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< Day 1 Outlook Day 3 Outlook >
 
WPC Day 2 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
 
Updated: 0815 UTC Sat Jul 20, 2019
Valid: 12 UTC Jul 21, 2019 - 12 UTC Jul 22, 2019
 
Day 2 Excessive Rainfall Forecast
 
Forecast Discussion
 
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 AM EDT Sat Jul 20 2019
 
Day 2
Valid 12Z Sun Jul 21 2019 - 12Z Mon Jul 22 2019 

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL 
PLAINS EAST INTO THE OHIO VALLEY... 

...Central Plains, Mid-MS Valley, OH Valley...
A front will continue to slowly move into the Central Plains, 
Mid-MS Valley into the OH Valley Sunday into early Monday. Models 
are coming into slightly better agreement on the orientation and 
timing of the front, especially across the OH Valley.  The GFS and 
now CMC are showing signs, however, of more organized convection 
as mid-level energy moves atop the aforementioned front.  The rest 
of the model guidance remains weaker with the impulses and the 
position of the jet axis a bit farther removed to the north and 
east.  Thus the GFS and CMC have higher QPF amounts across eastern 
KS into northern MO as an organized complex moves from SE NE into 
MO Sunday evening/night. Given the GFS has shown run to run 
continuity, the CMC is now showing similar features and GEFS 
probabilities support the higher QPF amounts, felt it should be 
incorporated into the model blend.   

With respect to the ingredients in place, moisture and instability 
will continues to pool right along and south of the boundary, with 
precipitable water around 2 inches and MUCAPE values over 3500 
J/kg. As previously mentioned, there continues to be uncertainty 
with respect to the interaction between the mid-level energy and 
the surface features, thus resulting in questionable organized 
convection in the central CONUS.  At this time, forecasting weak 
to modest mid-level impulse atop this surface boundary which 
should promote convection along the front from the Central 
Plains/Mid-MS Valley across the OH/TN Valley.  

Areal average QPF generally ranges between 1-2+ inches with 
locally higher amounts associated with convection. The two main 
areas of concern are across east KS/northern MO with the potential 
for organized convection and portions of the OH Valley where FFG 
are lower. Rain rates could climb over 1.5 inches/hour. The 
propagation of the convection along the front should limit the 
flash flood potential as it sinks south. However, if a complex 
forms as depicted by the GFS, some training could occur. There is 
enough signal to support isolated to potentially more widespread 
flash flooding concerns, therefore a Slight Risk was introduced to 
encompass these regions. 
 
...Southern Rockies...
As a front continues to dive south through the Northern Plains, 
settling into the Central Plains, Mid-MS Valley and OH Valley, a 
trailing boundary along the Front Range will act as a catalyst for 
convection during the afternoon into the overnight hours Sunday 
into Monday.  Mid-level high pressure will build overhead with 
impulses rounding this feature which too will promote vertical 
motion. At the surface, as the Canadian high builds south into the 
Northern Plains, easterly flow will enhance upslope flow during 
the afternoon. Moisture that pooled south of the aforementioned 
front will bank up against the high terrain with instability of 
over 2000 J/kg available during the afternoon/evening hours.  
These factors should promote convective initiation along the 
windward slopes of the Rockies in CO and NM.  Given fairly weak 
flow, convective cells should have fairly slow storm motion along 
the slopes with more erratic propagation as they grow upscale.  
Regardless, expect heavy rainfall is given decent moisture 
transport across this region. Hourly rain rates may approach 1 
inch/hour which is just shy of the one hour FFG (1.5 inches) 
across this region.  Again, given the uncertainty with respect to 
the evolution and storm motion, feel there could be some locations 
that see 2+ inches when all is said and done.  

Models have trended down with QPF for the 00Z forecast suite and 
thus have trimmed amounts slightly.  Though ensemble 
probabilities, albeit somewhat low, still highlight this region as 
exceeding 2 inches.  Models tend to do poorly within this flow 
regime/pattern and thus will maintain the Marginal Risk across 
this area with some refinements made based on WPC QPF. 

Pagano     
 
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
 

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