RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Wed Jul 15 12:33:02 UTC 2026.
No Mesoscale Discussions are in effect as of Wed Jul 15 12:33:02 UTC 2026.
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0700 AM CDT Wed Jul 15 2026
Valid 151300Z - 161200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MID-ATLANTIC...NORTHERN NEW ENGLAND...NORTHERN ROCKIES/HIGH
PLAINS...PACIFIC NORTHWEST...ARIZONA...AND SOUTH-CENTRAL TEXAS...
...SUMMARY...
There is a conditional risk for severe thunderstorms capable of
producing large hail and damaging winds across parts of the
Mid-Atlantic this afternoon and evening. Isolated damaging winds
appear possible for portions of northern New England, the northern
Rockies/High Plains, Pacific Northwest, and Arizona. A brief tornado
or two may also occur across parts of south-central Texas.
...Mid-Atlantic...
Hot temperatures are forecast south of a front that will be draped
across southern New England into the northern Mid-Atlantic by peak
afternoon heating. Coupled with dewpoints in the upper 60s to low
70s, this will contribute to a moderately unstable airmass, with
MLCAPE of 1500-2500 J/kg probable. The strongest mid-level height
falls/forcing for ascent associated with a shortwave trough over
Ontario/Quebec into New England are expected to remain generally
north of the surface front. Therefore, robust convective development
along/south of the boundary in the northern Mid-Atlantic remains
highly uncertain. Another factor that could limit thunderstorm
initiation is the potential for more muted instability across the
warm sector due to smoke from upstream wildfires.
With continued uncertainty regarding initiation, have maintained the
Marginal Risk across the Mid-Atlantic with no changes. However, on
the condition that surface-based thunderstorms develop, the presence
of seasonably strong mid-level winds and resultant 40-50+ kt of
effective bulk shear would support supercells/multicells capable of
both severe hail and damaging winds.
...Northern New England...
Within the zone of strongest forcing for ascent associated with a
mid-level shortwave trough moving quickly eastward from southern
Ontario/Quebec into New England today, a band of low-topped showers
and thunderstorms may develop during the afternoon in a weakly
unstable environment. Steepening low-level lapse rates, a
unidirectional/westerly wind profile with height through mid levels,
and 30-40 kt of flow around 1-2 km AGL will support the potential
for locally damaging wind gusts, assuming convection develops and
can become surface based.
...Northern Wyoming into Southern Montana...
A weak/embedded mid-level vorticity maximum evident on water vapor
satellite imagery over the northern Great Basin this morning will
move northeastward today across the northern Rockies and adjacent
High Plains. Diurnal heating across the higher terrain coupled with
the glancing influence of this subtle disturbance should foster the
development of scattered afternoon thunderstorms. Weak to moderate
instability is forecast, with a relatively deep and well-mixed
boundary layer across lower elevations. Recent guidance continues to
show some potential for upscale growth into a loosely organized
cluster with cold pool organization and a risk for isolated severe
wind gusts into the evening. However, the overall severe threat
should be tempered by modest deep-layer shear.
...Pacific Northwest...
Isolated to scatted thunderstorms should develop this afternoon
along and east of the Cascades from central OR into southern WA.
This convection will be aided by orogrpahic influences and modest
large-scale ascent preceding a closed upper low off the coast of the
Pacific Northwest. Recent NAM/RAP forecast soundings show a deeply
mixed boundary layer developing across this region through peak
afternoon heating, with weak MLCAPE present. Enhanced southwesterly
mid-level flow should support sufficient deep-layer shear for some
updraft organization, and isolated severe gusts may occur with the
stronger cores as they spread north-northeastward through the
evening.
...Arizona...
Weak east-northeasterly mid-level flow is forecast today across AZ
on the southern periphery of upper ridging extending across much of
the central CONUS. Daytime heating of a seasonably moist low-level
airmass across southern/central AZ will yield weak to moderate
instability by mid afternoon with a very well-mixed boundary layer.
This environment should support isolated strong to severe gusts as
convection initially develops over the Mogollon Rim and higher
terrain of southeast AZ, before subsequently spreading westward into
the lower deserts. However, a more organized severe wind threat will
likely be limited by weak deep-layer shear.
...South-Central Texas...
A weak mid-level low over southwest TX this morning should make only
slow westward progress through the period across the southern High
Plains. Modest winds at low levels veer to southwesterly with height
at mid levels per recent VWPs from KDFX/KEWX. Up to 100 m2/s2 of 0-1
km SRH may be sufficient for some low-level rotation and perhaps a
brief tornado or two with ongoing convection given a very moist
low-level airmass. This threat may continue through the day as the
boundary layer gradually destabilizes with filtered daytime heating.
..Gleason.. 07/15/2026
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Day 4-8 Outlook
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Wed Jul 15 2026
Valid 181200Z - 231200Z
...DISCUSSION...
The mid-level pattern will continue to transition toward a western
US ridge and eastern Canada trough during this forecast period. The
strongest mid-level flow across the US will be in the region between
the ridge and trough, namely the Upper Midwest into the Northeast
and Mid-Atlantic.
Ensemble guidance suites continue to indicate several stronger
mid-level short-wave troughs moving through the longwave trough
across eastern North America. In particular, one such trough will
move across the Great Lakes and Northeast on Saturday into Sunday,
with a secondary wave moving across the same general area late
Monday into early Wednesday. In between these main waves,
smaller-scale vorticity/speed maxima are likely to traverse the
region.
Prior cyclones moving across the region will have left behind a
surface boundary arcing from the Great Lakes into the Mid-Atlantic.
As each of the previously mentioned waves approaches this boundary,
the surface boundary will lift northward before being pushed farther
southward in the wake of the departing wave. By the end of the
forecast period, this boundary may push as far south as the
Southeast US.
Widespread showers and thunderstorms will be possible with each
passing wave, with more isolated potential in between the main waves
in association with any of the small/subtle vorticity/speed maxima
moving through the flow. The best areas for thunderstorms look to be
south of the better mid-level flow, which would tend to favor any
severe potential being driven by the degree of low-level
warming/steepening of the low-level lapse rates. At this time it
appears that the timing of the midlevel waves may favor early day
convection, especially across the Lower Great Lakes into the
northern Mid-Atlantic area. This early day convection may temper
afternoon heating and the overall organization/areal extent of any
severe potential. Thus, confidence remains too low to introduce
unconditional 15% severe weather probabilities at this time, despite
the acknowledgment that some severe potential is likely during this
time period.
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