Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
443 AM EDT Sun Jul 12 2020
 
Day 2
Valid 12Z Mon Jul 13 2020 - 12Z Tue Jul 14 2020 

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 
THE NORTHERN AND CENTRAL GREAT PLAINS TO UPPER MISSISSIPPI VALLEY 
AS WELL AS A PORTION OF THE NORTHEAST...

...Northern/Central Great Plains to Lake Superior...
A reinforcing shortwave trough swings a positively tilted trough 
around a low over the northern Canadian Prairies that will be over 
the western Canadian Prairies to the northern Rockies Monday 
morning to a negatively tilted trough over the eastern Canadian 
Prairies by Tuesday morning. This sends a cold front and embedded 
surface wave from the west-central Dakotas Monday morning to the 
MN/WI border and near the NE/KS line by Tuesday morning. Return 
flow ahead of this front will prime the Plains with elevated 
moisture and instability with the front providing the forcing for 
organized thunderstorms with efficient rain rates over much of the 
northern Plains (from central Nebraska and western South Dakota 
northeast across Minnesota into northern Wisconsin) through this 
time. Nearly all of this area has seen well above normal rainfall 
over the past two weeks with western South Dakota having 
particularly low FFG at this time (generally below 1.5 inches in 
3hrs). The surface low center track will shift across SD, but the 
timing looks to be such that the most vulnerable portion of the 
state (the far southwest) would avoid much diurnal instability. 
For Monday night more organized activity over northern MN ahead of 
the cold front may have a southern tail that becomes better 
aligned with the southerly inflow making for a potential Slight 
Risk in southern/central MN.


...Northeast...
A reinforcing shortwave trough shifts southeast from the northern 
Great Lakes, digging the trough over the Northeast through Monday 
night. Increasing southwesterly low level flow up the Eastern 
Seaboard ahead of a surface low developing on a cold front tonight 
brings elevated moisture across the Northeast. Given the potential 
for locally heavy rain up the Northeast Corridor which has had wet 
antecedent inches (particularly in NJ) maintained a Marginal Risk 
from the Philadelphia metro to eastern Maine and up to Lake 
Champlain. There is a risk for repeating activity, particularly 
from the Adirondacks to southern Maine which will have a pivoting 
front through much of the outlook period.

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