U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 090531 
Storm Prediction Center ac 090529 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1129 PM CST sun Dec 08 2019 

Valid 091200z - 101200z 

..no severe thunderstorm areas forecast... 

severe thunderstorms are not expected on Monday. 

A positively tilted large-scale 500 mb trough will progress across 
the central and eastern conus, coincident with a rapidly deepening 
surface low which will eject into the upper-Hudson Valley by the end 
of day 1/Monday, with multiple areas of thunderstorms possible 
across the eastern third of the conus, where marginal buoyancy can 
materialize. Elsewhere, a mid-level shortwave trough will traverse 
the southwest conus, where deep-layer ascent and cold air aloft 
(promoting marginal instability) may serve as a focus for isolated 
thunderstorm development. 

..eastern parts of the Ohio Valley... 
A strong cold front will accompany the aforementioned low, inducing 
convergence/low-level lift to eastern parts of the Ohio Valley into 
the northern Appalachians. Broad 850 mb warm air advection beneath steep (7.5+ 
c/km) mid-level lapse rates will promote marginal buoyancy (150 j/kg 
mucape), with convective showers and a few lightning flashes 
possible with the more intense cells, mainly within the 00-06z time 

..portions of the mid-south... 
Richer low-level moisture will be present ahead of the cold front, 
with surface temperatures warming into the 60s/70s and dewpoints 
exceeding 60 f through the day. Strong 850 mb warm air advection is also likely 
atop and behind the cold front, driven by the approach of the 
smaller 500 mb shortwave trough to the west. Marginally unstable air 
parcels into the Post-frontal regime will promote isolated 
thunderstorm activity late in the period (03-12z). 

..North Carolina coastline... 
Isolated thunderstorms will also be possible along the North 
Carolina coast, along the western periphery of a low-level moist 
axis of confluence ahead of the large-scale mid-level trough. The 
best time for storms would be during the first half of the period, 
as a small, embedded mid-level impulse briefly enhances deep-layer 
ascent across the area. 

..portions of the southwest... 
500 mb temperatures dropping below -20c will contribute to a pocket 
of steep mid-level lapse rates of 7.5+ c/km, which will translate 
eastward with the aforementioned 500 mb shortwave trough, supporting 
isolated thunderstorm potential in southern parts of Arizona/New 
Mexico during the day, and far West Texas later in the period. 

.Squitieri.. 12/09/2019 


Mesoscale Discussion

acus11 kwns 090048 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 090048 

Mesoscale discussion 2190 
National Weather Service Storm Prediction Center Norman OK 
0648 PM CST sun Dec 08 2019 

Areas affected...portions of eastern North Dakota into northwest 

Concerning...heavy snow 

Valid 090048z - 090645z 

Summary...heavy snow, with rates of up to 1 inch/hr will be possible 
through the overnight hours. In the near term, portions of central 
North Dakota and far northwest Minnesota may see rates occasionally 
approach 1 inch/hr. 

Discussion...a surface-925 mb low, currently located across 
southwestern SD, along with a well-defined 700 mb shortwave trough 
over ND, will continue to translate eastward through the evening. 
Ahead of the aforementioned low, moist warm air advection at 850 mb will persist 
from the southwest, with near-saturated air continuing to move 
northeastward at 700 mb (via waa), maintaining saturation of a 
low-level airmass while also promoting ample lift across the Red 
River valley (per latest mesoanalysis). Deep-layer ascent is 
occurring in a troposphere that is well-below freezing (based on 
recent rap forecast soundings), where precipitation is expected to 
be all snow (as also supported by latest kmvx dual-polarimetric 
data), with snow to liquid ratios exceeding 20:1 per latest sref 

Heavy snow has already been reported in the vicinity of Grand Forks, 
ND, and this area may experience the heaviest snowfall rates in the 
near-term. Ascent will be strongest in a northeast-to-southwest 
oriented zone of 700 mb frontogenesis, currently situated across 
central ND, and gradually progressing eastward with time. Latest 
high-resolution ensemble guidance suggests that 1.0 inch/hr snowfall 
rates may accompany this band through 09z across portions of 
north-central Minnesota. 

.Squitieri.. 12/09/2019 

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


Latitude...Lon 46149366 45889448 45919561 46009697 46089833 46309919 
46750003 47090023 47450011 47809974 48089865 48239738 
48189591 47869463 47019366 46529360 46149366