Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue May 20 2025 18:22:05

AWUS01 KWNH 201820
FFGMPD
ILZ000-IAZ000-202359-

Mesoscale Precipitation Discussion 0296
NWS Weather Prediction Center College Park MD
220 PM EDT Tue May 20 2025

Areas affected...Eastern Iowa...Northwest to Central Illinois...

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

Valid 201819Z - 202359Z

SUMMARY...Very slow moving thunderstorms, especially
near/downstream of compact upper-low may produce localized 2-4"
totals resulting in possible focused flash flooding incident(s).

DISCUSSION...GOES-E Vis/10.3um EIR loops depict a compact
upper-level low across far northeast MO.  Relatively clear skies
in proximity to the upper-low with ample low to mid-level moisture
as noted in RAP analysis and CIRA LPW has built localized wedge of
increased instability along the northeastern and eastern quadrants
of the circulation across E IA and much of central to southern IL.
 SBCAPEs have risen to 2000 J/kg near the upper-low increasing
steadily toward the southeast.  Moderate northwest wrapping branch
of the TROWAL shows sfc to 700mb PW around 1-1.25" with sfc Tds in
the low to upper 60s.   Strong deep layer convergence may be
limited in wind speed at 20-25kts from 925-850, but directionally
is more than sufficient to overcome weak capping for broad
destabilization.   Given this, modest rain-rates of 1.25-1.5" can
be supported, the greater concern is very slow/stationary cell
motions with forward (north, northeast and eastward) cell motions
likely to be near zero along and downstream of the upper-low's
path to the north-north east (allowing for 1-2 hours of heavy
rainfall).  As such spots of 2-4" totals are possible along the MS
River in E IA and NW IL.

Within the eastern/southeastern quadrant, deeper layer southwest
to westerly steering will allow for increased cell motions of
15-25kts toward the east across central IL, producing streaks of
1-2" totals.  This alone is not too concerning, however, given
compact nature of the upper-low, there will be multiple bands of
convergence allowing for a second round/repeat track of cells in a
few hour time span.  Narrower updrafts will make for intersection
of storm tracks to be more random in nature though may result in a
spot or two of 2-3" totals.

Last evening's moderate rainfall has moistened the upper 40cm of
soils with NASA SPoRT saturation ratios increasing to over 70%
across central and E IA, as well as southern IL and brought
central IL up to normal around 50%.  As such, FFG values are a bit
lower, near 1-1.5"/hr and 1.5-2.5"/3hrs.  As such, localized
exceedance is possible, though slightly higher near/along the
upper-level low's track near the MS River.  As such, a localized
flash flooding incident or two is possible through late evening
hours.

Gallina

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!98SFdPND8JK0l9clrcGygY1eqc-Fof8dzMJumkZ7Vc0mP5I2OBMuvsslOapLhdKBEiHR=
x3JlfoSXGuVBeDXOcsymNzw$  for graphic product...

ATTN...WFO...DVN...ILX...LOT...

ATTN...RFC...MSR...TIR...NWC...

LAT...LON   42329117 42309002 41948917 41438851 40588808=20
            39838844 39608915 39739004 39959030 40329047=20
            40519078 40629136 41089199 41769199=20

=3D =3D =3D
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