Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
440 AM EDT Fri Jul 30 2021
 
Day 1
Valid 12Z Fri Jul 30 2021 - 12Z Sat Jul 31 2021 

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS 
OF THE SOUTHWEST, GREAT BASIN AND CENTRAL ROCKIES...

...Southwest U.S. to the Northern and Central Rockies...
The threat for heavy to excessive rainfall will continue on Friday 
and Friday night as the northwestward propagation of mid- to 
upper-level energy across the Southwest U.S. supports another 
round of convection from late morning or early afternoon into the 
late evening hours.  Precipitable water values in the 1.5 to 175 
inch range are 2 to 3 standardized anomalies greater than 
climatology across the area for this time of the year.  The amount 
of moisture combined with the dynamics will again result in 
convection capable of supporting rainfall rates of 0.5 inch or 
more anywhere from the eastern Arizona and southern Nevada into 
portions of the Sierra Nevada range, the Great Basin/Intermountain 
Region and in proximity to the Uinta range.  The threat of flash 
flooding will locally be enhanced by slow cell motion due to the 
slow/weak steering flow.

Out over the other side of the Rockies, maintained the Slight Risk 
area extending from Colorado into southern/southeast Wyoming as 
deep-layer southeast flow will continue to tap deep moisture and 
draw it upslope and to higher elevations. The anomalous moisture 
and slow moving shortwave energy aloft should result in late day 
and evening storms capable of producing downpours...with the 
foothills and any impacted burn scar areas most vulnerable.
  
...Central Plains to the Mid Mississippi Valley..
Troughing across the region coupled with modest instability will 
increase chances of heavy rounds of precipitation with convection 
and training storms, especially Friday evening and during the 
overnight hours as precipitable water values sit in the 1.75 to 
2.00 inch range and MU CAPE values are still forecast to be near 
2000 J/kg. The threat of excessive rainfall is mitigated a bit by 
higher Flash Flood Guidance values.  On the other hand, the 
possibility of training or repeat convection is the main concern 
with some of these storms expected to drop heavier amounts.

Bann


 
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt