783 FXUS62 KRAH 122009 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 409 PM EDT Sun Sep 12 2021 .SYNOPSIS... High pressure centered just off the North Carolina coast will drift slowly eastward and further offshore through early this week, while continuing to extend westward into the Carolinas. && .NEAR TERM /THROUGH TONIGHT/... As of 330 PM Sunday... A 595 dam ridge at 500 mb over the TN Valley will slightly weaken and move east through tonight, becoming centered over the Carolinas by tomorrow morning. Continued height rises and subsidence from this ridge will result in clear skies and dry weather across central NC. At the surface, 1025 mb high pressure currently centered over SC will continue to move east and offshore, allowing for a lee trough to set up over VA and the NC Piedmont which is already evident from current surface analysis. The resultant southerly/southwesterly flow and 1000-850 mb thicknesses roughly 15-20 m higher than this morning also support lows tonight roughly 5 degrees warmer, in the lower-to- mid-60s. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 355 PM Sunday... A 592 dam mid-level ridge will be centered over NC on Monday, with any fronts staying well to our north, resulting in another day of sunny skies and dry weather. At the surface, high pressure will shift further east into the Atlantic, with a lee trough continuing to set up across VA/NC. S/SW low-level return flow around the high along with the mid-level ridge will cause continued warming, with high temperatures in the lower-90s. This is about 7-10 degrees above normal. The daily record high temperature at RDU for 9/13 is 94F, and while not expecting that record to be broken, it will get close. As the ridge shifts east and offshore, slowly increasing moisture will help bring lows Monday night a degree or two warmer than tonight, mostly in the mid-60s. && .LONG TERM /TUESDAY THROUGH SUNDAY/... As of 300 PM Sunday... Heights aloft will lower through the middle of the week as the ridge aloft builds east towards Bermuda and a trough pushes east from the Midwest to the mid-Atlantic. The ridge will then build slightly further west by the weekend, increasing heights across central NC through the period. High pressure at the surface will remain along the Appalachians and just off the Carolina Coast early this week, then the high off the coast moves northeast off the New England Coast through the end of the week. Weak surface high pressure will linger along the Appalachians and mid-Atlantic through the end of the week, with an Appalachian lee trough developing at times. The main forecast challenge will be with the track of a potential tropical system for the end of the week near the Carolina Coast. A surface low is expected to form near the Bahamas later this week while interacting with an upper-level trough, and the NHC has this area under a 50 percent chance of tropical cyclone development within the next 5 days. Current deterministic and ensemble trends have the potential low a bit further east away from the NC coast, but this could change as most models had various placements of the low. The exiting ridge will contribute to highs 5-10 degrees above seasonal normals on Tuesday, with temperatures lowering to the mid to upper 80s by Thursday. Southerly flow and a decrease in subsidence aloft will help the possibility of diurnal showers and thunderstorms to return to the forecast Wednesday through the weekend, however this could change depending on the track of the potential tropical system. Precipitable water values will be on the rise through the middle of the week, increasing from near 1 inch today to 1.50 inches on Wednesday. Dewpoints will increase to the middle 60s by mid-week, however heat index values will remain fairly close to the actual temperature. && .AVIATION /18Z SUNDAY THROUGH SATURDAY/... As of 155 PM Sunday... 24-hour TAF period: Confidence is high that VFR conditions and clear skies will prevail across central NC through the TAF period, thanks to a ridge of high pressure aloft. Winds will be light (less than 10 kts) from the south/southwest. Looking beyond 18Z Monday: High confidence in VFR conditions continues through Tuesday. Increasing moisture and low pressure may result in isolated to scattered showers and storms each afternoon/evening from Wednesday through Saturday, along with possible fog/low stratus each morning. However, confidence on details is still low. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...KC/Hartfield NEAR TERM...Danco SHORT TERM...Danco LONG TERM...JJT AVIATION...Danco