York to northern ME this aftn/eve... 
Surface observation and satellite data show that sufficient moisture has spread 
NE across upstate New York and northern New England to support strong 
storms...with precipitable water now at or above 1.50 inches. Largely unidirectional deep 
west-southwesterly flow should slowly increase through the day...with the 
strongest winds /700-500 mb speeds at or above 40 kts/ expected over far northern 
New York and northern ME. Combination of surface heating and convergence along lake 
breeze boundaries/terrain circulations should support bands of scattered 
afternoon thunderstorms ahead of cold front from upstate New York east-northeast across northern New 

Modest middle-level lapse rates will limit maximum buoyancy to around 1000 
j/kg despite presence of increased moisture. Nevertheless...given 
strength of deep west-southwesterly flow and its orientation parallel to the 
sources of low-level uplift...some potential will exist for embedded 
bowing segments with locally damaging wind. The storms should weaken 
with nocturnal cooling early tonight. 

..lwr Ohio/Tennessee valleys this aftn/eve... 
Surface low now located along the Arkansas-MO border should track slowly NE 
along cold front into southern Illinois by evening...in association with southern stream 
upper vorticity. Band of enhanced /40+ knots/ 700-500 mb flow on east side of the 
vorticity will overspread warm sector across western portions of Tennessee/Kentucky and 
southern Illinois/ind today...where precipitable water will remain at or above 1.75 inches. Although 
middle-level lapse rates will be weak...surface heating and confluence in the 
warm sector should support development of short lines/clusters of 
storms by early afternoon. These could yield a conditional risk for 
locally damaging wind and a couple tornadoes through early tonight. 

..TX/la this aftn/eve... 
North Texas mesoscale convective system should continue generally eastward into NE Texas/northwest la by early 
afternoon. New development likely will occur S and east of the system across 
parts of east central and southeast Texas as surface heating boosts MLCAPE to at or above 2000 
j/kg. Occasional locally damaging wind gusts and hail may occur with 
embedded bowing segments in the mesoscale convective system...and with the more isolated storms 
farther S. Modest deep shear /around 25 kts/ 
should...however...limit potential for widespread severe weather. 
Elsewhere...SW Texas mesoscale convective system should move/develop south-southeast to the Texas Big Bend by 
middle afternoon. This system should remain largely elevated atop outflow 
from previous mesoscale convective system...although it too could yield occasional instances 
of severe wind and hail given somewhat greater /30+ knots/ cloud-layer 
shear present in that region. Additional scattered storms may form over 
central and S Texas through tonight...ahead of trailing southern portion of 
Nebraska/Kansas upper trough. While this activity could yield a instance or two 
of severe hail...the wind/thermodynamic environment should be 
unfavorable for a sustained severe threat. 

..NE Washington/Idaho eastward into western/central Montana this aftn/eve... 
Low-amplitude trough now entering western Montana will continue east across the 
remainder of that state later today...while another disturbance 
moves east from Oregon into Idaho. Widely scattered storms now over northern Idaho/western Montana 
should move/develop mainly east through the day...affecting central/eastern 
Montana by late afternoon and evening. Inverted-v thermodynamic environment may 
yield a few strong/possibly severe downburst winds. Farther west...other 
diurnally-enhanced storms with a conditional risk for strong winds 
and perhaps marginally severe hail may occur over NE Washington and northern Idaho...in 
association with Oregon upper impulse. 

.Corfidi/picca.. 05/30/2015 

Mesoscale Discussion

acus11 kwns 301120 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 301120 

Mesoscale discussion 0841 
National Weather Service Storm Prediction Center Norman OK 
0620 am CDT Sat may 30 2015 

Areas affected...north central into northestern Texas 

Concerning...Severe Thunderstorm Watch 243... 

Valid 301120z - 301245z 

The severe weather threat for Severe Thunderstorm Watch 243 

Summary...strong surface gusts may remain possible with lingering 
storms spreading east of the watch area during the next hour or 
two...but a new watch is not currently anticipated. 

Discussion...strongest thunderstorm activity is spreading across and 
just south of the Dallas/Fort Worth metroplex...just ahead of an 
increasingly better defined convectively generated middle-level 
cyclonic circulation...and along the weak surface front trailing an 
impulse slowly progressing across the Ozark Plateau. Inhibition for 
moist boundary layer parcels along this boundary has continued to 
slowly increase...and latest objective analysis suggests Cape May be 
more modest east of the metroplex due to weaker middle-level lapse 

Three-Second Peak gusts recently at least approached severe limits 
at a number of observation sites across western portions of the 
metroplex. While it does appear that convection supporting this 
activity may be in the process of weakening...convection passing 
near/just south of the metroplex remains strong...and could still 
produce similar gusts through 12-13z. Beyond the next hour or 
two...it remains a bit unclear how much longer ongoing thunderstorm 
activity will maintain strength. But there is currently little 
evidence to suggest potential for substantive further strengthening. 

.Kerr.. 05/30/2015 

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


Latitude...Lon 33399631 33139526 32949491 32359447 31889494 31509621 
31539723 31789728 32119698 32759669 33399631