U.S. Severe Weather Forecast (Convective Outlook)

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Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0130 PM CST Tuesday Jan 27 2015 


Valid 272000z - 281200z 


..no severe thunderstorm areas forecast... 


... 
an isolated weak thunderstorm or two still appears possible this 
afternoon across parts of the Great Basin. Otherwise...the risk for 
thunderstorms elsewhere across the nation remains negligible. 


..20z outlook update... 
No changes have been made to the 1630z outlook. 


.Kerr.. 01/27/2015 


Previous discussion... /issued 0959 am CST Tuesday Jan 27 2015/ 


..synoptic setup/forecast... 
Pattern will somewhat deamplify this period as California/southern Nevada shortwave 
trough shears NE across the northern Great Basin...while deep New England 
system gradually pivots NE and weakens in response to impulse 
crossing Hudson Bay. Cold and/or dry air will once again prevail at 
lower levels east of The Rockies. 


A corridor of seasonably moist air will linger over parts of the lower 
Colorado valley in wake of departing upper trough. Buoyancy and lift in this 
region will...however...be too limited for diurnal storms. 
Farther NE across eastern/northern Nevada...there is some indication that middle-level 
cool pocket /aob minus 20 c at 500 mb/ associated with the trough 
will overspread 700 mb moisture band spreading northeastward from the lower Colorado 
valley. Combination of lift with the main vorticity maximum /now over S central 
Nevada/ and modest elevated buoyancy may support sufficient deepening of 
elevated convection to yield a small cluster or two of thunderstorms later 
today through early evening. 

Mesoscale Discussion


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Mesoscale discussion 0046 
National Weather Service Storm Prediction Center Norman OK 
0924 am CST Tuesday Jan 27 2015 


Areas affected...RI...ern Massachusetts...eastern New Hampshire...and much of Maine 


Concerning...heavy snow 


Valid 271524z - 272030z 


Summary...heavy snowfall with rates in excess of 1 inch/hour will 
continue through at least 20z across Rhode Island...eastern Massachusetts...eastern New Hampshire...and much 
of Maine. The axis of heaviest snowfall will shift northward with time. 


Discussion...surface mesoanalysis at 15z indicates a low southeast of Massachusetts with a 
minimum central pressure of 978 mb...moving northeastward with time. A closed 
upper low with an associated vorticity maximum is located just 
offshore the Rhode Island/Massachusetts coast...also moving northeastward. Middle-level frontogenesis 
and deep ascent associated with the upper low are the primary 
features responsible for the ongoing north/S oriented band of heavy snow 
across the discussion area. 


Latest surface observations show blizzard conditions continuing along 
the coast from Maine to Massachusetts with a strong pressure gradient between 
the surface low off the Massachusetts coast and high pressure across the eastern 
Canadian provinces. As both the surface and upper low move northeastward through 
20z...the axis of heaviest snowfall will continue to shift northward away 
from Rhode Island and eastern Massachusetts...and towards eastern New Hampshire and much of central/eastern Maine. 
Snowfall rates should begin to decrease after 20z as the surface low 
fills underneath the upper low circulation...and middle-level 
frontogenesis shifts northward and away from the discussion area. 


.Gleason/Peters.. 01/27/2015 


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


Attention...WFO...car...gyx...box... 


Latitude...Lon 41397175 42567179 44637103 46056883 46566782 45646757 
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41357043 41397175