Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 181953

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
253 PM EST Sat Feb 18 2017

A weak upper low moves east across the Carolinas tonight then off
the Carolina coast Sunday. A strong upper ridge moves in to start
the week, with much above normal temperatures. Another period of
light rainfall is possible mid week as a weak upper trough moves
through the region. A cold front approaches at the end of the week
with possible showers and thunderstorms.


As of 235 PM EST: water vapor imagery shows an upper low over
Arkansas early this afternoon and evidence of a plume of deeper
moisture wrapping up around the east side of the low circulation.
Upper divergence and dpva were forcing a wide band of mostly light
rain seen on radar imagery across the western half of the fcst area.
This band of precip...some of which was not reaching the ground,
should translate eastward across the region through late afternoon
and early evening. Precip amounts will generally be less than a
tenth of an inch. Think a chance of precip will suffice. Temps were
falling behind the fcst as the thicker cloud cover moves in.

The upper low will continue to move eastward, open up, and deamplify
tonight, carrying the forcing off to the east by early evening. East
of the mtns, developing downslope flow will eliminate any remaining
precip this evening. The center of the old low will move across the
Great Valley and Srn Appalachians during the early morning hours and
could provide the weak forcing necessary for some light precip,
especially toward daybreak as a WNW flow develops at low levels.
Temps should remain warm enough to keep almost all of the precip in
liquid form, except above about 6k feet. Low temps are expected to
be on the order of ten degrees above normal.

On Sunday, the WNW flow should continue to act on remnant moisture
over Ern TN to produce a few showers on the NC border through about
midday. Otherwise, an upper ridge to the west will build high
pressure into the region. Temps look like they will be well above
normal with highs about 15 degrees above normal, conservatively.


As of 2pm EST Saturday: By Sunday evening, southeast CONUS upper
shortwave will be well east of the area and a transitory upper ridge
will be moving in, with dry downslope northerly flow and clearing
skies.  This ridge will keep things dry and mostly clear on Monday,
with clouds increasing prior to the next frontal/upper wave system
due in Tuesday evening, with a chance from some showers in the
mountains as early as Tuesday evening.  Temperatures will be 10 to
15 degrees above normal Monday and Tuesday.  Winds will continue to
be northerly to northwesterly at 5 to 10 kts early on Monday,
veering to easterly and weakening as center of surface high settles
over the region Monday evening, and then picking-up from the
southwest on Tuesday in advance of the next trough.


As of 230 PM EST Saturday:  The medium range fcst period initializes
on Tuesday evening amidst weakening east coast ridging by way
of a progressive northern stream trough, while a close southern
stream upper cyclone moves out of the Rio Grande Valley into the
central Gulf of Mexico.  At the surface, the primary features of
note will be a broad anticyclone along the east coast and a cold
front extending across the Great Lakes region into the OH Valley.
Synoptic pattern evolution moving through the period will be
highlighted by total breakdown of the amplified east coast
upper ridge leading to migration of the elongated surface high
southward near Bermuda.  The aforementioned cold front looks to
stall across the OH Valley, possibly making it as far east as
the Central Appalachians, however not likely intruding into the
Southern Appalachians thanks to the repositioned surface ridge.
Meanwhile, guidance seems to have converged on some details
regarding the closed H5 cyclone moving through the Gulf, which
now looks a bit weaker, strongest in the ECMWF, with good track
agreement to the southeast toward southern FL.  Thus, little
if any impacts are expected across Northeast GA and the Western
Carolinas.  That said, weak moist upglide atop the offshore high
will at least warrant low end pops both Wednesday and Thursday.
Moving along, as the southern stream H5 low moves out of the
picture, a few days of southerly flow are expected across the
southeast states thanks to the Bermuda high, while a west coast
system gains strength and plows through the plains into the MS
River Valley by Friday.  Surface cyclogenesis beneath a modestly
deep upper low looks to yield a rather strong/progressive surface
cold front that will march across central CONUS and into the
Appalachian region either on Friday evening, possibly sometime
on Saturday.  Timing inconsistencies within the op guidance lead
to much uncertainty regarding the details, nevertheless, expecting
a strong and potentially convectively active fropa next weekend.
Behind said front, broad Canadian high pressure looks to dive
southward into the Plains by yielding drier yet cooler conditions
to round out the weekend.   Temperatures are expected to remain
well above normal, cooling to near normal at periods end.


At KCLT and elsewhere: expect clouds to thicken with ceiling
steadily dropping as deeper moisture plume and forcing ahead of an
upper low move steadily across the region through the early evening.
For the most part, ceiling will stay above 060, especially over the
east as a precip band is expected to weaken. Cannot rule out enough
light rain bringing the ceiling down into the MVFR category for a
period in the late afternoon, especially at KAND. The model guidance
suggests that conditions will drop to MVFR this evening after the
precip band moves through. Chances are best over the wrn Upstate of
SC but diminish from there. Have included a brief TEMPO at KCLT for
some light fog in the early morning hours, but confidence barely
enuf to mention. Wind should be mainly SW through late tonight, with
a change to NW in the pre-dawn hours with the passage of a boundary.
Downslope developing E of the mtns should take care of any
restrictions before sunrise.

Outlook: Expect VFR conditions from Sunday afternoon through early
next week. Another system may bring chances of precipitation and
restrictions to the area Tuesday into Wednesday.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High  93%     High  97%     High 100%
KAVL       High 100%     High  94%     High  83%     High  94%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High  90%     High  97%     High 100%
KAND       High  88%     Med   73%     High  94%     High 100%

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:



  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      72 2014     16 2015     54 1951      3 2015
   KCLT      76 2014     26 2015     55 1961      8 1958
   KGSP      75 2014     30 2015     55 1961      9 1958
                1916        1900                    1900


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      75 1939     26 1908     50 1951      4 2015
   KCLT      77 2014     31 2015     59 1939      7 2015
   KGSP      75 2014     33 2015     57 1939      9 2015




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