Yesterday’s Enhanced Risk did not materialize as planned. There was only one confirmed tornado report over northern Texas.
The Storm Prediction Center (SPC) has issued a Slight Risk for much of the Northern Great Plains today.
Associated with the Slight Risk is a very small 2% Tornado Threat Ring over a portion of the Dakotas.
The SPC is basing this threat on a surface low pressure system that has a warm front that is expected to move north and a trailing cold front that is expected to move east, placing much of the Dakotas in the warm sector by this evening. Dewpoints are forecasted to be in the 50s and steep lapse rates may enhance convection.
Synoptically speaking, the 300 mb NAM chart (from Unisys) shows a shallow and compact trough digging into the Dakotas this evening. The speed maxima will not quite reach the threat area in time to aid in the convection.
The 500 mb NAM chart shows some Positive Vorticity Advection (PVA) across southern North Dakota as a vorticity maxima creeps eastward.
The 700 mb NAM chart shows a strong pocket of rapidly-rising air associated with the PVA.
The 850 mb NAM chart shows strong Warm Air Advection (WAA) as the air cycles around the surface low, centered over western North Dakota by 0Z. Notice how the winds curve into this low pressure system, and thus across the thermal gradient from warm to cold.
The 12Z upper air sounding from Rapid City, SD, does not look impressive. Neither do any area soundings. There is no Convective Available Potential Energy (CAPE) in the area, and the surface Dewpoints are in the upper 40s. There is a relatively large, thick capping inversion and the 0-3 km average lapse rate was only 5.1 C/km.
The deep-layer shear was 20 kts, and the low-level shear was 11 kts. Overall, this was too weak to support severe storms.
The 12Z upper air sounding from Aberdeen, SD, is also equally unimpressive, with its lack of CAPE, 51 F surface dewpoint, 4.6 C/km 0-3 km average lapse rate, and strong inversion.
The shear was slightly better at Aberdeen, however. The deep-layer shear was 35 kts, and the low-level shear was 18 kts. As the low pressure system moves, it may force more moisture into this area of marginal shear.
TwisterData.com shows that the RAP has a pocket of CAPE developing by 21Z in the 2% Tornado Threat Ring.
TwisterData.com also shows some adequate, though not impressive shear that is close to overlapping the CAPE.
TwisterData.com also shows the dewpoints climbing into the mid to upper 50s by this afternoon.
Currently, the surface observations (from the SPC Mesoscale Analysis Map) show the low pressure system over western South Dakota, as shown by the wind field. Surface dewpoints have climbed considerably, reaching 61 F in southern North Dakota already this morning.
The Supercell Parameter peaks at around 4 over the next six hours. The lack of shear and CAPE overlap is part of this limitation.
The visible satellite imagery shows clear skies over the Slight Risk area, though some morning convection to the west. Its movement may hamper storm development.
The enhanced infrared satellite imagery shows that the morning convection is quite thick over western North Dakota.
The water vapor satellite imagery shows that the morning convection is along a moisture boundary, which is positioned over eastern Montana and extends into New Mexico.
Overall, I expect that there may be a marginally severe storm today. I’m not expecting a major tornado outbreak, and I’m certainly glad I didn’t try to drive to this threat from New Mexico yesterday (though I’ve never been to North Dakota, and that might be fun).
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC