398 FXUS62 KRAH 120832 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 330 AM EST Tue Nov 12 2019 .SYNOPSIS... A strong cold front will cross central North Carolina this morning, ushering in chilly arctic air that will persist through Thursday. Surface low pressure will develop along the Southeast coast late Thursday, and this will combine with an approaching upper level trough from the west to bring rain chances late Thursday through Friday. && .NEAR TERM /TODAY THROUGH TONIGHT/... As of 330 AM Tuesday... We've got a lot of interesting weather coming at us over the next 24- 30 hours -- widespread moderate rainfall, plummeting temps to near record cold lows, a likely brief rain/snow/sleet mix across the north, and blustery and gusty winds producing cold wind chills tonight. The most noteworthy change this morning compared to yesterday is the growing potential for a short period of mostly wet flakes and/or sleet on the back edge of the precip shield in areas along/north of Highway 64. Let's tackle each of these weather concerns one at a time. Overall picture: Cold front is currently moving through E TN toward the Appalachians. Its anafrontal structure features the deepest forcing for ascent (including mid level DPVA with the approaching mid level trough and what is some pretty impressive upper divergence associated with a couple of ideally juxtaposed upper jet cores) along and behind the front. As such, we should see WNW-to-ESE frontal passage attending the front edge of the most widespread precip pushing through central NC 10z-17z, with the back edge of this main precip shield crossing central NC 18z-02z. High pressure and subsequent clearing will start pushing into the area tonight, as the mid level trough axis shifts through the area. Rainfall: Based on the latest hi-res model output and upstream observations, most precip rates should generally range from a few hundredths to a tenth of an inch per hour, although some SREF members and the HREF mean suggest 3-hourly totals of one quarter to one half inch. Given the good deep layer lift and 1"+ PW streaming into the area, these higher totals seem very achievable. With any given location seeing several hours of precip, expect storm total amounts from two-thirds to around one inch. Plummeting temps: Models have been in good agreement on the falling temps today, and we're already seeing this post-front to our W. While it should take a few hours for the coldest and most dense air to work past the higher terrain, the rain-cooled air combined with CAA will lead to a steady drop today. Daily highs will occur prior to daybreak, with temps falling into the 40s along/NW of I-95 (and into the 30s in the Triad) by lunchtime. Everyone should be in the 30s by early evening and in the 20s to around 30 by 2 or 3 am. Temps just before sunrise Wed will approach records (see climate section below). Non-liquid precip chances: As models converge on an agreed-upon common timing of precip and vertical thermal structure, confidence is fairly high that the northern Piedmont and northern Coastal Plain (roughly along and N of Hwy 64) will see some wet flakes and/or sleet pellets mixing in with the rain on the back edge of the precip. But based on how the strongest and deepest lift (including fgen and that aforementioned strengthening upper divergence) is lining up vertically and temporally with the arrival of the cold air and within the DGZ, I have some concerns that we'll see a short period of sufficiently high precip rates to switch us over to mostly snow and sleet for a brief time, although likely no more than an hour. While the ground should be warm enough to prevent accumulation there (NC State Climate Office agnet stations confirm this), heavy enough rates may produce a light coating on elevated surfaces. Confidence in this scenario is not high enough to warrant any mention of accumulation at this time. But this is certainly something to be watched closely this morning. Winds: Sustained speeds of 12-18 mph are expected just behind the front today, with frequent gusts to 20-30 mph possible, given model projections of 925 mb winds of 30-40 kts just behind the frontal zone. The strongest gusts should occur starting late morning in the Triad then translating through the western and southern CWA through the afternoon. Winds should decrease a bit this evening but remain elevated with periodic gusts as the denser air pours into central NC and surface winds veer to NNE. Wind chills are likely to bottom out in the teens late tonight. -GIH && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... As of 245 PM Monday... To be updated shortly. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 205 AM Tuesday... As the upper level trough shifts off to the east the upper level flow over central NC will back around to more westerly then southwesterly through Thursday. Meanwhile, a shortwave in the northern stream flow will amplify as it swings through the Northern Plains toward the western Great Lakes. A southern stream low will also progress eastward through the Southwest US and into the Gulf Coast region. For central NC, the forecast should be cool and dry through the day Thursday. Thursday highs will still be below normal, but as the onshore flow increases during the day, warm air will advect in from the east, resulting in about a 10 degree difference from NW (mid 40s) to SE (mid 50s). As the northern and southern stream trough/low interact and approach the region, the forecast becomes much more complicated. While the models have come into better agreement, the solutions still have some differences. The trend for Thursday night through Saturday has been wetter (closer to the previous ECMWF solutions). An upper low will cutoff in the southern stream on Friday over the Gulf Coast as the northern stream trough dampens. Rain could start over central NC could start as early as Thursday eve/night, however the best chances and highest amounts will occur as the low slides up the Southeast and mid-Atlantic coast Friday night/Saturday. The highest rainfall totals will likely be along or just off the coast. Gut feeling and past experience still lean toward keeping any precipitation that does occur primarily liquid. However, there is still a possibility, albeit small, that some rain could mix with or briefly transition to snow on the NW side of the low. Regardless, do not expect any measurable frozen precipitation, though where rain occurs amounts will be measurable and best chances/highest amounts will be farther east. The low should shift offshore and begin lifting northeastward on Sunday, with a primarily dry forecast on Sunday and Monday. Below normal temperatures will continue through the weekend, nearing normals early next week. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 110 AM Tuesday... Poor aviation conditions will dominate over much of central NC from around sunrise through at least mid afternoon. The current VFR conditions across central NC will give way to MVFR conditions toward sunrise at western terminals and by mid morning in the eastern terminals, as a cold front crosses the area. Most of the rain and low clouds will be near and behind the frontal passage, which will occur 10z-12z at INT/GSO, 13z-14z at RDU, and 14z-15z at RWI/FAY. Near and behind the front, cigs will lower to MVFR with VFR to MVFR vsbys in steady rain. A sudden wind shift from SW to NW and NNW will occur with frontal passage, with winds sustained around 15 kts gusting to as high as 20-30 kts, strongest at INT/GSO. Rain will taper down from W to E during the mid to late afternoon, and NW terminals should become dry with clearing skies by 21z while eastern terminals will trend dry/clearing by 00z-02z. Winds will diminish a bit by mid evening but will stay in the 10-15 kt range with a few lingering gusts to 20-25 kt (mainly at INT/GSO) through 06z Wed as cold air rushes in. LLWS is possible for the next several hours at northern terminals (INT/GSO/RDU/RWI), with a 1500-2000 ft AGL wind from the SW at around 35 kts. Looking beyond 06z Wed, surface winds from the N and NNE will continue to diminish overnight. VFR conditions will dominate into Thu morning beneath surface high pressure. Then, on Thu, an upper trough approaching from the W and surface low pressure forming near the Southeast coast will combine to bring potential sub-VFR conditions and rain for late Thu through at least Fri, possibly lasting into Sat especially in the E. -GIH && .CLIMATE... Some record minimum and low-maximum temperatures for this week may be in jeopardy. DATE RDU GSO FAY Min Low Max Min Low Max Min Low Max 11/12 22 1957 44 1895 17 1943 42 1934 21 1957 39 1987 11/13 23 1977 39 1911 22 1977 35 1907 23 1911 43 1976 11/14 20 1977 39 1976 19 1986 38 1904 23 2013 45 1997 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Smith LONG TERM...KC AVIATION...Hartfield CLIMATE...RAH