Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
412 PM EDT Sat Jul 04 2020
 
Day 2
Valid 12Z Sun Jul 05 2020 - 12Z Mon Jul 06 2020 

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL PERSISTING OVER 
THE EASTERN DAKOTAS AND FAR NORTHWEST MINNESOTA ON SUNDAY...

...Northern Plains/Upper Mississippi Valley...

20Z update...

The alignment of upper-level flow/lift and low-mid level moisture 
over the Dakotas and Minnesota continue to favor organized 
convection. Several of the models are hinting that the heaviest 
amounts will occur near the border of Minnesota and eastern 
North/South Dakota- a couple of the hi-res models show a a few 
hours where the hourly rates may reach upwards of 1 to 1.75 
inches/hour across this area. The Slight Risk that was in place is 
still warranted and very minimal adjustments were made.

Campbell

Previous Discussion... The area will remain located between an 
upper level ridge over the central part of the country and low 
pressure over parts of Manitoba and Saskatchewan.  This leaves 
broad west to southwest flow aloft across the region that has 
multiple weak and difficult to time shortwaves embedded within 
that flow.  Those items, combined with a quasi-stationary front at 
the surface and residual outflow boundaries from ongoing/previous 
convection will play a role in where convection will continue to 
develop.  There will be plenty of moisture across the region with 
precipitable water values between 1.6 inches and 2 inches by 
Sunday afternoon...with the maximum values approximately 2 
standardized anomalies above climatology focused over a region 
with lowest flash flood guidance.  Considering the on-going 
chances for scattered convection impacting the same areas before 
the Day 2 outlook period begins on Sunday morning, the Slight Risk 
area remains in place with only modest adjustments needed based on 
the 04/00Z suite of numerical guidance.  

...Gulf Coast...

20Z update... PW values near 2 inches will be pooled over much of 
the Gulf coast and areas north during this time; which will aid in 
developing/sustaining widespread convection through this period. 
Most of the guidance has the bulk of the QPF aligned from 
Louisiana to Georgia with the highest amounts focused near the 
Mississippi River delta and across the Florida panhandle. The EC 
continued to be outlier with its much heavier qpf bullseye over 
West/Northwest Louisiana as indicted from the previous discussion, 
therefore minimal use of this solution was use for this forecast. 
The Marginal Risk area that was inherited only requirement minimal 
adjustment to reflect the latest WPC QPF.

Campbell

Previous discussion... Models continue to show broad upper level 
forcing over a very moist and unstable airmass along and the Gulf 
Coast region...with greatest coverage of precipitation and 
greatest chances for intense downpours looks to be from the 
afternoon through the evening across the area.  Spaghetti plots of 
2 inch per 6 hour rainfall amounts from high resolution guidance 
favored the area along the Gulf coast on Sunday morning which 
gradually lifts north throughout the day.  Other than the 04/00Z 
ECMWF, the models tended to agree in principle on the northward 
shift from the Gulf but certainly offered a variety of placement 
and amounts.  The 04/00Z ECMWF backed off its maximum QPF amounts 
associated with a well-defined MCV dropping southward across 
Louisiana during the day but remained about the only piece of 
guidance with an emphasis on that solution. 

...Western High Plains...

20Z update...

There continues to be a signal for heavy rain shower activity, 
however the spread remains moderate/significant in regards to the 
the exact location and intensity. Maintained the Marginal risk 
that was in effect for this region, somewhere in this area will 
likely have isolated flash flooding. 

Campbell

Previous discussion... Maintained the Marginal Risk area over 
parts of the Western High Plains from southwest Kansas into the 
Oklahoma/Texas panhandle region given a continued multi-model 
signal for locally heavy rainfall to develop Sunday evening/early 
Monday morning.  Model QPF values have come down a bit and Flash 
Flood Guidance values are at or above 2.5 inches per hour...but 
the area is near the western end of a stationary front that 
provides focus for rainfall along the Gulf and near a lee-side 
trough.  The Marginal Risk area was focused near the proximity of 
the best moisture transport and the boundaries.  Spaghetti plots 
from the SREF show the ARW members focusing some potential for 2 
inch QPF per 24 hours in southeast Colorado while the GEFS has a 
few members farther south. 

Bann

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