053
AWUS01 KWNH 161925
FFGMPD
MNZ000-NDZ000-170123-

Mesoscale Precipitation Discussion 1023
NWS Weather Prediction Center College Park MD
324 PM EDT Mon Sep 16 2024

Areas affected...near the northern ND/MN border

Concerning...Heavy rainfall...Flash flooding possible

Valid 161923Z - 170123Z

Summary...Showers and thunderstorms are expected to expand in
coverage and shift more towards a front as an upper-level cyclone
moves by the area and CIN reduces.  Hourly rain totals to 2.5"
with local totals to 4" are possible.

Discussion...A northeast-moving upper low in western ND along with
surface heating to leading to reduced CIN across portions of ND
near a stationary front, which was earlier reinforced with
convective outflow.  Precipitable water values of 1.5" lie near
the boundary.  Effective bulk shear of ~40 kts exists.  ML CAPE of
500-2000 J/kg exists, and is increasing.  Temperatures at 700 hPa
are 6-9C.

The expectation is for some convective expansion with time, as ML
CAPE increases beyond 2500 J/kg in the warm sector.  When CIN
reduces to zero, there is a question of whether the instability
shifts northward to the convection or if new convection forms
closer to the returning boundary.  The MPD area takes both into
account.  Also, the degree of effective bulk shear argues for
mesocyclones, which can be effective heavy rain producers.  At
some point, the activity will try to forward propagate, which
veering 850 hPa winds strongly suggest, but the returning front
should limit southward propagation, favoring a vector more to the
east with time.  While there is a signal for heavy rainfall in the
recent mesoscale guidance, there is a bit of spread, so
uncertainty is greater than normal.  The ingredients suggest
hourly totals to 2.5" and local totals up to 4".  Since it`s
falling over areas that received similar rainfall over the past 24
hours, depressing flash flood guidance values, flash flooding is
considered possible, with the more significant impact in urban
areas.

Roth

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...BIS...FGF...

ATTN...RFC...MBRFC...NCRFC...NWC...

LAT...LON   49929486 49489441 48689448 48109673 47879792
            47649882 47939969 48360027 49389767