U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 161249 
Storm Prediction Center ac 161247 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0647 am CST Wed Jan 16 2019 

Valid 161300z - 171200z 

..no severe thunderstorm areas forecast... 

isolated thunderstorms are expected late this afternoon and tonight 
across northern and central California. Gusty winds may accompany 
this activity. 

A progressive upper-level pattern will exist Continental U.S.-Wide through 
early Thursday. This will be highlighted by the eastward advancement 
of an eastern Pacific upper trough (around 130-140w at 13z) toward 
the West Coast tonight, with the potential for thunderstorms 
expected to increase across California. From The Rockies eastward, the low 
amplitude nature of the pattern along with seasonal temperatures and 
prevalent Continental trajectories will preclude thunderstorm 

..northern/central California... 
Given the large-scale scenario as previously described, considerable 
height falls and an eastward-advancing frontal band will reach the 
region around 03z. Scattered but weak elevated convection is 
initially expected ahead of the front through the afternoon into 
early evening, but much of this activity should struggle to attain 
depths necessary for lightning. However, with the arrival of more 
significant mid-level cooling, steepening lapse rates this evening 
coincident with the arrival of the frontal band will lead to a more 
conducive environment for isolated/embedded thunderstorms. 
Near-surface-rooted weak buoyancy may materialize this evening along 
the front which will likely result in one or more strongly forced 
bands of convection. Very strong southwesterly winds are expected 
just above the surface and there is some concern that these strong 
winds may mix to the surface, perhaps most likely in the Bay area 
vicinity where NAM/rap forecast soundings suggest as much as 200-350 
j/kg of MLCAPE coincident with 45-50 kt southwesterly winds around 
1km above ground level. 

Subsequent outlooks will reevaluate the merits of introducing low 
severe probabilities related to the potential for a couple of strong 
storms with convectively enhanced gusty winds this evening. 

.Guyer/Kerr.. 01/16/2019 


Mesoscale Discussion

acus11 kwns 130855 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 130854 

Mesoscale discussion 0019 
National Weather Service Storm Prediction Center Norman OK 
0254 am CST sun Jan 13 2019 

Areas affected...central Virginia and Maryland...including southern 
portions of the Washington D.C./Baltimore Metro area 

Concerning...heavy snow 

Valid 130854z - 131300z 

Summary...moderate to heavy snow now developing across parts of 
central Virginia and Maryland is expected to persist through mid to 
late morning, with rates (around or in excess of 1 inch per hour) 
likely maximizing in the 6-10 am EST time frame. 

Discussion...a broadly cyclonic 50-70+ kt 500 mb jet streak 
continues to gradually develop eastward across the northern Gulf 
Coast states, with its exit region now beginning to nose to the Lee 
of the southern Appalachians, toward the southern mid Atlantic coast 
through mid to late morning. It appears an associated broad area of 
strong upward vertical motion will include a period of strengthening 
lower/mid-tropospheric frontogenesis across Virginia and adjacent 
portions of the mid Atlantic. 

Across central Virginia into adjacent portions of central Maryland, 
where temperature profiles are expected to remain entirely below 
freezing, models indicate that lift may begin to become maximized 
within the favorable mixed-phase layer for dendritic ice Crystal 
growth by daybreak, and continue through mid to late morning. Aided 
by relatively high precipitable water content (up to around .70 
inches), one or more bands of heavy snow, at rates around or in 
excess of 1 inch per hour, appear possible. Forecast soundings 
suggest that this may persist for a 3-4 hour period at any 
particular location, generally in a narrow corridor from the 
vicinity of the Blue Ridge, north of Roanoke VA, east/northeastward 
through southern portions of the greater Washington D.C./Baltimore 
metropolitan area. 

.Kerr.. 01/13/2019 

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


Latitude...Lon 38287888 38517861 38657841 38977644 38497624 37937809 
37697891 37767939 38087930 38287888