U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 010600 
Storm Prediction Center ac 010559 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1259 am CDT Wednesday Jul 01 2015 

Valid 011200z - 021200z 

..there is a slight risk of severe thunderstorms MO to the Tennessee Valley... 

..There is a marginal risk of severe thunderstorms northern/Central High plains to the 

..there is a marginal risk of severe thunderstorms northeast / New England... 

..There is a marginal risk of severe thunderstorms Arizona... 

Scattered severe storms with a couple tornadoes...large hail...and 
damaging winds are expected across parts of Missouri in the late 
afternoon and evening. Storms with scattered damaging winds are 
probable midday into the afternoon across the Tennessee Valley. 

Upper trough over the lower Great Lakes to central Appalachians will 
progress across the northeast into New England through this 
afternoon with low-amplitude vorticity maxima persisting upstream 
across Ontario/Great Lakes. These will help maintain a broad 
cyclonic flow regime over much of the central/eastern Continental U.S. With several 
embedded minor middle-level impulses from the southern Canadian rockies to 
the Tennessee Valley. A Stout upper anticyclone will remain anchored over 
the eastern Great Basin. 

..MO area... 
An mesoscale convective system will be ongoing at 12z aided by robust low-level warm air advection. While 
this activity will diminish...in its wake...residual convective 
outflow amidst intense diabatic heating over Kansas should yield a 
strengthening baroclinic zone. With around 70 degree surface dew 
points...a corridor of moderate to large buoyancy will likely 
develop. Convection should form over parts of western MO by late 
afternoon. Veering winds with height should result in effective 
shear around 40 knots...aiding in a few supercells with large hail and 
tornadoes possible. Convection should grow upscale into an mesoscale convective system in 
the evening as a southwesterly low level jet intensifies with the risk transitioning to 
damaging winds. 

..TN valley... 
Low-level moisture advection from the lower MS valley in conjunction 
with strong diabatic heating should result in moderate to large 
buoyancy developing downstream of an mesoscale convective system expected to be ongoing at 
12z over MO. While this mesoscale convective system may decay for a time...remnant 
southeastward-propagating outflows should Foster surface-based development 
around midday. While deep-layer shear should be modest...one or more 
multicell clusters should form with damaging winds as the main 

..nrn Great Plains... 
A weak shortwave impulse over southern British Columbia should reach the 
Saskatchewan/Mt/ND border area at 02/00z. This should aid in 
isolated thunderstorms despite a nebulous surface pattern and predominately 
northerly low-level winds. But within a belt of moderate to strong 
middle-level nwlys...30-40 knots effective shear could Foster a couple 
supercells producing severe hail/wind. Given the lack of surface 
focus and low confidence in thunderstorm coverage...will maintain marginal 
risk probabilities this outlook. 

..northeast/New England... 
Current convection from eastern New York to eastern Virginia will likely be ongoing at 
12z across mainly southern New England. The strongest shear profiles will 
exist in the morning...but surface-based instability should be quite 
limited. Scattered diurnally driven thunderstorms should form across parts 
of New York into western New England in the afternoon beneath the middle-level 
thermal trough. While the combination of buoyancy and shear should 
remain modest...stronger updrafts will be capable of marginally 
severe hail and localized damaging winds. 

In the wake of relatively widespread convection currently...guidance 
is fairly consistent in suggesting both weaker middle-level elys and 
warmer middle-level temperatures this afternoon/evening. This suggests 
the degree of convection will be suppressed relative to recent days. 
Still...sufficient buoyancy/shear should exist for a risk of severe 
wind gusts with perhaps only isolated convection over the higher 

.Grams/leitman.. 07/01/2015 

Mesoscale Discussion

acus11 kwns 010854 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 010854 

Mesoscale discussion 1263 
National Weather Service Storm Prediction Center Norman OK 
0354 am CDT Wednesday Jul 01 2015 

Areas affected...Long Island / far southern New York / CT / Rhode Island 

Concerning...severe potential...watch possible 

Valid 010854z - 011000z 

Probability of watch issuance...40 percent 

Summary...line of storms over the lower Hudson Valley will move northeastward 
across Long Island and CT and potentially yield an isolated 
wind-damage risk as the squall line organizes further. 

Discussion...radar mosaic over the past hour has shown a 
consolidation of line segments into a larger-scale convective line 
over the lower Hudson Valley and areas S of NYC. Water vapor 
imagery shows a potent upstream shortwave trough over the central 
Appalachians becoming negatively tilted this morning. The 
increasing larger-scale forcing for ascent and strengthening 
middle-tropospheric southwesterly flow --sampled by the okx VAD from 35 to 55 
knots-- over the past few hours will support convective line longevity. 
Surface analysis places a wedge of higher Theta-E characterized by 
temperatures in the lower 70s with middle-upper 60s dewpoints over Long Island 
into much of CT. To the north over Massachusetts...warmer/more moist 
boundary-layer air will probably not penetrate the area as the 
convective line will outrun the northward advancement of a slow-moving 
warm front draped over southern New England. Relatively drier air above 
the near-surface layer may act to enhance or reinforce wind gust 
potential. As a result...strong to severe straight-line winds 
/gusts 40-60 miles per hour/ may yield isolated wind damage across southern New 
England over the next few hours. 

.Smith/Edwards.. 07/01/2015 

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


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40977188 40507359 41267389