160
FOUS30 KWBC 220810
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Sat Jun 22 2024

Day 1
Valid 12Z Sat Jun 22 2024 - 12Z Sun Jun 23 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
UPPER MIDWEST/UPPER GREAT LAKES AND NEW ENGLAND...


...Upper Mid West into the Upper Lakes...
The early morning active convection moving into the Upper
Mississippi Valley will continue to push eastward early day 1
toward the Upper Lakes. There may be training of cells in a west to
east direction at the beginning of day 1 along and north of the
stationary front still progged to lie west to east across northern
Iowa into southern Wisconsin. PW values expected to remain much
above average in the vicinity of this west to east front, 2 to 3
standard deviations above the mean, supporting the likelihood of
heavy totals spreading from the U.P. of Michigan/northern L.P. west
southwestward into southern Wisconsin/northern Illinois and
northeast Iowa. In the wake of the initial band of potentially
training convection, additional convection may form along and north
of the stationary front in response to additional upstream height
falls forecast to push east across South Dakota, southern Minnesota
and into Wisconsin. There is potential for overlap of the early
day 1 convection with the late afternoon convection from from far
northeast Iowas into southern Wisconsin. Across this overlap area,
the risk level was increased to moderate. This corresponds to where
the latest HREF neighborhood probabilities are high for 2" and 3"+
totals day 1, 60-90 and 40-80% respectively and 10-30% for 5"+
totals.

...Southern New England...
Another round of organized convection possible Saturday afternoon
along and to the south of the stationary frontal boundary forecast
to stretch in a west northwest to east southeast direction from
northern NY state into southern New England. There is potential for
overlap of where heavy rains have fallen over the past 24 hours
with new rains Saturday afternoon. The new slight risk area was
trimmed on the northern edge from the previous issuance, removing
areas north of Massachusetts, keeping it centered from across much
of CT, RI and MA. This will be in a region of better instability
and above average PW values to the south of the above mentioned
front. This matches well with where the new HREF neighborhood
probabilities show high probabilities for 1"+ and 2"+ amounts,
60-90% and 45-80% respectively and 20-60% for 3"+ totals.

...Southern Georgia into northern to central Florida...
No significant changes made to the marginal risk area from
southeast Georgia into northern and central FL. The weak surface
low off the northeast FL/GA coastal region expected to push slowly
westward and into coastal Georgia, accompanied by 2 to 2.25"+ PW
values. Slow moving cells near the center and diurnal convection
southward into northern to central FL will support locally heavy
totals. HREF neighborhood probabilities are high for 1", 2" and 3"+
totals in the marginal risk area, supporting isolated runoff
issues.

...Far South Texas...
Models are consistent in showing the next surge of high PW values,
to the north of low pressure moving east to west across the
southwest Gulf of Mexico/Bay of Campeche, moving into South Texas
day 1. Model consensus continues to be for the heaviest precip to
remain across northeast Mexico, with far South Texas on the
northern edge of this precip. A Marginal Risk was maintained from
the previous issuance given potential for locally heavy rainfall
amounts across regions that received heavy rains recently from
Alberto.

...Portions of the Southwest...
Latest models continue to show the upper-level trough over
California into the Southern Great Basin weakening day 1 as upper
ridging expands westward from the central to eastern U.S.. An area
of anomalously high precipitable water values will, however, expand
farther to the north and west, encompassing much more of southern
and central Arizona and continuing in New Mexico, with values 2 to
4+ standard deviations above the mean. There may likely be a lot of
clouds in this high PW axis, limiting instability potential.
However, there will still likely be at least scattered convection
across southern to central Arizona into southwest NM. HREF
neighborhood probabilities are showing high probabilities for 1"+
totals, from the Mogollon Rim southward into southeast Arizona,
with this region depicted in the marginal risk area where isolated
runoff issues are possible.

Oravec


Day 2
Valid 12Z Sun Jun 23 2024 - 12Z Mon Jun 24 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN NEW ENGLAND...


..Northeastern US...
The latest model suite is in fairly good agreement on the eastward
push of a well defined surface low across far southeast Canada
into far northern NY state and northern New England. The plume of
anomalous PW values ahead of this low will continue to lie across
much of the Northeast day 2 with values 2+ standard deviations
above the mean. Strong isentropic lift ahead of this low in the
anomalous PW plume will support potential for an axis of heavy
rains from far northern NY state, southern QB and across northern
New England. Changes to the previous slight risk area was to trim
the southern end across northeast NY state, Vermont and New
Hampshire to better fit the axis of heaviest model qpf. No changes
made to the marginal risk area along and ahead of the eastward
advancing cold front from the Upper OH Valley/Central Appalachians
into the NY state and New England to the south of the slight risk
over northern Maine. Convection likely to be fairly progressive
here given the expected fast movement of the front, but with PW
values above average along and ahead of the front, locally heavy
totals and isolated runoff issues possible.

...Portions of the Southwest...
The axis of much above average PW values, as high as 4 to 5
standard deviations above the mean across southern Arizona, will
persist across much of the Southwest day 2, expanding into southern
CA. Another round of scattered convection likely over much of
Arizona into portions of New Mexico. Not a lot of changes made to
the previous marginal risk area with continued low confidence in
where any isolated runoff issues may be given the weak model qpf
signal.

...Far South Texas...
PW values 2-2.5" and sustained east southeasterly low level flow
is expected to persist for most of the upcoming day 2 period
across northeast Mexico into South Texas. Similar to the day 1
period, model consensus is for the heaviest totals to be across
northeast Mexico with far South Texas on the northern edge of this
precip. Given no big changes overall to the pattern, the marginal
risk was maintained over far South Texas for isolated runoff
issues.

Oravec


Day 3
Valid 12Z Mon Jun 24 2024 - 12Z Tue Jun 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE UPPER MISSISSIPPI VALLEY, UPPER GREAT LAKES AND SOUTHWEST...


...Upper Mississippi Valley/Upper Great Lakes...
The surface frontal boundary oriented northwest to southeast from
the Northern Plains into the Mid Missouri Valley at the start of
day 3 will begin to push back to the northeast toward the Upper
Mississippi Valley/Upper Lakes region. Strengthening south
southwesterly low level flow into this front will raise PW values
to 1.5-2" along and to the northeast of the front. Shortwave energy
pushing eastward across the Northern Plains toward the Upper
Mississippi Valley will help strengthen isentropic lift over this
front and support for overrunning convection. There is not a lot
of agreement on placement of any heavy precip totals, but overall
some potential given the favorable set up. A broad marginal risk
was maintained that continues to encompass the current model qpf
spread.

...Southwest...
No significant changes expected day 3 to the large scale pattern
across the Southwest. PW values will remain anomalous from southern
California into the Southwest with a continuation of weak forcing
under the upper ridge axis stretching from the Southern/Central
Plains into the Southwest. Models continue to show potential for
widely scattered diurnal convection, with continued low confidence
with locations of any isolated heavy totals and isolated runoff
issues. No significant changes made to the previous marginal risk
area across portions of central to southern Arizona into southwest
New Mexico.

Oravec


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