Mesoscale Precipitation Discussion 0997
NWS Weather Prediction Center College Park MD
606 PM EDT Tue Oct 23 2018

Areas affected...Central and Southern Arizona

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

Valid 232206Z - 240236Z

Summary...Ongoing convection across portions of central and
southern Arizona will continue to pose a localized flash threat
with hourly totals of 1 to locally 2 inches possible.

Discussion...Radar returns from around central and southern
Arizona show isolated to scattered thunderstorms continuing to
develop. This activity is within an area of broad diffluent flow
ahead of a well-defined shortwave across the area. Instability
remains on the order of 1500-2000 J/kg per latest mesoanalysis in
a zone of near 60 degree dewpoints. PWATs have nudged upward in
the last few hours, now on the order of 1.2-1.4", which is near
record for TUS climatology.

All of these ingredients suggest the threat for flash flooding
will continue into the early evening hours until
heating/instability wanes and the lift moves east into New Mexico
as the shortwave progresses. With the unidirectional flow in place
still, there remains the potential for training convection. Recent
radar returns from EMX, FSX, and IWA suggest backbuilding and also
orographic effects are in play as well.

Area mesonet observations this afternoon indicate hourly totals of
0.5-1" with 3-hr totals near 2" in places across southern Arizona.
Given what's already fallen combined with the wet antecedent
conditions (and lower FFG), some flash flooding will remain
possible across the area.

Further east into New Mexico, there is less confidence on the
flash flooding potential as cloud cover has limited instability
quite a bit. So despite widespread showers and some embedded
thunderstorms, hourly rates per EPZ radar suggests the potential
for flash flooding is lower.

Taylor

ATTN...WFO...FGZ...PSR...TWC...

ATTN...RFC...CBRFC...

LAT...LON   35911135 34310938 30810972 31311148 33101268
            35281274