textproduct: Raleigh

SYNOPSIS

Weak high pressure will hold over the Southeast coast and eastern Carolinas this morning. A dry cold front will push southward through the region later today, settling just to our south as Arctic high pressure noses in from the north. Low pressure developing over the northern Gulf will track northeastward across the Southeast states and Carolinas late tonight through Friday.

NEAR TERM /TODAY/

As of 400 AM Thursday...

A weak surface trough will linger across the area today before being pushed south and out of the area by a dry cold front. Arctic high moving into the OH Valley begins to build into the area this evening. A mid-level srn stream wave will track ewd across nrn FL/GA and off the Southeast US coast this eve. Cloud cover will increase this aft and eve as the wave passes to the south, but the weather should largely remain dry through the afternoon. Highs will be near to slightly below normal, generally in the low to mid 50s.

SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/

As of 335 AM Thursday...

* Winter Weather Advisory in effect from midnight tonight through midnight Saturday for portions of the northern Piedmont and northern Coastal Plain of central NC. Up to an inch of snow accumulation and a glaze of ice accumulation are expected.

* Snow, and sleet (likely mixed with rain) are possible south of the advisory area between midnight and 10 AM Friday, however the duration of non-liquid precipitation will be shorter and accumulations will be below advisory criteria before the transition to all rain occurs.

* A brief period of freezing drizzle could occur (mainly over the advisory area) as the precipitation moves out Friday evening/night, but confidence in that occurrence is lower.

Overview: Aloft, a mid-level srn stream wave will track ewd across nrn FL/GA and off the Southeast US coast this eve, while a nrn stream s/w follows on its heels, tracking ewd across the srn Appalachians and Carolinas tonight/Fri and off the Carolina coast Fri night. The H25 170 kt jet should stay north of the area, oriented generally from W-E extending from the mid MS Valley to the DELMARVA and east. At the surface, Arctic high pressure will move ewd from the OH Valley to the Northeast US, ridging swd into the area through Thu night. Meanwhile, an area of low pressure over the nrn Gulf will begin tracking enewd into the Southeast US tonight. The ridge will likely hold over portions of central NC as the high shifts off the New England coast and the deepening low tracks newd across the Southeast US and along the Carolina coast on Fri. The low should continue ewd out over the Atlantic Fri night, with high pressure remaining over the area.

Temperatures: lows tonight in the upper 20s north to mid/upper 30s south expected. Fri highs will be well below normal, only reaching the low/mid 30s north to low/mid 40s south and with a bit of a breezy it may only feel like upper 20s to mid 30s across much of the area.

Precipitation: Isentropic lift will increase this eve/tonight, quickly saturating the mid levels, including the dendritic growth zone, by midnight. As precipitation begins, initially rain in most places, the lower levels will also saturate. Precipitation will continue into the morning, then could begin moving out of the area from W-E Fri afternoon or evening, end timing is still a bit uncertain.

Across the northern half of central NC (roughly along and north of HWY 64): the temperatures should wetbulb to near/below 0C tonight. The thermal profile, with temperatures through the column at or below 0C, should support a period of snow in the advisory area, perhaps mixing with rain south of the advisory area, into Fri morning. However, there is still some uncertainty wrt p-types from early Fri morn into Fri aft. The biggest p-type question will be if, when, and for how long some sleet or freezing rain may mix in, depending on the strength/depth of the warm nose aloft, and/or if there will be a transition to fzdz as dry air intrudes near/below the dendritic growth zone. The accumulations of snow and ice will hinge on these transitions and durations. For now expect a glaze of ice accumulation and up to an inch of snow in the advisory area. If the saturated layer below the dry air intrusion is deep enough and surface temps remain below freezing, a transition to fzdz is possible, which could result in some light ice accrual as the precipitation ends.

Across the srn half/third of central NC: largely expect precip to be rain, although cannot rule out a brief period of snow mixing in farther north.

Friday night: The precipitation should be out, or be moving out of the area Friday night, though some rain may linger across the southeast into/through the night. Lows should range from mid/upr 20s to low/mid 30s.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

As of 225 AM Thursday...

* Rain chances SE Sat, and continued chilly.

* Chilly, below-normal temperatures to persist into next week.

* Light precip chances late Sunday into Monday, with brief rain/snow mix possible.

Sat/Sat night: The frontal zone will hold SE of the area Sat, with weak high pressure sitting over the Carolinas. As we'll stay within a fast WSW mid level flow, the potential remains that subtle and hard-to-time perturbations will ride within this flow over SC and S/E NC Sat/Sat night. There is some model agreement on the right entrance region of the upper jet scraping across NC Sat afternoon, with associated enhanced upper divergence resulting in a brief northwestward bump in the NW edge of the precip shield toward the Triangle area. But the overall forcing for ascent appears to be modest and fleeting, with the bulk of the moisture in the mid and upper levels, given the lack of opportunity for moisture return in the low levels. As such, expect the chance for any rain to be largely confined to areas SE of the Triangle, with light amounts overall. Clouds will be abundant, especially over S and E sections, so it will remain chilly, with highs Sat in the mid 40s to around 50, followed by lows mostly in the mid 30s. -GIH

Sun-Wed: A central to eastern U.S. mean upper trough (with 500 MB heights ~2 S.D. below normal) and broad cyclonic flow will support a continuation of chilly, below-normal temperatures through the period, highlighted by a reinforcement of cold air behind a cold frontal passage Monday.

Monday and Tuesday will be the coldest days, with highs in the lower to mid 40s and lows Monday night dipping down into the lower to mid 20s, with some upper teens possible in the typically colder locations.

Sunday should begin mostly dry across the area, with steadier rain chances suppressed to the south along a stalled frontal zone lingering across the SE US. However, the approach of the next shortwave trough and aforementioned cold front may support a brief period of light rain Sunday evening and into the day on Monday. There is a low-end potential for the rain to briefly mix with or change over to snow across the northern Piedmont and northern coastal plain before ending, though little to no impacts are expected at this time.

Dry conditions will follow Tuesday and Wednesday with a clipper trough approaching from the west late in the period. -CBL

AVIATION /12Z THURSDAY THROUGH MONDAY/

As of 640 AM Thursday...

With the exception of isolated MVFR fog affecting RWI until around 13z this morning, VFR conditions are likely to hold across central NC today through at least mid evening (~04z Fri), but with increasing clouds. Weak high pressure over the eastern Carolinas will push SE and yield to a dry backdoor cold front that will drop S through the area later today, resulting in a shift of surface winds from light/variable this morning to light from the W or NW through mid afternoon. Winds will then shift to be from the NE at 7-10 kts, with a few 12-15 kt gusts, just behind the backdoor front starting late afternoon or early evening. Low pressure tracking NE from the N Gulf later today will bring increasing and thickening mid clouds from the WSW by afternoon, with slowly lowering bases. Clouds will become overcast after 22z, lowering further but still VFR through 04z, but after that, cigs are likely to lower to MVFR then to IFR W to E between 07z and 11z, with MVFR vsbys in rain mixed with snow, although it may be mostly snow after 09z at INT/GSO, with the potential for IFR vsbys.

Looking beyond 12z Fri, precipitation will continue to advance to the ENE across the rest of central NC, lasting through much of Fri, with a high chance of sustained sub-VFR conditions. This precipitation is likely to be mostly light snow at INT/GSO and a rain/snow mix at RDU and perhaps RWI, with rain elsewhere. Precipitation will end W to E late afternoon through the evening, perhaps as a little drizzle or freezing drizzle, but sub-VFR conditions are likely to hold through Sat morning. Rain chances producing a period of sub-VFR conditions will continue at FAY Sat through Mon, with the highest chance late Sun into early Mon. -GIH

RAH WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from midnight tonight to midnight EST Friday night for NCZ007>011-021>025.