textproduct: Raleigh

WHAT HAS CHANGED

* Rain chances continue to increase for Wednesday.

KEY MESSAGES

As of 250 AM Sunday...

1) Much cooler temperatures expected today, behind a backdoor cold front. Highs will be 15 to 25 degrees cooler than Saturday.

2) Much needed rainfall is possible this week in an active weather pattern.

DISCUSSION

As of 250 AM Sunday...

KEY MESSAGE 1... Much cooler temperatures expected today, behind a backdoor cold front. Highs will be 15 to 25 degrees cooler than Saturday.

Patchy rain persists over the S and E CWA, within mid level DPVA ahead of a shortwave trough extending from New England SW/WSW through VA into far NE TN. This is producing a somewhat messy set of surface lows/fronts, including a backdoor front extending from deepening surface low pressure off the Delmarva westward to weaker low pressure over Wrn VA, with a trailing front extending down through the W Piedmont of NC. As this shortwave trough progresses slowly E and SE today, the gradual height falls and weak DPVA aloft will mean a continued chance of rain over our S and E through much of the morning. As the backdoor front over S-central/SE VA drops southward through central NC, low level cooling, stabilizing, and condensation behind the front will bring considerable low clouds lasting through much of the day, as well as a supplemental chance for patchy drizzle into early afternoon. A brisk and gusty wind from the NNE and NE is also likely behind the front, lasting through the day as the front settles just to our S through this afternoon. These low clouds combined with CAA (leading to plummeting low level thicknesses) and a slow precip exit will favor highs today from the low 60s NE to the mid 70s SW, around 15 to 25 degrees cooler than yesterday's highs and roughly 5 to 15 degrees below normal. Weakening CAA by Mon will help temps moderate slightly, although with starting thicknesses around 30 m below normal, and continued periods of clouds tonight through Mon with a persistent mesohigh/ stable pool in place, highs Mon will still be below normal, ranging from around 70 to the mid 70s.

KEY MESSAGE 2... Much needed rainfall is possible this week in an active weather pattern.

Models continue to advertise a shortwave moving through the Central Plains and across the OH Valley and Mid-Atlantic states on Wednesday. The combination of strong forcing and a plume of 1.5-2.0" PW should result numerous showers and the potential for some storms, depending on the stability of the preceding airmass on Wednesday. However, this is a decent signal in several model runs that the most rainfall may be to our north (with the stronger upper forcing) and to our south (in the relatively more unstable airmass), with some degree of split over NC. At the moment ensemble guidance is generally centered around 0.50" with this event.

The cold front trailing the aforementioned system will become relatively stationary over the Southeast into the weekend. Troughing is generally favored over the eastern US, though with a high degree of complexity owing to blocking over the northern Atlantic and upper lows over Canada. A shortwave trough is forecast to track across the southern US late in the week, bring a good chance of rain to the drought-stricken region, but the track is uncertainty, and there are scenarios where it remains suppressed and NC is mostly dry. Thus confidence is low at this time.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

As of 140 AM Sunday...

Central NC terminals are mostly VFR at this hour despite widespread showers over much of the area, falling out of VFR cigs. But confidence is high that adverse aviation conditions will overspread central NC through 10z, lasting through at least early afternoon. The rain over the last 18 hours has been due to a surface low now over VA with a trailing cold front through the W Piedmont of NC. As this system pushes east, the rain will exit, soon after 11z at RDU, 13z at RWI, and 15z at FAY. Meanwhile, with the departing surface low strengthening off the VA coast, a backdoor cold front will drop S into NC, starting in the N 07z-09z and progressing S through 19z- 21z. Low clouds will spread in from the N behind the front, low-end MVFR cigs and vsbys much of the time but with periods of IFR cigs. Gradual improvement to VFR is possible from mid afternoon through early evening as cigs climb above 3000 ft AGL, however confidence in this occurrence and timing is low, and central NC terminals may see periodic bkn MVFR cigs lasting through 06z, with bkn clouds varying between 3000 ft and 3500 ft AGL. Surface winds will be light and variable until backdoor front passage, when winds from the NNE or NE at 12-16 kts with frequent gusts to 20-28 kts are expected, lasting from the predawn hours through early this evening, when gusts will die down but sustained winds will hold at 8-12 kts from the NNE.

Looking beyond 06z Mon, MVFR cigs will remain possible through tonight and into Mon morning, with a NNE breeze persisting. VFR conditions should then dominate through mid week, although as a couple of upper level disturbances cross the region, a few showers will be possible mainly NW (INT/GSO) Tue, with a better chance Wed/Wed evening areawide as a stronger low and front moves through, bringing gusty winds late Wed into Thu.

RAH WATCHES/WARNINGS/ADVISORIES

None.