Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Little Rock Arkansas
522 PM CST Wednesday Nov 25 2015
Updated to include the 00z aviation discussion below...
VFR conditions ongoing currently...but this will change this
evening and especially overnight at the northern and western sites as
moisture continues to stream north. MVFR or lower conditions will
be possible...and even the southeastern sites will also see some decreased
flight conditions later in the morning hours. There may also be
some -ra and dz...but widespread rainfall will hold off until
beyond this taf period.
Previous discussion... /issued 208 PM CST Wednesday Nov 25 2015/
Short term...tonight through Saturday night
At the surface...a cold front extended from western Kansas into
the far northern Great Lakes region. High pressure was located
over the southern Appalachians region. This was allowing for
Gulf moisture to advect into the region...as evidenced by
decreasing temperature-dewpoint spreads moving into southern Arkansas.
In the upper levels...ridging was centered over the central Gulf
Coast region...with a closed upper low moving into The Rockies.
This was allowing the Pacific to open up...with deep southwest
Over the course of the next 24-48 hours...the aforementioned upper
low is expected to expand southward...which will push the ridge
over the southeast toward the Atlantic Seaboard. In turn...the
surface front in the plains will move into the region. However...
as it gets further southeast...it will hit nearly parallel upper
flow...and this will act to slow down or even stall out the
boundary for a time.
Several waves will move through in southwest upper flow and
interact with the frontal boundary. This synoptic scale setup will
be extremely conducive for periods of rainfall beginning Thursday
night and continuing through the end of the period.
Heavy rainfall will be a big threat over the aforementioned
periods...and this will likely be in several waves. Low level
steering flow will be relatively weak...and in turn so will storm
motion. Also...model forecasts are showing impressive precipitable
water on the order of 1.60 to nearly 1.90 inches...which is near-
record for November.
Thunderstorms will be possible...but given little opportunity for
large-scale surface-based instability...have only included a
slight chance at this time.
Rainfall amounts of four to seven inches are likely...primarily in
areas along and north of the Interstate 30/Highway 67 corridor.
The highest accumulations...though...are likely to be in the
Ouachita Mountains...where amounts could push or exceed eight
It is for these reasons that we will be going with a Flash Flood
Watch for the aforementioned areas...beginning at 00z Friday...and
continuing through 12z Sunday.
Keep in mind...the speed of the surface front will play a big part
in dictating where the axis of heaviest rainfall sets up. Any
expected deviation could result in significant adjustments to
later forecasts. Areal coverage of the watch...as well as
expiration times may need adjustment with any significant changes
to the forecast.
Long term...Sunday through Wednesday
No significant changes for the long term period. Rain will continue
across much of the state Sunday...especially in the east...as the
upper low over the intermountain west slowly moves eastward. The main
question is exactly where this upper low will track and the effects
this will have on Arkansas weather. By midday Monday there is some
500-600 mile difference in the placement of the upper low between the
operational runs of the two global models...with the GFS being
further north and west with an upper low centered over the central
Wyoming/Montana boarder and the European model (ecmwf) centered over central
Nebraska. As such the GFS is dry on Monday while the Euro holds some
precipitation back across Arkansas during the day Monday. Stuck with the
previous shift/S decision to keep some slight chance probability of precipitation into
Monday...but that is a low confidence forecast. Both models are void
of precipitation come Tuesday though...so the long term looks to end on a
Made little appreciable changes to temperatures as well given the
uncertainty. Highs look to be in the upper 40s in the north to middle
or maybe upper 50s in the south. Overnight lows will be in the 30s
to low 40s.
With the expected rainfall over the next few days...it is
noteworthy that...if the forecasted amounts come to fruition...
there will be many locations that will see top 10 wettest
novembers. At a few locations...we could see the wettest November
on record. Again...that is if the current forecast holds up. For
example...current rainfall at Harrison in Boone County is at 4.89.
If six inches of rainfall happens...the monthly total will be at
10... will be their wettest November on record.
To give some perspective...listed below are a few locations with
November 2015 rainfall totals...forecast rainfall amounts...
and the 10th wettest November at each location.
Station Nov 2015 so far forecast 10th wettest Nov
Booneville 5.76 7 inches 8.33 in 1985
Little Rock 5.25 5 inches 9.03 in 1973
Mount Ida 4.32 6-7 inches 9.29 in 2003
Russellville 6.52 6-7 inches 7.81 in 1902
Subiaco 6.32 7 inches 8.28 in 2006
Waldron 6.87 7 inches+ 8.29 in 1988
Preliminary point temps/pops...
Batesville Arkansas 54 64 58 62 / 20 30 60 90
Camden Arkansas 59 69 62 68 / 20 30 40 60
Harrison Arkansas 53 62 56 56 / 20 40 90 100
Hot Springs Arkansas 58 65 62 65 / 20 40 60 80
Little Rock Arkansas 56 67 60 66 / 20 30 50 80
Monticello Arkansas 56 69 60 69 / 10 20 20 40
Mount Ida Arkansas 59 65 63 64 / 20 40 70 90
Mountain Home Arkansas 53 62 57 59 / 20 40 90 100
Newport Arkansas 54 65 58 62 / 10 20 50 90
Pine Bluff Arkansas 56 68 59 68 / 10 20 30 60
Russellville Arkansas 56 64 61 63 / 20 40 70 100
Searcy Arkansas 53 65 58 64 / 20 30 50 80
Stuttgart Arkansas 55 68 58 66 / 10 20 40 70
Flash Flood Watch from Thursday evening through late Saturday
night for Baxter-Boone-Clark-Cleburne-Conway-Faulkner-Fulton-