textproduct: Raleigh

SYNOPSIS

A backdoor cold front will hold just to our south and west through much of today, then lift back north as a warm front tonight. A strong cold front will sweep across the state on Monday, bringing dry and cool weather through Friday.

NEAR TERM /TONIGHT/

As of 1215 PM Sunday...

* Patchy fog, potentially dense at times, will be possible along and north of the I-85 corridor late this evening into the early overnight hours.

In-situ CAD is locked in by low overcast and drizzle/light-rain that is occurring at this time, especially over the Piedmont. Light rain and drizzle is expected to shift east and weaken through the evening hours. At the same time, the warm front to our south will begin to lift northward into the overnight hours. Moisture advection ahead of the warm front will likely result in rapidly lowering cloud bases after 03z and may result in patchy to areas of fog, potentially dense, as this cloud layer lowers to the ground. The most likely area will be the climatologically favored areas along and north of the I-85 corridor, but could be as far south as the Triangle. A non- diurnal temperature curve is expected tonight as the warm front gradually mixes northward into Mon morning, although this warming may be slower than forecast guidance suggest which typically mixes out the CAD regime too quickly. Forecast refinements will likely be needed once the strength of CAD develops.

SHORT TERM /MONDAY AND MONDAY NIGHT/

As of 1215 PM Sunday...

* Pattern change with the passage of a strong cold front, which will bring gusty winds, mostly light precipitation, and return temperatures to below normal.

* Southwest wind gusts of 20-30 mph will be possible ahead of the cold front with frequent 30-35 mph northwest winds after its passage.

* Low relative humidity and strong, veering wind gusts will result in increased fire danger to near Red Flag criteria behind the cold front Mon afternoon. Please see Fire Weather section below for more information.

No major changes from previous AFD. The wedge-front is expected to slowly mix northward into VA Mon morning, with even the slowest guidance suggesting it will clear the Triad around 12-15z, perhaps only hanging on in far northwest Forsyth. A deep sub-990mb low over the Upper Great Lakes Mon morning will shift into western Quebec by Mon evening and will drive a strong cold front east of the Appalachians Mon morning and traversing central NC by early afternoon. Since central NC should be within the warm sector at this point, as the boundary layer begins to heat, southwesterly winds ahead of the front (eastern Piedmont, Sandhills, and Coastal Plain) are expected to begin gusting 20-30 mph. Persistent cloud cover ahead of the front should limit the stronger wind gusts highlighted in the hi-res guidance. The strongest wind gusts will most likely be behind the front and when clearing of the low-overcast begins (16z northwest, 20z east). At this time, frequent wind gusts of 30 to 35 mph will be possible; infrequent gusts of around 40 mph should be expected as well. Pressure rises and CAA should continue well into Mon night and result in periodic gusts of around 25 mph becoming less frequent after 2 AM.

Precipitation is expected to spread east immediately along and behind the cold front, driven by strong 925mb FGEN overlapping intense H5 height falls of 100-150 dam in 12 hours. This intense forcing may provide a favorable setup for a narrow cold-frontal rainband to develop, which would be capable of locally heavier rainfall and briefly strong wind gusts. Latest hi-res guidance suggest timing of this feature, and the cold front forcing it, would be 12-18z from west to east across central NC.

LONG TERM /TUESDAY THROUGH SATURDAY/

As of 1225 PM Sunday...

* Gusty winds and low humidity Tuesday may bring a concern for adverse fire weather conditions, which could last into Wed.

* Chilly Tue with much below normal temperatures, then moderating to more seasonable readings Wed-Sat.

*Rain possible late Friday through early Sunday.

Tuesday will be the coldest day of the period as an Arctic high builds in behind a cold front, reinforced by a strong mid-level low over the Canadian Maritimes and a broad trough. Under northwesterly flow, strong cold air advection, highs are expected to be in the upper 30s to mid 40s. Gusty NW winds of 2025 mph will produce wind chills in the upper 20s in the morning and 30s through much of the day. Minimum RH values of 2030 percent combined with gusty winds of 20-25mph may bring localized fire weather concerns, though cold temperatures should limit the overall threat. Lows Tuesday night will drop into the mid 20s for the region one more night. Temperatures begin moderate to near seasonal normal for the remainder of the week with generally dry conditions through Friday. Breezy conditions continue Wednesday with gusts near 20 mph and minimum RH values dropping into the upper teens to mid 20s, mainly across the Northern Piedmont, potentially leading to another day of elevated fire weather concerns. Again, temperatures may limit the overall threat. The mid-level trough exits the East Coast Wednesday, though a broader longwave trough lingers over eastern the eastern US. This will support periods of fair to partly cloudy skies through Thursday. The good news is that New Years Eve celebrations across central NC should remain dry. Temperatures NYE around midnight are expected to be in the mid to upper 30s with a light westerly wind resulting in apparent temperatures in the low 30s. By late Thursday into early Friday, another weak cold front will move across the Ohio Valley and over Central NC bringing slightly cooler temperatures across the northern Piedmont before the front stalls to the south. By the weekend, the frontal boundary lingering from SC to TX will slowly creep into the region bringing the next chance for light precip, mainly on Saturday. However, precipitation timing has sped up slightly with the newest model runs, with rain chances now arriving late Friday night and exiting by early Sunday morning. Forecast confidence remains low as models differ on surface low track. The GFS remains the drier solution, tracking the low along the Gulf Coast and across N. Florida, while the ECMWF is wetter, lifting the low north over the Tennessee Valley and northern Georgia before exiting off the NC/SC coast early Sunday. Temperatures will trend slightly above normal by Saturday and Sunday with highs in the low to mid 50s and lows in the 30s.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

As of 1225 PM Sunday...

24 hour TAF period: High confidence in restrictions through much of the TAF period, but low confidence on the specifics.

INT/GSO are currently on the eastern edge of IFR visibilities. Model guidance suggests that the IFR visibilities should be well west of these sites, and have chosen to maintain an IFR visibility simply through a persistence forecast. Similarly, ceilings are right on the IFR/LIFR border. Farther to the east, RDU/FAY should maintain VFR visibilities along with MVFR ceilings through the afternoon, but think that the MVFR ceilings at RWI will be fleeting and that they should return to VFR ceilings for a few hours this afternoon.

A low-level jet will develop tonight, bringing LLWS to all terminals, although have delayed the introduction of LLWS to the FAY TAF, as it appears it will take slightly longer for the jet to move south. As a cold front comes through Monday morning around sunrise in the west, that will bring gusts between 20 to 30 kt and bring an end to the low level wind shear. While there could be some patchy drizzle overnight ahead of the front, think that the primary chance of rain will be with the frontal passage.

As low-level moisture increases overnight, conditions will drop at most terminals, with an extended period of LIFR at INT/GSO and IFR at RDU. Will maintain the patchy dense fog at INT/GSO inherited from the 12Z TAFs. Farther to the south and east, think that RWI will have more intermittent MVFR ceilings and that FAY will only have intermittent MVFR ceilings with the frontal passage itself.

Outlook: As the frontal passage continues, a line of gusty showers will remain possible Monday afternoon with gusts as high as 35 kt. Wind gusts should decrease to 20-25 kt after sunset, and any cig/vis restrictions should also come to an end around sunset. Beginning Tuesday, VFR conditions should dominate through the rest of the outlook period with high pressure.

FIRE WEATHER

As of 1215 PM Sunday...

A strong cold front is forecast to shift across central NC Monday morning through the early afternoon hours. Behind the front, and especially as skies begin to clear, strong downsloping winds, rapidly dropping relative humidity, and gradually veering winds, will pose an elevated concern for increased fire behavior. By 18z, sustained winds of 20 mph with gusts of 30 to 35 mph will become increasingly possible as relative humidity values rapidly drop below 30%. These parameters will likely overlap for 3-5 hours over a given area, first over the western Piedmont, and shift eastward through the eastern Piedmont, Sandhills, and Coastal Plain between 18z and 00z. After coordination with NCFS, we are planning to issue a RFW for central NC west of I-95 for Monday from Noon through 6 PM.

Marginally hazardous fire weather conditions will also be possible on Tues and Wed when relative humidity values will be exceptionally dry, in the low 20s and teens, during peak heating. Wind gusts and soil conditions will likely be the driving factors on whether any headlines will be needed each day. Gusts on Tues will be slightly stronger with frequent gusts around 20 to 25 mph expected.

RAH WATCHES/WARNINGS/ADVISORIES

None.