FOUS30 KWBC 211057
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
657 AM EDT Sat Jun 21 2025

Day 1
Valid 12Z Sat Jun 21 2025 - 12Z Sun Jun 22 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTHERN GREAT LAKES, INTERIOR NORTHEAST, AND NORTHERN ROCKIES...

11Z Update...
Expanded Marginal Risk south to match and be ahead of ongoing
activity in northern Wisconsin that has a training threat as it
shifts east over the northern Lower Peninsula of Michigan this
morning through midday.

Jackson

...Northern Great Lakes...
Convection will likely be ongoing at 12z this morning across
portions of the UP of MI. It still looks like the storm mode should
be a progressive squall line, which would limit the duration of
heavy rainfall and flash flood risk. However even the progressive
convection will be capable of heavy rates, with a high likelihood
of some 1"+ per hour totals, and a low chance of 2" per hour. Also
can not rule out some brief backbuilding/training on the southwest
flank of convection as it moves eastward. So while the flash flood
risk should be relatively low, localized hydrologic issues can not
be ruled out this morning. Convective and model trends suggest the
better threat is over the UP of MI, and so we were able to cut
back on the southern extent of the inherited risk area with this update.

...Northeast...
Not expecting much convection during the day across the Northeast,
however an uptick in activity is possible overnight into early
Sunday. By tonight steeper lapse rates advect into the region,
resulting in what should be a pretty rapid increase in MUCAPE over
western NY into portions of VT and NH. The ongoing MCS over MN and
MI should weaken as it approaches the Northeast this evening as
instability will not have increased yet. However the parent mid
level shortwave will remain upstream and expect an additional area
of organized convection to develop with this over southern Canada.
It is this next round that has a better chance of surviving into
portions of NY/VT/NH by later tonight.

The details of this remain unclear, but there should be enough
instability and low level moisture transport/convergence to
sustain some level of activity into the Northeast. Most indications
from the 00z high res guidance is for a quick moving area of
convection, and thus rainfall totals are not overly impressive.
However given the ingredients in place there does seem to be some
potential for an over performing area of convection with some brief
backbuilding characteristics. The better chance of this would be
along the instability gradient and southwest flank of
activity...probably central/upstate NY and/or portions of VT/NH. A
Marginal risk continues to suffice given the 00z suite of
models...however will need to closely monitor observational and
model trends through the day. Depending on how things evolve later
tonight into early Sunday there is some chance for an embedded
more focused flash flood risk within the broader Marginal, and can
not rule out the eventual need for a Slight risk.

...Northwest Montana...
A Marginal risk was maintained across portions of northwest MT
where rainfall will continue into today. By this time this region
will be within the comma head of the low, and looking at more
stratiform rain with lower rates. Thus probably not really a flash
flood risk by this point, but with an additional 1-3" of rain
pushing storm total rainfall towards 4" in spots, some possible
flood impacts still justify a Marginal risk. Snow levels will drop
towards 4000 feet by this time as well, so flood impacts will stay
below that level.

Chenard


Day 2
Valid 12Z Sun Jun 22 2025 - 12Z Mon Jun 23 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHEAST NEW MEXICO AND SOUTHWEST TEXAS...

...New Mexico and Texas...
Sunday is likely the beginning of what will be a multi-day period
of excessive rainfall potential over portions of west TX into NM.
The mid/upper level pattern features a near record to record ridge
over the eastern U.S. and a well-defined longwave trough over the
west. Southerly flow in between these features will supply ample
moisture to NM, with a connection all the way to the Caribbean Sea.
The better forcing from the western trough will generally hold of
until Monday and Tuesday (see the day 3 and 4 EROs), but by Sunday
we should at least have enough moisture and instability around for
scattered convective development. In fact PWs by Sunday should
already be getting towards climatological max values for late June
over portions of southwest TX and immediate adjacent areas of NM.
And while the better forcing arrives Monday, do note broadly
divergent flow at 250mb Sunday which could help sustain convection.

Given these ingredients we went ahead and upgraded to a Slight risk
for portions of southwest TX into Otero and Eddy counties in NM.
Expecting enough convective development Sunday afternoon/evening,
that combined with the near record PWs, suggests an isolated to
scattered flash flood risk should evolve over these areas. A bit
of uncertainty with how far north the Slight should extend into NM
with some models supporting a farther north expansion. However the
area currently highlighted shows the best overlap of the
NAM/RRFS/ECMWF and likely has the higher probability of seeing
flash flooding at the moment. The broad Marginal risk does still
extend into much of the rest of eastern NM and covers the
localized risk over those areas.

...Northern Minnesota...
Went ahead and added a small Marginal risk over portions of
northern MN with this update. The setup looks favorable for another
round of organized convection Sunday afternoon and evening across
this region. Strong shortwave energy ejecting into the northern
Plains, a strengthening axis of low level moisture transport, and
upwards of 4000 j/kg of MUCAPE will drive the convective threat.
The combination of extreme instability, PWs well over the 90th
percentile for late June, and a warm front focusing convection, all
point to a heavy rainfall threat. Some uncertainty with the exact
axis of convection, with some guidance focusing the bulk of
convection farther north into Canada. However both GEFS and ECENS
probs suggest some risk into northern MN, and the AIFS (which has a
history of good convective qpf placement) also favors northern MN.
Quite possible convection ends up blowing through quickly, so no
need for anything more than a Marginal risk at this time. But will
need to continue to monitor trends over the coming days.

Chenard


Day 3
Valid 12Z Mon Jun 23 2025 - 12Z Tue Jun 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NEW MEXICO AND WEST TEXAS, AND FROM KANSAS INTO IOWA...

...Southwest...
The overall pattern over the Southwest described in the day 2
discussion will persist into the day 3 period. By day 3 forcing,
moisture and instability should all be on the increase, and thus
expect convective coverage and flash flood risk to be on the
rise as well. The gradual approach of the west coast trough will
bring the right entrance region of the upper jet closer, and
continued moisture advection in between the trough and the east
coast ridge will push PWs well above the climatological 90th
percentile and towards late June max levels. Instability is a bit
of a question as cloud cover debris from Sundays activity could
play a role...however the model consensus is for increased
instability compared to Sunday, with values averaging 1000-2000
j/kg over much of eastern NM into far west TX. Not a ton of deep
layer flow, so convection forming on/near terrain should slowly
move off the terrain and allow for some cell merger activity. The
expected convective coverage should eventually erode instability
enough that activity trends down by overnight...but not before what
should be a more widespread isolated/scattered flash flood risk
over eastern NM and west TX where a Slight risk remains. The
western edge of this risk area was adjusted eastward a tad, as
model trends now support a slightly farther east axis.

Some uncertainty on where any more focused risk could evolve, but
the better model clustering is over southwest TX into southeast NM
and consider the threat over this corridor a higher end Slight
risk. This includes the sensitive Sacramento Mountain burn scar
areas, where localized significant flash flood impacts are a possibility.

...Central Plains to MS Valley...
A Slight risk remains from portions of central KS into southeast
NE and much of central and northern IA where convection along a
stationary front poses an isolated to scattered flash flood risk.
Model guidance indicates convective development along/near this
front Monday afternoon, with some persistence and/or upscale
development possible Monday evening as low level moisture
transport increases. Corfidi vectors over this area are divergent,
indicating a favorable environment for slow moving/backbuilding
convection near this front. PWs should be well over the 90th
percentile for late June along this front, as the same plume of
moisture over the Southwest will be in place here as well. Thus
any training of convection will pose a flash flood risk.
Maintenance of instability is probably the main question mark, as
the pool of forecast instability is not overly impressive and
neither is the magnitude of the low level jet...so the extent of
convective persistence into the overnight is a bit unclear.
Nonetheless, the unanimous model signal for organized convective
development, combined with the stationary front/convergence and
high PWs supports at least an isolated to scattered flash flood
potential. Thus the Slight risk was maintained. Overall models are
in fairly good agreement with the favored convective axis, and thus
not much change was needed to the inherited risk area.

Chenard

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