BBS: TELESC.NET.BR
Assunto: MESO: Nws Weather Prediction Center College Park Md
De: COD Weather Processor
Data: Mon, 25 May 2026 18:59:22 +0000
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AWUS01 KWNH 251859
FFGMPD
AZZ000-260045-
Mesoscale Precipitation Discussion 0236
NWS Weather Prediction Center College Park MD
257 PM EDT Mon May 25 2026
Areas affected...Central and Northern Arizona
Concerning...Heavy rainfall...Flash flooding possible
Valid 251857Z - 260045Z
SUMMARY...Slow-moving, pulse-type convection driven by an
upper-level low will produce localized but occasional intense
rainfall rates. While regional soils are exceptionally dry, these
intense rates over steep terrain, locally hydrophobic soils, and
potential burn scars will make highly localized flash flooding
possible through this evening.
DISCUSSION...Regional radar and GOES-West WV imagery this
afternoon depict a relatively moist and unstable environment
across central and northern Arizona, driven by a slow-moving
upper-level low. The cold core associated with this upper low has
established steep mid-level lapse rates. Despite a dry sub-cloud
layer, continued surface heating has yielded SBCAPE values in the
1000-1500 J/kg range. Concurrently, a somewhat anomalous moisture
plume has pushed PWATs to around 0.75 inches which is more than
sufficient for locally heavy rainfall rates when combined with the
instability across this high-elevation environment.
Given the proximity of the upper low, the kinematic environment is
characterized by very weak effective bulk shear (generally <20
kts) and weak deep-layer mean steering flow. This is resulting in
a pulse convective mode with nearly stationary or erratic,
slow-moving cells. Recent MRMS data indicates these cells are
somewhat efficient after initially moistening the column, and are
dropping 0.25 to 0.50 inches of rain in 15-minute intervals
(equivalent to 1-2 in/hr rates) before the updrafts collapse. The
12Z HREF/REFS guidance highlights a 20-30 percent probability of
exceeding local Flash Flood Guidance (FFG) and 1 in/hr rates, with
a few HREF members suggesting localized totals could approach or
exceed 2 inches where cells anchor or merge.
While NASA SPoRT soil moisture and USGS streamflow data indicate
the region is exceptionally dry, the desert environment in this
region is highly sensitive to short-duration, high-intensity
rainfall. The baked, rocky terrain will tend to promote enhanced
runoff with these higher rainfall rates. The flash flood threat
will be notably isolated, but rather acutely focused on normally
dry arroyos, slot canyons, and steep terrain along or near the
Mogollon Rim. Furthermore, any stationary cores that develop over
recent burn scars will carry a risk for debris flows and channel
runoff.
Orrison
...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!9Z0ytRndCSgoeOo8m_k2qFUhQ2f-yoYzHuLybsphvRaLsm3FOZjaEx4UpC_2xRQUvSp3=
59y3695oDF01uBWybj8A6Lo$ for graphic product...
ATTN...WFO...FGZ...PSR...TWC...VEF...
ATTN...RFC...STR...NWC...
LAT...LON 36601203 35841076 34761005 33610997 33171079=20
33821223 34191327 35001403 35871416 36531349=20
=20=20=20=20=20=20=20=20=20=20=20=20
=3D =3D =3D
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