Flash Flood Guidance
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AWUS01 KWNH 151912

Mesoscale Precipitation Discussion 0855
NWS Weather Prediction Center College Park MD
311 PM EDT Sun Sep 15 2019

Areas affected...Southwest New Mexico...Southeast Arizona...

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

Valid 151910Z - 160030Z

SUMMARY...Developing thunderstorms in moderately unstable, deep
moisture environment potentially repeating may pose possible
isolated flash flooding concerns through early evening hours.

DISCUSSION...GOES-WV suite denotes an elongated mid-level trof
just west of the AZ/NM border with two centers of rotation.  The
northern one, likely stronger at the right entrance to the upper
level outflow channel, appears to be centered NW of SJN with a
secondary shortwave center over SE Graham county, AZ.  This
secondary wave appears to be situated between 5-7H based on AMV
and RAP winds and choatic VWP from EMX through this layer.
Additionally, this wave appears to be pivoting eastward with the
northern more anchored or slightly lifting north.  This has been
providing relatively strong 850-7H flow across the region with
strong deep moisture convergence across NE Graham, N Greenlee and
Southern Navajo/Apache counties.  As such, deep moisture up to
1.4" TPW and with modest lapse rates between 850-6H (per proximity
12z ROAB in TUC/EPZ) has supported solid MLCAPEs to reach around
1500 J/kg.  This will support stronger/broader updraft cores,
which appear to be organizing better along the central AZ/NM with
some cooling tops over -50C and additional development starting to
organize across far SE AZ/SW NM in recent 1-mintue visible GOES
West imagery.

The storms further north, have a deeper southerly flow and
steering flow to support the potential for training/repeats though
eastward propagation vectors may reduce this threat.  Still Hi-Res
CAMs continue to be most bullish with increased rainfall threat.
Instantaneous rates over 1.5"/hr are possible with hourly totals
near .75-1" which is about the 1hr FFG threashold in hard-pan soil
conditions (as well as some isolated complex terrain).  So
isolated flash flooding is considered possible through 00z.

The cells across SE AZ/SW NM, ahead of the shortwave moving east,
will have less duration but definitely higher instability/moisture
to work with and may have rates even higher but the duration is
likely to be less, so unless multiple lines develop (which appears
plausible given current N-S oriented bands in visible imagery),
rainfall totals may remain less than 1" and flash flooding is less
possible even though environmental parameters are better.


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



LAT...LON   35240902 34800822 33820815 32810778 31890725
            31680725 31680808 31230815 31220936 31291042
            31711037 32281005 33630997 34890977

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