AWUS01 KWNH 262100

FFGMPD

WIZ000-MNZ000-IAZ000-270243-



Mesoscale Precipitation Discussion 0521

NWS Weather Prediction Center College Park MD

459 PM EDT Thu Jun 26 2025



Areas affected...Central WI...Northeast IA...Southeast MN



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



Valid 262058Z - 270243Z



SUMMARY...Thunderstorm coverage will increase along and north of a

frontal boundary draped over southern WI this afternoon and

evening. Repeating rounds of strong thunderstorms both along the

frontal boundary and with assistance from approaching storms from

the west may cause flash flooding.



DISCUSSION...20Z surface analysis shows the location of the

west-to-east oriented frontal boundary well, with a more organized

complex of storms over southeast MN as a remnant MCV tracks

towards central WI. Strong 925-850mb theta-e advection is underway

over the Upper Midwest and will slowly inch the stationary front

north as a warm front this evening. The influence of this

low-level theta-e advection is evident in the increasing MUCAPE

field in central WI as RTMA 3-hr trends show as much as 600-1,000

J/kg MUCAPE increases over the past 3-hours alone. The Upper

Midwest remains ideally positioned beneath the diffluent

right-entrance region of a 250mb jet streak and PWs are steadily

rising. By 00Z tonight, the highlighted region is expected to see

PWs range between 1.75-2.0", which is generally above the 97.5

climatological percentile per ECMWF ensemble guidance. With MUCAPE

along the boundary near 2,000 J/kg, and even areas as far north as

Green Bay likely to see up to 500 J/kg of MUCAPE, the stage is set

for widespread thunderstorms that could contain up to 2"/hr

rainfall rates.



Aiding in the efficient rainfall production is the presence of

vertical wind shear and helicity. Effective bulk shear values >40

kts and effective SRH values >100 m2/s2 support thunderstorms

potentially sustaining mesocyclones, which are very efficient

rainfall producers. In addition, low-mid level RH values are

averaging close to 90% and warm cloud layers per the 18Z RAP for

this evening are pegged to be as deep as 13,000ft. West-Central WI

also sports highly saturated soils with NASA SPoRT-LIS 0-40cm soil

moisture percentiles well above the 90th percentile. As isentropic

ascent and low-level moisture advection increase along and ahead

of the approaching surface trough, there is the concern for

repeated rounds of thunderstorms in parts of the region. Once the

cold front approaches the region between 00-02Z, storm motions

over central WI should be more continuous off to the north and

east. Until then, however, there is a concern for training storms

across portions of central WI, far southeast MN, and far northeast

IA. Flash flooding is possible this evening, particularly in areas

with sensitive soils and where storms train along and north of the

frontal boundary in southern WI.



Mullinax



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



ATTN...WFO...ARX...GRB...MKX...MPX...



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



LAT...LON   45329101 45168840 44458740 43388785 43118856 

            43048972 42779142 43249248 43759278 44959268 

            

