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< Day 2 Outlook
WPC Day 3 Excessive Rainfall Outlook Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 1934 UTC Sat May 28, 2022
Valid: 12 UTC May 30, 2022 - 12 UTC May 31, 2022
Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
336 PM EDT Sat May 28 2022
Day 3
Valid 12Z Mon May 30 2022 - 12Z Tue May 31 2022
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY...
A deep mid-level trough centered over the Intermountain West will
shed a closed low northeastward on Monday, with this feature
shearing out into an open wave across the Northern Plains by the
end of D3. At the same time, a secondary shortwave will intensify
as it digs across the Pacific Northwest, while downstream across
the eastern CONUS a large mid-level ridge amplifies. Together,
these will keep the primary trough axis anchored across the High
Plains during Memorial Day.
The evolution of this trough will allow an upper jet streak to
round the base and intensify towards 110 kts Monday, placing
favorable LFQ diffluence for ascent into ND/MN. At the same time,
a surface low beneath the upper trough will swing a cold front
eastward through the day. Ahead of this front, impressive
thermodynamic advection will occur on 850mb flow reaching as high
as 50kts from the south, driving PWs to 1.5" and MUCape of nearly
2000 J/kg. The associated theta-e ridging within this warm sector
will likely pivot north/northwest into a strengthening deformation
axis north of the surface low, driving locally enhanced ascent,
and there is likely to be widespread showers and thunderstorms
across the Northern Plains and Upper Mississippi Valley on Monday.
The guidance continues to feature some longitudinal spread in the
placement of heaviest rain due to uncertainty in the speed and
placement of the low and associated forcing. However, this spread
has decreased, and both the GEFS and ECENS ensemble means indicate
a threat for more than 3" of rainfall near the ND/MN border and
arcing into eastern SD. This area seems favorable as storm motions
may be a bit slower along the deformation axis, producing the
greatest threat for training. The inherited SLGT risk still looks
good for the area of heaviest rainfall, with the threat for flash
flooding also aided by antecedent rainfall expected on D2. Only
minor adjustments were needed to account for latest guidance.
A secondary area of enhanced rainfall may develop late Monday
night from eastern KS into western IA as the LLJ ramps up and
impinges into the eastward moving cold front, and this is
reflected by an increase in GEFS/ECENS probabilities. At this time
there is too much uncertainty in amounts and placement for a
targeted SLGT risk addition, but it is possible one will be needed
for this area with later updates.
Weiss
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt
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