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Mesoscale Discussion 1479 |
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Mesoscale Discussion 1479
NWS Storm Prediction Center Norman OK
1201 PM CDT Wed Aug 11 2021
Areas affected...Far eastern West Virginia...northern and central
Virginia...and portions of Maryland.
Concerning...Severe potential...Watch possible
Valid 111701Z - 111830Z
Probability of Watch Issuance...60 percent
SUMMARY...Storms are expected to move off the higher terrain of the
Appalachians and pose a threat for damaging wind gusts this
afternoon/evening.
DISCUSSION...Convective initiation has begun in the higher terrain
in Randolph and Pendleton Counties and vicinity. The airmass is
still capped in the lower elevations according to SPC Mesoanalysis,
but with rapid surface heating, expect the remaining inhibition to
be eroded within the next hour. Visible satellite gives further
support for this as cumulus have started to form in the lower
elevations across northern Virginia. The 12Z LWX RAOB showed
moderately steep mid-level lapse rates (~7 C/km) but very weak
effective shear (6 kts). These steep mid level lapse rates combined
with temperatures in the low 90s and dewpoints in the upper 60s has
combined for MLCAPE around 2000 J/kg per SPC mesoanalysis. Some
additional heating may bring greater instability and MLCAPE around
2500 J/kg within the next hour. In addition, the airmass will be
very supportive for strong downdrafts with DCAPE already around 1200
J/kg.
Storm organization is not anticipated given the shear profile is not
forecast to improve much from the LWX 12Z RAOB. However, the
favorable thermodynamic environment and storm density, which should
lead to clustering, should be sufficient for a damaging wind threat.
A watch may be needed in the next 1 to 2 hours.
..Bentley/Thompson.. 08/11/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...AKQ...LWX...RNK...PBZ...RLX...
LAT...LON 38657994 39327924 39687826 39707725 39517665 38617656
37657686 37087780 36997884 37147975 37678024 38657994
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