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Severe Possible severe threat 12/16/19
- Thread starter PEA_RIDGE
- Start date
SPC AC 150659
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1259 AM CST Sun Dec 15 2019
Valid 161200Z - 171200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF LA...SOUTHERN AND CENTRAL MS AND FAR WEST-CENTRAL AL...
...SUMMARY...
Scattered severe storms are expected Monday into Monday night from
the Sabine River Valley through Louisiana, Mississippi, Alabama and
the western Florida Panhandle. Damaging wind gusts, tornadoes and
isolated hail are all possible.
...Sabine Valley to the Gulf Coast States...
Forecast guidance continues to trend slightly southward with the
evolution of the mid/upper trough ejecting across the Plains on
Monday, as well as in the evolution of the surface low over the
lower MS Valley region. Latest guidance is in good agreement that a
weak low will develop over northern LA with an inverted trough
extending northeast across MS into TN/KY. The low will track
northeast along the trough/frontal wave the TN Valley vicinity
around 00z and the central Appalachians by 12z Tuesday. A trailing
cold front will push eastward across the lower MS Valley, located
from eastern TN to near Mobile AL and the western Gulf of Mexico by
the end of the period.
A strong southwesterly jet continues to be forecast, and 700 mb
winds around 40-55 kt will be in place across much of the South
Monday morning. An 850 mb low level jet around 35-50 kt also is
forecast to persist across the Gulf Coast states for much of the
period. Strong southerly low level flow will transport mid 60s F
dewpoints as far north as central MS/AL with 70s F dewpoints closer
to the coast. While cloud cover will limit stronger heating, this
rich boundary-layer moisture beneath 6.5-7.0 C/km lapse rates will
result in MLCAPE values from near 500-1500 J/kg. Furthermore,
impressive vertical shear will support rotating updrafts/supercells.
Some uncertainty in storm mode remains, as deep-layer flow above
around 1-2 km is generally parallel to the surface front, which
would generally support more linear and/or cluster storm modes.
However, some guidance shows considerable backing of low level winds
ahead of the front, resulting in rather large low level hodographs
and increased frontal convergence. If this scenario pans out, mixed
modes including bowing line segments/clusters and semi-discrete
supercells will be possible. Regardless of storm mode, damaging
winds appear likely given relatively fast storm motion and strong
flow in the presence of an adequate thermodynamic environment.
Tornadoes will also be possible, via mesovortex processes in line
segments, as well as with any discrete supercells that develop.
Finally, midlevel lapse rates are stronger than typical across the
region, which will aid in hail production with more isolated storm
modes.
Various guidance has indicated a secondary and/or later threat may
emerge over portions of southern AL toward the western FL Panhandle.
A lead impulse as been evident in the last several forecast cycles
and this could support convection well ahead of the cold front, or
aid in further development/persistence of severe storms from Monday
evening into the overnight hours. Uncertainty is higher in this
scenario compared to the rest of the outlook area, but the Slight
and Marginal risks have been shifted eastward to account for this
possibility.
...MAXIMUM RISK BY HAZARD...
Tornado: 5% - Slight
Wind: 30% - Enhanced
Hail: 15% - Slight
..Leitman.. 12/15/2019
New HRRR they just released looked nasty for these areas
That run of the hrrr causes some serious stomach issues, look at all them kidney beans 
One thing I’m noticing with soundings tommorow is that low level lapse rates aren’t the best and there’s basically no temp/dp seperation, so there may be cloud cover, which may limit low level lapse rates, but the moist BL may allow decent 3CAPE, hodographs are definitely impressive along with SRH, and 1km shear at nearly 40kts can easily can spin something, also mid level lapses are pretty good, which is not that typical, if you see some separation between the temp/DP tommorow with sunshine, there may be a more nastier setup 
What concerns me is that you don’t don’t often see near loaded gun soundings in LA often, with such steep lapse rates, storms that fire won’t be your typical high shear low cape moist adiabatic crapfest, but instead a more springish airmass
Well that went up in a hurry
Z
Zander98al
Guest
The long range 18z HRRR looks nasty tommorow. Any chance of a upgrade to moderate?
accu35
Member
- Joined
- Jan 5, 2017
- Messages
- 8,278
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Hows what looking? The event is tomorrow
Z
Zander98al
Guest
00z model runs are coming out now i imagine people will post on the event here soon.
The new models I mean sorry
thanksgivingbrown
Member
WHERE CAN I FIND THIS PRODUCT
Z
Zander98al
Guest
WHERE CAN I FIND THIS PRODUCT[/QUOTE go to the forecast tools on the spc convective outlook website. Or atleast thats how i know to get what he has.
Hrrr is definitely concerning with them warm sector supercells, low level lapse rates look better and there’s more separation between the temp/DP at the BL along with better SFC-3KM lapse rates, 3CAPE is high aswell, nice moist column at lower levels, impressive setup for unusually large hail for this time of the year tommorow aswell, if things look like this tommorow, we may see a strong or perhaps a few strong tornadoes, this threat needs more attention vs digital snow 
also look at that cool gigantic dry layer 
also look at that cool gigantic dry layer
Z
Zander98al
Guest
Welp this doesnt look good. The strongest updraft helicity swaths line up within the enhanced area. I imagine the tornado threat will be the greatest early on when storms look to be discrete and then for any storm that forms ahead of the line or gets broken up in the line.
