Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230719 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 315 AM EDT Fri Mar 23 2018 .SYNOPSIS... Cold high pressure will continue to build in from the northwest today, before moving offshore Friday night. An area of low pressure will approach from the west Saturday and cross our region Saturday night and Sunday. && .NEAR TERM /TODAY THROUGH FRIDAY NIGHT/... As of 315 AM Friday... Mid level ridge axis has shifted offshore, with surface high pressure over the western Great Lakes edging in to maintain cool air advection today, suppressing high temperatures despite strong sunshine. Pressure gradient relaxes during the afternoon, with lighter northwest winds than past couple of days, 10-12 mph gusting to 20 mph. Will thus be a little more pleasant given highs edging up slightly to mostly mid 50s north, with potentially some low 60s in the southern counties. Initially clear skies with a cool airmass in place will allow for decoupling early tonight and mins will fall to the mid 30s across the north towards midnight, with temps bottoming out within a degree or two of freezing across the northern tier by morning to mostly mid 30s across the south. Concurrently, a low pressure area will be migrating east across the Plains, which will back the low level flow and gradually increase moisture advection into the southwest Applachians after midnight. Precipitation will gradually spread eastward as the isentropic lift strengthens and the airmass saturates, but it appears that appreciable chances for rain or a mix of rain/snow will hold off until after sunrise Saturday morning. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 330 PM Thursday... A low pressure system forming over Missouri will drop southward through the Carolinas over the weekend bringing a fair amount of rain and possibly some winter P-Types to the northern portions of our forecast area. Synoptically this system is neither a true Miller A or B scenario as the low drops in from the northwest instead of from the southwest and true secondary low never forms west of the mountains. Most of the jet dynamics with this system remain well to the north of the area, but as the low comes through Early Sunday morning an upper level jet streak passes to the southwest which will help bring some lift to the area. There is high confidence that this event will bring a good amount of rain to the area through the weekend, which won`t be favorable for any outdoor plans. At this time, models are predicting up to an inch of rain for this event with higher amounts across the northern half of the forecast area. Winter P-Types: There are many factors that make this a low confidence event for winter p-types at this time. An analysis of surface wet bulb temperatures show period Saturday morning of below zero wet bulbs across the Triad and VA border counties. The best chance for some snow mixing in would be right around 12z but the precipitation may not actually be in the Triad yet at that time or just arriving. When it does, it will have a lot of dry air to overcome in the low levels making sublimation a possibility for any snow. By the time those surface layers moisten up, temperatures may be too high to support snow. At that point, expect much if not all of the precipitation on Saturday to fall as rain. Expect high temperatures in the low to mid 40s across the north with mid 40s to low 50s in the south. Sunday morning will be the best chances for some accumulating snow as thermal profiles are more supportive of it and moisture and cold air are in place simultaneously. The problem is that forecast soundings lose a lot of the lift at this time and moisture in the dendritic growth zone is drying out. That would favor more sleet than snow. Therefore have added very small accumulations north of I- 85 and east to Halifax of less than a half of an inch on Sunday morning. Otherwise this should be a rain or rain/sleet event for points south. Sunday, temps will be in the low 40s across the Triad for highs with closer to 50 degrees in the south. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 130 PM Thursday... Mostly dry weather is expected during the beginning and mid part of the work week, although the clouds should hang on through at least Mon evening (and perhaps into Tue in the western CWA) as a semi- anchored surface high, centered over SW Quebec into the Maritimes, ridges SSW through NC, locking the wedge air mass over central NC. Mid level ridging will steadily build over the eastern CONUS through mid week, between deep closed lows over the Desert Southwest and over the NW Atlantic, ensuring a lack of forcing for ascent and continued tranquil weather (albeit with periodic cloudiness). Model solutions start to diverge Wed/Thu with the GFS trending more progressive, weakening and lifting out the NW Atlantic low, which allows the E Coast ridge to weaken and move east. The ECMWF and Canadian keep the Atlantic low in play with a southward drift, which keeps the mid level ridge over the Southeast. The slower blocking pattern is preferred, which will mean a trend to increasing sunshine and warming temps starting Tue and especially Wed/Thu, when low level thicknesses will reach or exceed seasonal normals with a modifying surface air mass. -GIH && .AVIATION /06Z FRIDAY THROUGH WEDNESDAY/... As of 115 AM Friday... 24 Hour TAF Period: VFR conditions will continue through the 24 hour TAF period as surface high pressure moves across the southeast U.S. Skies will be mostly clear/mostly sunny skies today, with mid/high clouds beginning to stream after 00Z from the northwest ahead of a mid level short wave. This wave will icrease moisture advection into the west, with ceilings lowering progressively, although remaining VFR, through 12Z Saturday. Outlook: The appproaching storm system will result in a trend to MVFR Saturday morning at INT/GSO/RDU, and Saturday afternoon at RWI/FAY. Meanwhile, precipitation will be spreading in from the NW, with ceilings at INT/GSO trending to IFR Saturday afternoon. The precipitation is expected to start off as a wintry mix in the morning, changing to all or mostly rain by mid day. IFR conditions will be widespread Saturday night, with a trend to MVFR Sunday, and further to VFR by Monday. VFR is expected for the remainder of the mid week. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...mlm NEAR TERM...mlm SHORT TERM...Ellis LONG TERM...Hartfield AVIATION...mlm is the U.S. government's official web portal to all federal, state and local government web resources and services.