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January 30th-31st,
2013: Strong Cold front with Damaging Winds
Event
Overview –
On
Wednesday night, January 30th-31st, a strong cold
front crossed eastern NC producing destructive wind gusts ahead and along
the front. Wind gusts reached
45 to 60 mph leaving trees down, homes and property damaged and many
without power across the area.
Synoptic
Overview –
A potent
upper level trough across the central US slowly migrated eastward as the
associated surface low continued to deepen. Strong warm air advection
developed ahead of the front Wednesday as high pressure shifted offshore.
In response to this, a Wind Advisory was posted across the area Wednesday
through the overnight hours. Partly cloudy skies during the day with some
surface heating allowed winds to become elevated (20kts with higher gusts)
well ahead of the front. Clouds
increased through the late afternoon which reduced mixing allowing winds to
subside a bit. With southerly
flow advecting across the cool sea surface
temperatures (lower 50s), the atmosphere was stable ahead of the front.
With CAPE values around 100-200j/kg and low LI values, instability was low.
The low level jet (50kts) coupled with the upper level jet (140kts) aloft
would yield ample lift and an organized line of precipitation. The column shear was unidirectional,
with the possibility of tornadoes limited. With such a strong low level
jet, anticipated heavy precipitation would bring strong winds aloft to the
surface by way of momentum transfer. Therefore, the main area of concern
was the potential for destructive winds given such impressive wind shear.
Ample moisture was never in question with this system since the southerly
flow was tapping into the GOM moisture allowing precipitable
water values to rise to around 1.75” (over 2 standard deviations
above climatology for the month of January). The Storm Prediction Center
(SPC) did have Eastern NC in a Slight Risk days in advance. Although the
tornado threat was low, SPC did issue a Tornado Watch across the area a few
hours before the main line arrived.
With such strong shear, any localized area of spin could produce a
weak tornado.
There
were 7 Severe Thunderstorm Warnings issued and another 6 Special Marine
Warnings issued as the front crossed the area. There were no missed events
and all but one warning were verified.
Figure Overview
–
Below
are a series of figures that help illustrate the event starting from the
morning before the front arrived through the overnight hours as the front
moved offshore. A deep mid and upper level trough anchored across the
central CONUS early Wednesday morning with an impressive jet signature
noted at 250mb (Figure 1 and 2). The low levels were becoming saturated
through the day as strong southerly flow was bringing Gulf of Mexico (GOM)
moisture through the Carolinas (Figure 3). SPC had placed the Carolina’s
in a Slight Risk for convection well before the system was supposed to
arrive (Figure 4a). With
ingredient not conducive for Tornadogenesis across
the area, SPC placed our area in a less than 2% probability of Tornadoes
(Figure 4b). Damaging winds was the main threat with most of the area in a
15-30% chance of damaging wind outlook issued by SPC (Figure 4c). By Wednesday evening, the front was
crossing the Appalachians and heading toward the east coast (Figure
8). The upper level jet was
starting to become more defined and the diffluence
zone aloft was collocated across Eastern NC (Figure 5 and 6). This would
aid in ample lift ahead and along the surface cold front. The low levels were continuing to
become moist with dew point increasing under southerly flow. Based on the upper air analysis, it
clear that the shear is unidirectional. This can also be observed through
the VAD wind profile (Figure 7).
With unidirectional flow and very little instability, tornadoes have
a hard time developing. As the
front approached, winds were steadily increasing as the low levels were
very well mixed (Figure 8).
Based on the Skew-T analysis and VAD wind profile, the 60kt low
level jet (LLJ) could enable any heavy showers to bring strong gusty winds
to the surface. The progression
of the cold front and observations through the event can be seen in Figure
9. The main front came through
Eastern NC between 06z-10z Wednesday night/Thursday morning. A map of all the local storm reports
(LSR) across the southeast and mid-Atlantic highlights the damage this
potent and sharp cold frontal system created (Figure 9). A list of
individual LSRs across our area can be here with an
interpolated map of these reports (Figure 10).
Figure 1. Upper Air map at 250mb of the
upper level jet structure the morning before the event.
Figure 2. Upper Air map of 500mb of
Heights and Temps the more before the event.
Figure 3. Upper Air map at 850mb of
Heights, Temps and Dew points the morning before the event.
 
Figure 4a. SPC placed Eastern NC in a
slight risk for severe weather; Figure 4b. Tornado probability less than
2%.
Figure 4c. Severe Wind Probability around
15-30% across much of Eastern NC.
Figure 4. Upper Air map at 250mb of the
upper level jet structure that evening as the front approached the
area.
Figure 5. Upper Air map of 500mb of
Heights and Temps that evening as the front approached the area.
Figure 6. Upper Air map at 850mb of
Heights, Temps and Dew points the evening as the front approached the area.
Figure 7. Wind Profile at MHX as the
front approached between 07-08Z
Figure 8. LAPS Sound at 03Z as the front
crosses central NC.
Figure 9. Loop of the 0.5 degree
reflectivity and observation from 06-09z.
 
Figure 8. Surface observations with
frontal analysis the evening before (left) and the morning after the event
(right).
Figure 9. Local Storm Reports the morning
of the 30th through the morning of the 31st (as the
front moved offshore).
Figure 10. An interpolation of
non-thunderstorm and thunderstorm wind gusts.
Case Study Team:
Lara Pagano
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