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Day 2 Outlook >
WPC Day 1 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 2338 UTC Thu Aug 16, 2018
Valid: 01 UTC Aug 17, 2018 - 12 UTC Aug 17, 2018
Day 1 Excessive Rainfall Forecast
Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
746 PM EDT Thu Aug 16 2018
Day 1
Valid 01Z Fri Aug 17 2018 - 12Z Fri Aug 17 2018 


...Mississippi Valley/Midwest...
An MCV moving across OK combined with a preceding outflow boundary 
and convection forming on the northern side of an ML CAPE gradient 
and south side of an upper low are leading to thunderstorm 
activity with heavy rainfall, expected to zip eastward from 
southeast KS into southern MO as outflow boundaries intersect from 
west to east.  The atmosphere remains highly unstable (especially 
across AR). Given the locally heavy antecedent rainfall across 
portions of OK, southeast KS, northern AR and western TN...there 
is a conditional flash flood threat into the overnight.  Should 
convection form in this instability axis then an increased flash 
flood threat would result.  Feel the Slight Risk remains warranted 
for now.

The Marginal risk across the Upper MS Valley is maintained.  An 
outflow boundary near a surface low is leading to convection 
creeping southward into southern WI, which is maximizing now.  The 
combination of available instability and significant PW values 
lead to the promise of hourly totals to 2.5" until the storms die 
somewhere near the WI/IL border during the next 3-4 hours.  The 
pulse nature and small scale nature of cells may limit the overall 
duration of heavy rates. Still would anticipate pockets of 2"+ 
amounts, warranting a Marginal flash flood risk, with isolated 
warnings expected. 

...Southwest U.S....
An active Monsoon day started early, with high PWs, plenty of 
instability, and an upstream upper trough across CA and NV 
instigating thunderstorms with heavy rainfall.  Hourly rain totals 
to 2.5", with local amounts in the 3-4" range, are possible until 
convection dies roughly around 05z.  A new MPD is likely to be 
issued in this area.  Restricted the reach of the marginal and 
slight risks per convective trends.

Day 1 threat area:

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