Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
722 PM EDT Fri Aug 21 2026
Day 2
Valid 12Z Sat Aug 22 2026 - 12Z Sun Aug 23 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE MID-
ATLANTIC...

...20Z Update...

The Slight Risk area over the Mid-Atlantic was trimmed up a bit to
account for QPF trends/placement in the most recent CAM runs. This
area also aligns well with where the HREF and REFS have the highest
probabilities (50-60%) of 2" in 6 hrs. Localized areas within the
Slight that received heavy rainfall yesterday and today may see
high-end Slight impacts. Elsewhere, the surrounding Marginal Risk
area was maintained and expanded to include portions of the Ohio
Valley and eastern Great Lakes where QPF has trended up in the
vicinity of a strengthening low pressure system. This pattern may
allow for some lake-enhanced precipitation across portions of Ohio,
Pennsylvania, and New York. Given recent heavy rains in the Ohio
Valley, the Marginal was expanded to include portions of Ohio and
West Virginia that may be sensitive to flooding with additional
precipitation on Saturday. The Marginal Risk area across the
Intermountain West was also maintained and expanded to include more
of the northern Rockies as anomalous moisture pushes north across
the region.

Dolan

...Previous Discussion...

...East Coast...

Large scale pattern will continue its evolution into a much more
amplified setup with a deepening mid-latitude trough extending from
Canada all the way into the eastern CONUS. This places the entrance
region of an upper level jet in favorable position over an airmass
with precipitable water values of 2 to 2.25 inches as a few robust
disturbances rotate around the leading edge of the trough which
will support heavy rainfall along the eastern seaboard. Current
model consensus is a moderate to heavy QPF footprint extending from
coastal SC all the way up into ME. Primary concern for excessive
rainfall is along and east of I-95 in the Mid-Atlantic due to the
heavy/excessive rain that occurred on Thursday as much as the with
expected rainfall amounts in the Day 2 period.

...West...

Persistent ridging across the Western U.S. will finally begin to
shift back over the Plains as a robust trough over the Pacific
Ocean makes headway into the Pacific Northwest and begins pushing
the pattern downstream and flattening the ridge up top. The
progression of the trough will lead to an influx of both regional
moisture and ascent as the trough makes progress into OR/WA as we
move into the middle part of the weekend. PWAT anomalies are
anticipated to surge upwards of 2-3 standard deviations above
normal for this time of year as far north as Idaho and western
Montana with the rest of the West firmly entrenched within a +1
standard deviation PWAT anomaly, good enough to maintain a
persistent monsoonal type pattern over the Desert Southwest and
Great Basin into the Central Rockies. A broad MRGL risk over much
of the Western U.S, east of the Pacific coast states will suffice.

Bann


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