U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 210034 
Storm Prediction Center ac 210033 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0633 PM CST sun Jan 20 2019 

Valid 210100z - 211200z 

..no severe thunderstorm areas forecast... 

thunder threat will linger primarily across portions of northern and 
central California. 


Early-evening water-vapor imagery depicts a well-defined upper low 
off the northern California coast with an associated short-wave trough 
shifting east toward northern California in line with latest model guidance. 
Earlier strong storms that developed along the front over the 
Sacramento Valley have weakened considerably as they shifted into 
the higher terrain of the Sierra Nevada. 00z sounding from Oak 
exhibits buoyancy in the lowest 4km which is likely insufficient for 
thunderstorm development in the short term. However, significant 
mid-level cooling over the next 6hr, in association with the upper 
trough, will contribute to deeper buoyancy that should support 
updrafts capable of generating lightning. For these reasons have 
maintained at least 10% thunder probability for much of northern and 
central California. 

.Darrow.. 01/21/2019 


Mesoscale Discussion

acus11 kwns 201802 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 201801 

Mesoscale discussion 0042 
National Weather Service Storm Prediction Center Norman OK 
1201 PM CST sun Jan 20 2019 

Areas affected...New England 

Concerning...winter mixed precipitation 

Valid 201801z - 202200z 

Summary...moderate to heavy snow is falling across much of the 
northeast this morning. This is expected to continue through the 
afternoon with areas currently seeing freezing rain/sleet and rain, 
eventually changing to snow. 

Discussion...a 988mb surface low is currently being analyzed near 
Providence, Rhode Island at 17z. This low will continue to deepen as it moves 
northeast back over the Atlantic Ocean later this afternoon. Cold 
air is working in rapidly west of this low pressure center which is 
changing mixed precipitation back to snow from west to east. Winds 
between 1 and 2 km have switched from south-southeasterly to west 
northwesterly in the last 2 hours on the kenx vwp indicating this 
surge of Arctic air is deepening. In addition, kenx WSR-88D 
correlation coefficient data shows the transition line moving 
rapidly east across Berkshire County in western Massachusetts. 
However, in these areas, precipitation will also be coming to an end 
soon due to dry air intrusion and limited deformation band 
precipitation. Further north into Vermont and New Hampshire and 
Maine, ongoing moderate to heavy snow is expected to continue with 
snowfall rates in excess of 1 inch per hour across much of this 
area. The exception will be in eastern Maine where warm air aloft 
may build in later this afternoon and switch the snow to sleet or 
freezing rain for a period. Sleet seems like the more likely 
precipitation type considering the depth and magnitude of the cold 
air below this warm nose, but there have been upstream observations 
in the mid to upper teens reporting freezing rain, so freezing rain 
cannot be ruled out. 

Strengthening northwest winds will likely lead to blowing and 
drifting snow in much of the discussion area which will continue 
impacts through the afternoon and evening, even after precipitation 
comes to an end. These gusty winds may also exacerbate impacts in 
areas which saw significant ice accretion on trees and powerlines. 

.Bentley.. 01/20/2019 

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


Latitude...Lon 44247182 44847146 45397106 45827055 46147038 46677011 
47176963 47556925 47486830 47056770 46526766 45926758 
45696741 45406722 45006691 44746691 44436751 44176818 
43936877 43726921 43627007 43237045 42957055 42647059 
42347076 42177111 42047153 42077222 42267284 42637293 
43877212 44247182