Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 221158 AAA
AFDFFC

Area Forecast Discussion...UPDATED
National Weather Service Peachtree City GA
758 AM EDT Sun Apr 22 2018



.PREV DISCUSSION... /Issued 453 AM EDT Sun Apr 22 2018/

SHORT TERM /Today through Monday/...

Primary concern is timing of heavy rainfall and strong winds. Model
guidance continues to show intense upper low with corresponding
strong sfc cyclone just east of it moving east over lower MS valley.
Sfc low unusually deep with sfc pressure around 1006mb and possible
even deeper mesolow over AL by 00Z Mon. Very strong pres gradient
will set up at that time and persist overnight with 25-35kt low
level flow and high moisture transport in response. Rainfall rates
still approaching 1-2 in per 3-6hrs mainly 00Z-15Z Mon with total
amounts 2-4 in, but will likely verify higher in spots as is usually
the case. While some elevated convection possible, thankfully MUCAPE
will remain below 250 J/kg and no SB or MLCAPE expected through
tonight. Have issued wind advisory and flood watch based on the
level of threat expected tonight.

By Monday, dry slot expected to wrap into middle GA and with some
breaks in the clouds and steep lapse rates, could see some MLCAPE
approach 2000 J/kg by afternoon. Vertical wind shear will be weaker
and sfc/upper forcing further east, so do not expect any severe
storms at this time. Could see a couple get strong with small hail
up to 1 in possible but may have to watch this in case things go
awry.

SNELSON

LONG TERM /Monday Night through Saturday/...

Upper closed low slowly dampens and lifts north into the longwave
energy by late Tuesday. Models indicating a bit more instability
present - parts of east for Monday evening and then again Tuesday
afternoon for the northern majority, so have included slight
chance thunder with shower mention and trend highest pops to the
north. Nam BUFR soundings indicate some decent low level lapse
rates too and given a pretty low freezing level at 10 kft or
lower, wouldn`t be surprised if a few cells resulted in some small
hail or graupel (especially Tuesday afternoon). Will need to
watch for lingering flooding and runoff concerns into the
beginning of the fcst period given the expected 3-4 inches mainly
in the short term.

Wednesday should be a brief reprieve ahead of a continued active
pattern with only some slight to low end shower chances in the
north ahead of another shortwave/frontal system for Wednesday
night into Thursday (Euro a bit less progressive than the GFS). A
second disturbance could impact the CWA as a quicker cold front
with less enhanced moisture present for Friday (GFS) or slower
system that cuts off farther south and taps into more Gulf
moisture to make for a rainy Saturday (Euro). Have not bought into
the less consistent Euro solution so for now have kept chance pops
of showers for Thursday, slight pops Friday, and dry Saturday.
Will fine tune given hopefully better consensus in future updates.

Temps should stay generally a bit cooler than climo norms through
period though expect some later period temps to be adjusted given
aforementioned model inconsistency with active jetstream pattern.

Baker

HYDROLOGY...
A Flood Watch has been issued for portions of north GA (mainly
along the I-85 corridor) from this evening into Monday afternoon.
With widespread 2 to 4 inches, and locally higher amounts, expect
isolated flash flooding to be an issue. Of particular concern
will be the areas with training storms (rain that continually
develops and moves over the same location) or areas that have
extremely high rainfall rates, even over a short period of time.

&&

.AVIATION...
12Z Update...
Scattered showers beginning to develop so have VCSH in most
airports. Cigs yet to go below 2500ft but as precip continues to
develop expect them to fall to just above IFR or around 1200ft.
East sfc winds still on track to be strong today becoming
13-18kts with gusts to 25-28kts this afternoon then peak between
00Z and 06Z Tue at 18-23kts with gusts 28-33kts. Not seeing any TS
so far in observations and lightning detection and instability
will be limited so have continued to keep out of fcsts except for
KCSG and KMCN after 01Z when instability could increase enough
there.

//ATL Confidence...12Z Update...
Medium on IFR timing.
High on all other elements.

SNELSON

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          66  54  65  55 /  70 100  90  70
Atlanta         64  56  70  56 /  80 100  80  40
Blairsville     58  49  59  50 /  70 100  80  80
Cartersville    63  54  68  54 /  80 100  80  50
Columbus        70  62  77  57 /  90 100  60  20
Gainesville     61  53  62  55 /  70 100  90  70
Macon           70  60  77  56 /  70 100  80  40
Rome            63  55  69  54 /  80 100  70  50
Peachtree City  65  57  74  55 /  80 100  80  40
Vidalia         73  62  76  60 /  40  90  80  50

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
Flood Watch from this evening through Monday afternoon for the
following zones: Banks...Barrow...Clarke...Clayton...Coweta...
Dawson...DeKalb...Fayette...Forsyth...Gwinnett...Hall...Henry...
Jackson...Lumpkin...Madison...Newton...North Fulton...Oconee...
Rockdale...South Fulton...Spalding...Walton...White.

Wind Advisory from 8 PM this evening to 7 AM EDT Monday for the
following zones: Banks...Barrow...Bartow...Bibb...Bleckley...
Butts...Carroll...Catoosa...Chattahoochee...Chattooga...
Cherokee...Clarke...Clayton...Cobb...Coweta...Crawford...Crisp...
Dade...Dawson...DeKalb...Dooly...Douglas...Fannin...Fayette...
Floyd...Forsyth...Gilmer...Gordon...Gwinnett...Hall...Haralson...
Harris...Heard...Henry...Houston...Jackson...Jasper...Jones...
Lamar...Lumpkin...Macon...Madison...Marion...Meriwether...
Monroe...Morgan...Murray...Muscogee...Newton...North Fulton...
Oconee...Paulding...Peach...Pickens...Pike...Polk...Pulaski...
Rockdale...Schley...South Fulton...Spalding...Stewart...Sumter...
Talbot...Taylor...Towns...Troup...Twiggs...Union...Upson...
Walker...Walton...Webster...White...Whitfield...Wilcox.

&&

$$

SHORT TERM...SNELSON
LONG TERM....Baker
AVIATION...SNELSON



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