Scientific Forecaster Discussion

000 fxus62 krah 230106 afdrah Area forecast discussion National Weather Service Raleigh NC 910 PM EDT Mon Apr 22 2019 Synopsis... high pressure will settle over NC tonight and Tuesday. This high pressure will gradually move off the southeast coast mid-week, as a weak backdoor front dips southward into North Carolina. A cold front and upper level trough will approach from the west late Thursday and Friday, bringing a good chance of showers and storms Friday. && Near term /through tonight/... as of 910 PM Monday... With light winds and clear skies, excellent radiational cooling is expected overnight. Lows are forecast to drop into the mid 40s to around 50, coolest in the rural and low lying areas. && Short term /Tuesday through Tuesday night/... as of 155 PM Monday... Continued dry, but with increasing clouds starting late Tue. The flat mid level ridge axis will slowly shift eastward over the southeast states, while the weak surface high pushes to our southeast off the East Coast of Florida. A Lee surface trough and low level thermal ridge will set up through the NC Piedmont Tue, resulting in deep mixing topped by rising heights. With continued subsidence and warming thicknesses to around 15 M above normal under plentiful sunshine, highs should be in the 80-85 range. As the mid level ridge axis eases eastward off the southeast coast Tue night, it will continue to flatten, a result of a deepening shortwave trough crossing the St. Lawrence Valley. This feature will drag a backdoor front south-southeast toward the NC/Virginia border overnight, leading to increasing clouds, particularly across north NC. Weak wind fields and the continued dry column will keep our weather dry ahead of this front Tue night, but the increase in clouds will help keep it mild, with above-normal lows in the mid-upper 50s. -Gih && Long term /Wednesday through Monday/... as of 315 PM Monday... Wed/Wed night: while the backdoor front is expected to drop through Virginia toward NC, it appears unlikely to make much southward progress. The departure of the strong shortwave trough off New England and the approach of deep positively tilted troughing pushing through the Southern Plains during this period should help push mid level heights back up over the southeast, and this resumption of ridging over the Carolinas should keep the front largely north of the state. That said, models do hint at a prefrontal trough -- a weak wind shift with minimal to no thermal contrast -- developing over northern NC late Wed. There may be just enough column moistening in its vicinity for a few sprinkles late Wed into Wed night. But forecast soundings show considerable dry air below 850 mb with a largely westerly or northwesterly wind component, facilitating the low level drying. As such, will keep pops low, slight chances mainly across the north late Wed into Wed night. Highs 80-85 (warm thicknesses balanced with greater cloud cover). Lows in the upper 50s/lower 60s. Thu through Fri night: this period presents our greatest upcoming shot at wet weather. The southern stream mid level trough will head east over the east Continental U.S. And amplify as it absorbs northern stream energy. Clouds will increase further over NC with strengthening SW flow in the mid levels and a greater fetch of Gulf moisture as the surface high drifts further offshore and the surface cold front approaches. Based on timing shown by the latest model runs, we should see showers and a few storms moving into northwest sections late Thu, spreading over the remainder of central NC Thu night/Fri with the approaching DPVA and increasing prefrontal precipitable water. Pops should taper down west to east as the trough axis pushes offshore late Fri night with the cold front crossing the region. Expect highs in the upper 70s north and low-mid 80s S Thu, and in the mid-upper 70s Fri. Lows in the 50s behind the front Fri night. Sat through Mon: Sat/Sat night look dry, behind the trough and within modified Canadian surface high pressure. Forecast uncertainty grows by sun/Mon as the mid level flow flattens across much of the central and eastern conus, with only minor perturbations acting within rebounding precipitable water as moisture streams in from the Atlantic and Gulf. With strong forcing mechanisms lacking and with varying influences from northern stream features, will have just slight chance pops both days, a nod toward climatology. After a brief cooling back to near or slightly below normal temps Sat, readings should head back up above normal sun/Mon as thicknesses climb once again. -Gih && Aviation /00z Tuesday through Saturday/... as of 910 PM Monday... Confidence is high that VFR conditions will hold over central NC for the next 24 hrs. Expect clear skies through tonight, then sunny skies Tuesday. Winds will be calm tonight and light/variable on Tuesday. Looking beyond 00z Wed, VFR conditions should prevail until later in the week. A backdoor cold front will dip southward into NC late Wed into Thu, bringing a chance of showers and a stray storm or two, but VFR weather should be dominant. Sub-VFR conditions become more likely starting Thu evening, peaking Fri/Fri night, as an upper trough moves in from the west. VFR conditions under weak surface high pressure should return for Sat. -Gih && Rah watches/warnings/advisories... none. && $$ Synopsis...Badgett/Hartfield

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