Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Peachtree City Georgia
1000 PM EST Friday Dec 6 2013
cold front currently pushing through the Atlanta area and should
make slow progress southward. Line of heavy showers and isolatd
thunderstorms along the frontal boundary with some lighter rain
behind the front. Have made a few tweaks to probability of precipitation according to radar.
Temperatures in northwest corner lower than forecast and have tried
to adjust the temperature grids to account for this.
short term /tonight through Saturday night/...
the area remains in a wet pattern through the short term. This
afternoon...scattered showers have developed across the northern and
western part of the County Warning Area. Mesoanalysis shows areas in western Georgia
with 500+ j/kg of MUCAPE and 30kts of low level wind shear.
Conditions are still in place for the possibility of isolated severe
storms this afternoon and the most likely area remains across
western Georgia this afternoon into tonight. The threats remain
damaging wind and isolated tornadoes but again any severe storms
should be isolated. For the second half of tonight the instability
is near zero and the low level shear decreases and thus the severe
threat diminishes. With the front slowly shifting southward the
better precipitation coverage will move across the northern portion
of the County Warning Area overnight and although the precipitation coverage
decreases towards sunrise...scattered showers should still remain
across the area. May have somewhat of a lull in coverage on Saturday
but then the better chances return again for Saturday night across
north Georgia as The Wedge builds in. After 06z
tonight...instability is near-zero so no mention of thunder after
tonight...only showers. The threat for severe diminishes
overnight...but then the focus turns to rainfall amounts. See the
Hydro section for more details.
Temperatures are near a model blend and are a challenge with the
cold front moving in and helping to cool temperatures but the clouds
remaining in place and helping to moderate temperatures. Will see
considerably cooler temperatures across most of the County Warning Area tomorrow as
compared to the highs today. Around a 20 degree difference between
today and tomorrow for a high temperature in atl.
Long term /Sunday through Friday/...
medium range model trends show no significant departures from
recent previous runs. Although cooler air moves in behind the next
cold front early next week...upper flow turns zonal at best from
the persistent southwesterly flow and better cold air remains
north of the state through next week. See previous long term
forecast discussion below.
Previous long term forecast discussion...
Long term /Sunday through Thursday/...
/issued 337 am EST Friday Dec 6 2013/
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.
a round of rain forecast overnight combined with additional rain
expected Sunday night into Monday will allow for the potential of
2.5 to 5 inches of rain across north Georgia through Tuesday.
Isolated higher amounts are possible. These amounts will allow for
possible minor flooding across north Georgia. See the hydrologic
outlook /esfffc/ for details.
frontal boundary just south of rmg will continue to sink slowly
south. Scattered showers ahead of the boundary will affect the taf
sites...but more widespread rain should spread over the taf sites
after frontal passge late tonight and Saturday morning. Isolated
convection possible but too difficult to time for the taf sites.
IFR ceilings overnight with some LIFR possible through 14z. Winds
southwest 10kt with occasional gusts...becoming northwest 10kt by
12z with higher gusts.
//atl confidence...00z update...
medium to high confidence on wind. Medium on all other elements.
Preliminary point temps/pops...
Athens 56 60 44 48 / 60 60 70 90
Atlanta 48 54 45 53 / 90 50 70 80
Blairsville 46 52 41 47 / 100 50 80 90
Cartersville 45 52 44 51 / 100 50 80 90
Columbus 55 58 52 66 / 70 60 50 50
Gainesville 52 57 43 45 / 80 40 80 90
Macon 60 63 51 62 / 60 60 50 50
Rome 45 52 43 52 / 100 50 90 90
Peachtree City 49 53 47 57 / 80 50 70 70
Vidalia 65 73 54 66 / 30 40 40 30