textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated Aviation Discussion.

KEY MESSAGES

1. Increased Fire Danger across the area this afternoon, with a Fire Danger Statement in effect for our NC and GA counties. Above normal temperatures return today and persist through at least the end of the week. Very low-to-critical relative humidity is forecast each afternoon, keeping the fire danger elevated through Friday. Any fire that develops will catch and spread quickly. No outdoor burning! 2. Trending towards a wetter pattern this weekend into early next week. However, there may be a brief lull in precipitation Sunday into Monday behind a departing cold front and ahead of the next system. A cooling trend develops this weekend into Monday before warmer temperatures return Tuesday.

DISCUSSION

Key message 1: Increased Fire Danger across the area this afternoon, with a Fire Danger Statement in effect for our NC and GA counties. Above normal temperatures return today and persist through at least the end of the week. Very low-to-critical relative humidity is forecast each afternoon, keeping the fire danger elevated through Friday. Any fire that develops will catch and spread quickly. No outdoor burning!

A high amplitude ridge over the Great Plains this morning will move steadily east through the end of the week, albeit weakening and beginning to break down by Friday, as an upper cyclone broadens over the northern Great Plains/Canadian Prairie. While surface high pressure has relinquished its grip across our forecast area...with a lee trough expected to somewhat enhance S/SW flow later today...moisture flux into the CWA remains weak to non-existent. Thus the air mass is expected to remain relatively dry through the end of the work week, even as temperatures warm significantly beginning today under rising heights aloft. Max temperatures today are forecast to be around 5 degrees above climo...almost 10 degrees warmer than Tuesday. Although surface dewpoints will continue to creep up, the warmer temps will result in yet another afternoon of widespread 20-30% RH. Winds will also increase a bit over previous days, with perhaps a few gusts in the 15-20 mph range expected this afternoon. These factors will result in elevated wildfire danger across the area, and the Fire Danger Statement will be expanded to include northeast GA. (A reminder that a statewide burn ban remains in effect for South Carolina as well as NC.)

Conditions continue to warm Thursday as heights continue their rising trend, and Thursday's maxes are expected to increase by another 4-5 degrees...placing them around 10 degrees above normal. Surface dewpoints will continue their positive creep, but the warmer conditions are expected to add to our streak of days with critical afternoon RH (at least for a part of the area). Fire Danger Statements may again be necessary. The warming trend plateaus in the Thu/Fri time frame, with Friday's forecast maxes being very similar to Thursday. Dewpoints may creep up just enough to preclude critically low values being met Friday afternoon. In fact, some short term guidance sources suggest humidity will increase enough for isolated showers to develop along the ridgetops...and a 20 PoP is carried for this Fri afternoon.

Key message 2: Trending towards a wetter pattern this weekend into early next week. However, there may be a brief lull in precipitation Sunday into Monday behind a departing cold front and ahead of the next system. A cooling trend develops this weekend into Monday before warmer temperatures return Tuesday.

A cold front approaches out of the west Friday night into Saturday before tracking across the forecast area Saturday evening into Saturday night. The latest global models are in agreement that dry conditions will linger through Friday night before rain chances finally return Saturday so removed PoPs Friday night. The NBM is trending drier Sunday into Monday and cooler regarding highs on Monday with the front expected to push well south of the GSP CWA and as dry high pressure attempts to build in from the north. Depending on how far south this high is able to sink, drier conditions may return briefly Sunday into Monday (which lines up with the latest NBM PoP trends). However, global models are not in agreement regarding how far south the high will track so confidence on PoPs Sunday into Monday is low. Rainfall amounts over the weekend should remain light and generally half an inch or less across most of the GSP CWA per the latest NBM. The mountain zones still appear to have the best chance to see higher rainfall amounts compared to locations east of the mountains. The latest NBM has gone up slightly regarding rainfall totals this weekend compared to this time yesterday and appears to be more aligned with the 18Z ECMWF. The 18Z ECMWF generally shows 0.25" to 0.75" rainfall across the GSP CWA this weekend as it shows wetter conditions with the cold front on Saturday. Meanwhile, the 18Z GFS shows lower rainfall amounts over the weekend, ranging mostly from a few hundreths of an inch to 0.25", as it shows drier conditions with the cold front on Saturday. 12Z LREF probabilities have trended down for much of the forecast area compared to this time yesterday regarding the potential exceeding half an inch of rainfall. Probabilities are now highest across Swain, Graham, and Macon counties with the LREF showing a 30% to 50% chance of exceeding half an inch of rainfall. Elsewhere, the LREF shows less than a 25% chance of rainfall exceeding half an inch. All this to say, confidence on rainfall amounts remains low with global models not in agreement as well as LREF probabilities of >0.50" of rainfall trending downward.

A low pressure system will approach out of the west early next week, bringing rain chances back Monday night into Tuesday. This system may give us a better shot at higher rainfall totals but with this being towards the end of the forecast period confidence remains low. The 12Z LREF shows a 50% to 60% chance of exceeding half an inch of rainfall across the southwestern North Carolina mountains, the South Carolina mountains, and the Georgia mountains Monday night into Tuesday, with a 30% to 45% chance across the rest of the GSP CWA. In regards to rainfall exceeding an inch, the 12z LREF only shows a 20% to 30% chance west of I-77.

Although a cooling trend is expected in regards to highs this weekend into Monday, afternoon temperatures will remain above normal through the weekend before dropping a few degrees below normal Monday. Below normal highs will be short lived with Tuesday's highs expected to rebound back above normal. Lows will remain above normal through the period with no concerns regarding frost or freeze.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: The air mass will remain dry over the Terminal Forecast Area through at least tonight, resulting in continued VFR conditions. SCT mostly thin high clouds will continue to clear out through the morning, with SKC conditions expected for the bulk of this forecast period...except for maybe some FEW/SCT high-based cumulus/stratocu in the 070-090 range this afternoon. Winds will be mostly light SSW early, increasing to around 10 kts at most sites by late morning/early afternoon. Some gusts of 15-20 kts are possible during the afternoon, mainly across the Piedmont. Winds become light/variable overnight.

Outlook: Dry, VFR conditions are expected to persist thru the work week as broad sfc high pressure lingers over the region. A frontal system is expected to bring showers and associated restrictions this weekend.

GSP WATCHES/WARNINGS/ADVISORIES

GA...INCREASED FIRE DANGER from 11 AM EDT this morning through this evening for GAZ010-017-018-026-028-029. NC...INCREASED FIRE DANGER from 11 AM EDT this morning through this evening for NCZ033-035>037-048>053-056>059-062>065- 068>072-082-501>510. SC...None.