SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1153 PM CDT Sun Sep 15 2019
Valid 171200Z - 181200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TUESDAY THROUGH
TUESDAY NIGHT ACROSS PARTS OF THE NORTHERN ROCKIES THROUGH MUCH OF
THE NORTHERN PLAINS...
...SUMMARY...
Strong thunderstorms may impact parts of the northern Rockies
through much of the northern Plains Tuesday through Tuesday night,
accompanied by at least some potential for severe weather.
...Synopsis...
Within the westerlies, models continue to indicate substantial
mid-level trough amplification near the northern Pacific coast
during this period, in response to another strong, digging short
wave trough and embedded closed low. As this occurs, downstream
mid-level ridging is forecast to remain prominent along an axis
across the Great Lakes into Hudson Bay. Within southwesterly flow
between these two features, a couple of short wave impulses are
expected to remain progressive. The lead impulse may undergo
considerable deformation northeast of the Dakotas through northwest
Ontario and the upper Great Lakes region, as it approaches the crest
of the mid-level ridge. The much more vigorous upstream impulse
appears likely to maintain considerable strength while accelerating
northeastward out of the Great Basin through the Dakotas by 12Z
Wednesday.
Beneath this regime, modestly deep surface troughing, to the lee of
the northern Rockies at the outset of the period, appears likely to
develop eastward across the northern and central Plains, while an
embedded cyclone migrates from eastern Montana into Manitoba. A
trailing cold front probably will begin to overtake the surface
troughing across the northern Plains by late Tuesday night.
Between the surface troughing (and developing cyclone) and
low/mid-level ridging to the east, it appears that confluent
low-level flow, near the nose of a persistent 30-50 kt
south-southwesterly 850 mb jet, will maintain seasonably moist air
supportive of moderate CAPE across eastern portions of the northern
Plains. While much drier boundary layer conditions are forecast to
prevail across the higher Plains into the northern Rockies, daytime
heating is expected to contribute to steep lapse rates and deep
boundary mixing.
...Wyoming through the northern High Plains...
The steepening low-level lapse rates, coupled with strong mid-level
forcing for ascent and cooling in the exit region of 50-70 kt
southwesterly 500 mb jet, are expected to support sufficient
destabilization to initiate thunderstorm activity by midday Tuesday
across the higher terrain of western into central Wyoming.
As activity gradually intensifies and spreads northeastward toward
the western Dakotas through early evening, sub-cloud evaporative
cooling will contribute to strengthening downdrafts, aiding downward
mixing of higher momentum to the surface. At least scattered strong
to severe gusts appear possible, before the onset of diurnal cooling
across the Plains.
...Eastern Dakotas into western Minnesota...
As some combination of conglomerate convective outflow and the
surface cold front surge into the more moist environment across the
eastern Dakotas Tuesday evening, there appears potential for renewed
vigorous thunderstorm development. Given the strength of the
low-level jet, and the presence of CAPE probably in excess of 2000
J/kg, considerable upscale convective growth appears possible
beneath difluent upper flow. This may be accompanied by at least
some severe hail and wind risk, and spread into western Minnesota
before weakening overnight.
...MAXIMUM RISK BY HAZARD...
Tornado: 2% - Marginal
Wind: 5% - Marginal
Hail: 5% - Marginal
..Kerr.. 09/16/2019
Read more
