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FOUS30 KWBC 192006
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
406 PM EDT Sat Oct 19 2024

Day 1
Valid 16Z Sat Oct 19 2024 - 12Z Sun Oct 20 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN AND WESTERN HIGH PLAINS...

...New Mexico/Texas Panhandle into Southeast Colorado...

16Z update... Everything is still shaping up for a widespread,
heavy rain event across this region today. A minor expansion of
the southern bounds of the Slight Risk farther into southeast New
Mexico was made to account for the uptick in QPF with the latest
CAM and deterministic guidance. It`s still looking to be a higher
end Slight Risk for the northeast portion of New Mexico where 4/4+
inches will concentrate.

Campbell

Several rounds of heavy to potentially excessive rainfall are
expected across portions of northeast New Mexico into southeast
Colorado through tonight given a highly diffluent upper flow
pattern between a well defined closed low over northern Arizona and
a southerly subtropical jet coming out of Mexico, this pattern has
induced a 20 to 35 knot low level jet from the Gulf of Mexico into
West Texas...resulting in the axis of a 1 inch precipitable water
plume moving into place. Given short term CAM guidance...one round
of convection that developed prior to the beginning of the Day 1
period on Saturday morning should gradually weaken by mid-morning
followed by a relative lull in activity...followed by convection
becoming reinvigorated later this afternoon/evening that persists
into the overnight hours. With a variety of coarser-grid models and
higher resolution CAM guidance pointing to the potential of 4
inches of rainfall in northeast New Mexico through 12Z
Sunday...thinking is that this is a higher-end Slight risk. Also
bolstering that idea is the consistency with which guidance has
kept roughly the same area for the placement of moderate to heavy
rainfall amounts. The greatest concern for excessive rainfall is
near recent burn scars.

...Northwest...
Maintained a Marginal risk from previous outlooks in this period as
an atmospheric river slowly sags southward across parts of
Washington state today. Model agreement remains good that the
Olympic range and the far northern Cascades are in the best
position for 3 to 5 inches of rain given the 1.00 to 1.25 inch
precipitable water plume being directed normal to the terrain. Over
time the axis will slowly sag southward with the magnitude of the
moisture plume weakening with time.

Bann

Day 2
Valid 12Z Sun Oct 20 2024 - 12Z Mon Oct 21 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN AND WESTERN HIGH PLAINS AS WELL AS THE PACIFIC
NORTHWEST...

Plains...

21Z update... The latest guidance continues to favor a slower
progression with the upper low therefore favoring a more westward
placement of the QPF than the previous cycle and WPC forecast. The
latest WPC QPF was adjusted and primarily focuses the highest
totals over Northwest New Mexico. The inherited Marginal Risk area
was offset with this change therefore the whole area was shifted
westward about 2-3 tiers of counties; which removed portions of
western Kansas and the Oklahoma and Texas Panhandles from the
Marginal while now including more of northern and central Arizona
and southern Colorado.

Campbell

Maintained the Marginal Risk area with much change needed from
portions of New Mexico and the Texas panhandle northward into
Colorado and Kansas given the model guidance which showed the
threat of rain persisting into the Day 2 period. The overall threat
of excessive rainfall should be diminishing once the upper low
near the 4-corners region starts to weaken and lift northeast and
once surface pressure east of the Front Range begin rising. Latest
WPC deterministic QPF, the NBM and HREF generally produce an
additional 1 to 1.5 inches of rainfall on Sunday into early Monday
that has a considerable amount of overlap with the footprint of
heaviest rainfall from Saturday. With rainfall rates likely to be
lower than on Saturday and a smaller window of rainfall...felt a
Marginal risk area should cover the risk.

Northwest...

21Z update... No changes were necessary for this part of the
country at this times.

Campbell

Maintained the Marginal risk area in parts of Washington state
with only minor modification. The deepest moisture and heaviest
rainfall rates should be shifting southward as a cold front makes
its way inland from the eastern North Pacific. However...there
looks to be a period in the Olympics and far northern Cascades of
Washington that should get into rainfall associated with the
surface and upper low location just north of the border...allowing
for a continuation of the excessive rainfall threat into Sunday.
The additional rainfall amounts only look to be under 1.5
inches...but it will be in addition to the 2 to 4 inch amounts on
Saturday/Saturday night. Precipitable water values begin the period
in the 1.00 to 1.25 inch range along the immediate coast and taper
off to values closer to 0.50 to 0.75 inches in the northern
Cascade...with values decreasing markedly after 00Z.

Bann

Day 3
Valid 12Z Mon Oct 21 2024 - 12Z Tue Oct 22 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell


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