U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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Storm Prediction Center ac 151619 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1119 am CDT Wed Aug 15 2018 


Valid 151630z - 161200z 


..there is a slight risk of severe thunderstorms over parts of 
South Dakota and Nebraska... 


... 
The main severe-storm threat area is over parts of the north-Central 
Plains region this afternoon and evening, for large hail and severe 
gusts. 


... 
Water vapor loop shows a vigorous shortwave trough tracking eastward 
across northeast Wyoming. This system will move into South Dakota/NE this 
afternoon, with strengthening winds aloft and height falls spreading 
across the region. Thunderstorms are ongoing this morning along the 
South Dakota/NE border, which will likely leave an outflow boundary that could 
provide the focus for re-development later today. 12z cam solutions 
are consistent in the development of intense storms by late 
afternoon, tracking east-southeastward across the slight risk area 
into the evening. Forecast soundings show rather steep mid level 
lapse rates and MLCAPE of 1500-2000 j/kg, along with strong 
deep-layer shear. This will promote the development of a few 
supercells capable of very large hail, damaging winds, and perhaps a 
tornado or two. 


..eastern Colorado/nm and the Texas Panhandle... 
Strong heating is occurring early today over southeast Colorado and 
northeast nm, with weak upslope low-level flow. Ample mid/upper 
level moisture combined with moderate cape values, will result in 
scattered thunderstorms over this region by mid-afternoon. These 
storms will spread eastward across the marginal risk area during the 
evening. The strongest cells will be capable of gusty/damaging 
winds and hail. 


..OK into in/KY... 
Multiple clusters of thunderstorms are ongoing this morning from the 
Ozarks into the lower Ohio Valley. Pockets of heating around these 
clusters will allow for the development of afternoon thunderstorms. 
Wind fields aloft are marginal for convective organization, but high 
surface dewpoint values and rather strong winds in the 1-3km layer 
suggest a few storms could occasionally produce gusty/damaging 
winds. 


..northeast states... 
Fast northwest flow aloft is present today across eastern Canada, 
and will spread into parts of New York and New England later today. 
Multiple progressive shortwave troughs embedded in the flow will 
help initiate scattered thunderstorms that track into the marginal risk 
region this afternoon and evening. Relatively steep lapse rates and 
MLCAPE values of 1500+ j/kg may result in hail and/or gusty/damaging 
winds in a few of the stronger cells. Forecast coverage intense 
cells suggests that marginal designation is appropriate today, but some 
potential exists for an upgrade later today if coverage exceeds 
expectations. 


.Hart/squitieri.. 08/15/2018 


$$ 

Mesoscale Discussion


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acus11 kwns 151626 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 151626 
mez000-nhz000-vtz000-151830- 


Mesoscale discussion 1294 
National Weather Service Storm Prediction Center Norman OK 
1126 am CDT Wed Aug 15 2018 


Areas affected...much of ME...northern New Hampshire 


Concerning...severe potential...watch unlikely 


Valid 151626z - 151830z 


Probability of watch issuance...5 percent 


Summary...increasing thunderstorm coverage expected with isolated 
damaging wind gusts and/or hail possible. 


Discussion...airmass ahead of a shortwave trough moving through 
southern Quebec continues to destabilize amidst mid 60s dewpoints 
and ample daytime heating. Widely scattered convection has been 
observed thus far with storms struggling to maintain updrafts. As 
heating continues and the forcing for ascent increases, the 
expectation is for more overall thunderstorm coverage and 
persistence. Given the moderate instability (i.E. MLCAPE around 
1500-2000 j/kg), a few stronger updrafts capable of damaging wind 
gusts and/or hail are possible. However, the overall severe 
potential will be mitigated somewhat by the presence of generally 
modest mid-level flow and resulting lack of strong vertical shear. 


.Mosier/Hart.. 08/15/2018 


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


Attention...WFO...car...gyx...btv... 


Latitude...Lon 46497014 47096958 47376903 47186802 45956787 45416767 
44786827 44506882 44276953 44187051 44147117 44427167 
45117144 45837028 46497014