Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 182036

Area Forecast Discussion
National Weather Service Little Rock AR
336 PM CDT Sun Mar 18 2018

.SHORT TERM...Today Through Tuesday

As of mid-afternoon, large-scale ridging aloft continues shifting
east with a deep trough digging into the Four Corners region.
Locally, a weak quasi-stationary surface boundary is draped across
north-central TX into northern LA and continues drifting south,
despite model solutions suggesting otherwise. Marginal forcing
along the frontal surface aloft, coupled with increasing broad
upper divergence and embedded impulses, continues generating
showers. Coverage and intensity has increased gradually as seen in
mosaic radar imagery, likely tied to the aforementioned lifting

As the trough continues pushing toward the area, surface
cyclogenesis will continue in the lee of the Rockies, with a
quickly-deepening surface cyclone arcing through northern OK
overnight and crossing northern AR Monday morning. This feature
will not deepen significantly but will achieve its minimum
pressure rapidly. Despite being stacked under the parent upper
low, guidance continues advertising a strong system, which is
supported by objectively analyzed mass and dynamic forcing fields.

At the surface, a complex frontal structure is anticipated in
association with the surface cyclone. As the main low approaches,
expecting the meandering quasi-stationary boundary to our south to rapidly
lift north, beginning in TX, with the boundary becoming oriented
nearly north- to-south across western AR by 12Z Monday. A cold-
front-like structure extending south from the surface low will
quickly sweep eastward, and the northern portion of this will
eventually occlude. Given this frontal geometry, a very narrow
corridor of enhanced moisture sandwiched between the cold and warm
fronts will push east, and there should be at least modest elevated
instability within this zone. Forecast soundings indicate robust
CAPE aloft with significant capping in the upper boundary layer
(morning model runs did exhibit a wet bias, which may generate
anomalously high forecast CAPE values). Regardless, the main
limiting factor in this setup appears to be the amount of CIN
given the magnitude of the low- level inversion.

That said, dynamic forcing is progged to increase markedly after
00Z, most notably near and immediately southeast of the upper/surface
low position. Impressive wind fields are expected throughout much
of the troposphere in that region, with a 50+ kt H850 jet
developing atop the narrow warm sector after 06Z, and a 100+ kt
jet at H300 through the same time. While the kinematics are quite
impressive, there could be phasing issues between the positioning
of better moisture -- dew point temperatures in the upper 50s to
low 60s F -- and strongly capped pre-frontal instability. A
significant forecast question not yet resolved is how much dynamic
forcing can compensate for strong CIN to lift parcels above the
inversion where better instability is realizable.

All in all...the severe threat is virtually nil until better
dynamics arrive in the pre-dawn hours Monday. Even then, the
likelihood of severe convection will be highly conditional. Hail
appears to be the primary threat, but steepening lapse rates aloft
on the order of 7 C/km coincident with some mid-level drying may
promote damaging winds, especially if downward momentum transport
can translate energetic flow aloft to near the surface.

By late morning into afternoon, the system will exit to our east
with rapid clearing in the dry slot. Winds will also increase
markedly across the southern two-thirds of the area, with westerly
winds sustained between 10 and 15 kts and gusts to 25 kts
possible. Wrap around moisture on the back side of the system will
bring slight chance PoPs back across much of the area Tuesday
morning into afternoon, before moisture exits and much drier air
filters in. Additionally, temperatures will not drop significantly
in the immediate wake of the front. By Tuesday, however, a
noticeably cooler air mass will be established, with highs only
reaching the low 50s F north to near 60 F in far southern AR.



.LONG TERM...Tuesday Night Through Sunday

Not a lot of value added changes will be forth coming this afternoon
as the medium range models remain in relatively good agreement
amongst themselves and whats currently in the forecast. What ever
differences that do exist, do not really show up until late in the
period when the model spread becomes a little more significant. As
such, model differences will be blended this afternoon.

Period initiates with upper trough to the east of the area with
upper ridging located over the intermountain west. This will result
in broad cyclonic flow over the state. Even so, temperatures look to
average a few degrees above normal for this time of the year. The
aforementioned upper ridge will translate east with time as next
upper low approaches the west coast keeping the area dry with a
gradual warming trend through Thursday.

Rain chances do begin to increase Friday as low pressure kicks out
of the western trough and moves into the central plains. Parent low
expected to pass to the north of the state Friday night and into
Saturday with a frontal boundary moving through the state in
response. Models are in some disagreement what the front does after
but enough agreement exists that the boundary could stall over the
area and become parallel to the upper flow that ongoing rain chances
are warranted.


Batesville AR     56  49  69  42 /  40  90  60  20
Camden AR         62  57  75  47 /  60  50  10  20
Harrison AR       57  48  64  40 /  70 100  50  30
Hot Springs AR    58  52  72  45 /  70  70  10  30
Little Rock   AR  57  52  73  46 /  50  70  30  30
Monticello AR     61  57  75  47 /  60  50  30  20
Mount Ida AR      59  53  71  45 /  60  70   0  30
Mountain Home AR  58  48  64  39 /  40 100  70  30
Newport AR        56  51  68  44 /  40  90  70  20
Pine Bluff AR     58  54  74  46 /  60  60  30  20
Russellville AR   58  51  70  47 /  60 100  20  30
Searcy AR         56  50  71  44 /  40  70  50  20
Stuttgart AR      58  54  73  46 /  40  60  40  20

.LZK Watches/Warnings/Advisories...NONE.


Short Term...COOPER / Long Term...GOUDSWARD is the U.S. government's official web portal to all federal, state and local government web resources and services.