Area Forecast Discussion
Issued by NWS Little Rock, AR

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FXUS64 KLZK 211144
AFDLZK

Area Forecast Discussion
National Weather Service Little Rock AR
644 AM CDT Mon Sep 21 2020

.UPDATE...

Updated to include the 12z aviation discussion.

.AVIATION...

VFR conds are ongoing across the CWA with general trend of
lowering ceilings C/S AR this afternoon/evening. Marginal MVFR
ceilings will be possible near SHRA/+SHRA. VFR conds will prevail
over Nrn sites through the TAF cycle. Mentioned VCSH for S/SErn
terminals which will slowly spread Nwrd through the afternoon and
become -SHRA after 02/03z Tuesday.

&&

.PREV DISCUSSION...(ISSUED 413 AM CDT Mon Sep 21 2020)
SHORT TERM...Today Through Tuesday Night

Dry and cool weather will continue for many across AR today ahead of
a plume of tropical moisture streaming Nwrd. Looking nationally, an
upper ridge will be centered over the MS Valley and linger invof
TN Valley by the end of the period. Along the gulf coast, cyclonic
flow can be depicted at H500 associated with TS Beta, with
additional upper troughs over New England and over the extreme Nrn
plains.

Looking higher in the atmosphere, at H250, a subtle but important
shortwave trough will emerge from the Srn Rockies and quickly move
towards the region today. By mid-day Tuesday, mesoscale forcing for
ascent at H250 is anticipated to generate a mid-level cyclone (non-
tropical) at H500. Regardless of the fact the region will be under
the influence of broad upper high pressure, this upper low will
deepen and become a cut-off low from continued divergence aloft.
Moisture from the the remnants of Beta will then entrain into
this upper low system. The aforementioned upper cyclone will be
located invof NW AR/SW MO/NE OK/SE KS to end the period.

Over AR, PoPs will begin to increase over SW AR in response to
increasing atmospheric moisture coupled with passing upper level
energy this afternoon. As the upper low develops, PoPs will continue
to increase across the state, with rainfall potentially heavy at
times on Tuesday into Tuesday night. Right now, the current
thinking is the ground can absorb much of this rainfall thus no
hazard headlines will be mentioned in this forecast package.
Additionally, with NE/E surface flow, the potential for severe
weather appears low at this time thanks to stable air advecting
into the lowest portion of the atmosphere. Environmental profiles
across AR will promote a large amount of veering with respect to
height on Tuesday, so these anticipated stable conditions at the
surface will be monitored closely.

During the short term, one to three inches of rainfall will be
possible over SW portions of AR, with lower amounts found further
N and E. In fact, NE sections of the state will receive very
little rainfall through Tuesday night, however rainfall is
expected to continue into the long term period. Temperature wise,
highs today will top out in the lower 70s across SW AR, mainly
due to increasing cloud cover and increasing PoPs, to near 80
degrees over NE AR. Highs on Tuesday will be in the mid 60s to
near 70 degrees, also due to abundant cloud cover, widespread
precipitation, and Erly winds near the surface. Overnight lows
will remain in the 50s and 60s. Dew point temperatures will slowly
creep upwards through the period, however PW will increase
significantly this afternoon as the lower/middle portion of the
atmosphere experiences return flow.

LONG TERM...Wednesday Through Monday

Models remain in reasonably good agreement this morning sans the NAM
solution which is an extremely wet outlier with QPF being produced.
As such, a general blend of the ECMWF and GFS was used to produce
the forecast with a lean towards the slightly more consistent ECMWF.

Period initiates with remnants of Beta along the Upper Texas coast
and drifting slowly to the northeast. Meanwhile a upper level
low, which developed at the conclusion of the short term period,
will be located over the far NW corner of the state. The upper low
will tend to draw moisture from Beta with widespread showers and
isolated thunderstorms across the forecast area. Precipitation
rates will likely be on the higher end with the overall slow
movement of both Beta and the upper low as they drift to the east.

PWATS remain in the 1.0 to 1.5 inch range with an additional inch to
an inch and a half of rain with locally higher amounts possible
through Thursday. While widespread flooding is not expected, this
amount of additional rain on top of what will fall Tuesday could
result in some localized flooding, especially over the southeast.
With clouds and precipitation expected Wednesday, temperatures will
be well below normal with some recovery Thursday.

Friday looks to be the driest day of the period with temperatures
warming into the lower to middle 80s. Attention will then turn to an
upper trough dropping into the nations midsection Saturday. The
approaching trough will keep temperatures mild but will also pull
Gulf moisture back up across portions of the state with afternoon
showers and thunderstorms possible. The best chances will remain
over the east and southeast where moisture will be deepest.

A strong cold front will then move through the state Saturday night
and Sunday with another chance of showers and thunderstorms as the
active pattern of late continues. Models continue to hit at cooler
temperatures very late in the period as a highly amplified pattern
develops across the Conus with a deep trough over the Ohio Valley
putting the state in a deep northwest flow aloft.

&&

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

$$


Aviation...JONES



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