U.S. Severe Weather Forecast (Previsión convectiva)

día tres

acus01 kwns 210447 
Storm Prediction Center ac 210446 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1146 PM CDT Tue Mar 20 2018 

Valid 211200z - 221200z 

..no severe thunderstorm areas forecast... 

a few thunderstorms are possible Wednesday afternoon and evening 
across parts of central/northern California and the Great Basin. 

A mid-level trough across the eastern US will amplify through the 
day, corresponding to a speed maximum rounding its base and 
intensifying over the southeast. At the center of the trough, a 
closed low will deepen near/offshore the mid-Atlantic coast during 
the afternoon and evening. Farther west, a strong southwesterly jet 
will push ashore the West Coast, bringing plentiful precipitation to 
parts of California. 

..California and the Great Basin... 
Under the influence of the aforementioned Pacific jet, low-level 
Theta-E will increase across parts of California and adjacent 
portions of the Great Basin today. While surface heating may be 
limited by multi-layered cloud cover, adequate warming/moistening of 
the boundary layer may yield enough surface-based buoyancy for a few 
deeper convective cores by afternoon/evening. Forecast soundings 
from the region indicate buoyancy profiles sufficiently deep for a 
few lightning strikes. Additionally, a strong storm or two (capable 
of gusty winds and small hail) may develop, considering the expected 
strength of the convective-layer flow. 

As the mid-level low deepens near the mid-Atlantic coast today, a 
plume of steep 700-500mb lapse rates will advance around its eastern 
periphery, impinging upon the coastal mid-Atlantic and southeastern 
New England through the day. Areas of convection are likely to 
develop from near the Jersey coast northeastward to southeastern 
Massachusetts. A few of these convective elements may deepen enough 
for a lightning strike or two; however, onshore coverage is 
currently expected to remain sparse enough to preclude a 
general-thunder area. 

.Picca/Gleason.. 03/21/2018 


Mesoscale Discussion

acus11 kwns 210156 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 210155 

Mesoscale discussion 0164 
National Weather Service Storm Prediction Center Norman OK 
0855 PM CDT Tue Mar 20 2018 

Areas affected...portions of WV and western/central Virginia 

Concerning...heavy snow 

Valid 210155z - 210800z 

Summary...a band of moderate to heavy snow will develop 
northeastward across WV and western/central Virginia this evening 
and overnight. Snowfall rates around 1 inch per hour are likely, 
especially in the higher terrain. 

Discussion...a shortwave trough will pivot northeastward across the 
mid-Atlantic this evening/overnight, while a large-scale upper 
trough over the Ohio/Tennessee Valley transitions to a closed low. Forcing 
for ascent preceding the shortwave trough will encourage development 
and deepening of a surface low off the NC/Virginia coast through the early 
overnight hours. A separate area of weak low pressure will remain 
over WV/far southwestern Virginia. A front will extend between these two 
lows, with a cold low-level airmass in place across much of the 
mid-Atlantic to the north of the front. 

Moderate to heavy precipitation is ongoing this evening across 
southwestern Virginia into parts of WV in association with the previously 
mentioned shortwave trough. The 00z sounding from Roanoke, Virginia shows 
a modest (around 3.7 degrees c) low-level warm nose centered around 
820 mb. As mid-level temperatures cool with the shortwave trough 
passage, the low-level thermal profile is likewise forecast to 
quickly fall below freezing across WV and parts of western/central 
Virginia. Indeed, recent surface observations and mping reports across 
southwestern Virginia are indicating a fast transition from rain to snow, 
with some sleet mixed in at the leading of the precipitation shield. 

Continued east-northeasterly winds in the surface-850 mb layer will 
enhanced uplift along the Blue Ridge and Appalachian Mountains this 
evening and overnight. Snowfall rates of 1 inch per hour appear 
likely across much of the discussion area, especially in the higher 
terrain where this low-level uplift will be maximized. Most recent 
high-resolution guidance is in reasonable agreement in the placement 
of this moderate to heavy snowfall axis through about 08z. 
Precipitation may lessen/shift farther eastward after this time as 
the coastal low develops northeastward over the western Atlantic and 
the shortwave trough moves away from this region. 

.Gleason.. 03/21/2018 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 36998146 37498166 37918170 38398135 38708084 38878036 
38907998 39057954 39317912 39457873 39457833 39327795 
38877784 37997819 37257893 36777983 36608045 36658104