Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk
Area (sq. mi.)
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 211615
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1115 AM CDT Sun Oct 21 2018
Valid 211630Z - 221200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON ACROSS PARTS OF CENTRAL AND EASTERN ARIZONA...
A couple of strong storms may impact portions of central and
southern Arizona this afternoon, accompanied by some risk for severe
hail and locally strong wind gusts.
Within the main branch of westerlies emanating from the mid-latitude
Pacific, amplified large-scale ridging appears likely to rebuild
across western Canada and the Pacific Northwest/northern
intermountain region/Rockies. Downstream troughing east of the
Plains will persist, but the cyclonic regime is expected to become
less amplified, as a strong embedded short wave trough continues
accelerating east-northeast of the northern Mid Atlantic/southern
New England coast.
Models indicate that a significant cold front associated with the
short wave will advance southward through the remainder of the
Florida Peninsula/Keys by 12Z Monday. However, the southwestern
flank of the frontal zone is forecast to stall and return northward
across the western Gulf of Mexico, and possibly into parts of Deep
South Texas. This is expected as broad upper troughing, and an
embedded mid-level cyclonic circulation, gradually progress inland
of the California coast, within a belt of westerlies emanating from
the southern mid-latitude/subtropical eastern Pacific.
Moisture return on southerly low-level flow has contributed to
sufficient destabilization for scattered ongoing thunderstorm
activity across parts of southern Nevada/northwest Arizona and
southwestern Utah. This has been supported by forcing for ascent
associated with one short wave impulse embedded within the
large-scale troughing, now progressing northward into the Great
In its wake, another perturbation appears in the process of
progressing northeastward toward the lower Colorado Valley. Models
suggest that this could be accompanied by initiation of scattered
thunderstorm activity across parts of central/southern Arizona as
early as mid afternoon. This is where/when higher low/mid-level
moisture content (characterized by precipitable water up to around 1
inch) may contribute to CAPE up to around 1000 J/kg, beneath at
least modestly steep mid-level lapse rates.
Lower/mid-tropospheric wind fields appear likely to remain rather
modest to weak in strength. However, perhaps aided by 50+ kt
southwesterly flow in the 300-250 mb layer, shear through the depth
of the convective layer will be strong, and may contribute to
potential for sustained/organized storms accompanied by at least
some risk for severe hail and locally strong surface gusts through
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z