Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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003 FXUS62 KRAH 222028 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 325 PM EST Mon Jan 22 2018 .SYNOPSIS... A cold front will approach from the west today, and cross central NC Tuesday morning. High pressure and associated seasonably cool and dry conditions will follow for mid-week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 325 PM Monday... Just minor tweaks required to the near term forecast. Still appears windy conditions are probable late tonight into Tuesday. Veil of high clouds across central NC resulting in a fairly uniform temperature field at mid afternoon with most locations in the lower 60s. Some breaks in the high clouds noted coming into the western Piedmont at 1930Z, so some potential for some warming from insolation, though that window is narrowing rapidly. Expect most highs in the 60-65 degree range. Temperatures will remain mild overnight as cloud cover thickens and low level sly flow strengthens. Expect the sfc winds to pick up close to midnight; thus, most locations will likely record their min temps this evening, with temperatures holding steady or slowly rising overnight. Near term model guidance still suggest that best lift for organized showers across central NC will be very late tonight, likely closer to 08-09Z. Have accordingly adjusted evening PoPs down a bit to reflect this trend. Kinematics with this system impressive with strongly curved hodographs depicted across the region around 12Z Tuesday. However, models still depict weak or non-nonexistent sfc based instability. The models may be underplaying this as the models depicted weak instability over the lower MS Valley early this morning where isolated reports of wind damage and a few tornadoes occurred. Did note that the severe weather reports occurred in an axis where sfc dewpoints were near or slightly higher than 60 degrees. If this holds true, may see an isolated threat for a severe storm in vicinity of our eastern periphery after daybreak Tuesday. Otherwise a strengthening low level jet (on the order of 50-60kts) will gradually mix to the sfc, resulting in breezy/gusty sfc winds after midnight. Wind gusts 20-25kts probable across the Piedmont with stronger gusts increasing after daybreak. Expect a broken band of scattered-numerous showers to work its way into the Piedmont after 06Z, with the leading edge of the showers in vicinity of the highway 1 corridor in the neighborhood of 09-10Z. Have increased PoPs to category across most of the Piedmont as appears most locations will receive some amount of rain from this event.
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As of 325 PM Monday... Band of scattered-broken showers will be ongoing at daybreak across the heart of central NC, and is expected to move east and exit our coastal plain counties by 15-16Z. Strong kinematics and the potential for a narrow band of sfc based instability will enhance a small threat for a strong or locally damaging wind gusts with a heavier shower or isolated t-storm through 15Z. This threat appears highest along and east of I-95. Otherwise a sfc cold front will cross central NC Tuesday morning, with rapid clearing expected in its wake as the dry slot associated with a deep, mature cyclone over the Great Lakes streaks into the Carolinas. The mixing that will ensue after the clearing will translate the strong winds a thousand feet or so above the surface downward, contributing to sfc wind gusts 30-40 mph. This period of strong gusty winds expected to last an hour or two after the initial clearing, with gusts 25-30 mph probable into the afternoon. The increasingly sunny skies, breezy sw winds, and early morning temperatures in the mid 50s to around 60 support temperatures warming into the 60s across the Piedmont, and around 70 in the coastal plain and Sandhills. This seems plausible as the 850mb trough does not cross our region until mid-late afternoon, delaying cold air advection until late in the day or after sunset.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... As of 253 PM Monday... Cold and dry air advection behind Tuesday`s front will surge east quickly overnight with low level thicknesses falling ~35 meters by 12Z Wednesday morning. Mins in the (fortunately) well mixed airmass will bottom out in the low to mid 30s, as opposed to the potential for upper 20s if we were to have better radiational conditions in combination with model consensus thicknesses ~1305 meters. The cool airmass settling into the area will linger for a couple of days, aided by modest reinforcement as a short wave skates across the Ohio Valley on Wednesday night, veering low level flow more northwesterly through Friday. Stacked ridging which originates over the northern Gulf will edge over the area, with sunny skies, rising heights and lighter flow encouraging a modest warmup on Friday. Highs Wednesday and Thursday will range mostly from 50 to 55, a couple of degrees above normal, warming to mostly mid 50s on Friday. Morning lows will be below freezing, 28 to 32 degrees, both Thursday and Friday mornings. Warm air and moisture advection will be on the increase as a return flow regime sets up Friday night. Clouds will be spreading in from the south by early Saturday, and overspreading the area during the day. Models diverge significantly as to the progression of a short wave digging south into the northern Great Lakes. The 12Z ECMWF amplifies the wave pattern south into the western Gulf, producing a deep, frontogenetic zone with a surface low developing over southern LA and lifting into central AL. This would be much slower, wetter solution than the GFS, which keeps the flow much flatter and essentially pushes a much drier, weaker frontal zone southeast through the area and offshore Sunday. Will give a nod to the ECMWF`s longer range skill and stretch fairly high PoPs from the Saturday night period through Sunday night. Hopes are raised that this might produce a widespread heavier event to alleviate moderate drought conditions across the area. Highs Saturday and Sunday will be mild...upper 50s to mid 60s, with lows in the 40s. We should be drying out Monday, with highs near or above normal (50 to 55) regardless of which model turns out to be more correct. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... As of 105 PM Monday... While VFR parameters will persist through 21Z across central NC, an approaching frontal system will bring an increased threat for adverse aviation conditions to central NC tonight into Tuesday. A sly flow will advect enough low level moisture to cause a deck of stratocu to develop and progress nwd late this afternoon and this evening. This deck of MVFR ceilings will likely encroach upon the KFAY vicinity by 21-22Z, and across the remainder of the TAF sites between 00Z-04Z. A low level jet will strengthen overhead this evening and into the overnight. While sfc winds at the sfc will be sly 8-12kts, winds just above the sfc (~1000-1500ft AGL) will be sly 45-50kts, creating low level wind shear conditions. The frontal system will be just west of our region prior to daybreak leading to an increase in shower activity across the western Piedmont including the Triad terminal by 06Z, and in proximity of KRDU and KFAY by 09Z. Per latest model soundings, enough instability may reside aloft to support a thunderstorm or two, primarily between 08Z-14Z. The cold front will sweep eastward across our region early Tuesday morning. Rapid clearing is anticipated, leading to VFR parameters in the Triad vicinity shortly after 12Z, and in proximity of KFAY and KRDU by 15Z, and KRWI by 16Z. Sfc winds will remain blustery ahead and behind the front with southwesterly sfc winds frequently gusting 25-35kts, with sporadic gusts 40-45kts possible. The strong wind gusts should subside after 21Z Tuesday. VFR parameters expected Tuesday night through Saturday morning as high pressure will be the main influence on our weather. Another frontal system will begin to impact the Carolinas late Saturday into Sunday, possibly leading to a period of sub-VFR parameters. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...mlm AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.