Tip:
Highlight text to annotate it
X
Good afternoon. This is Jason Deese with the National Weather Service here in Peachtree
City GA with a briefing on potential wintry weather Thursday afternoon and night. There
is still some uncertainty with the forecast but confidence is increasing in accumulating
snowfall for the Georgia mountains and widespread travel impacts due to a brief period of black
ice.
We will get to the specifics of this winter weather scenario in a moment, but let's
take a second to look at the current situation as relates to rainfall amounts. This graphic
shows the rainfall accumulations we have received since 7am this morning. Across far north Georgia
already 5 inches of rain has fallen, with pockets of 6 plus inches. You can see the
tight gradient of rainfall where the amounts go to zero quickly across southern sections
of the forecast area. So how much more rain are we going to get?
This graphic shows the additional precipitation expected through Friday morning. This is liquid
equivalent amounts, so it includes both rain and the liquid equivalent of snow. North Georgia
could see an additional 1 to 2 inches of rain with 2 to 3 inches possible across northeast
Georgia. Central Georgia will continue to see the lower amounts. This additional precipitation
could result in additional rivers going into minor flood and a few rivers already in flood
going into moderate flood. A flood watch still remains in effect for much of north Georgia.
So lets get back to the winter weather expected and take a look at the setup and what we expect
over the next several days. The current cold front that has been lingering across the state
will shift south through Thursday with colder air infiltrating the area in its wake. As
this occurs, low pressure is expected to develop over the northern gulf which will spread moisture
back to the north to affect the remainder of the southeast. Changes since the forecast
yesterday include more precipitation on the cold side of this low and thus an increase
in expected snowfall amounts across north Georgia.
We are still looking for the main feature to be a cold upper level storm system that
will shift east from Alabama and move through Georgia Thursday afternoon and night. Typically
systems like these produce isolated pockets of brief moderate snowfall which makes it
more difficult to come up with anticipated average snowfall amounts.
Here is a snowfall probability map for this event and we really want you to focus on the
most likely areas for accumulating snowfall as opposed the specific values shown on the
map. From this map we see the best chances for accumulating snow will be across portions
of north Georgia. With other areas...although snow or a mix of snow and rain will be possible...temperatures
well above freezing initially and the recent warm conditions will allow anything that falls
to melt as it reaches the surface. As with the rainfall maps earlier, we see a tight
gradient from the extreme northwest zones through the remainder of north Georgia. We
will discuss specific snowfall accumulations later in this briefing.
Radar Reflectivity
Radar Reflectivity
Radar Reflectivity
Radar Reflectivity
Radar Reflectivity
Radar Reflectivity
Overall, warm soil temperatures will keep snow from initially sticking, however as the
ground begins to cool, snow will begin accumulating on surfaces. Soil temperatures have been coolest
across northwest Georgia, where values are in the 40s. This indicates the area where
snow will become accumulating the quickest.
So lets put it all together and show graphically what the potential is for winter weatherThursday
afternoon and night. The north mountains continue to have the potential for the largest amounts
of accumulating snowfall with 2 to 4 inches. Generally north of a Rome to Gainesville line,
outside of the mountains, around a ½ inch to 1 inch of snow accumulation is possible.
South of this and north of a Carrollton to Athens line, up to a ½ inch of snowfall is
possible. South of Carrollton to Athens, rain will be mixed with snow and little to no snowfall
accumulation is expected. All of these areas, generally north of a Columbus to Macon to
Washington line have the potential for black ice Thursday night and Friday morning. Based
on these expected accumulation values and transportation impacts due to the black ice,
a winter storm watch has been issued for north
Based on these expected accumulation values discussed on the previous slide and transportation
impacts expected due to the black ice, a winter storm watch has been issued for north Georgia
generally north of the I-20 corridor beginning Thursday afternoon and through Friday morning.
As air temperatures drop below freezing and the roadways become wet, black ice is a concern
across north and portions of central Georgia. The area highlighted in the light blue box
shows the below freezing temperatures expected for the Atlanta metro area. Temperatures should
drop below 32 degrees around midnight and increase above freezing by 9am. This time
will be delayed in the mountains where it could take a little longer to warm up.
This is a good time to review winter weather safety tips, especially those in the north
Georgia mountains.
So in summary, confidence is beginning to increase with this event of rain changing
to snow Thursday afternoon into Thursday night. The greatest snowfall amounts are expected
to be across the north Georgia mountains with the potential of 2 to 4 inches of snow. Amounts
will decrease south of there to little or no accumulation expected across the northern
portions of central Georgia. Impacts will continue into Friday morning as black ice
is expected across north Georgia and portions of central Georgia. This will cause widespread
travel impacts. We will be putting together another briefing and post it to the web by
2pm on Thursday.