Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Fri Sep 29 2023
Valid 12Z Fri Sep 29 2023 - 12Z Sat Sep 30 2023
...A MODERATE RISK OF EXCESSIVE RAINFALL IS IN EFFECT OVER
PORTIONS OF THE NORTHEAST...
...Mid-Atlantic into Northeast...
An upper-level trough will support the amplification of an
inverted surface trough and low pressure system off the
Mid-Atlantic/Northeast Coasts today. There will be thunderstorms
with heavy rainfall and serious flash flooding concerns over parts
of the northern Mid-Atlantic and Northeast. Rounds of showers and
thunderstorms, which began overnight, will continue and pickup in
intensity through the morning rush hour. Some of the 00z hi-res
guidance didn't capture the 01z-02z storms that moved into the New
York Metro so there is a concern that this under performance may
continue into the day 1 period. This antecedent rainfall has also
primed surfaces for runoff of subsequent rainfall. A favorable low
level jet, shallow instability and substantial surface
frontogenesis will combine to produce efficient rainfall rates on
the order of 0.25-0.5"/hr from northeastern New Jersey to coastal
Connecticut where a Moderate Risk of Flash Flooding is in effect.
Anywhere from 2-6" of rainfall are expected to accumulate by later
this evening when the greatest threat of flash flooding will
subside. Areas that are prone to flash flooding across the New
York Metro Area will likely experience flash flooding today, so
turn around don't drown!
...Upper Midwest/Great Lakes...
Shortwave energy propagating south-north into Canada will drive
showers and scattered to isolated thunderstorm activity over the
Upper Midwest today. Another inverted surface trough will direct
and enhance anomalous moisture plume with PWATs of 1-2" into much
of Minnesota and northwestern Wisconsin. Rainfall totals of 1-2
inches are possible over portions the Upper Midwest by tomorrow
The back end of a slow moving cold front will act as a focus for
scattered to isolated showers and thunderstorms today. A Marginal
Risk area was continued to account for any localized flash
flooding concerns that may arise.
The Day 2 outlook will be updated by 0830Z.
The Day 3 outlook will be updated by 0830Z.
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt