textproduct: Raleigh

SYNOPSIS

An in-situ cold air damming ridge will extend across the Carolinas and Virginia today, while coastal low pressure will rapidly strengthen while tracking along the East Coast. Cold high pressure will follow and migrate across the Southeast, while modifying, through Thursday.

NEAR TERM /THROUGH TONIGHT/

As of 1200 PM Tuesday...

As the main surface low moves off the VA/NC coast early this afternoon and tracks northeast along the US coastline, rain will taper from west to east. Most of central NC should be dry by late afternoon. High pressure over Tennessee will gradually build in tonight, bringing clearing skies and a continued northwest breeze with occasional gusts up to 20 mph. Highs today will remain in the upper 40s to around 50. Overnight lows will fall into the midupper 20s across the northwest and generally the lower 30s elsewhere, with most locations at or below freezing.

SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/

As of 1200 PM Tuesday...

Quiet weather will continue on Wednesday as high pressure remains in control of the Mid-Atlantic. Expect mostly sunny skies with light and variable winds through the day. Highs will run about 10 degrees below average, ranging from the mid to upper 40s, with a few low 50s possible across the south. Overnight, calm winds and reduced cold advection will allow temperatures to fall into the upper 20s to around 30 degrees.

LONG TERM /THURSDAY THROUGH TUESDAY/

As of 355 PM Tuesday...

An Arctic surface high will move east from the Upper MS Valley on Thursday morning to become centered over the northern Mid-Atlantic on Thursday night. Meanwhile a shortwave over the Southern Plains will spawn a surface low over the NW Gulf which moves to the north- central Gulf Coast on Thursday night. Despite skies becoming mostly cloudy to overcast as the system begins to spread Gulf moisture into the area, Thursday afternoon's highs will be a bit milder, ranging from around 50 in the far north to upper-50s in the far south. A dry cold front on the leading edge of the high to our north will move through central NC in the evening. Forecast lows Thursday night are chilly despite the overcast skies, ranging from mid-20s far north to mid-30s far south.

The aforementioned shortwave will flatten as it moves through the OH Valley and Mid-Atlantic on Friday. At the surface, models depict the area of low pressure moving NE to just off the coast of the Carolinas late Friday. As Gulf moisture overruns the surface ridging that will be in place from the high to our north, precipitation will begin to spread across the Carolinas. Confidence in timing and amounts is still low as guidance has been waffling back and forth, but the 12z GFS now aligns more with the ECMWF on an earlier start time, with both models (and around half of their ensemble members) bringing in mid-level WAA induced precipitation from the south and west by late Thursday night and early Friday morning. The NAM is now coming into range, and while not quite as fast as the GFS/ECMWF, it still brings in precipitation by early to mid morning. This faster timing means the greatest confidence in precipitation is now on Friday afternoon and evening, when POPs are likely to categorical. The GFS also wraps up a deeper coastal low now like the ECMWF, and overall QPF has ticked back slightly upward, around a third of an inch to an inch (lowest NW, highest SE).

The main potential hazard with this event is the possibility of some frozen precipitation over the northern Piedmont and northern Coastal Plain at the start, but there is still a lot of uncertainty. An earlier start time as depicted by the latest guidance would result in a better chance for snow and ice as it gives more time for precipitation to fall while we are still under the influence of the cold high to our north before it moves offshore. Partial thickness nomograms from both NAM and GFS BUFKIT soundings indicate a period of snow transitioning to sleet and freezing rain for several hours on Friday morning around the Triad. While surface temperatures look pretty marginal, forecast model soundings indicate fairly cold air in the mid-levels with a fairly isothermal temperature profile. This may favor more sleet and snow vs freezing rain. A brief wintry mix will even be possible farther south at places like RDU, while much of the southern Piedmont, Sandhills, and central/southern Coastal Plain should be warm enough for mainly rain. However, given the spread in guidance and that this is still three days away, the forecast is certainly subject to change, and it is important to stay tuned for the latest updates. The progressive nature of the pattern will allow for the high to quickly move east into the Atlantic on Friday afternoon, cutting off our cold air source. So any frozen precipitation will change over to plain rain even in the far north by Friday late afternoon or evening. The temperature forecast confidence is low on Friday as well due to the previously mentioned factors, but it will certainly be chilly with highs in the mid-30s to mid-40s.

As high pressure moves in from the west behind the departing low, rain will come to an end on Friday night and temperatures will drop into the upper-20s to upper-30s. Additional shortwaves then look to pass through our region, spawning additional waves of surface low pressure riding along the stalled front to our south. One looks to be on Saturday night/Sunday and another stronger one on Sunday night/Monday. So continue some low-end POPs during this time, but confidence on details is very low. At this time expecting mainly liquid precipitation, but there will be enough chilly air around that something frozen can't be ruled out across the north. This weekend's forecast highs are in the mid-40s to lower-50s both days, with lows in the upper-20s to mid-30s. Behind a cold frontal passage on Sunday night, forecast highs decrease to lower-40s to lower-50s on Monday and Tuesday, with lows in the 20s.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

As of 1255 PM Tuesday...

Widespread stratiform rain has just about moved out of the eastern terminals. In its wake, lingering drizzle and lowering cloud bases within the cool/moist CAD airmass will likely continue to lock in LIFR cigs and MVFR/IFR vsbys until northwesterly downsloping winds behind a front push drier air into the area, clearing low cigs from northwest to southeast this afternoon/evening. As with the previous TAF issuance, opted for slowest guidance eroding low clouds as conditions have yet to improve even in the NC Foothills. The front may still bring a period of gusty winds to the Triad terminals, but duration and intensity is decreasing within latest guidance. Other than a surge or two of SCT/BKN MVFR cigs after the LIFR cigs clear, mostly clear skies are anticipated tonight as VFR conditions return to the region.

Outlook: Another storm system is expected Fri into Sat and will likely bring flight restrictions to all central NC terminals. A period of snow/sleet remains possible for the northern terminals (GSO/INT/RDU) Fri morning before transitioning to all rain by the afternoon.

RAH WATCHES/WARNINGS/ADVISORIES

None.