Area Forecast Discussion
Issued by NWS Little Rock, AR

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495
FXUS64 KLZK 100545 AAB
AFDLZK

Area Forecast Discussion...UPDATED
National Weather Service Little Rock AR
1145 PM CST Mon Dec 9 2019

.AVIATION...10/06Z TAF Cycle

A cold front has moved across the state, bringing a precipitation
band, with a N/Erly oriented axis, extending from Mena towards
N/Ern AR. At Nrn terminals, Nrly winds of 10-12 kts and gusts of
20 kts with VFR ceilings will persist through daybreak Tues
morning, and calmer winds following through the period. For Cntrl
and Srn terminals, Strong Nrly winds will continue through
daybreak, with conditions deteriorating Tues morning as -RA
transitions to -RASN/-SN resulting in MVFR VIS and CIGS with
periods of IFR CIGS possible at PBF and LLQ Tues afternoon. Precip
will move from the NW to the SE through the day, with VFR
conditions returning to Cntrl/Srn sites late Tues evening.

&&

.PREV DISCUSSION...(ISSUED 619 PM CST Mon Dec 9 2019)
AVIATION...
A cold front is moving across C AR as of 00z. N of the front,
MVFR ceilings prevail, meanwhile S of the front, VFR conditions
prevail. Winds behind the front are from the NW at 10 to 15 kts
gusting to 25 kts, however S of the front, SW/W winds of 5 to 15
kts are common. Ceilings will lower through the period as precip
develops by 8z. Ceilings will become MVFR with RA transitioning to
-RASN/-SN across C and S terminals during the afternoon. Precip
will end from NW to SE through the day.

PREV DISCUSSION...(ISSUED 324 PM CST Mon Dec 9 2019)
SHORT TERM...Today Through Wednesday

.Widespread rainfall transitioning to wintry mix likely tonight
through Tuesday afternoon, but significant impacts unlikely...

Changes with this forecast cycle...

Narrowed the areal coverage of potential low-end snow accumulation
and decreased total amounts to only a few tenths of an inch...

This afternoon, observations show an impressive display of large-
scale thermal advection with widespread temps in the 60s and 70s
with readings near 80 degrees over far southern AR and northern
LA. As of 21Z, the main player in this forecast...a strong cold
front...is moving through far northwestern AR with temps already
in the upper 30s to low 40s in NE OK and SW MO. Winds are stout as
well with sustained speeds up to around 20 kts and gusts up to 35
kts. Expecting the front to lumber southeast through the state
this evening as an incoming H500 trough lifts out of the Desert
Southwest.

Large scale forcing for ascent will continue increasing and
rainfall will develop and overspread most the area by late
afternoon into evening, save for northwestern AR. Multiple forcing
mechanisms will be at play with this system, including broad
isentropic lift along the frontal surface aloft, frontogenetical
forcing in the lower troposphere, conditional instability aloft,
and favorable jet dynamics. The best moisture will generally
reside over southwestern through east-central AR ahead of the
approaching H500 trough and in the immediate vicinity of the
frontal boundary. Mid-level drying is likely farther upstream of
the front.

As cold air advects in tonight, rain will become mixed with sleet
and snow with the transition zone gradually sagging south through
Tuesday morning. The most likely timing for changeover over
northern areas will be late tonight into the pre-dawn hours
Tuesday...near dawn across central AR...and late morning into the
early afternoon for points south.

Confidence in seeing wintry precip is relatively high with this
system, although the combination of well above-average temps
today, marginally cool soil temps, and uncertainty regarding the
relative timing of cold air with respect to departing moisture
cast doubt on us seeing more significant snow accumulation (i.e.,
totals of an inch or more). Model progs do hint at multiple bands
of strong frontogenesis in the 850 to 700 mb layer through the
morning hours Tuesday and there will likely be some elevated
instability, especially across central into eastern and
southeastern AR. If a transition to snow occurs quickly enough
before this forcing wanes, isolated areas could see higher
snowfall rates and perhaps a bit more snow on the ground.

Still not sold on this idea so kept storm total accumulation on
the order of a few tenths of an inch at most. The most favorable
juxtaposition of near-freezing temps, dynamic forcing, and
moisture will exist over central, eastern, and portions of
southeastern AR, but even then, the phasing of these variables is
iffy at best. Generally tried to confine accumulation to these
areas based on this reasoning.

Winds will gradually subside Tuesday morning as precip quickly
moves out of southeastern AR. Some small modification in temps is
expected into the afternoon hours, although highs will generally
remain in the upper 30s to near 40 degrees with the coldest air
over southeastern and eastern AR. A modified Arctic air mass will
settle in Tuesday night as surface ridging builds in from the
north. Temps will fall into the 20s over the entire area and some
icy spots will be possible on still- wet roads. This could lead to
localized travel impacts and will be closely monitored over the
next several forecast cycles.

Skies will clear rapidly NW to SE late Tuesday into Wednesday
morning and highs will climb back into the 40s to low 50s by
Wednesday afternoon.

Cooper

LONG TERM...Wednesday Night Through Monday

Not many changes made to the long term portion of the forecast this
afternoon, with somewhat better agreement among model solutions
through the upcoming weekend. Surface ridging will remain in place
briefly before progressing eastward later this week which will bring
a return of southerly winds to the area. In response, temperatures
will slowly moderate into the weekend.

The flow aloft will remain zonal and mostly quiet, but as the
weekend approaches a shortwave trough will traverse the state. At
the surface, a cold front will approach from the west. Rain chances
at this point remain east of the area, where low level moisture is
greater. An increase in cloud cover will likely be noted, mainly
across the eastern half of the forecast area.

Near the end of the period it appears that a fairly substantial H500
trough will approach from the west. As moisture increases in the
swrly flow ahead of the trough, chances for precip will increase.
With temps cooler by this point, some wintry precip isn`t out of the
question early next week.

67

&&

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

$$


Aviation...GREEN



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