Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
708 PM EDT Mon Oct 03 2022

Day 1
Valid 01Z Tue Oct 04 2022 - 12Z Tue Oct 04 2022

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST AND THE COASTAL MID-ATLANTIC STATES...


...Coastal Mid-Atlantic States...
A strong coastal low that is nearly stationary centered off the
coast of the Delmarva continues to wrap bands of mostly light to
moderate rain into portions of the Mid-Atlantic. The bands could
develop some convective elements across the Eastern Shore
overnight, and some of the activity over Long Island has shown
some modest convective tendency recently.  Most of the convection
has been confined to areas over the ocean east of center.  There
is greater uncertainty than usual as to where the core of the
heaviest rain will set up, so the Marginal Risk area is focused on
where rain is ongoing now along with some of the mesoscale
guidance projections, which have been shifty as of late.


...Southwest...
A shortwave dropping into the base of the upper-level trough will
encounter a rather moist airmass has triggered rounds of diurnally
driven convection. Any of these thunderstorms may produce moderate
to heavy rainfall with the potential for flash flooding over the
next several hours, especially across areas of complex terrain and
burn scar areas. QPF amounts may be as high was 1 to 2 inches
therefore the Marginal Risk remains in effect for the Four Corners
region and into parts of the lower Colorado Basin.  The risk area
was expanded per recently issued Mesoscale Precipitation
Discussion #1073.

Roth/Wegman/Campbell


Day 2
Valid 12Z Tue Oct 04 2022 - 12Z Wed Oct 05 2022

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST AND THE SOUTHERN ROCKIES/HIGH PLAINS...

...2030Z Update...

No changes made with this update. The expected precipitation
across much of NM and small portions of the neighboring states
remains unchanged.

Across the mid-Atlantic through southern New England, there
remains significant disagreement among the guidance on rainfall
locations and intensity. Thus far today, rainfall rates have been
unimpressive even in the areas getting the heaviest rain, largely
staying under 1/4 inch per hour. Thus, despite continued large
differences on where the core of the heaviest rain will be, think
rainfall rates on the whole will remain under values needed for
flash flooding. Note that portions in today's MRGL risk (southern
NJ, northern DE & Philadelphia) have low FFGs, such that rapid
training may result in an isolated flash flooding risk. Thus, a
future upgrade to a MRGL in this area may be needed for Tuesday,
but is not expected at this time.

Wegman

...Previous Discussion...

The shortwave trough will continue to dip southeast across the
southwestern U.S., pushing a cold front farther south and east
into the southern Rockies and High Plains during this period. The
anomalously moist airmass will remain pooled near the boundary
which will continue to maintain and support diurnal thunderstorms.
Some of these storms may reach or exceed 0.50 inch/hr intensities
which increases the risk for potential flash flooding. A Marginal
Risk for excessive rainfall remains in effect from southern
Arizona/New Mexico to central Colorado and the panhandles of
Oklahoma and Texas.

Campbell

Day 3
Valid 12Z Wed Oct 05 2022 - 12Z Thu Oct 06 2022

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST AND THE SOUTHERN ROCKIES/HIGH PLAINS...

...2030Z Update...

No changes to the previous forecast were made with this update.
Expected precipitation across much of NM remains unchanged from
the previous. There is certainly some room for a localized upgrade
to a SLGT along the mountains, particularly the Sacramento
Mountains, but that will be dependent on how much rain is picked
up in this area both today and Tuesday.

For the Northeast, the coastal low will finally begin to move out
to sea on Wednesday. There will likely be lingering rain along the
Jersey Shore north to coastal RI/MA, but rainfall amounts should
stay below FFG thresholds.

Wegman

...Previous Forecast...

The frontal boundary will continue to press southward into the
Southern Plains. Showers and thunderstorms will persist along this
boundary, producing moderate to heavy rainfall across parts of the
Southwest and Southern Rockies. The threat for excessive rainfall
will remain elevated given the recent wet pattern and available
moisture to tap into. A Marginal Risk covers New Mexico, eastern
Arizona, southern Colorado and parts of western Texas.

Campbell


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