Valid 192000Z – 201200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTHERN AZ AND THE LOWER CO RIVER VALLEY…
Isolated severe hail and/or gusts are possible over parts of
southern Arizona and the lower Colorado River Valley region.
…20z Update — Southeast CA/Southern AZ…
A band of showers and thunderstorms is tracking northeast across
southern AZ early this afternoon. Modest heating beneath increasing
cloud cover and slowly increasing boundary-layer moisture has
resulted in weak instability across far southern AZ. As midlevel
lapse rates continue to steepen and shear profiles increase into
this evening, a few strong storm capable mainly of marginally severe
hail are possible. The previous outlook remains on track and no
changes have been made with this update.
.PREV DISCUSSION… /ISSUED 1019 AM CST Tue Nov 19 2019/
…Southeast CA/Southern AZ…
A cut-off low currently off the coast of Baja CA will open up and
become more progressive tonight, tracking into northwest Mexico and
the southwest states. Strengthening winds aloft and low-level
destabilization ahead of this system will result in a MRGL risk of
strong storms across parts of southeast CA and southern AZ this
afternoon and evening.
Low-level moisture is sparse at present, but is forecast to increase
dramatically this afternoon as southerly low-level winds strengthen
and transport moisture northward out of Mexico. Dewpoints are
expected to rise into the 50s by late afternoon across the region,
with lower 60s along the southern AZ border. Increasing lift ahead
of the upper low will result in scattered thunderstorms
overspreading the region later today.
Two corridors of organized thunderstorms are depicted by most 12z
CAM solutions. First, over southeast AZ where stronger winds aloft
and vertical shear profiles could result in a few rotating storms.
CAPE values will be limited in this area, but a localized damaging
wind gust or severe hail report is possible – mainly in the 20z-04z
The other area of concern will be along the Colorado River valley
where low-level moisture return will be focused. Vertical shear
profiles will be considerably weaker in this area, but
thermodynamics could be sufficient for a risk of hail in the
In both areas, the overall severe risk is limited due to weak
instability and limited moisture.