Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
402 am EDT sun Apr 19 2015
Short term /today through Monday/...
Local area is entering into a strongly diffluent pattern aloft as
a shortwave moves through central Alabama. All this adding to the
overall upward vertical motion and with precipitable water values
rising rapidly...coverage of -ra and -shra has likewise increase.
Last evenings sounding put ffc at around 1.22 precipitable water value which
model initializations are now putting it close to 1.75 in...so
quite an increase. Big question initially is the convective
potential for the remainder of the overnight period into this
morning. Stable environment remains in place over much of the
area...more than models would indicate...with mostly low clouds and
zero cape over north Georgia. Cape axis remains over south Georgia
and should progress north through morning with areas from csg to mcn
affected first. Even areas within this instability axis have
exhibited very little lightning thus far and will likely cap at
isolated chances for now.
Looking like best chances of strong to severe will be over the
east and southeast sections of the forecast area today where the
greater instability will be possible. 850 jet of 40 knots along
with 0-1 km helicity of 250 m2/s2 will lead to a continued slight
risk of severe storms mainly this afternoon in these areas.
Will get a break late this afternoon through tonight as next
shortwave approaches from the lower Mississippi Valley. Pre
frontal boundary prognosticated to move through between 12z and 15z
Monday for northwest Georgia and 15z to 21z elsewhere. Looks like similar
shear values and target areas of east and southeast portions for
this event but perhaps more instability to work with. Nam12 shows
cape values in excess of 200 j/kg move from the Gulf Coast into southeast
portions. As front moves through with aforementioned shear
values...should see another severe threat with isolated tornadoes
not out of the question.
As far as hydrology concerns...certainly looks as though there
will be some isolated minor flooding of the normally prone areas
but not sure enough to warrant Flood Watch at this point. Wpc quantitative precipitation forecast
indicates an inch to an inch and half spread over the next 2 days.
With quantitative precipitation forecast under performing thus far this morning...would like to
see how convective potential evolves before deciding on any
Long term /Monday night through Saturday/...
Medium range models are in pretty good agreement through the extended
forecast period...at least west/respect to the larger scale patterns. As
would be expected the later into the run the more there are
differences in strength and timing of some of the smaller features...
but overall a general blend and concentration on the larger scale was
used for the long term forecast grids.
Period starts out with the current system moving into the region
now finally exiting...ushering in a drier and seasonably mild
airmass in its wake for Monday night through Tuesday. Moisture return
begins Wednesday as the surface ridge slips east of the state. Weak
short waves in the westerly upper flow and a weak cold front bring at
least a slight chance for precipitation back into the north. This
weak frontal boundary hangs around through the end of the work week
keeping slight chance to low chance probability of precipitation in the forecast. Better
chances for rain sweep back in for the weekend as a stronger short
wave sweeps through the region. Both the GFS and the European model (ecmwf) are
generating a decent surface low over the region associated with this
short wave. Enough instability with the middle week system for a chance
of thunderstorms...although lack of strong dynamics and marginal
nature of the instability point to minimal chances for severe
weather. Weekend system showing even less instability...but stronger
dynamics indicate at least a slight chance for deeper convection.
IFR and LIFR conditions have been a little ahead of schedule this
morning ahead of main -ra shield moving from SW to NE. Lower
confidence forecast as to if this LIFR will persist or lift
slightly as heavier rain showers moves through the terminals. For
now...show marginal improvement through daybreak after which will
need to monitor for thunderstorms and rain potential. Moved timing of these thunderstorms and rain
back in latest taf set slightly to begin at atl after 14z. Slow
improvement to MVFR through noon with winds shifting to the SW and
//Atl confidence...06z update...
medium on LIFR persistence.
High on remaining elements.
Preliminary point temps/pops...
Athens 74 61 78 52 / 100 40 60 20
Atlanta 74 62 75 53 / 100 30 50 10
Blairsville 70 57 71 47 / 100 50 60 20
Cartersville 76 61 75 50 / 100 40 60 10
Columbus 79 65 81 55 / 100 20 40 5
Gainesville 71 61 73 51 / 100 40 60 20
Macon 77 64 81 54 / 90 30 40 10
Rome 77 61 74 49 / 90 30 60 10
Peachtree City 76 61 77 51 / 100 30 50 10
Vidalia 79 67 83 60 / 80 50 40 20