Mesoscale Precipitation Discussion 1213
NWS Weather Prediction Center College Park MD
1057 PM EDT Sat Sep 05 2026

Areas affected...Northeast Colorado...Southwest Nebraska &
Southern Panhandle...

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

Valid 060300Z - 060800Z

SUMMARY...Localized flash flooding remains possible for areas out
of Sand Hills or South Platte River Valley for a few more hours
before complex become forward propagating limiting duration at any
specific location.

DISCUSSION...GOES-E WV suite shows favorable mid to upper level
environment remains across the central High Plains as a subtle
shortwave lifts northeast across E WY along the northwest edge of
the larger scale ridge that is anchored along or just east of
100W. ML 6.9um also notes some higher cirrus with more of a
southwest to east-northeast orientation out of central CO toward W
KS.  The combination of features continues to support strong
divergence pattern over Northeast CO into SW NEB, outflow
continues to strengthen due fed as a response to earlier
convective activity with AMV suggesting 60-70ks across the Sand
Hills into southern SD.  As such, low level flow continues to
strengthen out of the south and southeast with 850mb flow around
25-30kts from the SE becoming strongly convergent in response to
the 850mb low forming across NE CO.  Combine this with 700mb due
south jet providing further sub-tropical moisture connection per
CIRA LPW in the complex with slight confluence from southwesterly
700mb flow off the Front Range to further support short-term
back-building of convection toward the cyclone over the last few
hours.  Outflow boundaries have gusted westward and 3.9um SWIR
loop and observations denoted the increase in overall moisture
with Tds in the 50s now back as far west as 82V and GXY, and some
60s as far west as AKO, IML and SYF.   Total PWat estimates are
starting to reach 1.6-1.7" and with little sub-cloud evaporation,
rates are increasing to 1.5"/hr locally. 

The back-building should start to reduce with time as forward
propagation should be drawing the convective cores eastward toward
06-07z.  However, there remains a small window where back-building
southerly inflow at 850-700mb will counter strengthening
southeasterly inflow and cell residency may result from some
short-term periods of repeating or even cell mergers being within
the northeast (downshear) quadrant of the developing cyclone.  As
such spots of 2-3" totals remain possible resulting in potential
for localized flash flooding.   Hydrologically, the FFG values are
highly variable due to larger sand hills across SW NEB and
naturally absorptive soils in the broader South Platte River
Channel proper.  However, there are still some rugged, rockier
locations across NE CO that will likely shed some of the higher
rate totals.  As the complex forward propagates into stronger
southeasterly flow, overall totals should diminish across NW
KS...south-central NEB.  

Gallina

ATTN...WFO...BOU...CYS...GLD...LBF...

ATTN...RFC...KRF...NWC...

LAT...LON   41750245 41460157 40940119 40490125 39950195
            39760277 39930364 40410421 41050412 41560353