Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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512 FXUS62 KRAH 211909 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 310 PM EDT Wed Mar 21 2018 .SYNOPSIS... A powerful upper level low will move off the Northeast coast tonight. Cool high pressure will build in from the northwest Thursday into Friday. A warm front will approach from the southwest on Friday, stalling just to our south as a strong upper level disturbance crosses the region, bringing unsettled weather over the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 310 PM Wednesday... Areas of light rain south, and light snow north this morning has become patchy light rain across the entire area as the lowest 3-4 ft of the atmosphere has warmed well into the 30s-lower 40s. A s/w seen on water vapor imagery rotating around the backside of the deep upper level low will cross central NC this evening. Ahead of this feature, expect scattered rain showers across the region. While the lowest 3-4 thousand ft will cool back into the 30s by early evening, the atmosphere will dry out aloft in the favored dendrite growth zone, prohibiting snowflake formation. Thus expect the bulk of the showers to remain liquid. The advection of a slightly drier air mass at the surface in conjunction with a blustery west-nw wind will aid to evaporate residual moisture off area roadways. Thus, while overnight temperatures will drop close to freezing across the Piedmont and northern coastal plain, not anticipating problems with black ice early Thursday morning. Skies will gradually clear later this evening into the overnight.
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As of 310 PM Wednesday... Thursday, the deep upper level low will scoot off the New England coast. It will remain breezy due to the difference between high pressure over the lower MS Valley and the deep low off of New England. A series of upper level perturbations in the nw flow aloft will pass overhead. During max heating, the lift provided by this system coupled with marginal moisture through the column may support a few isolated rain showers, primarily over the far northeast Piedmont into the coastal plain. At this time, it appears coverage will be too limited to mention in the forecast. A 850mb thermal trough to our nw will maintain low level cold air advection Thursday. This will result in max temps a solid 10-13 degrees below normal for late March, ranging from near 50 across the far north to the mid 50s across the south. Sfc high pressure will nose into central NC from the sw Thu night. this should allow the sfc winds to decouple. With the cool dry air mass in place, overnight temperatures should tumble into the upper 20s-lower 30s.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 100 PM Wednesday... A dry start to the long term for a day at least as surface high pressure lingers west of the area keeping skies clear but cool, with northwesterly downslope flow prevailing. This will keep high temperatures down in the lower 50s across the northeast to upper 50s in the southwest. Clouds will increase in the west on Friday night in response to a low developing over Missouri and a warm front extending eastward ahead of it. Any precipitation associated with this front will hold off until Saturday afternoon but a slight chance exists that precip could come in a bit earlier in the Triad. As the low approaches, it will begin to dive south of the area which could once again present some winter P-type issues for at least the northern half of the forecast area. Current forecast soundings along the I-40 corridor appear cold enough for at least a wintry mix of precipitation. There is a lot of uncertainty as far as the snow question is concerned. One is will there be enough moisture in the dendritic growth zone to support snow. Another is the amount of lift available through that layer. Temperatures are another concern especially further south and east because soundings indicating a possible weak warm nose that will play a role in determine exactly what falls from the sky. Bottom line is precip chances through the weekend are high, but north of route 64, it is unclear exactly what it will be. Southern portions of the CWA should bet on all rain at this point. Precipitation looks to end by Sunday evening which is welcome news for the morning commute on Monday which will be fairly cold but most likely unhindered by winter weather. Temps Saturday and Sunday in the upper 40s to low 50s. Monday will most likely start out very cloudy as high pressure to the northeast moves into a favorable location for cold air damming. This could present a drizzle threat for much of the day, especially in the Triad. Highs Monday still only in the upper 40s to mid 50s. By Tuesday the high starts to push southward over the Carolinas which may help to start to break some of the cloud cover and add a few degrees to the afternoon high, mid 50s. By Wednesday the high finally slips south and east of the area and a much welcome southerly return flow ensues. This will bring a very noticeable difference in the weather and the temperatures as highs climb into the low 60s across the north to near 70 degrees in the south. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... As of 135 PM Wednesday... Widespread MVFR ceilings will slowly lift to the low end VFR category after 21Z across central NC as drier air gradually overspreads the lower levels of the atmosphere. Sfc winds will become blustery, gusting 18-23kts through early evening, mainly across the northern terminals. Skies will gradually clear from the sw this evening with mostly clear skies expected most TAF sites after 08Z. The VFR conditions expected to persist through Friday morning. Another period of unsettled weather is anticipated late Friday through the weekend into Monday as a series of low pressure systems affect our area. This will likely lead to extended periods of sub VFR ceilings with instances of sub VFR visibilities due to precipitation, some of which may be wintry in nature late Saturday through early Sunday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...KCP NEAR TERM...WSS SHORT TERM...WSS LONG TERM...Ellis AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.