Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
637 am EST Monday Dec 9 2013
Previous discussion... /issued 331 am EST Monday Dec 9 2013/
.Continuous rain over northwest Georgia may lead to isolated flooding...
Short term /today through Tuesday night/...
latest surface analysis shows wedge remaining in place from the
middle Atlantic through the Carolinas and east central Georgia.
Widespread low clouds continue within The Wedge with mainly 2 to
4 mile visibility but isolated values below a mile for the
southeast corner as well. Just off the surface...moderate
southwest flow is pushing moisture up and over The Wedge
resulting in widespread light to moderate rain from Haralson to
white counties and points northwest. In fact...elevated flow has
become strong enough(around 45kts) to allow for isentropic
induced thunderstorms embedded within the moderate rain just
north of the Atlanta metropolitan.
For the remainder of today...elevated wind core at 025mb should
progress eastward with best isentropic upglide going along with
it. This should allow rainfall rates to diminish through middle
morning but orientation of rain axis should remain fairly steady
state over northwest Georgia. Wedge will begin to break down as
well which will also aid in reducing rainfall potential but for
east central zones...not buying as quick an eroding scenario as
what models depict. I do therefore keep temperatures in this region more
in line with a cad scenario...some 3 to 5 degrees below guidance.
For tonight...initially it will be similar to tonight with patchy
drizzle and fog areawide and best chances of rain for the
northwest corner. This will change as we approach daybreak as a
strong shortwave pushes into the Tennessee Valley and
consolidates precipitation axis...once again over northwest Georgia.
Should see some quick movement however to this rain shield as
trough catches up and given lighter quantitative precipitation forecast amounts...any flooding
Low level wind core increases to near 50 kts once again ahead of
the trough over most of the forecast area and we will not longer
have the subsidence of a wedge to save US. Although instability
looks to be non existent...would not be surprised to see some
strong damaging gusts in just the shower activity as it moves
through Tuesday. Finally get some clearing late Tuesday with good
agreement among the short term models.
Long term /Wednesday through Sunday/...
GFS and European model (ecmwf) are coming into better agreement through the
extended especially with respect to the weekend system. Extended
begins with high pressure over the Ohio Valley in control of most
of the eastern third of the country behind the early week frontal
passage. Very dry air in place but enough of a pressure gradient
will remain in place to keep winds from going calm overnight...
which in turn prevents temperatures from bottoming out early in the
period. Weak wave pushes through Wednesday night which may serve
to increase clouds but should not bring any precipitation to the area.
The bigger story will be toward the weekend. Ridging increases
aloft on Friday in advance of strong trough deepening over the
Desert Southwest. Surface low develops in the Lee of The Rockies
in the Southern Plains and as it works its way east...it
overspreads moisture and precipitation across the area especially
on Saturday. May have a weak hybrid cad in place depending on how
far offshore the surface high has moved by that point. Introduced
a brief rain/snow mix Saturday morning as current timing brings
moisture in with temperatures in the lower 30s across north Georgia. Have
also increased probability of precipitation to likely on Saturday based on model
agreement...though European model (ecmwf) is just a touch faster than GFS. Front
moves quickly out Saturday night...though European model (ecmwf) is advertising a
secondary shortwave pushing through Saturday night.
Overall maximum temperatures look to be fairly close to average...with larger
swings in low temperatures...starting off on the cool side with dry high
pressure and place and gradually increasing toward the weekend
with the increasing moisture.
as mentioned above...expect low level wind core which is
responsible for heavier rain showers and embedded thunderstorms and rain to lift out quickly
this morning leaving behind more in the way of light to
occasionally moderate rain. 6 hour ffg is low and in some cases
below 2 inches but even going on high side of guidance...I am
having a tough time realizing these values. Still feel normal
problem areas could briefly go into minor flood but isolated
nature precludes issuance of a Flood Watch at this time.
not much variance at all to ceilings the last 24 hours and expect LIFR
conditions to continue into this morning with brief period of
vlifr also possible. By early afternoon...as winds shift to
northwest...do lift ceilings slightly into the IFR range but no
additional improvement expected this taf set. Band of rain showers will
affect ryy and perhaps fty and pdk but largely remain north of
atl. More vlifr expected Monday night before winds pick up around
daybreak and lead to high ceilings but increased rain showers chances. Winds
look to increase with low level jet Tuesday morning through early afternoon.
//Atl confidence...12z update...
low on wind shift direction today.
Medium confidence on ceiling improvement today.
High on remaining elements.
Preliminary point temps/pops...
Athens 47 47 57 36 / 50 40 60 0
Atlanta 50 46 53 36 / 60 50 80 0
Blairsville 45 44 50 29 / 100 100 100 0
Cartersville 48 42 49 30 / 100 80 80 0
Columbus 64 56 59 40 / 40 40 60 0
Gainesville 44 44 54 35 / 80 70 80 0
Macon 61 57 64 39 / 30 40 70 0
Rome 48 42 46 29 / 100 100 100 0
Peachtree City 54 48 53 34 / 60 50 80 0
Vidalia 64 63 67 47 / 20 20 50 0