U.S. Severe Weather Forecast (Convective Outlook)

Day Three

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Storm Prediction Center ac 221944 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0244 PM CDT Mon Oct 22 2018 

Valid 222000z - 231200z 

..there is a marginal risk of severe thunderstorms across portions 
of eastern/northern Arizona...extreme southeastern Utah...and far 
western New Mexico... 

Isolated large hail will remain possible through the early evening 
across eastern/northern Arizona, extreme southeastern Utah and far 
western New Mexico. 

..20z update... 
No changes have been made to the marginal risk area across parts of 
the southwest. Greater coverage of thunderstorms is still expected 
across northern Arizona into The Four Corners region this afternoon, 
which will remain in closer proximity to forcing associated with an 
upper trough over southern Nevada/Utah and northwestern Arizona. Generally 
isolated thunderstorms driven mainly by terrain-induced circulations 
will be possible with southward extent in southeastern Arizona and far 
western nm. Around 35 kt of effective bulk shear noted in recent 
mesoanalysis should support some updraft organization/rotation, and 
isolated instances of large hail remain the primary risk. 

.Gleason.. 10/22/2018 

Previous discussion... /issued 1110 am CDT Mon Oct 22 2018/ 

..eastern Arizona, southeast Utah and western New Mexico... 

Corridor of greatest instability will evolve this afternoon across 
Southeast Arizona along low-level moist axis where surface dewpoints are 
currently in the 50s f. Diabatic heating will support up to 1500 
j/kg MLCAPE in Southeast Arizona with much weaker instability (mlcape 
near 500 j/kg) farther north and east where low-level moisture is 
more limited. Widely scattered showers and thunderstorms persist 
this morning from northern through Southeast Arizona. This activity will 
develop northeast in association with ascent attending a vorticity 
maximum rotating through base of an upper trough. Unlike yesterday, 
timing of the vorticity maximum is not ideal, and the deeper ascent 
will gradually shift north of the zone of greater cape located 
across Southeast Arizona. Nevertheless, at least weak instability will 
evolve as the surface layer destabilizes within a more favorable 
zone of ascent from northern Arizona into southeast Utah and northwest nm, 
supporting potential for storm intensification where wind profiles 
(30-35 kt effective bulk shear) will be supportive of marginal 
supercell structures. Much weaker ascent or subsidence is expected 
farther south across southern Arizona which should contribute to a more 
sparse coverage of storms capable of hail. 


Mesoscale Discussion

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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 222037 

Mesoscale discussion 1591 
National Weather Service Storm Prediction Center Norman OK 
0337 PM CDT Mon Oct 22 2018 

Areas affected...northeast Arizona 

Concerning...severe potential...watch unlikely 

Valid 222037z - 222230z 

Probability of watch issuance...5 percent 

Summary...isolated storms may become capable of producing hail and 
gusty winds this afternoon into early evening. Threat is expected to 
remain too marginal for a ww. 

Discussion...as of mid afternoon storms are developing over a 
portion of the rim of north central Arizona fostered by deeper forcing 
for ascent accompanying a northeast-advancing shortwave trough. 
Diabatic heating is destabilizing the boundary layer, but limited 
low-level moisture with dewpoints in the 40s f is resulting in 
MLCAPE near or below 500 j/kg. A corridor of modest winds aloft 
within base of the upper trough is spreading through this region 
with 30-35 kt effective bulk shear supportive of both multicells and 
some marginal supercell structures. This environment will promote 
some potential for a few instances of hail and gusty winds through 
early evening, but overall threat should remain limited due 
primarily to the marginal thermodynamic environment. 

.Dial.. 10/22/2018 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 34521071 35081151 36001170 36851013 36750951 36120928 
35200987 34521071