Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sat Sep 23 2023 04:01:55

AWUS01 KWNH 230401
FFGMPD
WIZ000-MNZ000-IAZ000-230900-

Mesoscale Precipitation Discussion 1093
NWS Weather Prediction Center College Park MD
1201 AM EDT Sat Sep 23 2023

Areas affected...northeastern IA...southeastern MN...southwestern
WI

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

Valid 230400Z - 230900Z

Summary...Localized 1-2"/hr rainfall rates may continue, producing
additional totals as high as 2-4". Isolated instances of flash
flooding are possible.

Discussion...An MCV continues to drift slowly northward this
evening, situated near the left-exit region of a ~110 kt jet
streak over the Great Basin/Central Rockies. Semi-discrete, slow
moving convection has been ongoing in northeastern IA in
association with this MCV, producing locally heavy rainfall rates
of 1-2"/hr (per MRMS estimates and a few corroborating
observations). Southerly low-level moisture transport looks to
continue into this region (just north of a quasi-stationary
surface front), and otherwise the mesoscale environment is
characterized by MU CAPE of 250-500 J/kg (and likely increasing to
500-1000 J/kg, per RAP analysis), precipitable water values of
1.4-1.7 inches (between the 90th percentile and max moving
average, per DVN sounding climatology), and 20-30 kts of effective
bulk shear.

Guidance has not done a great job handling the ongoing convection,
as most of the 00z HREF members (including more recent HRRR runs)
depict convection a bit too far north. That said, they do have the
right idea with the strength and magnitude of the ongoing
convection. This aspect is a bit concerning, as the 00z HREF has
come in with a notable uptick in the intensity through 09z, and
this is likely owning to the increasing instability that the RAP
is depicting. While immediate near-term trends have been the
opposite (with rainfall rates having come down a bit per MRMS
estimates), there may be another flare up of convection in
association with the MCV given the somewhat favorable environment
and trend in the CAM guidance. This would suggest relatively high
odds of some localized 3" exceedance (as high as 30-50%, per 00z
HREF 40-km neighborhood exceedance probabilities), most favored
across far northeast IA into southeast MN.

Churchill

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!_C1H1j6Ob_YW9aCYAjqsBPnOeQuUqMgbm20xqkB0-vGbqExMgBbI42l6FcnP2IRU-BQ0=
v-jmhznNQBQw7zQwhAFCW8g$  for graphic product...

ATTN...WFO...ARX...DMX...DVN...MPX...

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

LAT...LON   44789184 44199083 42739075 42279116 42379237=20
            43189347 44329302=20

=3D =3D =3D
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