296 FXUS62 KRAH 182017 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 317 PM EST Mon Feb 18 2019 .SYNOPSIS... Cold high pressure will move across the Great Lakes on Tuesday and then extend south into the middle Atlantic and Carolinas. A storm system will approach from the southwest late Tuesday and move across the region on Wednesday and early Thursday. && .NEAR TERM /THROUGH TUESDAY/... As of 135 PM Monday... Temperatures over performed a bit during the day Monday, primarily thanks to the rapidly clearing skies behind the FROPA along with delayed and weaker than progged CAA regime struggling to make it east of the mountains. Afternoon temps have been able to warm into the low to mid 60s area wide. Tonight, expect partly cloudy skies, with lows dipping into the low to mid 30s. High pressure will continue to track eastward across the Great Lakes Monday night into early Tuesday, before descending south along the lee side of the Appalachians in CAD like fashion. With a shallow area of cool northeasterly flow at the surface and weak WSW flow aloft, expect clouds to clutter rapidly Tuesday morning and begin to descend throughout the day. This will help to inhibit high temperature potential, with highs only expected to reach the mid 40s area wide by mid to late afternoon. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... As of 315 PM Monday... ...Continued threat of light icing and a wintry mixture across the interior and northern Piedmont late Tuesday night into Wednesday morning... A strong and cold 1038 hPa high pressure system will move into the PA/NY region Tuesday night and weaken as it pushed off the New England coast late Wednesday. The high is transient but located in a favorable location to establish a CAD regime late Tuesday that will extend into Thursday. Dry air with surface dew points in the teens will extend south from the DC area across eastern VA into eastern NC on Tuesday afternoon. At the same time, a strong upper level trough will exit the western U.S. and move into the Central Plains as a 100+ kt jet develops over TX and moves northeast on Wednesday. A strengthening low and mid level southerly flow will moisten the atmosphere and provide lift across central NC late Tuesday through Wednesday night providing periods of precipitation. As with many winter storms, the arrival of the cold air and the precipitation will be key to the p-type and impacts. A band of light precipitation driven by mid level warm advection will lift north across the western Piedmont Tuesday evening producing an area of light precipitation, mainly in the form of rain but some sleet may be mixed in. This will be conversational in nature and should have no impacts given temperatures in the lower 40s. As the low level flow strengthens ahead of the approaching upper level trough, isentropic lift will increase primarily in the 295 to 300K layer resulting in a region of largely low and mid level ascent. This results in area of warm advection precipitation that will overspread the region from southwest to northeast between midnight and daybreak Wednesday morning. Forecast soundings suggest that the deep layer moisture and ascent will be confined below 600 hPa. Given this and the strong warm nose that develops at 800 hPa Wednesday morning with a southwest flow at 50 kts, don't expect much snow although a few flakes could mix in toward the VA border around midnight. The precipitation will produce some wet bulb cooling as the surface layer becomes saturated. Not surprisingly the NAM is the coolest guidance with the wet bulb freezing line pushing south into northern Richmond, Cumberland and western Wilson counties which should serve as the farthest extent of any freezing rain potential. The GFS is notably warmer in the surface layer Given the GFS is notably warmer at the surface and similar in the partials. Will lean toward the cooler NAM solution given its skill to handle these patterns more skillfully. This will support a changeover from rain to freezing rain as temperatures fall to 32 or 31 in the damming region from Albemarle to Raleigh to Warrenton northwestward. Given the marginal surface temperature, the light precipitation amounts, some lulls in the precipitation and moderate temperatures ahead of the event, expect ice accumulations will be limited and mainly confined to locations near and north of I-85 where a light glaze is possible with radial ice accumulations of 0.05 inches or less. Temperatures will moderate ever so slightly After sunrise on Wednesday, and any freezing rain will diminish from south to north and end during the mid morning. Lows will range in the 31 to 32 range in the northern Piedmont and the mid 30s elsewhere. A well established CAD regime will remain in place on Wednesday and Wednesday night with periods of light rain continuing. Highs on Wednesday will range in the mid 30s across the Triad and in the mid to upper 40s across the Sandhills and southern Coastal Plain. Temperatures will be steady or rise a degree or two on Wednesday night under overcast skies and periods of light rain, drizzle and mist. Most NWP systems blast the CAD away on Thursday with the exception of the NAM. GFS MOS provides a high of 66 in GSO on Thursday and 77 at FAY. While the CAD should weaken, given the pattern and the lack of a well defined erosion mechanism, still feel it will remain in place longer and more resilient than much of the guidance says. Will undercut guidance and go with highs in the lower 50s in the Triad to the upper 60s southeast. Huge bust potential with the temperature forecast so stay tuned. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 315 PM Monday... A quasi-stationary cold front will sag south through NC on Friday before inching back north Saturday. This will allow numerous weather features to track from SW to NE across central NC, introducing rather persistent POPs from Friday morning through Sunday afternoon. Model QPF through this period varies from around a half inch across the Coastal Plain to just over an inch across the northwestern Piedmont, with locally higher amounts possible. Depending on how much precipitation falls earlier in the week, this may enhance the river flood potential late week. The persistent rainy pattern looks to come to an end on Sunday evening at the hands of a progressive FROPA expected to slide west to east across the mid Atlantic with high pressure filling in on its heels Sunday night into Monday. Overnight low temps through the period look to remain rather sturdy, with lows in the 40s predominantly ahead of the front, with some mid to upper 30s prevalent behind the early week FROPA. Highs vary a tad more, primarily thanks to another CAD event likely to strengthen Friday night into Saturday before eroding in a WAA regime on Sunday ahead of the front. Expect highs in the 50s on Friday, a rather large CAD induced gradient on Saturday (40s NW to 60s SE), low 70s on Sunday (assuming a complete CAD erosion in the warm sector), to low 60s behind the cold front Monday afternoon. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... As of 1250 PM Monday... VFR conditions are expected to continue at all TAF sites through the next 24 hours. High pressure will remain in control tonight before strengthening and building south in CAD type fashion on Tuesday. This will allow for, at times gusty, northwest winds to become more northerly/northeasterly overnight with CIGs beginning to thicken and descend as early as Tuesday afternoon. CIGs should remain above 5kft at all terminals at least through 18z Tuesday. Outlook: Deteriorating aviation conditions will continue Tuesday afternoon/evening, with MVFR/IFR CIGs and VSBYs arriving as early as Tuesday night before persisting into Wednesday. Some light icing will be possible, primarily at KINT/KGSO but plausibly at KRDU/KRWI Wednesday morning as temperatures fall close to freezing. The light sleet/freezing rain mixture should transition back to all rain by late morning, with poor aviation conditions likely to persist much of the week as several rounds of rain showers are expected to impact the central NC terminals. && .EQUIPMENT... KRAX is still suffering from poor data quality issues in the 0.5 and 0.9 degree elevation slices. This will impact several radar products, including rainfall estimates. Users should use the data with caution. We appreciate your patience as our engineers and technicians solve the problem. We will provide updates when they are received. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Blaes NEAR TERM...JM SHORT TERM...Blaes LONG TERM...JM AVIATION...JM EQUIPMENT...RAH