Valid 171300Z – 181200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING ACROSS THE NORTHERN HIGH PLAINS…AND TONIGHT FOR
MN AND VICINITY…
…SUMMARY…
A few severe storms with damaging winds and large hail are expected
across the northern high Plains area this afternoon/evening, and
overnight across Minnesota and vicinity.
…Northern High Plains this afternoon/evening…
A midlevel shortwave trough over the northern Great Basin will eject
northeastward to ND tonight. Surface cyclogenesis is expected near
the northwest ND/northeast MT/SK border by this evening, and this
cyclone will move northeastward into southern MB overnight. Strong
forcing for ascent will accompany the cyclone (within the left-exit
region of the mid-upper jet), but lingering convective inhibition
and only modest low-level moisture/buoyancy will tend to limit storm
coverage/intensity. Still, there will be enough downdraft and
momentum transfer potential to support at least isolated
severe/damaging winds from eastern WY/western SD this afternoon into
western ND this evening.
…MN area today into tonight…
A cluster of thunderstorms is ongoing this morning across central
MN, in a zone of focused low-level warm advection associated with a
compact midlevel shortwave trough. This zone of ascent will spread
northeastward toward the MN Arrowhead by early afternoon. Though
the convection will be slightly elevated this morning, there will be
some potential for a strong storm or two with hail by early
afternoon along the southern flank of the convective cluster. There
will be no clear focus for additional thunderstorm development this
afternoon across MN, in the wake of the ejecting shortwave trough.
East of the surface cold front moving across the Dakotas tonight, a
low-level jet will strengthen to 50 kt from NE to MN. This will
occur along the low-level moist axis, where moderate buoyancy will
persist well into the overnight hours. A pre-frontal, mixed-mode
band of slightly elevated storms is expected to form tonight near
the SD/MN border and spread northeastward and eastward overnight.
The increasing low-level flow and MUCAPE near 2000 J/kg will support
a threat for at least isolated damaging winds and marginally severe
hail.
…TX coastal plain through early Wednesday…
A weak tropical low south of Matagorda will drift northward to the
Fort Bend/western Harris County area by 12z Wednesday. There is
some potential for strengthening with this system prior to moving
inland, though wind fields are not expected to become strong enough
to support a threat for supercells/tornadoes. Otherwise, training
convection and very heavy rainfall will be the main concern.
..Thompson/Kerr.. 09/17/2019
$$