Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
824 PM EDT Wed Jun 29 2022

Day 1
Valid 01Z Thu Jun 30 2022 - 12Z Thu Jun 30 2022

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL OVER PORTIONS
OF THE SOUTHEAST AND THE SOUTHWEST AS WELL AS SOUTHERN FLORIDA...

...Southwest...
The Marginal Risk area was maintained for portions of Arizona and
southwest New Mexico where moisture (precipitable water values of
a little less than 1.0 inches) will be lingering in a region of
light and variable low level flow. Models indicate moist
southwesterly flow developing upstream...resulting in a plume of
higher precipitable water values that noses towards Arizona and
(in a few cases) near the site of recent flash flooding. With soil
moisture well above the 98th percentile for much of this area,
isolated flash flooding and runoff is a concern.  

...Southeast...
23Z Update -- Expanded the Marginal Risk area a bit to the north
across more of central MS and central-northern AL-GA, based on the
latest observational and mesoanalysis trends, along with the 18Z
CAMs (including HREF 40km neighborhood exceedance probabilities).

Hurley

16Z update -- Hi-res solutions keep rainfall rates upwards of 1-2
inches/hour across the Gulf Coast and points to the north.
Marginal Risk in effect covers most of the locations with
increased sensitivity for excessive rainfall and isolated flash
flooding concerns; however, it was expanded into southern South
Carolina. Storms associated with a MCV tracking through Georgia
and South Carolina could produce 2 to 3 inches/hour this afternoon.

Campbell



Day 2
Valid 12Z Thu Jun 30 2022 - 12Z Fri Jul 01 2022

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE WESTERN GULF COAST...

...Western Gulf Coast into the Central Gulf Coast...

21Z update... The QPF across the western/central Gulf Coast
continues to have an increasing trend and the new WPC QPF ranges
from 2 to 7 inches; the bulk of the higher amounts are expected to
fall between the Corpus Christi and Houston metros. Some of the
CAMs are indicating rainfall rates upwards of 3 to 4 inches/hour
which could easily exceed the 3-hr FFG of 3 to 5 inches across the
Gulf Coast. In coordination with the local forecast offices, an
upgrade to a Slight Risk was made.

Campbell

Low pressure system that has been spinning through the Gulf makes
it's way onshore by this period bringing with it ample moisture
and potential for heavy rainfall. Models have started to converge
on the heavier QPF amounts leaking onshore through portions of
southeast Texas. Upwards of 2-4" with some models indicating even
higher amounts during the 24-hr period are expected. PWATS peak
around 2.4" for the period well above the 90th percentile for this
time of year. Steering flow is around 25-35 kts which may push
cells along at a quicker pace, but should we see any training
storms in the region, flooding concerns will certainly arise.

...Southwest into the Central Great Basin...

21Z update... The Monsoonal moisture is progged to move further
into the Plains and as such the new WPC QPF has increased.
Convection tracking from the Front Range into Nebraska and Kansas
may produce heavy showers with rates of 0.50 inch/hour or greater.
The 3-hr FFG is as low as 2 inches and these rates may reach or
exceed local FFG. The Marginal Risk was expanded eastward to
encompass portions of southwest Nebraska and northwest Kansas.

Campbell

A plume of moisture will continue to impact the region as a moist
southwesterly flow sets up. Precipitable water values nearing 1.4"
will stream into an area previously hit with heavy rainfall and
flash flooding. Much of the area sits above 98% soil moisture and
well into 600%+ of normal precipitation over the past week. QPF
amounts alone during this period do not overly impress, but given
the antecedent conditions and burn scars throughout the region,
flooding will still pose a threat going into the day 2 period.
Portions of eastern Arizona will see rainfall during the day 1
time period which when combined with the additional rainfall
expected on day 2, will only prime soils even more for the
potential for flooding.

...Southwest Florida...

21Z update... Over the Marginal Risk area still highlights the
locations with an elevated threat for isolated flash flooding.
Minor reshaping of the boundary was made to reflect the latest WPC
guidance.
Campbell

Slow moving cells pushing over more urbanized areas will bring a
continued threat into the day 2 period for portions of southwest
Florida. PW values peak near 2.25" well above the 90th percentile
for this time of year. Pockets of 600+% of normal precipitation
has been observed over the past week for areas within the Marginal
Risk area and will be more susceptible to isolated flooding
concerns through the period.

Chiari





Day 3
Valid 12Z Fri Jul 01 2022 - 12Z Sat Jul 02 2022

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST UP INTO THE SOUTHEAST AS WELL AS THROUGH THE
MIDWEST...

21Z update... Only minor reshaping of both Marginal Risk areas
were made for this update. Overall, the general locations where
there is an elevated threat for excessive rainfall and isolated
flash flooding have already been identified. The changes reflect
the latest WPC QPF and trends.

Campbell

...Gulf Coast into the Southeast...
A continued plume of moist southerly flow will impact areas along
the Gulf Coast bringing ample moisture with PW values peaking near
2.3". Much of this area will be impacted with rainfall during all
3 periods which will bring FFG values even lower and prime soils
for more isolated flash flooding. There is quite a bit of overlap
between all 3 periods covered in the EROs during this mornings
issuance and carrying over a Marginal for this area seemed like
the likely scenario to message the concern for repeated days of
rainfall.

...Midwest...
As a frontal boundary drapes across the Central Great Plains
increased instability and PWATs reaching 1.2-2.2" will create
periods of heavy rainfall for the region. Parts of southern
Colorado have been hit hard over the past few days with rainfall
with soil moisture sitting above the 98th percentile. Pockets of
200-600% of normal precipitation has occurred from generally an
area of southern Colorado eastward into Nebraska and parts of
Kansas. With global guidance showing 1-3" of QPF over the period
with pockets of 4+", felt a Marginal Risk area was necessary to
show the potential for isolated flooding through the period.

Chiari



Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt