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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1131 AM CDT Thu Jul 25 2024

Valid 251630Z - 261200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
CENTRAL AND NORTHEAST MONTANA...

...SUMMARY...
Scattered severe thunderstorms capable of 60-75 mph gusts are
forecast across portions of central and northeast Montana late this
afternoon into the evening.

...Montana/Northern Rockies to Great Basin...
Water-vapor imagery this morning shows an upper-level trough moving
east from British Columbia toward Alberta/Saskatchewan, with
strengthening cyclonic westerlies overspreading the northern
Rockies/Montana.  Model guidance continues to indicate scattered
thunderstorm development initiating off the higher terrain this
afternoon, and in advance of a cold front across central Montana. 
Forecast soundings shows large to very large surface
temperature-dewpoint spreads (40-60 F) later this afternoon.  A
downward mixing of 30-40+ kt ambient southwesterly to westerly flow
in the 700-500 mb layer may contribute to severe-caliber wind gusts
in consolidating outflows, as convection spreads eastward into this
evening toward eastern Montana and possibly western North Dakota.

Farther south over the Great Basin, model guidance appears to be
trending towards greater storm coverage (numerous) and associated
ability for storm outflow.  The 12 UTC hr** in particular (and
recent HRRR runs) shows a potential corridor of outflow surging
convection from northeast NV into northwest and northern UT during
the 23-04 UTC period.  Some consideration for a Slight Risk was
given but uncertainty precludes an upgrade at this time.  

...Arizona...
Lingering early day outflow/cloud cover via yesterday's relatively
active convection should generally abate by afternoon. As the
boundary layer diurnally warms and destabilizes, thunderstorms are
again likely to initiate across the Mogollon Rim and adjacent
mountains of southwest New Mexico this afternoon. Given the position
and movement of the mid-level high, somewhat stronger (around 15 kt)
northeasterly steering flow will remain focused across southeast
into adjacent portions of central Arizona.  Severe gusts will be
possible later this afternoon into the mid-late evening as storms
progress south-southwestward across the lower deserts of central and
southern AZ.

...Carolinas/Mid-Atlantic States...
Midday visible-satellite imagery shows and extensive cloud shield
across much of NC into the southern half of VA.  The 12 UTC GSO raob
featuring poor lapse rates and meager buoyancy contrasted with the
MHX raob (2000 J/kg MLCAPE) and a much more moisture-rich airmass. 
Thinner cloud cover near the coast will aid in widely scattered
storms developing this afternoon largely removed from the southern
fringe of large-scale troughing over the Mid-Atlantic
states/Northeast.  An isolated risk for locally severe gusts may
develop for several hours this afternoon into the early evening.

Farther north, breaks and thinning of cloud cover will promote
stronger heating across northern VA into the northern half of the
Chesapeake Bay vicinity than areas farther south.  Widely scattered
storms are forecast to develop per the latest 12 UTC hr** guidance
within this corridor by mid-late afternoon.  A belt of 40-50 kt
southwesterly 500-mb flow may enhance storm vigor, and a few
downdrafts may yield a risk for isolated 45-60 mph gusts capable of
localized damage.

...Upper Texas Coast and Southwest Louisiana...
Extensive showers and some thunderstorms are ongoing along the Texas
coast early today.  Influenced by a weak mid-level disturbance, some
guidance suggests that a strengthening of low-level winds/shear may
occur.  However, mid-level winds will remain weak, while the
aforementioned convection should considerably limit destabilization
inland. These factors seem likely to minimize the potential for
anything beyond a very weak/transient circulation.

..Smith/Karstens.. 07/25/2024