textproduct: Greenville-Spartanburg

SYNOPSIS

The passage of a strong cold front today will bring windy conditions and usher in a cold airmass. Near-normal temperatures return mid to late week. A low pressure system could bring precipitation to the area for the weekend.

NEAR TERM /THROUGH TONIGHT/

As of 112 AM EST Monday:

Key Message #1: Patchy dense fog and precipitation through this morning, ahead of an arriving cold front.

Deep stacked low will shift from the Northern Great Plains into the Great Lakes Region tonight into the daytime period as the surface low bombs out. Lingering CAD wedge has shown signs of retreating as winds have turned increasingly southwesterly as the attendant cold front that's currently draped across the OH/TN Valleys into the Lower MS Valley encroaches the CWFA. Steady low clouds will remain in place with some areas of dense fog ahead of the front. Observations have been variable and doesn't support a full on Dense Fog Advisory, so will hold off from issuing one for now but will continue to monitor throughout the night. The cold front is expected to move into the NC/TN border around daybreak and complete a full fropa by the early afternoon hours. A broken line of showers are expected along the front, with the best chances for precip being in the mountains and gradually diminishing as the line slips east off the terrain. Non-diurnal trend in temperatures are expected as values increase slightly from current observations during the night as low-level WAA moves in ahead of the front.

Key Message #2: Cold front completes passage early this afternoon and will induce brisk wind gusts across the area and bring sharply colder temperatures for the mountains.

As the front slips through the area by the early afternoon hours, strong CAA and rapid height falls will overspread the area. In response, temperatures will drop throughout the day across the mountains and start the same non-diurnal trend by the early afternoon hours across the Piedmont zones. Downslope winds behind the front will offset the drastic cool down across the Piedmont and allow highs to top out in the upper 50s to lower 60s before the CAA overcomes the downslope component by lunchtime or a little after. Tight pressure gradient throughout the vertical column will support gusty winds across the CWFA, with very strong gusts across the higher elevations, mainly above 4000' (gusts up to 60 mph). Boundary layer mixing will allow some of the stronger gusts to mix down across the lower mountain elevations as well between 35-50 mph. The current Wind Advisory is well placed in the northern mountain zones and a High Wind Warning in Avery County as the average winds are even higher across the county, especially at the ridgetops. The timing for the highest wind gusts will be from this afternoon through tonight. As the post-frontal regime settles in behind the front, dry air entrainment should lead to a significant drop in RH values to go along with the ongoing wind gusts. With temperatures peaking earlier than peak heating, minimum RH values should hold off from reaching the criteria of 25% for a Red Flag Warning, despite lower RH values (25-35%) and wind gusts between 20-30+ mph, and dewpoints tanking into the teens and twenties across the Piedmont zones. Conditions justify an Increased Fire Danger Statement, but fuel moistures are elevated from recent conditions, so will hold off on an IFD as well.

Key Message #3: Cold air settles in tonight with lingering gusts across the mountains, leading to single digit to below zero wind chills.

Very cold airmass becomes fully entrenched across the region tonight as colder thicknesses move into the area with broad cyclonic flow aloft. Continental surface high (~1035mb) shifts over the central CONUS overnight tonight. Tight pressure gradient remains over the mountains, keeping gusts in place with overnight lows dropping into the teens. Wind chill values will be in the single digits, with below zero across the higher elevations with winds remaining elevated. There is only a very short window of opportunity for Cold Weather Advisory criteria to be reached across the northern mountains. As a result, held off on a Cold Weather Advisory at this time. Mostly clear skies elsewhere as overnight lows drop 5-10 degrees below normal, but could end up closer to 5 than 10 degrees below normal as boundary layers will struggle to fully decouple despite good radiational cooling conditions otherwise.

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/

As of 1225 AM EST Monday...

Key Message #1: Diminishing wind and dry conditions Tuesday and Wednesday.

The pressure gradient relaxes throughout the day on Tuesday but never fully goes away as the center of surface high pressure remains to our west. This keeps a lee trough over the area through the period. Will likely still be windy across the mountains Tuesday morning before diminishing through the afternoon but remaining breezy through Wednesday night. Low end breezy conditions will linger Tuesday afternoon elsewhere and return Wednesday afternoon. The air mass becomes very dry, leading to critical RH values across much of the area both afternoons. This combined with the gusty winds could lead to increased fire danger. Highs 10 to 15 degrees below normal across the mountains and 5 to 10 below normal elsewhere on Tuesday will rise to near normal Wednesday. Lows 5 to 10 below normal Tuesday night rise to near or a little below normal Wednesday night.

LONG TERM /THURSDAY THROUGH SUNDAY/

As of 1255 AM EST Monday...

Key Message #1: Dry with milder temperatures Thursday and Friday.

A dry cold front drops across the area on New Year's Day and stalls south of the area on Friday. Dry weather continues across the area with breezy to windy conditions on Thursday. Highs will be a few degrees above normal both days, with lows near to slightly below normal.

Key Message #2: A southern stream low pressure system could bring precipitation to the region on Saturday.

Guidance now in pretty good agreement the timing and location of the southern stream low pressure system moving over or just south of the area Saturday. They are also in better agreement on the forecast thermal profile, keeping the precip all liquid, even across the mountains. Dry high pressure returns for Sunday as the low tracks into the Atlantic. Temps will be near normal both days, but Saturday's lows could end up warmer and highs cooler depending on how the precip develops and any resulting cold air damming.

AVIATION /06Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: Widespread LIFR/IFR flight conditions outside of the mountains tonight, ahead of an encroaching cold front. Expect these restrictions to remain in place through daybreak and a few hours after. Brief improvement from VLIFR has developed as southwesterly winds increase, but kept some mention of VLIFR restrictions in a TEMPO during the pre-dawn hours. A band of precip will move across the area as the cold front pushes in just before daybreak through the rest of the morning hours. Timed out the best chance for -RA based on terminal location through a PROB30. Expect very drastic improvements to VFR behind the cold front with winds shifting to a west-northwesterly component or northwesterly and skies clearing. Frequent strong gusts (20-30 kts) can be expected through the afternoon and into the evening hours at all terminals following the frontal passage. Dropped off the gusts at all the terminals besides KAVL after 00Z Tuesday.

Outlook: Dry and VFR conditions linger through Friday. Winds remain strong and northwesterly at KAVL and across the mountains into Tuesday.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...High Wind Warning from 1 PM this afternoon to 7 AM EST Tuesday for NCZ033. Wind Advisory from 1 PM this afternoon to 7 AM EST Tuesday for NCZ049-050-501-503-505. SC...None.