Area Forecast Discussion Issued by NWS Little Rock, AR
000
FXUS64 KLZK 120517
AFDLZK
Area Forecast Discussion
National Weather Service Little Rock AR
1217 AM CDT Tue Mar 12 2024
...New AVIATION...
.SHORT TERM...
(This evening through Wednesday)
Issued at 219 PM CDT Mon Mar 11 2024
Calm and dry conditions are expected through the short term as high
pressure controls the weather pattern. Surface winds will be light
and variable during the overnight period while being out of the
south/southwest during the afternoon hours. Additionally, mid to
high level clouds will be possible around the state.
Model data is indicating some light rain chances across portions of
the northwest late Tuesday night...chances are on the low side and
any rain that does fall will be light. The next widespread rain
chances return to the state in the long term period.
High temperatures are expected to be in the lower 70s to lower 80s
through the period with overnight lows in the lower 40s to mid
50s.
&&
.LONG TERM...
(Wednesday Night through next Monday)
Issued at 219 PM CDT Mon Mar 11 2024
Wednesday night through Thursday night...
A strong upper level trough is expected to be located over the
Rockies of the United States Wednesday night, with a potent
shortwave trough diving south into the larger trough`s western axis.
This shortwave is progged to be strong enough to actually cause the
larger scale upper trough over the Rockies initially to retrograde
back to the southwest over southern Nevada, California and Arizona
by early Friday morning. As this retrograde occurs, the upper trough
looks to dig south into the sub-tropical jet stream aloft, bringing
a bunch of tropical Pacific m moisture north over the southern U.S.
and northern Mexican Rockies in southwest flow aloft over the
southern plains and Arkansas. With the flow aloft deforming from
westerly to southwesterly and increasing in intensity, lee side
cyclogenesis originally setting up over the Texas and Oklahoma
panhandles is expected to push northeast, dragging a continental
polar airmass south in its wake. Because the upper low begins to
retrograde and is NOT progressive in nature, this surface low
pressure and frontal system are expected to remain largely
stationary throughout the day on Thursday giving surface southerly
winds an additional 24 hours to bring rich Gulf of Mexico moisture
north across Arkansas by Thursday afternoon.
With moisture in place Thursday afternoon, a shortwave trough
embedded in the sub-tropical jet stream will move northeast from the
southern plains, just southeast of the delayed frontal boundary over
the central plains, and set everything in motion headed towards
Arkansas Thursday afternoon. The timing of the cold front is
expected to play a large role in the chances for severe weather
across Arkansas on Thursday and Thursday evening. The March 11th 12Z
model guidance indicated that the cold front wouldn`t start to move
across Arkansas until after sunset on Thursday. If this pans out,
the greatest severe weather chances would likely remain over the
western portion of the state as that is where the frontal boundary
will provide lift for thunderstorms before the ground has had a lot
of time to cool off. If the front is faster to arrive, or perhaps
more likely, if there are so many storms that develop along the
front that those storms help push the front to the east earlier than
12Z model guidance suggests, the threat for severe storms could
certainly spread east into portions of central Arkansas.
Assuming one to two thirds of the state are impacted by storms
before the ground cools off so much that they become elevated, the
primary threats for storms appear to be large hail, damaging winds,
and tornadoes, but specifically the types of tornadoes that we find
embedded in squall lines. The strong forcing along the front and the
bountiful moisture available out ahead of the front both favor many
storms developing together in close proximity which limits the
opportunity for discrete rotating storms, or the variety of which
typically give us the longer track and strong tornadoes.
Thursday/Thursday night`s environment is not very supportive for
those types of tornadoes. That aside, the threat for damaging winds
and large hail remains and will pose a threat to those locations
that see organized thunderstorm activity before the ground cools
off. Even if storms are too slow to pose a significant severe
weather threat to Arkansas, the large scale environment is
supportive of flash flooding.
Regarding the flash flooding threat Thursday and Thursday night, the
combination of a very humid upper level troposphere due to the so
called "Pineapple Express" sub-tropical jet stream aloft and the
rich low-level Gulf moisture will create an environment favorable
for efficient precipitation processes. While initially steep mid-
Troposphere lapse rates will be in place over Arkansas Thursday
afternoon, the deep lift along the front will combine with the
moisture aloft to bring lapse rates in the entire troposphere close
to moist-adiabatic levels. Precipitable water values are expected to
climb up to 1.5" Thursday afternoon, and continue to climb to 1.75"
by early Friday morning, which represents near record values for
this time of year. With the cold front moving only slowly to the
southeast due to the anchored southwest flow aloft, a prolonged
frontal passage, while it will dampen the severe weather threat to
some degree, it will cause the flooding threat to increase. With
vegetation greening up early due to a warm winter, and with soil
moisture pretty close to normal, think that there is room for
infiltration and certainly storage in area lakes and rivers for
runoff, so do not think widespread flooding will be a problem.
However 1 to 2 inch per hour rainfall rates certainly look possible,
and these rainfall rates over any location in Arkansas any time of
year pose a flash flooding threat, so that will likely be something
we have to contend with Thursday night into Friday morning.
Friday and Saturday...
As mentioned above, because the larger scale trough retrogrades and
takes on the characteristics of a cut-off low, southwest flow is
expected to remain anchored in place as we head into the weekend.
This flow regime aloft is expected to cause the front to stall out
over central Louisiana on Friday. This front will attempt to lift
north on Friday afternoon into Friday night, but most model guidance
indicates that the cooler air north of the front is too dense/heavy
for the retreating front to actually retreat into Arkansas. However,
rich Gulf moisture is expected to use the stalled frontal boundary
as an onramp onto an elevated highway, spreading heat and humidity
north over the front and back north over southern Arkansas. This
will cause scattered elevated showers and thunderstorms to redevelop
over the southern half of the state for late on Friday and then
again on Saturday. This doesn`t look like a complete rain out for
these areas for both days and northern Arkansas should be far enough
removed from the overrunning to receive any additional rainfall, but
rain chances will be present for both Friday and Saturday before
things clear out on Sunday for the entire state.
Sunday and Monday...
The cut-off low is expected to fill in/weaken throughout the weekend
to the point that it represents little more than a weak, albeit slow-
moving, shortwave trough come Sunday. A stronger northern stream
trough is expected to dive southeast over the Great Lakes region and
reorient the flow aloft from southwest to northwest, finally
ushering in a true change in airmass from maritime tropical to
continental polar. The word "polar" makes it sound worse than it is,
while the naming convention is accurate, it`s really just dry and
cool Canadian air moving across the state. Sunday night into Monday
morning does have a real chance to see a freeze however, which isn`t
really all that strange in terms of climatology, but with many
plants greening up early this year, it is worth mentioning and
planning for just in case folks got an early start to their gardens
this year. Otherwise the weather will be cooler for certain, but
calm and quiet as we head into early next week.
Cavanaugh
&&
.AVIATION...
(06Z TAFS)
Issued at 1210 AM CDT Tue Mar 12 2024
High pressure has moved east of Arkansas and surface southerly
flow has returned. Mainly high clouds are expected central and
south through the period. Late in the period there will be a
slight chance of showers in the northwest.
&&
.PRELIMINARY POINT TEMPS/POPS...
Batesville AR 73 55 76 61 / 0 10 10 20
Camden AR 74 55 76 62 / 0 0 10 10
Harrison AR 72 54 76 59 / 0 20 10 20
Hot Springs AR 73 54 75 62 / 0 0 10 20
Little Rock AR 75 56 78 63 / 0 0 10 20
Monticello AR 73 56 77 63 / 0 0 10 10
Mount Ida AR 73 55 76 62 / 0 10 10 20
Mountain Home AR 73 53 76 59 / 0 10 10 20
Newport AR 71 53 76 61 / 0 10 10 20
Pine Bluff AR 73 54 77 62 / 0 0 10 10
Russellville AR 74 53 77 60 / 0 10 10 20
Searcy AR 73 51 77 60 / 0 0 10 10
Stuttgart AR 72 55 76 63 / 0 0 10 10
&&
.LZK WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...73
LONG TERM....66
AVIATION...51