Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Little Rock Arkansas
502 PM CST Sat Jan 31 2015
Updated to include the 00z aviation discussion below...
A storm system will approach from the west this evening...with
rain chances increasing overnight through Sun morning. These rain
chances will then decrease from northwest to southeast during Sun afternoon as a
cold front surges southeast across the area. Breezy srly winds may be
seen overnight into the first part of sun...but then switch to the
west and northwest behind the front. Gusts behind the front could exceed
20 kts in some places. Conditions will go from VFR this evening to
MVFR and IFR overnight...especially under any rainfall. Under the
heaviest rainfall..LIFR conditions could be seen. These conditions
will improve slowly behind the front...but MVFR stratus could sill
persist for several hours behind the front.
Previous discussion... /issued 250 PM CST Sat Jan 31 2015/
Short term...tonight through Tuesday night
Abundant middle and high level clouds have been noted across the forecast area today
as the sub tropical jet stream has taken control upstairs.
Meanwhile...a very dry airmass remains in place at the lower levels up to
around 5k feet as noted by morning sounding data and this factor will continue to
affect the timing of rainfall expected to affect the area tonight.. middle
afternoon temperatures ranged from the middle 40s to middle 50s across the forecast area.
The split flow regime over the middle south will transition to a northwesterly flow
late this weekend and into early next week. The upper level low...
currently over northern Baja California...will become cutoff and meander over that region
for a few days. Meanwhile...a strong northern stream upper trough will drop
southeastward through the Central Plains and pass across the forecast area Sun night and Monday.
As a result...wet weather...albeit brief...will affect Arkansas over the next
24 to 36 hours. The models continue to agree the surface low now over the eastern
rockies will continue to develop as it heads eastward tonight and sun. Rain will increases
and gradually overspread the forecast area from the west tonight and sun. Onset of
rainfall remains the main forecast concern until the drier airmass in the
lower levels eventually becomes saturated. Continue to indicate incrsg probability of precipitation from west
to east tonight...although did slow down the onset compared to current
Periods of rain are expected sun...with a slight chance of thunder still
included over parts of central and southern Arkansas. The low pressure system will pass north
of Arkansas sun and Sun night. The associated cold front will sweep through the forecast area from the
northwest during the day on sun as well. Rain chances will diminish from the west Sun
afternoon and early sun evening.
Canadian high pressure will follow the frontal passage for the remainder of the period.
Temperatures on Monday will be noticeably colder as the ridge settles over the middle
south. Temperatures will recovery some on Tuesday as the high shifts eastward and a
S/southwesterly wind flow returns...with temperatures approaching seasonal norms.
Long term...Wednesday through Saturday
The main forecast concern for the long term is whether or not wintry
precipitation will make an appearance late Wednesday night and
during the day Thursday. It should be noted that there is
considerable spread between the models as it pertains to precipitation type
so this is far from a certain forecast at this time.
With that said...there is agreement on the overall pattern across
the lower 48. A quasi zonal pattern will be set up across the northern
tier states on Wednesday...with a system set to eject NE across Texas from
northern Mexico or southern New Mexico. As time GOES on more energy will dive
south from Canada to transition the zonal pattern to a an eastern
trough/western ridge upper flow by Thursday. The initial southern wave
ejecting east across Texas will stay mainly south of the state...but
should be close enough to warrant keeping some slight rain chances
in the forecast for the far south on Wednesday and Wednesday night.
The trailing energy dropping south through the plains is where the
key differences lie...with the European model (ecmwf) being completely dry as that
disturbance passes by...and the GFS developing a substantial area of
precipitation as the associated cold front and Arctic air mass move south into
the state. The GFS has consistently shown this wetter solution over
the last couple of days so have continued to side more with the GFS
with regard to temperatures and precipitation chances. In that light...an
area of rain/snow mix will be kept for essentially the northern half
of the forecast area on Thursday. However...have limited precipitation
chances to 25-30 percent maximum at this time. Precipitation will linger
into the evening Thursday but will push east by Friday morning for
dry conditions to round out the long term period. Temperatures will
be below normal from Wednesday night through the end of the
week...but above normal temperatures should creep back into the
state by next weekend as upper heights build and deep southwesterly
flow spreads across the arklatex region.
Again...it must be stressed that while the current forecast will
advertise some wintry precipitation on Thursday...there is considerable
uncertainty. While the GFS has been consistently colder/wetter...the
Euro has been just as consistently dry...so it is probably best to
not get too excited about next Wednesday/Thursday just yet.
Preliminary point temps/pops...
Batesville Arkansas 43 52 27 37 / 80 100 10 0
Camden Arkansas 50 61 30 44 / 80 100 10 0
Harrison Arkansas 42 46 21 36 / 100 90 10 0
Hot Springs Arkansas 48 56 28 42 / 100 100 10 0
Little Rock Arkansas 47 57 30 40 / 90 100 10 0
Monticello Arkansas 49 61 32 41 / 70 100 20 0
Mount Ida Arkansas 49 54 26 41 / 100 100 10 0
Mountain Home Arkansas 42 49 24 36 / 100 90 10 0
Newport Arkansas 43 53 28 37 / 70 100 10 0
Pine Bluff Arkansas 48 59 31 40 / 70 100 10 0
Russellville Arkansas 44 53 27 40 / 100 100 10 0
Searcy Arkansas 44 54 28 38 / 80 100 10 0
Stuttgart Arkansas 47 56 30 39 / 70 100 10 0