Freeze Watch 1, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
208 PM EDT Wed Mar 31 2021

.SYNOPSIS...
A strong cold front will move off the Carolina coast early Thursday.
Unseasonably cold high pressure will build in behind the front
tonight and settle over the region for the rest of the week. Expect
an upper level ridge to build over the region from Sunday into next
week, continuing dry, but warmer weather. The next rain maker will
approach our region in the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 150 PM: CWA undergoing gradual process of pattern change. An
almost full-latitude trough is moving into the Mississippi Valley
today, and a sharp upper ridge remains off the East Coast,
maintaining a shallow sfc airmass over which isentropic lift
produced a stratus deck which lingers over most of the CWA. Broad
area of modest and mostly stratiform precip extends across the
Piedmont within this warm advection regime, enhanced by upper
divergence provided by jet streak near the Ohio River. Cold front
has reached the Cumberland Plateau of TN/AL. Now that precip band
has mostly shifted past the Appalachians following the better
prefrontal forcing, and with that area not looking to destabilize
enough to have any threat of convection, looking more likely
we will be able to let the Flash Flood Watch go for the SW mtn
zones. Final decision on that to be made shortly.

Although the pattern was reminiscent of in-situ CAD, only having
a weak inversion, we're seeing ceilings continue to lift across
our southern zones, but the arrival of the rain seems to be having
a stabilizing effect. Our window for severe wx has been reduced
a bit. Modestly strong shear is already present aloft, owing to
the gradient ahead of the approaching trough. Any surface-based
storms that are able to fire later today could still produce some
damaging wind, but recent downward trends in HRRR output suggest
the area of risk likely has shrunk to our southeast, where enough
warming has occurred and little enough rain fallen to anticipate
continued destabilization. The shear is mostly unidirectional,
and 0-1km shear/helicity don't look likely to increase enough to
create a particularly notable tornado risk. Nevertheless 0-3km shear
is 30-40 kt and still could see strong gusts accompanying a broken
line of cells in the aforementioned area. Can't downplay the flash
flood threat with this line given high PW and line-parallel shear,
but confidence not currently high enough (and issues likely too
isolated) to warrant expansion/reissuance of Watch.

By late evening, cold air will be undercutting the warmer air at
mid-levels in our mountains, with arrival of the true cold front. In
the wake of the front, we develop a pressure difference of 6-8 mb
across the mtn chain that persists into the overnight hours. The
combination of cold advection flow and strong pressure gradient
should lead to strong winds coming over the top of the Appalachian
Divide and then sinking down the Blue Ridge Escarpment. Guidance
suggests enough potential for occasional gusts upwards of 50 mph in
a narrow corridor near the Escarpment, so a Wind Advisory will be
issued starting at 00Z. The cold advection will also start to change
precip over at the high elevations, but with an interesting wrinkle
in that the near-sfc temps will fall below freezing while warmer air
remains above 5k feet initially. This could lead to a brief period
of potentially light freezing rain at some of the highest elevations
before the entire column drops below freezing after midnight and
changes any remaining precip over to light snow. At this point,
any accumulations would be limited to elevations generally above
5000 feet, so a Winter Weather Advisory will not be issued.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 230 AM Wednesday: Strong 850 mb CAA and a tight pres grad
across the mountains will keep gusty NW winds thru the day. May
approach advisory criteria, so will have the Wind Advisory go
thru 00z Friday. It will be breezy elsewhere, as well, and with
max temps 15-20 deg below normal, it will feel like early February
rather than early April. A few snow showers may linger along the TN
border early in the day, but accums should be localized and light.

Winds will begin to slacken off Thursday aftn into Thursday night,
but stay up enough that we should stay mixed overnight. Still,
with the CAA, temps should fall into the teens to mid 20s in the
mountains, and upper 20s to lower 30s across the Piedmont. Our
Frost/Freeze program turn on date is April 1st for the Piedmont,
except for the I-40 corridor, so a Freeze Warning will likely be
needed. It's still too early for a Freeze Watch, but one may be
issued later today, if confidence remains high. Will continue to
mention in the HWO. The current forecast lows for April 2nd approach
or break record lows (see Climate section below for more info).

Friday will lingering breezy conditions, and combined with low RH,
may have some fire wx concerns, depending on how much the fuels are
able to dry out Thursday. Highs will be 15-20 deg below normal,
despite full sunshine. The center of the Canadian high pressure
will settle over the area Friday night, allowing winds to become
light or calm. Good radiational cooling should allow temps to fall
into the 20s to mid 30s. So areas of frost and light to moderate
freeze is expected again across the area.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 230 PM Wednesday: Sunday into early next week high pressure
will be centered over the southeastern CONUS leading to building
heights and dry conditions while a low pressure system meanders
around in the western Atlantic offshore of the northeastern United
States. Temps are expected to gradually warm late this weekend into
the middle of next week due to westerly and northwesterly flow at
the 850 mb level across the forecast area. High temps should be near
normal Sunday becoming roughly 5 to 7 degrees above normal early
next week. RH vales in the 30s are expected late this weekend into
early next week. Despite high pressure leading to light winds during
this time of low RH, fire weather could be a concern.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
At KCLT and elsewhere: Complicated fcst this afternoon with
wedgelike sfc cold pool generally hanging on by a thread,
with flight category ranging from IFR to VFR following effects
of multiple rounds of precip. Strategy was to use TEMPO this
aftn for possibility of worsening conditions due to return of
precip. However, at KHKY and KAND, upstream activity appears solid
enough to expect more steady state conditions for the aftn. Chance
of TSRA appears smaller than once thought, and now too isolated
to mention, but can't be completely ruled out; best chance now
appears this afternoon to early evening. Strong wind gusts would
be a concern with any TSRA; LLWS risk not especially great due to
veered sfc winds, but also can't be ruled out. Expecting another
round of precip to accompany cold front into at least the mtns
later this evening, possibly into the Piedmont; impact would be a
return to lower cigs and locally reduced vsby. Winds will shift to
NW with front and stronger than typical gradient gusts will linger
the remainder of the period. Gusts exceeding 30 kt are expected
at KAVL. -SHSN expected along the TN border late tonight and some
of Thursday, but not affecting any TAF site.

Outlook: VFR expected from Thursday morning onward. Expect gusty
N to NW winds to continue Thursday, then abating Thursday night.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       Med   73%     High  86%     High 100%     High 100%
KGSP       Med   73%     Med   76%     High 100%     High 100%
KAVL       Med   75%     High  83%     High  96%     High 100%
KHKY       Med   74%     Med   74%     High 100%     High 100%
KGMU       Med   75%     Med   72%     High 100%     High 100%
KAND       Med   68%     High  80%     High  85%     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 are available at
the following link:

www.weather.gov/gsp/aviation

&&

.CLIMATE...
RECORDS FOR 04-02

               MAX TEMPERATURE         MIN TEMPERATURE
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      87 1946     41 1915     58 1945     25 1924
   KCLT      86 2014     42 1901     64 1945     28 1881
                2010
                1978
   KGSP      88 2012     49 1901     62 1979     26 1902

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Flash Flood Watch until 8 PM EDT this evening for GAZ010-017.
NC...Wind Advisory from 8 PM this evening to 8 PM EDT Thursday for
     NCZ033-049-050-053-065-501-503-505-507-509.
     Flash Flood Watch until 8 PM EDT this evening for NCZ051-052-
     058-059-062>065.
SC...Wind Advisory from 8 PM this evening to 8 PM EDT Thursday for
     SCZ003.
     Flash Flood Watch until 8 PM EDT this evening for SCZ001>003.

&&

SYNOPSIS...DEO
NEAR TERM...PM/Wimberley
SHORT TERM...ARK
LONG TERM...AP
AVIATION...Wimberley
CLIMATE...GSP

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
524 AM EDT Wed Mar 31 2021

GAZ018-026-028-029-NCZ068>072-082-508-510-SCZ004>014-019-010930-
Stephens-Franklin-Hart-Elbert-Cleveland-Lincoln-Gaston-Mecklenburg-
Cabarrus-Union NC-Greater Rutherford-Eastern Polk-Greater Oconee-
Greater Pickens-Greater Greenville-Spartanburg-Cherokee-York-
Anderson-Abbeville-Laurens-Union SC-Chester-Greenwood-
524 AM EDT Wed Mar 31 2021

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina, western North Carolina and upstate South Carolina.

.DAY ONE...Today and tonight.

A late season strong cold front is forecast to push through the area
this afternoon aiding in the development of numerous showers and
thunderstorms. A few of these storms may be severe producing damaging
wind gusts. An isolated weak, brief tornado cannot be ruled out.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Behind the front, expect much colder temperatures with a freeze
likely Thursday night and possibly again Friday night. A freeze
warning will be needed for the Piedmont south of I-40 where the
growing season will have commenced.

.SPOTTER INFORMATION STATEMENT...

None.

GAZ010-017-NCZ051-052-058-059-062>064-SCZ001-002-010930-
Rabun-Habersham-Swain-Haywood-Graham-Northern Jackson-Macon-
Southern Jackson-Transylvania-Oconee Mountains-Pickens Mountains-
524 AM EDT Wed Mar 31 2021

...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING...

This Hazardous Weather Outlook is for northeast Georgia, western
North Carolina and upstate South Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flash Flood Watch.

A late season strong cold front is forecast to push through the area
this afternoon aiding in the development of numerous showers and
thunderstorms. A few of these storms may be severe producing damaging
wind gusts.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

NCZ065-SCZ003-010930-
Henderson-Greenville Mountains-
524 AM EDT Wed Mar 31 2021

...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING...
...WIND ADVISORY IN EFFECT FROM 8 PM THIS EVENING TO 8 PM EDT
THURSDAY...

This Hazardous Weather Outlook is for western North Carolina and
upstate South Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flash Flood Watch.
   Wind Advisory.

A late season strong cold front is forecast to push through the area
this afternoon aiding in the development of numerous showers and
thunderstorms. A few of these storms may be severe producing damaging
wind gusts.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

.SPOTTER INFORMATION STATEMENT...

None.

NCZ033-049-050-053-501-503-505-507-509-010930-
Avery-Yancey-Mitchell-Buncombe-Caldwell Mountains-Burke Mountains-
McDowell Mountains-Rutherford Mountains-Polk Mountains-
524 AM EDT Wed Mar 31 2021

...WIND ADVISORY IN EFFECT FROM 8 PM THIS EVENING TO 8 PM EDT
THURSDAY...

This Hazardous Weather Outlook is for western North Carolina.

.DAY ONE...Today and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

A late season strong cold front is forecast to push through the area
today and may support strong to severe thunderstorms and localized
flooding. Behind the front, there will be scattered snow showers with
minor accumulations above 3500 ft near the Tennessee border.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Wind Advisory.

.SPOTTER INFORMATION STATEMENT...

None.

NCZ035>037-048-056-057-502-504-506-010930-
Alexander-Iredell-Davie-Madison-Catawba-Rowan-Greater Caldwell-
Greater Burke-Eastern McDowell-
524 AM EDT Wed Mar 31 2021

This Hazardous Weather Outlook is for piedmont North Carolina and
western North Carolina.

.DAY ONE...Today and tonight.

A late season strong cold front is forecast to push through the area
this afternoon aiding in the development of numerous showers and
thunderstorms. A few of these storms may be severe producing damaging
wind gusts.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

ARK