Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
901 PM EST Thursday Mar 5 2015
It has been quite the close call for north Georgia this evening
with coldest of the air right on the heels of the back edge of the
precipitation shield. Reports of sleet and even some light snow
mixing in across the far northern tier before precipitation pulled out
but by and large for the remainder of the area...it has been a
rain event. This is shown in 00z ffc sounding which came in with a
very strong warm nose at 750 mb of over 6c. This went back below
freezing at 890mb which is why we had a few reports of sleet
mixing in at times this evening.
Regardless of who saw what with this event...roads likely remain
wet over much of the area as temperatures plunge into the middle 20s. Winds
are helping to dry things out with gusts to 20 kts common place.
Impressive 70kt at 8k feet on sounding shows potential still there
for continued surface gusts which should further aid in drying
this overnight period. However...wind sheltered locations as well
as the normally prone areas to moisture on roadways will freeze
overnight and Special Weather Statement looks good to keep in effect through Friday
Previous discussion... /issued 730 PM EST Thursday Mar 5 2015/
Previous discussion... /issued 249 PM EST Thursday Mar 5 2015/
Short term /tonight through Friday night/...
have shortened the Winter Weather Advisory period... which now ends
at 7 PM this evening. This is largely due to latest hires models and
overall radar trends showing the rain ending across north Georgia
between 5-7 PM this evening. This will greatly reduce any potential
threat of sleet... snow or ice accumulations... albeit they
would be very light if occur as precipitation is light and limited.
Area observations are indicating the cold shallow air near the
surface finally beginning to spread over the Ridgeline stretching
from NE Alabama across central Tennessee... with some spots across far northwest
Georgia seeing temperatures near or at freezing... but mainly in the higher
elevations. The cold air will continue to spread into north Georgia
through the afternoon and evening...and any lingering light
rain/drizzle could producing some sleet/flurries or even a light
glaze of freezing rain on elevated surfaces through 7 PM this
evening. After 7 PM... expect the deeper moisture and precipitation to have
mostly pushed south and east of the advisory area across north
Georgia. However... although the sleet and freezing rain threat will
be ending... the black ice threat will worsen by this evening as
most of north Georgia temperatures fall below freezing between 5 and 7 PM.
Once the advisory has ended... we will continue to Post and update a
Special Weather Statement for all areas with a black ice threat
overnight. Latest projected lows for tonight has increased the
potential black ice area for tonight... and is now generally along
and north of a Columbus to Macon to Warrenton line.
Otherwise... expect cloudy...breezy and cold conditions through the
evening... then winds diminish after midnight tonight but the clouds
and cold air continue. Expect clouds to scatter by Friday afternoon
for most areas. The added sunshine should help most areas get above
freezing on Friday... with areas generally along and south of a La
Grange to Atlanta to Gainesville line seeing temperatures get above
freezing between 9-10 am Friday... and the rest of north Georgia
between 11 am and 1 PM Friday... except some of the higher
elevations may hold off until middle Friday afternoon. Lows Friday
night will drop at or below freezing for most of north and central
Georgia... and although the black ice threat will be diminished due
to some drying on Friday... especially if the sun appears... we
still cannot rule out a few patches of black ice Friday night where
ground moisture lingers.
Long term /Saturday through Thursday/...
mainly only tweaks to the long term based on the latestguidance.
extended forecast period remains a bit vague concerning best chances
for precipitation. Upper flow is weak and generally zonal to
slightly southwesterly downstream from a persistent but weak trough
over the southwestern U.S. By middle-week this feature is showing signs
of shifting east which may help to increase rain chances a bit
through the end of the forecast. In the meantime any weak waves
moving out of this western trough lift through the region...but
timing and strength of any enhanced lift would be too uncertain
right now. All-in-all this just continues my trends from previous
cycles with slight chance to low chance probability of precipitation broad-brushed across
the forecast area by Monday through the end of the forecast. At the
surface...weak high pressure slowly migrates across the region
through early next week. GFS builds in a wedge type pattern by early
to middle-week and that is supported by the persistent upper-level
confluence over the middle-Atlantic region and New England. Ridge
center is not especially strong...1030mb...and source region is not
expected to be excessively cold so only slight moderation of
temperatures is expected at this time and by Thursday the confluent
upper region shifts well off the East Coast allowing The Wedge to
break anyway. As the surface ridge moves off-shore late in the
period return flow off of the Gulf of Mexico may allow for some
increase in instability...but little if any surface or upper-level
focus for organized thunderstorms appears present at this time.
still dealing with one final round of -ra for atl so included a
short term tempo with this taf set. Also of not is the IFR at ryy
and surrounding sites so there is an opportunity for some IFR
within the first couple of hours of the 00z issuance.
Otherwise...wind becoming the big story with gusts close to 30 kts
at times. Expect a downward trend to these after midnight but
certainly have increased the gust potential in the short term.
MVFR conditions for the remainder of the overnight with
improvement after 16z Friday.
//Atl confidence...00z update...
medium on wind shift and MVFR duration.
High on remaining elements.
Preliminary point temps/pops...
Athens 31 46 29 59 / 30 5 0 0
Atlanta 28 46 33 58 / 10 5 0 0
Blairsville 23 43 26 54 / 10 5 0 0
Cartersville 24 45 26 56 / 10 5 0 0
Columbus 32 49 32 61 / 30 5 0 0
Gainesville 27 45 33 57 / 10 5 0 0
Macon 32 50 28 61 / 40 5 0 0
Rome 25 43 25 55 / 10 5 0 0
Peachtree City 27 47 26 59 / 20 5 0 0
Vidalia 42 51 33 61 / 40 5 0 0