Aug 13, 2020 1630 UTC Day 1 Convective Outlook
Updated: Thu Aug 13 16:30:15 UTC 2020 (20200813 1630Z Day 1 shapefile | 20200813 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20200813 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 39,566 478,287 Fargo, ND...Moorhead, MN...West Fargo, ND...Bemidji, MN...
SLIGHT 67,635 768,739 Bismarck, ND...Grand Forks, ND...Aberdeen, SD...Watertown, SD...Mandan, ND...
MARGINAL 241,683 7,527,973 Oklahoma City, OK...Tulsa, OK...Shreveport, LA...Little Rock, AR...Billings, MT...
Probabilistic Tornado Graphic
20200813 1630 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
2 % 23,724 441,177 Fargo, ND...Grand Forks, ND...Moorhead, MN...West Fargo, ND...Bemidji, MN...
Probabilistic Damaging Wind Graphic
20200813 1630 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
30 % 40,202 532,609 Fargo, ND...Bismarck, ND...Moorhead, MN...West Fargo, ND...Bemidji, MN...
15 % 67,246 716,238 Grand Forks, ND...Aberdeen, SD...Watertown, SD...Mandan, ND...Hibbing, MN...
5 % 240,193 7,391,076 Oklahoma City, OK...Tulsa, OK...Shreveport, LA...Little Rock, AR...Billings, MT...
Probabilistic Large Hail Graphic
20200813 1630 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 91,850 932,797 Fargo, ND...Bismarck, ND...Grand Forks, ND...Moorhead, MN...Aberdeen, SD...
5 % 209,893 6,167,605 Oklahoma City, OK...Tulsa, OK...Little Rock, AR...Billings, MT...Broken Arrow, OK...
   SPC AC 131630

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1130 AM CDT Thu Aug 13 2020

   Valid 131630Z - 141200Z


   A couple of clusters of organized thunderstorms may develop across
   parts of the northern Great Plains late this afternoon through
   tonight, accompanied by a risk for severe wind gusts and hail.

   A belt of stronger westerlies across the northern mid-latitude
   Pacific is trending more zonal, but remains amplified downstream,
   near and north of the Canadian/U.S. border.  This includes
   large-scale mid-level troughing inland of the British Columbia and
   Pacific Northwest coast through the Canadian Prairie provinces and
   adjacent portions of the U.S. Great Plains, and downstream ridging
   across the Upper Midwest and adjacent Great Lakes region into the
   Hudson Bay vicinity.

   Within the large-scale troughing, a deep embedded mid-level low is
   forecast slowly shift northward into eastern portions of the
   Canadian Northwest Territories during this period.  As this occurs, 
   a significant short wave impulse is forecast to dig across and east
   of the Montana Rockies by late tonight, and the westerlies may
   gradually begin to split.  This is a source of model spread and the
   associated influence on downstream flow remains at least somewhat
   unclear.  However, a preceding short wave trough is currently in the
   process of pivoting  northeast of the Saskatchewan/North Dakota
   border vicinity.

   Meanwhile, in lower latitudes, a subtropical high, centered along a
   major axis from the Southwest into the southern Great Plains, will
   remain prominent through today and tonight, with subtropical ridging
   centered over the western Atlantic also influential along the south
   Atlantic coast.  Weak troughing likely will linger between the
   ridging near/east of the middle and lower Mississippi Valley.

   In association with this regime, seasonably high moisture content
   air will remain focused either side of the weak southern trough
   axis, and south of a remnant surface frontal zone near southern New
   England and northern Mid Atlantic coastal areas into the Ohio
   Valley.  However, boundary layer dew points continue to increase
   within lee surface troughing across the Great Plains, beneath steep
   mid-level lapse rates associated with a plume of warm and capping
   elevated mixed-layer air.

   ...Eastern Dakotas/northern Minnesota...
   In association with the lead short wave impulse migrating north of
   the international border area, a modest low within the lee surface
   troughing may migrate from the central Dakotas through the Red River
   Valley vicinity by early this evening, before continuing or
   redeveloping northward through eastern Manitoba/northwestern Ontario
   tonight.  Within the warm sector of this low, southward along a
   trailing wind shift/weak cold front, it appears that boundary layer
   moistening will contribute to large CAPE in excess of 3000 J/kg.

   To varying degrees, latest model output continue to suggest that
   low-level forcing, beneath difluent mid/upper flow, will be
   sufficient to overcome mid-level inhibition and allow for the
   initiation of storms near/east of the Red River Valley.  Although 
   mid/upper flow probably will remain fairly weak across this region,
   it appears that a 30+ kt south-southwesterly 850 mb jet may
   contribute to sufficient shear to support an upscale growing,
   organized cluster of storms by this evening.  If this occurs,
   initial storms may pose a severe hail/isolated tornado threat,
   before strong wind gusts become the primary threat, until convection
   weakens in waning boundary layer instability overnight.

   ...Southeastern Montana into Dakotas...
   Boundary-layer moisture will remain maximized (though more modest
   than across the eastern Dakotas) along the wind shift/weak cold
   front trailing southwestward/westward near the North and South
   Dakota state border area into the higher terrain of southern
   Montana.  This is expected to contribute to sufficient CAPE to
   support vigorous high based thunderstorms within the post-frontal
   upslope flow regime across southeastern Montana by early this
   evening.  It appears that this will be aided by substantive
   mid-level cooling and forcing for ascent associated with the
   approaching troughing, and deep-layer shear, due to pronounced
   veering of winds with height beneath 40-50 kt cyclonic 500 mb flow,
   may become quite strong.

   It seems increasingly probable that thermodynamic profiles,
   including a relatively dry sub-cloud layer with steep lapse rates,
   coupled with the strong shear, will become conducive to the
   evolution of an organized convective system capable of producing a
   swath of severe wind gusts.  This may commence across parts of
   southeastern Montana by early evening, then continue into and
   through the overnight hours, aided by inflow of increasingly moist
   and potentially unstable air with eastward extent, roughly near and
   north of the North and South Dakota state border area.

   ...Parts of central Great Plains...
   The lee surface trough likely will be the primary focus for any
   thunderstorm development late this afternoon and evening.  Mid-level
   inhibition still appears likely to result in sparse storm coverage,
   but models continue to suggest a weakness within the capping will
   allow for a couple of storms, particularly across parts of central
   Nebraska into northwest Kansas.  Shear beneath modest westerly to
   northwesterly mid-level flow may be sufficient to enhance activity,
   contributing to a risk for locally severe wind and hail.

   ...Southeastern Great Plains into lower Mississippi Valley..
   Given the moist environment characterized by moderate to strong
   potential instability, it is possible that inhibition may be weak
   enough to allow for thunderstorm redevelopment this afternoon along
   the eastern edge of the plume of warmer and more strongly capping
   elevated mixed-layer air.  Beneath weak to modest northwesterly
   mid-level flow, if storms are able to initiate, this environment
   probably will be conducive to strong storms which could produce
   locally severe wind and hail.  

   Additional thunderstorm development is possible overnight, aided by
   a zone of enhanced mid-level warm advection.

   ..Kerr/Smith.. 08/13/2020