Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 250250
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1050 PM EDT Mon Apr 24 2017
A deep and vigorous low pressure system will slowly move from
the South Carolina coast to near Cape Hatteras by late Tuesday.
Expect drier and warmer weather Tuesday and Wednesday. A
dissipating cold front crosses our region Thursday and Friday.
.NEAR TERM /THROUGH TUESDAY/...
As of 1040 pm EDT, recent HRRR runs continue to bring the relatively
good coverage of persistent light to moderate showers westward into
the I-77 corridor from the NC central piedmont through the early
overnight hours. The current FFA will be maintained although the
threat of additional flooding continues to slowly diminish as rates
fall and the banding focuses more on I-40 than CLT metro late this
Otherwise, the forecast remains generally on track with the area
entrenched in an unseasonably cool wedge, well removed from the sfc
based unstable air which is mainly east of I-95. Banded forcing
northwest of the departing low pressure circulation will keep
intermittent bands of showers pivotting west into the Piedmont
overnight. An additional half inch to inch of rain will be possible
in some areas east of I-77 through the early morning hours.
A much improved day is on tap for Tuesday with the flow through a
deep layer backing to the NW as the sfc/upper flow wobbles toward
the mid-atlantic. Maximum temperatures are expected to be 12-15 deg
F milder than today`s chilly readings.
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 100 PM Mon: Heights rise Tue night and Wed as a shortwave
upper ridge moves overhead. A strong subsidence inversion accordingly
will develop. With weak warm/moist advection occurring in the low
levels, as well as saturated soils across the area, there is
potential for low stratus and perhaps some dense fog to develop early
Wed morning, particularly over the Upstate and NE GA. That afternoon,
the same inversion should be strong enough to stifle convection
across the whole CWFA, so PoPs will be kept below slight chance. Max
temps are expected to be 6 to 9 degrees above normal.
Wed night into Thu, the upper ridge axis will be just to our east. A
full-latitude trough will be hot on its heels, centered near the
Mississippi River at 12z Thu. This trough will be associated with a
low over the western Great Lakes, and a frontal zone that will
impinge on the western CWFA by 00z Fri. A plume of midlevel moisture
preceding the trough suggests increasing clouds/PoPs. Elevated tstms
will be possible in the aftn, but sfc-based convection continues to
be suppressed by poor lapse rates resulting from either the ridge or
from the moisture aloft. The best-verifying blend of guidance
suggests max temps will top out 5 to 8 degrees above normal, held
down a bit more by the cloud cover.
.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 200 PM Mon: Friday and Saturday will see the resurgence of a
late-spring pattern over the Carolinas and Georgia, as the upper
pattern amplifies. Temps will trend upward under continued
southwesterly flow; the warmest day looks to be Saturday, when a few
spots may hit 90. Convection will be limited by a weak capping
inversion on Friday, but the warming temps overcome that Saturday.
By Sunday the ridge will have drifted east slightly, allowing
slightly better lapse rates and still greater instability. Given the
pattern, we`ll maintain diurnally driven PoPs, with chances trending
up from day to day. As one might expect, weak wind profiles result in
little shear, and sfc-to-midlevel theta-E differences are high.
Together these findings suggest pulse storm threats from the stronger
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
At KCLT: Occasional showers will impact the airfield through the
early overnight before gradually becoming more scattered in nature
through daybreak. Ceilings have bounced around quite a bit this
evening in the MVFR range but should settle quickly back into the
IFR to LIFR range overnight. Expect slow recovery through the day on
Tuesday as abundant low level moisture persists and the departing,
stacked low pressure system wobbles only slowly to the coastline.
NNE winds will vary back toward NW through the period, generally at
less than 10 kt going forward.
Elsewhere: Shower coverage will steadily diminish across the
mountains and foothills as the low pressure system migrates toward
the coast through the period. Shower chances will be best at KHKY
through the early morning hours. Ceilings may bounce around a bit
this evening but should settle into IFR then LIFR most areas
overnight. Slow recovery is expected Tuesday morning, but weak
downsloping will aid lifting and scattering through Tuesday
afternoon. Expect northerly winds to turn more NW with time, and
possibly WSW at KAND late in the period.
Outlook: Conditions should continue to improve through Wednesday
dry air works in behind the departing low. Return flow moisture
ahead of the next system will develop late in the week.
03-09Z 09-15Z 15-21Z 21-00Z
KCLT Low 51% Med 66% Med 72% High 83%
KGSP Med 70% Med 70% Med 66% High 85%
KAVL Med 66% Med 72% Med 78% High 100%
KHKY Low 53% Med 66% Med 61% Med 77%
KGMU Med 66% Med 64% Med 61% High 85%
KAND High 85% Med 61% Med 70% High 85%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
NC...Flood Watch until 8 AM EDT Tuesday for NCZ035>037-056-057-
SC...Flood Watch until 8 AM EDT Tuesday for SCZ009.