Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Jackson MS
932 PM CST Sat Dec 27 2014
Gulf moisture continues to stream northeastward into our area this
evening. The radar currently shows a big push of heavy rain into the
eastern half of our County Warning Area. Behind this push is mostly scattered light
to moderate showers. The severe threat seems to be waning so will be
taking that out of the severe weather potential statement and graphics. Hi-res model guidance
suggests rainfall activity will be waning in the coming hours before
dawn and then another push of some light activity after dawn Sunday.
Will be maintaining the Flash Flood Watch...though precipitation amounts
have not amounted to any serious flooding yet. The watch may need to
be trimmed some depending on the 00z model guidance.
The going forecast looks pretty good however. The hourly temperatures and
dewpoints were adjusted to reflect the position of the front. /10/
IFR to LIFR ceilings will continue areawide tonight through Sunday as a
low pressure center moves to the NE along the Natchez trace corridor.
Widespread rain is expected to continue tonight as well then taper
off from the west Sunday morning as the trailing cold front slowly
moves east across region. A few thunderstorms will be possible over the southeast portions
of the area mainly this evening. Winds will shift to the northwest/north after
frontal passage...and become gusty in the Delta Region as strong high pressure
builds into the region. /22/
Previous discussion... /issued 316 PM CST Sat Dec 27 2014/
Short term...tonight through Sunday night...WV imagery this
afternoon showing middle/upper level system continuing to dig
south...now entering northwest Mexico. To the east...mid/upper level
anticyclone remains nearly stationary over the Carribean. Resulting
flow in between has become increasingly south-southwest allowing the moisture
rich air (pwats near 2 inches) over the northwest Gulf of Mexico to be
Already...elevated convective clusters moving over southeast MS have
produced substantial rains with sporadic street flooding being
reported. Latest hrrr data is indicating convection will fill back
in along the middle 60 dewpoint axis...currently bisecting la...as it
moves into western MS early this evening. Believe the axis of
heaviest rains will set up along the eastern flank of the dewpoint
gradient which will occur coincide with the axis of highest precipitable water
coming in off the northern Gulf of Mexico. The NAM...hrrr...GFS...
and European model (ecmwf) all have similar quantitative precipitation forecast solutions.
While precipitable water values as high as we are seeing is anomalous enough (+3
Standard deviations)...even more amazing is the fact that the
majority of the moisture seems to be located below 700 mb when
looking at area soundings from this morning and afternoon. Above 700
mb profiles are quite dry. This has allowed for convective
destabilization as moisture continues to stream in and is most
likely responsible for the elevated storms with hail that we are
currently seeing. Believe this will continue to be a problem tonight
until the column can become substantially saturated. Will continue
to outlook our limited severe threat...but move it a little further
north based on current trends. There still appears to be a limited
tornado threat over the southern fringes of the forecast area where
more in the way of surface based convection can get going.
Frontal boundary moving through after midnight will allow rainfall
to wane somewhat. However...do expect it to break out again Sunday
as whats left of phasing middle level wave works its way through.
Rainfall will taper off rapidly after midnight Sunday night./26/
Long term...Monday through Saturday...surface high pressure ridging
will build in on Monday across the arklamiss with cooler highs
ranging from the low to middle 50s. Little change is expected Tuesday...
but colder air will move in Tuesday night as cold high pressure noses
into the region. New years evening day temperatures will only climb into
the 40s and lower 50s. New years evening will be cold with lows Wednesday
night falling into the upper 20s/low 30s.
The pattern over the area will begin to change on Thursday as the
surface high shifts to the east and an upper trough deepens over the
southern planes. Moisture will increase over the area Thursday night
into Friday with showers on the increase Friday afternoon. The
global models diverge on their solutions Friday night into Saturday
with the GFS taking the surface low north and the European model (ecmwf) further
south. Either way showers and storms will be on the increase as we
get into the weekend with another round of heavy rainfall and
possibly some severe storms./15/26/
Preliminary point temps/pops...
Jackson 52 54 42 53 / 100 97 94 8
Meridian 58 62 45 56 / 100 94 95 14
Vicksburg 48 50 40 52 / 100 98 89 6
Hattiesburg 59 67 48 59 / 100 63 82 7
Natchez 50 52 41 53 / 100 95 87 5
Greenville 43 46 37 50 / 100 89 75 7
Greenwood 46 48 39 51 / 100 96 85 9
MS...Flash Flood Watch through Sunday afternoon for msz026>033-
La...Flash Flood Watch through Sunday afternoon for laz026.