< Day 2 Outlook
WPC Day 3 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 2024 UTC Wed Jul 15, 2020
Valid: 12 UTC Jul 17, 2020 - 12 UTC Jul 18, 2020
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
427 PM EDT Wed Jul 15 2020
Valid 12Z Fri Jul 17 2020 - 12Z Sat Jul 18 2020
...THERE IS A SLIGHT RISK OVER THE NORTHERN RED RIVER OF THE NORTH
...2030 UTC Excessive Rainfall Discussion...
Only change was to expand the Slight Risk area in eastern North
Dakota and northwestern Minnesota given the persistent wet
conditions with the most recent bout of moderate to locally heavy
rainfall occurring as recently as Tuesday. The signals from the
models have been consistently showing a signal for some 1 to 1.5
inch rainfall amounts in the Day 3 period...with the better chance
for heavier rain north of the international border. The Margial
Risk area surrounding the Slight Risk area was largely untouched.
Only some minor adjustments were made to the Marginal Risk area
extending from the Mid-South to New England...and those changes
were largely made to fit the latest guidance and not the result of
a change in forecast reasoning.
...0830 UTC Excessive Rainfall Discussion...
...Northern Great Plains to Lake Superior...
A shortwave trough that reaches the WA coast Thursday will shift
east across MT Friday. Return flow behind the leading ridge axis
and ahead of the trough brings elevated moisture across northern
Plains with PWs reaching 2 standard deviations above normal by
18/00Z over the eastern Dakotas which spreads east to Lake
Superior through Friday night. The combination of increasing
moisture at the diurnal peak puts the heavy rain focus over
eastern ND into northern MN where many areas have had well above
normal rainfall recently. Of particular note is the northern Red
River Valley of the north (north of Grand Forks) as well as
central MN southeast from Fargo. As of now guidance indicates the
heavy rain axis may be closer to the northern area than the
southern, so in coordination with WFO FGF raised a Slight Risk for
only areas north of Grand Forks. Strong upper level westerly flow
should keep activity generally progressive with large organized
thunderstorm clusters likely. Given the elevated moisture, Slight
Risk may be needed wherever the heaviest axis is forecast.
...Mid-South...Tennessee Valley...Mid-Atlantic to New England...
A slow moving/stalled frontal boundary near or south of the Ohio
River should provide a focus for ongoing activity Friday with 2
inch PWs (1.5 to 2 standard deviations above normal) and ample
instability continuing a heavy rain threat. Farther northeast the
frontal wave that lifts across the eastern Great Lakes Thursday
night drags a cold front into New England during the day Friday.
There is still sensitivity from heavy rain from Fay over northern
NJ/southern NY, but confidence is not there yet for significant
rainfall over that particular area. Otherwise the upper Hudson
Valley has been rather dry recently before pockets of heavy recent
rainfall in interior New England. Should the focus of heavy rain
become apparent over any particularly sensitive areas a Slight
Risk would be warranted.
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt