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WPC Met Watch

Mesoscale Precipitation Discussion: #1086
(Issued at 1116 PM EDT Wed Oct 13 2021 )

MPD Selection

Graphic for MPD #1086
Mesoscale Precipitation Discussion 1086
NWS Weather Prediction Center College Park MD
1116 PM EDT Wed Oct 13 2021

Areas affected...Northeast Texas to HIll County to Southern

Concerning...Heavy rainfall...Flash flooding likely

Valid 140315Z - 140915Z

SUMMARY...Highly efficient, repeating thunderstorms in the Hill
County to Southern Texas likely to produce flash flooding.  Lower
but non-zero flooding potential in deeper moisture axis north into
Northeast Texas...

DISCUSSION...Regional RADAR mosaic denotes a strong squall line
across northeast Texas pressing eastward along the southeast
quadrant of height-falls of northeastward moving shortwave.   CIRA
LPW suite depicts deep moisture axis extends across northeast
Texas into E Ok, but a subtle mid-level ridging has lead to
localized mid-level drying to support enhanced cold pools and
eastward propagation over the last few hours.  This will reduce
residency at any given locale, but there does remain ample
moisture through the cloud layer up to 2" (though mainly loaded
below 7H).  This will continue to support sub-hourly totals of
1.5-2" from Navarro northward along near a weak surface wave along
the surface front.   As such flash flooding remains possible
particularly over urban locations, as denoted by OU Flash output
over 400-800 cfs over eastern DFW metro.   Unlike further south,
instability is more limited and likely to be exhausted over the
next few hours with best enhancement/dynamic ascent with the
shortwave moving into OK (see MPD 1085).

Hill county southward...
Flash flooding potential is starting to ramp up in earnest.  
Aforementioned shortwave is lifting north-northeast into OK with
the trailing edge of the trof angling back across the Hill county.
 Deeper layer moisture denoted in the CIRA LPW is starting to
emerge through the 7-3H layer off the NE Mexican Plateau to
combine with surging mid to upper 70s Tds off the western Gulf
across South Texas.  Shortwave ridging from the approach of Pamala
will allow for the trof axis to linger and increase in
intersection with southwest to southerly flow enhancing deep layer
moisture convergence especially deepening the tropical rainfall
layer into the mid-levels.   At the surface high theta-E fairly
untapped unstable air is one supporting low level moisture flux to
enhance Total PWat values of 2.25-2.5", while uncapped MLCAPEs of
1000-2500 J/kg in axis as far northas  Williamson/Bell/Milam
counties (generally where the mid-level trof inflection occurs
back toward the west).

As such, GOES-E IR shows the deep very cold convective tops
reaching -75 to -80C at times from the Hill country back to SW
Webb county.   Given limited dry air and orientation to the
approach of Pamala's vorticity center, eastward propagation is
likely to be a bit more limited than further north, increasing
residency time.  Combine this with that deep moisture, rain rates
of 3"/hr are likely, with example of 1.45"/15 minutes near Blanco,
TX earlier this evening.  Given these rates and residency time,
localized totals near strongest thunderstorms of 6-8" are possible
by 09z.  This is particularly a concern for considerable flash
flooding across the Hill country of I-35 from Williamson to Bexar
counties where terrain is more complex and prone to rapid rise
flooding.  Still south of Bexar, FFG values are much higher at
3-4"/hr and 5"/3hr, but there will be localized cells that are
likely to be exceeded resulting in flash flooding.




LAT...LON   33739587 33609483 32239489 30039680 27809791
            27059875 27259975 28409979 29399949 30239896
            31699754 33369680

Last Updated: 1116 PM EDT Wed Oct 13 2021

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Page last modified: Wednesday, 13-May-2015 19:29:02 GMT