Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
645 am EST Friday Dec 6 2013
Previous discussion... /issued 337 am EST Friday Dec 6 2013/
.Record highs in jeopardy this afternoon...
.after a brief respite rains to return late today...
Short term /today through Saturday night/...
continue to see periods of rain showers with embedded thunderstorms and rain roll through
roughly the same areas of west central Georgia and up through the
Interstate 85 corridor. Earlier rotation seen in a few storms has
abated but now middle level wind gusts more apparent as activity
reaches the northeast mountains. All this has been in a zone of
enhanced low and middle level moisture characterized by precipitable waters in the
99th percentile for this time of year. Fortunately...zone does
look to be lifting northward so as to allow areas from Carrollton
through the northern Atlanta metropolitan to dry out a bit.
Middle and upper level heights will build ever so slightly though
this afternoon which should be just enough to shunt most
significant precipitation north of the area for the balance of today.
Have kept near categorical in for far northwest counties because of this
but tapered very quickly to silent 10 probability of precipitation for the southeast
corner of the forecast area. Temperatures today will be highly dependent
on how quickly cloud cover erodes or for that matter if it does.
Feel with heights building aloft...should see enough of a break in
clouds in precipitation and clouds to warrant values close to guidance.
This would break a few a records across the area per climate
As far as severe potential...will be a very close call today as
wind core tries to come in sync with best instability. Models in
general indicating this will not happen as impressive 65kt 850mb
wind core shifts from Alabama and Mississippi into the Tennessee
Valley...largely bypassing the northwest Georgia counties. In addition...305k
surface indicates pressure along that surface conducive of capping
much like what was depicted the last nonevent. Despite these
factors...still cannot completely rule out an isolated severe wind
gust or brief tornado.
Front pushes through Friday night into Saturday with continued
moderate rain potential but doesnt get all that far before next
impulse dives into the Central Plains with surface reflection over
the northern Gulf of Mexico. Return moisture aloft will result in
quickly increasing probability of precipitation in favorable isentropic upglide setup.
North Georgia looks to be targeted once again with another half an
inch to inch of rainfall expected.
Long term /Sunday through Thursday/...
extended begins with southwest flow continuing aloft as surface
high over the Great Lakes continues ridging down the eastern
Seaboard in a diabatically enhanced classical cad setup.
Isentropic upglide keeps high pop-low quantitative precipitation forecast precipitation across the area
early on Sunday but as a strong trough and surface cold front
approach Sunday night...precipitation increases across the area.
See Hydro section below for more detail.
South of The Wedge front...as the synoptic cold front approaches
on Monday...all models have MUCAPES increasing to over 500 j/kg.
Not too impressive but enough to keep mention of slight chance
thunder in the area Monday afternoon in that warm sector...where
high temperatures will be in the middle 60s to middle 70s. Best shear will be
along and behind the cold front where 0-1km bulk shear will be
approaching 35kt while 0-6km shear is upwards of 60-70kt. Just
not sure how well these two will line up. So for now...isolated
thunder still looks good and cannot rule out strong to isolated
severe storms but will monitor forecast trends over the next
couple of days.
Cold front pushes through by Tuesday night bringing a much cooler
airmass to the region. Current grids reflect only a brief overlap
of the cold airmass and light precipitation...bringing a rain/snow mix
into portions of north Georgia early Tuesday before the moisture
sweeps out. This will need to be refined with later forecasts. 00z
GFS and European model (ecmwf) are in fairly decent agreement through the
extended...with hints of the beginning of a hybrid damming event
just beyond the end of the period.
With majority of activity waiting until later this evening...area
creeks will have sometime to recover. Would not be surprised to
see a few go into flood this evening with next precipitation batch
but reduced totals from HPC leads ME to hold off on any watch
product at this time.
Could see some hefty amounts Sunday night and Monday morning
across areas that will have seen at least a couple of inches of
rain up till then...cannot rule out the potential need for a Flood
Watch by that point. Storm total quantitative precipitation forecast through the extended is
another 2-3 inches across northwest Georgia...with almost an inch
of that prognosticated to come between 06-12z Monday.
lower ceilings have been slower to develop than expected with mainly
MVFR around the atl area terminals. Still feel there is an
opportunity to realize some IFR...especially considering large
expanse of IFR moving in from southwest of csg. Ceilings should gradually
improve through the day...becoming MVFR where they are not already
and possible VFR for csg and mcn. Have continued to pushed back
rain showers/thunderstorms and rain chances beyond 03z for this cycle. In the wake of the
rain showers...lowered ceiling are expected with good agreement on LIFR for a
possible extended period Friday night.
//Atl confidence...12z update...
medium on LIFR potential this morning and rain showers/thunderstorms and rain timing.
High on remaining elements.
Preliminary point temps/pops...
Athens 75 57 59 47 / 40 70 60 60
Atlanta 75 49 54 46 / 40 80 50 60
Blairsville 67 46 52 43 / 50 90 60 80
Cartersville 72 45 50 44 / 50 90 60 70
Columbus 80 55 59 52 / 30 80 60 30
Gainesville 71 51 54 45 / 50 80 60 70
Macon 80 60 65 52 / 20 60 60 40
Rome 71 45 50 43 / 60 100 60 80
Peachtree City 76 50 55 47 / 30 80 60 50
Vidalia 79 65 72 58 / 20 40 60 40