501
FOUS30 KWBC 210808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Fri Jun 21 2024

Day 1
Valid 12Z Fri Jun 21 2024 - 12Z Sat Jun 22 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MID MISSOURI VALLEY INTO THE UPPER MISSISSIPPI VALLEY...

...Portions of the Mid Missouri Valley into the Upper Mississippi
Valley...

The surface frontal boundary currently stretching west to
east from southern WY, across northern NE, into central IA and
northern IL will continue to be the focus for another round of
convection riding along and north of the boundary late Friday
afternoon into Friday night. Additional shortwave energy expected
to eject east northeastward day 1 from the lee of the Central
Rockies into the Upper Mississippi. This will support another round
of organized convection in an axis of PW values 2 to 2.5+ standard
deviations above the mean. Latest hi res guidance is in good
agreement on this overall potential for another round of
convection, differing only on timing and latitude of the max
convective precip axis. With stream flows high across eastern South
Dakota into southern Minnesota and much of Iowa, and the above
mentioned likelihood of another round of heavy convective rains,
the risk level was kept at moderate. The slight and moderate risk
areas fit well with with the latest HREF neighborhood probability
axes for 1, 2 and 3"+ totals day 1, where probabilities are high.
Changes to the previous outlook were to tighten the gradient on the
northern side of the outlook to better fit current qpf consensus
and to expand the slight risk farther to the south into northeast
Nebraska, also to better fit model qpf consensus.

...SOUTHWEST COLORADO, SOUTHEAST UTAH AND NORTHWEST
NEW MEXICO...

MOdel consensus is for another round of late afternoon convection
to fire ahead of additional shortwave energy pushing east
northeastward across the southern Great Basin and into the Central
Rockies region. With PW values forecast to remain anomalous ahead
of the next round of shortwave energy, locally heavy rainfall
amounts are likely. This is reflected in the latest HREF
probabilities for .50+/hr totals with scattered areas of high
probabilities in the risk area. The previous slight risk area was
narrowed to better match where the new HREF neighborhood
probabilities are high for .50" hourly amounts and 1"+ totals for
the day 1 period.

...Portions of New York State into southern New England...

An axis of PW values 2+ standard deviations above the mean
expected along and ahead of the cold front slowly sinking
southward day 1 across northern New York State into New England. Hi
res consensus is for another round of scattered to organized
convection moving in a general west to east direction along and to
the south of this front across much of NY State save for the far
northern and western portions, northeastern Pennsylvania into
southern New England. HREF neighborhood probabilities are high for
1 and 2"+ amounts across these areas. The previous marginal risk
area was decreased in size, primarily on the western side, to
better fit the above mentioned high HREF neighborhood probability
areas.


Oravec

Day 2
Valid 12Z Sat Jun 22 2024 - 12Z Sun Jun 23 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
UPPER GREAT LAKES AND UPPER MISSISSIPPI VALLEY...

The day 1 height falls supporting additional heavy precip across
the Upper Mississippi Valley/Mid Missouri Valley will be pushing
into the Upper Great Lakes day 2. Hi res models suggest a well
defined MCV will persist into early day 2 as it pushes from the
Upper Mississippi Valley into the Upper Lakes. With PW values
expected to remain anomalous ahead of this MCV, 2-3 standard
deviations above the mean, heavy rains are likely across the Upper
Lakes on Saturday. This is reflected in the 12 hr HREF neighborhood
probabilities ending 0000 UTC Sun that are high for 1 and 2"+
totals from northeast Wisconsin into the northern L.P. of Michigan.
Convection also likely to become increasingly organized late
Saturday afternoon in an axis of increasing instability, MUCAPE
values 1000-1500, PW values 2-2.5" and area of enhanced upper
difluence along the trailing cold front moving across northern
Illinois, Iowa, into northeast Kansas and northern Missouri. Heavy
rains are possible along and ahead of this trailing front, with the
slight risk drawn southward into northern Illinois to cover areas
of relatively lower ffg values.

...Portions of the Southwest...
The upper trof over California into the Southern Great Basin during
day 1 will weaken day 2 as the eastern upper ridge expands
westward. The anomalous area of PW values will, however, expand
farther to the north and west, encompassing areas from southeast
California, into central to southern Arizona and western New
Mexico, with values reaching 3 to 4 standard deviations above the
mean. Not a lot of confidence on any scattered convection in this
high PW axis, but locally heavy rainfall amounts and isolated
runoff issues are possible.

...Far South Texas...

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 will move into South Texas day 2. Model consensus is 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 southern Georgia into North Florida...

The weak surface low approaching the Southeast coast day 1 will
weaken further day 2 as it pushes into south central Georgia.
Simulated radars from the NAM NEST and FV3LAM show potential for
some slow moving cells in the vicinity of this weak low level
circulation, which will be accompanied by an axis of above average
PW values. Locally heavy precip totals possible near this weak low
level center, southward into North Florida where a marginal risk
was maintained from the previous issuance.

Oravec


Day 3
Valid 12Z Sun Jun 23 2024 - 12Z Mon Jun 24 2024

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

The mid to upper level height falls pushing heavy precip potential
into the Upper Lakes day 2 will continue to press eastward day 3
into the Northeast. The anomalous axis of PW values 2 to 2.5+
standard deviations above the mean across the Upper Lakes day 2
will also push into northern NY State and Northern New England day
3 ahead of surface low pressure moving eastward across these areas.
The NAM is an outlier with a farther southward surface low track
and subsequently farther south heavy precip axis compared to the
remainder of the global guidance. Consensus is for an axis of heavy
rains from far northern NY State into Northern New England, where
a slight risk was maintained.


...Portions of the Southwest...

Not a lot of large scale changes day 3 across the Southwest from
day 2 with a broad marginal risk area depicted across areas from
far southeast California, through much of Arizona and into
northwest New Mexico.   PW values will continue to remain 3 to 4
standard deviations above the mean in a region of generally weak
forcing. Additional scattered convection likely across these
areas, with locally heavy totals and isolated runoff issues
possible.

...South Texas...

PW values 2-2.5" and sustained east southeasterly low level flow is
expected to persist for most of the upcoming day 3 period across
northeast Mexico into South Texas. Similar to the day 2 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 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