Mesoscale Discussion 1349

Issued

Jul 19, 2017, 12:05 PM MST (19:05 UTC)

Expired

Jul 19, 2017, 2:30 PM MST

In force

2 hr

Issued by

the Storm Prediction Center

Chance of a watch

5%

Counties Cochise County, AZ, Coconino County, AZ, Gila County, AZ, Graham County, AZ, Maricopa County, AZ, Pima County, AZ, Pinal County, AZ, Santa Cruz County, AZ, Yavapai County, AZ

The Phoenix radar (KIWA), 62 km from the middle of the area, began a volume at 19:03 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

101 
ACUS11 KWNS 191906
SWOMCD
SPC MCD 191905 
AZZ000-192130-

Mesoscale Discussion 1349
NWS Storm Prediction Center Norman OK
0205 PM CDT Wed Jul 19 2017

Areas affected...Portions of Arizona

Concerning...Severe potential...Watch unlikely 

Valid 191905Z - 192130Z

Probability of Watch Issuance...5 percent

SUMMARY...The risk for a few strong thunderstorms will exist into
the evening hours. A couple of marginally severe storms cannot be
ruled out, though Watch issuance will not be necessary.

DISCUSSION...Low-level lapse rates are steepening in response to
widespread insolation from southeast and south-central AZ through
central and into northwest AZ, behind scattered to widespread
convective debris clouds from the lower Colorado River Valley arcing
into southwest AZ. Rich deep moisture is in place across the area,
with 12Z soundings at Phoenix AZ, Tucson AZ, and Las Vegas NV
indicating 1.5-2.0-inch PW -- i.e., near record values per the SPC
Sounding Climatology. Visible satellite images indicate increasingly
agitated cumulus development over the higher terrain, with initial
thunderstorm development ongoing from this activity. Thunderstorms
will experience an increase in coverage and a modest increase in
intensity during the next few hours, while drifting westward and
northwestward into the evening hours. A slight enhancement to the
mid-level flow peripheral to an MCV moving across southern AZ may
support loose organization for convective structures in
south-central and west-central AZ -- spreading off the Mogollon Rim
to the lower deserts. Across the entire region, sufficiently steep
low-level lapse rates and small-scale merging outflows may support
locally strong wind gusts -- perhaps reaching marginally severe
levels on a very isolated basis. Small hail may also occur over the
mountains. The lack of stronger deep shear, and modest magnitude of
mid-level lapse rates, will mitigate the overall severe risk.

..Cohen/Coniglio/Hart.. 07/19/2017

...Please see www.spc.noaa.gov for graphic product...

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

LAT...LON   31511124 32941255 34331343 35671366 36431286 36411199
            35311105 33620963 32780925 31550955 31511124

Mesoscale Discussions in Arizona, 2017Every mesoscale discussion in 2017

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.