U.S. Severe Weather Forecast (Convective Outlook)

Day Three

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Storm Prediction Center ac 230528 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1228 am CDT Tue Oct 23 2018 

Valid 231200z - 241200z 

..there is a marginal risk of severe thunderstorms across eastern 
Arizona and far western New Mexico... 

Scattered thunderstorms may produce marginally severe hail and gusty 
winds over parts of eastern Arizona and western New Mexico this 
afternoon and early evening. 

A weak southern-stream mid-level wave - initially positioned over 
Baja California - will traverse portions of the southwest today and 
reach The Four Corners region tonight. Downstream of this wave, a 
powerful mid-level trough will amplify southeastward into the 
northeastern Continental U.S.. ridging will persist across the central U.S. 
Between the two disturbances. 

At the surface, a trough will remain positioned across the lower 
Colorado River valley and vicinity and move very little through the 
forecast period. Meanwhile, a low near southeastern Ontario will 
migrate through New York state, then reorganize and deepen late near 
coastal areas of southern New England. An anticyclone will build 
southeastward across much of the central and southern U.S. In the 
wake of the coastal low. 

..Arizona and western New Mexico... 
Scattered precipitation should be ongoing at the beginning of the 
forecast period over New Mexico due to lift associated with the 
upstream wave. West of the precipitation shield, models indicate 
surface warming beneath modestly steep mid-level lapse rates (around 
7.5-8c/km) resulting in weak to moderate instability. Storms should 
redevelop in central Arizona during the afternoon and grow upscale 
into loosely organized clusters while migrating northeastward, with 
an attendant threat for isolated hail/wind given the favorable 
thermodynamic profiles. 

..New York into southern New England... 
Cold temperatures aloft associated with the approaching mid-level 
trough will contribute to enough destabilization for afternoon 
convection producing a few lightning strikes. Though instability 
profiles will be weak, steep lapse rates and convection may result 
in enough downward Transfer of higher-momentum air for a low-end 
threat of isolated wind gusts - especially in portions of southern 
New England beneath a belt of stronger mid/upper flow. Flow should 
be weaker in New York state, however. The severe-wind threat 
currently appears to be too low/unfocused for any probabilities, 
although an upgrade to marginal may be needed in later outlooks if a 
corridor of locally gusty thunderstorm winds can materialize. 

.Cook/jirak.. 10/23/2018 


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