Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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513 FXUS62 KRAH 151920 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 220 PM EST Sun Jan 15 2017 .SYNOPSIS... A cold front will drop southward and exit the southern counties by early this evening. High pressure will build in behind the front and reinforce a cold air damming airmass over the area through Monday night. && .NEAR TERM /THROUGH TONIGHT/... As of 1035 AM Sunday... Little change in our sensible weather this afternoon. Early morning upper air analysis depicts a deep wly flow over the region with weak caa noted at 850mb. Moisture is mainly confined to the lowest 10k ft of the atmosphere, with the lowest 5k ft rather damp. Variably cloudy skies will persist with periods of partial sun more likely across the Sandhills and southern Piedmont compared to the rest of the forecast area. A surface cold front poised to enter our northern coastal plain counties late this morning will drift south-southwest this afternoon. Low level cold air advection behind this boundary fairly weak. Still, should see a wide range in high temperatures this afternoon across central NC,varying from around 50 in the far northeast, to the lower 60s across the southwest. If sun is more prevalent this afternoon across the south, high temperatures may end up being 3-4 degrees warmer than forecast. ~WSS Tonight: The cold front will push south of the area by this evening, with weak cold advection and a light northeast wind overnight. The H9 flow will swing around to southerly after midnight, resulting weak (and shallow) isentropic lift in the western Piedmont. As a result, some patchy light rain or drizzle should break out and drift east through the Piedmont through Monday morning, with low clouds eventually engulfing the entire area. Lows 38-45. ~SMITH && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... As of 350 AM Sunday... CAD will persist Monday as the parent surface high shifts to the Mid-Atlantic coast and then eventually offshore. The main impacts look to be from just widespread low clouds since the H9-H85 flow is weak (< 30kt) and the flow aloft is flat. Low clouds will result in highs several degrees cooler than today, but the lack of precip should keep highs within a couple degrees but on the cooler side of guidance; 45-52. The aforementioned surface high will shift offshore Monday night, but our CAD airmass should linger without an erosion mechanism. Warm advection will start to increase over the western Piedmont, on the eastern flank of a prefrontal LLJ over the Tenn Valley. Most of the associated rain will be west of the mountains, but their could be a few areas in the Foothills and flirting with the western piedmont by Tuesday morning. Lows 42-46. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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As of 220 PM Sunday... Models continue to come into better agreement with the overall pattern through Friday. There are still small timing issues and differences in precip chances/timing over central NC. Generally, expect multiple rounds of wet weather with dry periods in between. Timing and amounts are still a challenge. The weather could get very interesting for late next weekend and early the following week. Tuesday through Wednesday Night: The wedge will probably linger through early Tuesday, however the models erode it by the aft/eve as the return flow from the high offshore and the southerly flow ahead of the approaching front both increase. Meanwhile aloft, the remnants of a closed low over the Baja gets absorbed into the northern stream as a shortwave that swings through the Great Lakes through and into the Mid-Atlantic Wednesday/Wednesday night. The wave should be strong enough to dampen/suppress the ridge. The surface low and attendant front will approach the area Tuesday night, swinging through by late aft/eve Wednesday. As a result, expect best chances for rain to be late Tuesday through Wednesday from west to east. Temperatures will be above normal, slightly cooler in the NW Tuesday (mid to upper 50s), but otherwise expect highs in the 60s and lows in the mid 50s Tuesday night. With the expected frontal passage late Wednesday, overnight lows will be lower, mid 40s north to around 50 degrees south. Thursday through Friday Night: There is surprising agreement between the models for this period, though there are some differences, the pattern is similar. Expect two additional rounds of precipitation during this time, with a period of dry weather in between. A fleeting surface high and upper level ridge will move through/build over the area Thursday while another low moves out of the desert southwest northeast toward the Great Lakes. The moisture advection into the Gulf coast states Thursday night combined with the sufficient forcing from the low will result in another round of rain moving into the Carolinas from the southwest Friday/Friday Night. Temperatures should be fairly steady during this time, highs in the upper 50s to mid 60s and lows in the 40s. Saturday and Sunday: This part of the forecast period gets quite interesting and the model agreement make it even more ominous. Although, this far out it is hard to jump on board completely. Fingers crossed for some changes. As of the latest model runs, a strong low will come onshore in the Pacific NW Friday/Friday night digging a trough south and east toward TX Saturday and Sunday. In the wake of the low that moves through Central NC Friday night, a ridge builds aloft over the southeast U.S. while the surface low strengthens over the Midwest. Very strong southerly flow advects very warm moist air into the Gulf Coast states late in the weekend. There is a bit of uncertainty whether a CAD wedge will set up and hold over NC or not and thus temperatures are low confidence, but do expect increasing chances for rain late Sunday into early in the week.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 1230 PM Sunday... VFR parameters across central NC this afternoon will deteriorate this evening as a blanket of low stratus develops over the region. This deck of MVFR ceilings should begin between 00Z-04Z, with widespread MVFR ceilings by 06Z. In addition, should see patches of light rain develop over the western Piedmont after 00Z,some of which will cross the KINT and KGSO terminals. This added moisture will likely lower ceilings into the IFR category in the Triad after 06Z. The adverse aviation conditions with IFR/MVFR ceilings will persist through Monday and into Monday night. Ceilings may temporarily lift into the VFR category later Tuesday. However, aviation conditions will likely tank Tuesday night into Wednesday as a cold front approaches and crosses our region. Behind the front, VFR conditions anticipated for Thursday and Friday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...SMITH NEAR TERM...WSS/SMITH SHORT TERM...SMITH LONG TERM...KC AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.