335
AWUS01 KWNH 171801
FFGMPD
COZ000-NMZ000-AZZ000-UTZ000-172355-

Mesoscale Precipitation Discussion 1315
NWS Weather Prediction Center College Park MD
200 PM EDT Thu Sep 17 2026

Areas affected...eastern AZ into NM

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

Valid 171758Z - 172355Z

SUMMARY...Localized to scattered areas of flash flooding are
expected across a broad area of central/western NM into portions
of eastern AZ through 00Z. Maximum hourly rainfall of 1 to 2
inches and sub-hourly 15-minute rainfall totals peaking near 1
inch will be likely.

DISCUSSION...GOES East visible imagery at 1745Z showed a mixture
of sky cover across AZ into NM with building cumulus along areas
of higher terrain and towering cumulus in the Sacramento
Mountains. The region resided within broadly confluent low to
mid-level flow between a shearing mid-level impulse approaching
the Four Corners and an expansive ridge centered over AR. While
moisture values are lower today compared to yesterday across the
Southwest, standardized anomalies of precipitable water of +1 to
+3 remained from eastern AZ into central NM. Mean steering flow
veered from 10 kt/southerly near the Mexican border to 25
kt/southwesterly in southern CO. Daytime heating is well underway
at this hour but 17Z estimated instability was weak across NM with
only a couple small regions of 500 J/kg, while 500 to 1000+ was
estimated along the eastern Mogollon Rim in AZ via the 17Z SPC
mesoanalysis.

Continued surface heating should allow MLCAPE to expand in
coverage through the afternoon with locations reaching 500-1500
J/kg by 21Z via the latest RAP forecast. Thunderstorms are
expected to form, likely first across the Sacramento Mountains
given the character of building cumulus there, followed by other
areas of higher terrain across the region by mid-afternoon. The
anomalous moisture and southerly steering flow should allow for a
few areas of repeating and training cells capable of generating
hourly rainfall of 1 to 2 inches. 700 mb flow was near 30 kt over
northwestern NM which should provide added orographic ascent into
the southern San Juan Mountains into southern CO, although
instability drops off sharply with northward extent into
southwestern CO which should temper rain rates to the north. The
enhanced 700 mb flow is likely to weaken as the previously
mentioned upper wave moves downstream but upstream instability
over eastern AZ into northwestern NM should allow for at least a
few robust cells with potential for hourly rainfall over 1 inch.

While the coverage of flash flooding is not expected to be
widespread this afternoon, at least isolated to scattered areas
appear likely with the greatest impacts across burn scars, low
water crossings and normally dry washes.

Otto

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

ATTN...WFO...ABQ...EPZ...FGZ...GJT...PUB...TWC...

ATTN...RFC...FWR...STR...TUA...NWC...

LAT...LON   37750731 37710686 37210580 37020436 36560382
            35950401 34470455 33560490 32610506 32280572
            32090638 32270711 32550759 32740798 32940844
            33110878 33470946 33821024 34261085 34621108
            34981102 35471088 36131024 36710939 37450848