Missoula, MT...Great Falls, MT...Bozeman, MT...Butte, MT...Helena, MT...
Probabilistic Graphic
Probability of severe weather within 25 miles of a point. Hatched Area: 10% or greater probability of significant severe within 25 miles of a point.
Day 2 Prob. Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
5 %
74,268
591,151
Missoula, MT...Great Falls, MT...Bozeman, MT...Butte, MT...Helena, MT...
SPC AC 050552
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1252 AM CDT Fri May 05 2017
Valid 061200Z - 071200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE NORTHERN ROCKIES...
...SUMMARY...
Isolated strong/severe thunderstorms may develop over portions of
western/central Montana and vicinity Saturday afternoon and evening.
A strong storm or two may also develop near the southern
Appalachians during the afternoon and early evening.
...Synopsis...
A persistent, amplified mid-level trough will remain established
east of the Mississippi Valley Saturday, as multiple embedded
impulses rotate around its periphery. Farther upstream, a ridge will
slowly build eastward across the Plains states, while a closed low
pushes ashore the southern California/northern Baja coasts. In turn,
broad southerly mid-level flow is forecast to persist from the
Desert Southwest northward to the northern Rockies.
...Portions of the northern Rockies...
With the aforementioned flow regime over the region, the combination
of subtle embedded impulses, diurnal heating, and orographic
influences will likely yield convective development over higher
terrain from the Great Basin northeastward to Montana. Near and
ahead of a cold front pushing east across western Montana, a pocket
of somewhat greater surface moisture (e.g., dew points in the
40s/lower 50s) will combine with sufficiently cool mid-level
temperatures to promote modest mixed-layer CAPE (around 500-1000
J/kg). In turn, as storms move north/northeast off higher terrain,
they may be capable of isolated strong/damaging gusts, enhanced by
ample sub-cloud evaporation. Additionally, effective shear on the
order of 35-40 kt may favor a supercell or two that propagates
east/northeastward into greater buoyancy over north-central Montana.
Any such cell would be capable of isolated large hail and damaging
winds. Convective intensity is then expected to wane during the late
evening and overnight hours.
...Southern Appalachians...
A mid-level shortwave trough and related speed maximum will
translate south/southeast from the upper Great Lakes towards the
southern Appalachians during the day. A related surface low will
advance southeast towards the region as well, with a cold front
trailing to its west. While surface moisture will be quite limited
along/ahead of the front, with dew points in the 40s to lower 50s,
cold mid-level temperatures will likely encourage weak mixed-layer
CAPE supportive of isolated thunderstorms. Organized severe weather
is not expected, but strong west/northwesterly convective-layer flow
and steep low-level lapse rates may enable a few stronger wind gusts
(in addition to small hail).
..Picca.. 05/05/2017
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