Valid 042000Z – 051200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM WESTERN NORTH
DAKOTA INTO NORTHWEST MINNESOTA…
…SUMMARY…
Thunderstorms capable of isolated severe hail and wind are possible
this afternoon and evening across parts of the northern Great Plains
to northern Minnesota.
…Discussion…
Only minor changes were made to the previous outlook and are
described below, otherwise the forecast is on track.
1) Added a small 5-percent wind probability primarily over parts of
southern AL. There were recent instrument-measured gusts (49-kt
gust at KMOB and 43-kt gust at KPRN). In addition to the measured
gusts, some movement to convective outflow compared to stationary
pulse storms in areas outside of the 5-percent, and steepened 0-2 km
lapse rates, all suggest some localized strong/damaging gusts are
possible for a few more hours over this region.
2) A gradual shift of the Dakotas/MN Slight Risk farther west where
recent trends in HRRR guidance indicate storms developing over
eastern MT/western ND later today and perhaps a lowering of storm
coverage towards the MN Arrowhead.
..Smith.. 08/04/2019
.PREV DISCUSSION… /ISSUED 1129 AM CDT Sun Aug 04 2019/
…North Dakota through northern Minnesota…
Late this morning a cold front extends from northwest MN through
southwest ND into eastern MT. Low-level dewpoints range from the low
60s in southwest ND to around 70 F in the central and eastern part
of the state. With 7-7.5 C/km mid-level lapse rates in place the
atmosphere should become moderately unstable with 2000 J/kg MLCAPE
expected as the surface layer warms. A small cluster of storms is
already underway in vicinity of the front near Bismark. This
activity is developing in association with ascent accompanying a
progressive vorticity maximum moving through western ND, and new
development downstream along the front is expected as the atmosphere
destabilizes. Deep-layer, unidirectional vertical shear profiles
will increase to around 40-45 kt supporting potential for storm
organization with a few supercell structures and bowing segments
likely with isolated large hail and damaging wind the main threats
this afternoon into the early evening.
…Southwest South Dakota through northwest Nebraska…
Expansive outflow boundary from morning storms is moving south
through southwestern SD and should eventually stall near the SD/NE
border. North of this boundary the atmosphere will slow to recover
today and have therefore lowered the risk area to MRGL. However, the
atmosphere should become moderately unstable along and south of the
boundary where additional storms will likely develop this afternoon.
Wind profiles with 30-40 kt effective bulk shear will support both
multicell and possibly some supercell structures with large hail and
locally strong to damaging wind gusts the main threat into the early
evening.
$$