Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
407 AM EDT Mon Jun 05 2023
Valid 12Z Mon Jun 05 2023 - 12Z Tue Jun 06 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN HIGH PLAINS...
...Southern Plains through the Northern Rockies...
Not a lot of changes made to the previous Excessive Rainfall
Outlook for this time period as the persistent, stagnant blocked
flow persists across the nation. There will continue to be an axis
of above average PW stretching from the Southern to Central High
Plains, through the Central to Northern Rockies and into the
Northern High Plains. Embedded in this high PW axis will be
numerous vorts that will help enhance uvvs and convective
activity. The last several days, areas of the Southern High
Plains from northeast NM into the TX/OK Panhandle have seen some
organization and locally heavy totals than other areas that have
not seen as much overlap. For this reason, we continue to depict
a slight risk area from northeast NM into Northwest TX where
models again show potential for additional convection. There is a
typical amount of model qpf spread but at least some consensus in
the models for additional convection across areas that are more
hydrologically sensitive given recent rains. The slight risk area
fits well with where the latest HREF neighborhood probabilities
are high for 1"+ rains and overlap with the above mentioned heavy
rains over the past few days. HREF probabilities are also high
for 1"+ amounts in spots through the marginal risk area, but do
not have the consistent overlap with recent heavy rain areas of
previous days as do sections of the Southern High Plains.
...Central California coast Range into the Sierra Nevada...
A strong closed low offshore of Southern California will be
swinging steadily northeastward to a position at the coast Monday
afternoon at which time it is then expected to slow significantly.
An increasingly upper difluent flow pattern to the north and
northeast of this closed low will support increasing scattered
convection Monday afternoon from the central California Coast
Range, northeastward into the Sierra in a region where PW values
will be rising to 1 to 2+ standard deviations above the mean.
The previous marginal risk area was expanded to the southwest from
the Sierra to the Central California Coast Range where the latest
HREF probabilities show some potential for hourly rainfall rates
of .50-1" in this anomalous PW axis from Monday afternoon into
evening. With stream flows remaining above average, isolated flash
flooding possible. In addition, some of this heavy rain potential
may occur across burn scar regions from the past several years.
A marginal risk was maintained along and ahead of the
strengthening frontal boundary forecast to stretch northwest to
southeast from south central Canada into eastern portions of the
Northern Plains and Upper MS Valley. With PW rising to 2+
standard deviations above the mean in an axis of MUCAPE values
1000-2000 J/kg in the vicinity of this front, locally heavy
rainfall amounts are possible. The simulated radars from the
latest CAM guidance suggests potential for slow moving cells in
the vicinity of this front. With areas of higher than average
stream flow as per the National Water Model from south central MN
northwestward along the MN/ND border, isolated runoff issues
possible from hourly rainfall rates of 1"+ with these slower
moving cells. The marginal risk area agrees well with the latest
CSU first guess fields which shows a marginal risk across eastern
ND into northwestern MN.
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