U.S. Severe Weather Forecast (Convective Outlook)

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999 
acus01 kwns 301249 
swody1 
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 
valleys... 


..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 
Texas. 


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 
England. 


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


000 
acus11 kwns 301551 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 301551 
ohz000-inz000-kyz000-ilz000-301745- 


Mesoscale discussion 0843 
National Weather Service Storm Prediction Center Norman OK 
1051 am CDT Sat may 30 2015 


Areas affected...S-cntrl into east-central Illinois / southwestern through central and into 
north-central ind 


Concerning...severe potential...watch unlikely 


Valid 301551z - 301745z 


Probability of watch issuance...20 percent 


Summary...scattered thunderstorms are forecast to develop this 
afternoon. A few of the stronger storms may be capable of an isolated 
damaging wind risk. 


Discussion...visible satellite imagery shows a swelling cumulus field 
across the Wabash River valley amidst ample surface heating as temperatures 
rise through the 70s and into the lower 80s with dewpoints in the 
upper 60s. A shortwave trough evident in water vapor imagery over 
the Ozark Plateau will move downstream to the NE towards the Ohio/MS 
river confluence by middle afternoon while a surface low develops northeastward 
from southeastern MO into S-central Illinois. Marginal to pockets of moderate 
buoyancy /500-1200 j per kg MLCAPE/ will likely develop as the 
airmass destabilizes further. 30-knots 500 mb flow on the southeast-side of the 
middle-level disturbance will act to support isolated strong 
quasi-discrete cells but the overall marginal shear will yield a 
multicell Mode. Nonetheless...the moist airmass coupled with 
moderate unidirectional southwesterly flow fields will probably yield at 
least some potential for localized wind damage this afternoon. 


.Smith/Mead.. 05/30/2015 


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


Attention...WFO...iln...lmk...iwx...ind...pah...lot...ilx...lsx... 


Latitude...Lon 38068950 38728943 40638738 41058640 41108531 40748478 
40298472 38398675 37838775 37748891 38068950