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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

                            
000
FXUS64 KHUN 232001
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
201 PM CST Sat Feb 23 2019

.NEAR TERM...(Tonight)
Issued at 200 PM CST Sat Feb 23 2019

A crazy day continues weatherwise. Luckily we had a small break from
the more concentrated heavier rainfall we have had over the past
several days this morning. However, a line of showers and 
thunderstorms has been moving east from eastern Arkansas into western
Mississippi. Ahead of this line, clouds have broken up some near a 
warm front that has moved just north of Tupelo into western 
Tennessee. Strong advection of much warmer and more moist air along 
with some sunshine has allowed temperatures to climb into the lower 
70s with dewpoints in the upper 60s. This has created between 1000 
and 3000 J/KG of surface based CAPE in that area. Further east in 
northern Alabama, this advection has not been quite as strong and 
cloud cover a bit more entrenched. So surface based CAPE values have 
only climbed to between 500 and 1000 J/KG at this time. Strong values
of bulk shear, helicity, and steep mid level lapse rates are all in 
place over these areas ahead of the approaching line of developing 
storms. Thus, a tornado watch was issue west of Alabama for 
Mississippi and western Tennessee, eastern Arkansas, and northeastern
Louisiana through 8 PM.

Some scattered showers and thunderstorms have also developed ahead 
of that near the AL/MS border. Over northwestern Alabama, between
some insolation and strong warm/moist air advection surface and
elevated instability should continue to increase west of I-65. Expect
mainly scattered showers and thunderstorms to continue to develop
over the next few hours. Believe stronger to severe thunderstorm
development may hold off until around 2 or 3 pm, when stronger
low level forcing occurs and better instability is in place. Any
discrete storms that do form over the next few hours ahead of the
line will need to be watch closely for tornadoes. Expect the watch to
be extended eastward sometime between 3 and 6 PM. This will mainly
depend on how quickly any scattered thunderstorm activity really gets
going. Likely would be a tornado watch. Given all the other
parameters in place, large hail and damaging winds will be possible
this afternoon and evening as this consolidating line of
thunderstorms pushes east across the area through midnight or just
afterwards. 

Based on observational, satellite imagery, and model guidance: the 
line of thunderstorms ahead of the front should move very quickly 
aided by a strong southwesterly to westerly mean flow ahead of this 
storm system. Another round of heavy rainfall between 1 and 2 inches 
with locally higher amounts near 3 inches is expected late this 
afternoon through tonight with this activity. The main dynamics with 
this system do lift northeast late this evening into the overnight 
hours with this system. This should keep the heaviest rainfall will 
mainly be in northwestern Alabama into southern middle Tennessee and 
the worst of the severe weather potential near that area as well.

.SHORT TERM...(Sunday through Monday)
Issued at 200 PM CST Sat Feb 23 2019

Finally, a break from the wet weather still holds in model guidance
on Sunday onward through Monday. Cooler and drier air will move into
the area during this period. Highs will drop into the 50s and lows 
into the 30s under sunny skies.

.LONG TERM...(Monday night through Friday)
Issued at 200 PM CST Sat Feb 23 2019

This dry and sunny trend will continue through Tuesday. Models are 
continuing to have a hard time handling weak upper level disturbance 
that move through a modifying zonal flow and precipitation associated
with it Tuesday night through next weekend. For now kept with 
blended model output with a slight warming trend and isolated to 
widely scattered showers off and on during that period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1137 AM CST Sat Feb 23 2019

LIFR cigs (~400 ft) will persist at KMSL while IFR cigs (~600 ft)
will persist at KHSV through 22Z. A warm front will lift north of the
area during the early afternoon, with some improvement to the cigs
expected by 22Z, though cigs will still remain around 1500 ft. A cold
front will push through the region late tonight, with showers and
thunderstorms moving across the region ahead of the front. The bulk
of this activity should reach KMSL between 01Z and 03Z and KHSV
between 03Z and 05Z. These storms will produce gusty winds and the
potential for severe hail. Isolated storms are possible ahead of
this, and have introduced -TSRA at KMSL by 22Z and KHSV by 01Z. 
Timing is uncertain, so amendments may become necessary later in the 
afternoon. Storms will end between 03Z and 05Z, with conditions 
quickly improving at the terminals as the cold front moves through 
the region. Outside of thunderstorms, winds will remain gusty through
the day and into the morning hours on Sunday. 


&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Flash Flood Watch until midnight CST tonight for ALZ001>010-016.

TN...Flash Flood Watch until midnight CST tonight for TNZ076-096-097.

&&

$$

NEAR TERM...KTW
SHORT TERM...KTW
LONG TERM...KTW
AVIATION...73


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at weather.gov/huntsville.