Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
635 am EST Thursday Jan 29 2015
Previous discussion... /issued 319 am EST Thursday Jan 29 2015/
Short term /today through Friday/...
latest regional surface analysis shows a 1028mb surface high
centered over the eastern Virginia and North Carolina with
ridging extending through the sandhills of South Carolina and the
Golden Isles of Georgia. Meanwhile...next weather maker is moving
into the northern plains in the form of a low pressure system
centered over Illinois with trailing cold front through the
Missouri Valley and into the deep south. A look at the initialized
upper level features shows strong jet streak through the arklatex
which is putting high clouds on the fast track through the local
area with broken high clouds the rule at this hour.
For today...models are consistent in showing two distinct waves of
potential precipitation moving across the area but neither one
overly impressive. Simulated reflectivity from the local WRF and
hrrr both indicate first impulse moving across extreme north
Georgia by middle morning and persisting through early afternoon.
Limited moisture with this first wave will result in low end
chance probability of precipitation at best.
Slightly better chances along the actual front and have bumped up
values to Middle Range chance between 22z and 04z roughly as precipitation
axis translates from the mountains into the remainder of north
Georgia including the Atlanta metropolitan. Low level moisture increases
during this timeframe with column becoming saturated from the
surface to 8k feet and even with meager lift...should be
sufficient values to warrant continued chance probability of precipitation as front moves
into central Georgia. Amounts look to be very light with only a
tenth of an inch every 6 hour block for this event.
Front pushes south of the area for the remainder of the short
term with high bridging north of the area providing for a cold
northerly flow. Will stick close to a bias corrected blend for
temperatures through this time period.
Long term /Friday night through Wednesday/...
main focus of forecast is with precipitation chances associated with
advection of Gulf moisture and developing surface low ahead of a
broad upper trough for Sunday into Monday. General guidance
consensus backs off on the strength of system...delays the onset
of precipitation...and pushes a weaker surface high farther south ahead of it
/no longer resulting in a cad wedge/. All considered now less
likely of any different p-types Sunday morning than just rain
showers. Have barely held onto slight chance snow in highest
elevations of far northeast early. The best chance of any wintry
precipitation looks to be on the back side of system on Monday...though
discrepancies exist as to how strong the Gulf low is and if any
wrap around moisture is present /GFS the more bullish solution/.
Enough of a potential given prognosticated thermal profiles to include
slight chance of transition to light snow Monday morning before
all is said and done. Little to no accumulation is still expected.
Widespread rain showers look to be the main story with this
system now and total quantitative precipitation forecast has been fairly consistent with amounts
ranging from 1 inch north to half inch central Georgia.
Zonal flow returns to the southeast Continental U.S. Early next week...then
another impulse along the subtropical jet brings some Gulf
moisture back into the southern portion of the area for Wednesday.
Of course differences exist in the timing and extent of the
moisture northward but have for now just included low end chance
keeping mainly across central Georgia. Moisture/temperature profiles
indicative of rain showers.
VFR for the first part of the forecast with just an increase in
high clouds. This will transition to middle clouds by late this
afternoon across the atl taf sites and then lower to MVFR as a
cold front approaches this evening and into the overnight hours.
There is some indication that ceilings could dip into the IFR range as
-ra develops but enough uncertainty at this point to just keep
MVFR. Good consensus on wind shift which should be around 18z
today to the SW.
//Atl confidence...12z update...
medium on IFR potential late this evening.
High on remaining elements.
Preliminary point temps/pops...
Athens 57 35 54 28 / 10 30 0 0
Atlanta 57 37 51 31 / 10 30 0 0
Blairsville 52 31 42 24 / 20 40 5 0
Cartersville 58 35 47 25 / 20 30 5 0
Columbus 61 42 57 31 / 5 30 5 0
Gainesville 55 35 49 28 / 10 30 0 0
Macon 58 40 56 30 / 5 30 5 0
Rome 58 36 47 26 / 20 40 5 0
Peachtree City 59 36 52 26 / 10 40 0 0
Vidalia 63 46 58 34 / 5 30 10 0