321 FXUS62 KRAH 280612 AFDRAH AREA FORECAST DISCUSSION National Weather Service Raleigh NC 112 AM EST Fri Jan 28 2022 .SYNOPSIS... Canadian high pressure will weaken over the Mid Atlantic and Carolinas today, while low pressure organizes off the Southeast coast. That coastal low pressure will undergo rapid intensification off the coast of NC and VA tonight, as a vigorous mid and upper level trough pivots east across the Carolinas. Arctic high pressure will follow and build across the Southeast through Saturday night. && .NEAR TERM /THROUGH TONIGHT/... As of 840 PM Thursday... Current forecast is in good shape. The surface ridge centered over and just off the Delmarva peninsula and NJ will continue to ease eastward overnight. A batch of moisture to our west in the 700-500 mb depth with a swath of upglide at 295-300K will continue heading E from KY through NC through Fri morning, supporting the forecast trend from partly cloudy to mostly cloudy skies. Temps have fallen off this evening but this should slow a bit with the incoming clouds, despite the current dewpoints in the mid teens to lower 20s. Only minor tweaks to lows in the 20s. -GIH Previous discussion from 326 PM: Visible satellite shows high clouds exiting off the NC coast and leaving clear blue skies across the region, which will remain into early tonight. In the upper levels, a positively tilted shortwave is evident on water vapor imagery which extends from the upper Great Lakes down towards the Four Corners region. Upstream of the trough axis there is a jet streak over west- central Canada that will dive south tonight and further amplify this shortwave trough, and tilt towards a neutral orientation, as it moves eastward overnight. The downstream resulting southwesterly flow aloft will usher in mid-level moisture increasing cloud cover late tonight. At the surface, high pressure will continue to weaken and lead to light to calm winds overnight. Lows will be warmer compared to this morning due to the increased cloud cover providing better insolation overnight; leading to mid to upper 20s area wide. && .SHORT TERM /FRIDAY THROUGH SATURDAY/... As of 300 PM Thursday... ..Accumulating snow expected Friday evening/night through early Saturday.... Overview: A potent mid-level shortwave trough over the southern Great Plains Friday morning will dive eastward and will continue to deepen/amplify as the two branches of the jet stream collide over the Carolinas and SE US Friday night/early Saturday. In response to the incredibly strong synoptic scale ascent/h5 height falls, an area of low pressure will spin up off SE coast Friday morning and will then to undergo rapid deepening and quite possibly bombogenesis late Friday night/early Saturday as it races north, well off the NC coast. Friday: Given that the coastal low will be well offshore, central NC will see little to rain from the coastal system and thus it will remain mostly dry through the daylight hours. Highs ranging from lower 40s north to mid/upper 40s south. Friday night: The arrival of the strong forcing/lift associated with the amplifying northern stream trough diving into the region Friday evening, coincident with a surface cold front that will push southeast through the area, will lead to the development of precip back across the western NC that will push east overnight. The resultant deep column cooling will result in a fairly efficient/quick change-over from rain to snow, with any transition p- type of freezing rain/sleet being very short-lived and inconsequential. Biggest question and largest source of uncertainty continues to be just how precip/moisture will be available over interior/inland sections Friday night. There has been a rather significant change in the model guidance over the past 24 hours, trending wetter across the western Piedmont, and drier/less precip across the coastal plain/I-95 corridor, in response to a mid-level dry slot that models are starting to hone in on. Liquid equivalents are expected to range from a around 0.20" across the west to just under 0.10" across east NC. As one can see, this margin of error is razor-thin in terms of precip forecasting and can easily make or break a forecast. With that said, the latest forecast now shifts the highest snowfall totals across the western Piedmont, where the highest water- equivalent is forecast and where the best potential for banding exists. Expect most areas along and west of US 1 to see light snow of 1 to 2 inches, with the potential for some very localized/focused higher amounts over the western/NW Piedmont. Conversely, given the trend of lower liquid amounts across the coastal plain with the dry slot, snowfall totals are generally less 1 inch with the potential for some locations to see as little as a dusting. Given there is still quite a bit of model spread and forecast uncertainty, will hold off on issuing any headlines with the afternoon package, deferring in hopes that forecast confidence will continue to increase upon review of the full suite of 00z/28 model guidance. Saturday and Saturday night: Any lingering snow across the coastal plain counties will exit the a little after daybreak. Expect cold and blustery conditions(wind gusts of 25 to 35 mph), in the wake of the deepening low pressure system moving up the northern Atlantic coast with yet another shot of cP air into the SE US. Highs in the upper 20s/lower 30 north to mid 30s south. However, the blustery winds will result in wind chills/apparent temps in the teens to lower 20s! Clouds should scattered out with sunshine returning from west to east during the late morning and into the afternoon. Winds will eventually decouple overnight making for very cold temps Saturday night, especially in areas where there is adequate snow cover. Lows ranging from lower teens north to upper teens south with wind chills in the single digits north to lower teens south. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 245 PM Thursday... A clipper system on Sunday across the Great Lakes will dive southeast into the Mid-Atlantic Sunday afternoon and evening, before moving offshore overnight into Monday. The only impact from this will be mid and high-clouds streaming into the Carolinas as the low to mid-levels are very dry with surface dewpoints in the single digits. At the surface, high pressure over northern FL and low pressure over OH will favor return southerly flow to push highs into the upper 30s in the NE to the low to middle 40s in the S and SW. Clouds Sunday night and continued stirring of the surface winds with the clipper will result in overnight lows warmer but still below normal in the low to middle 20s, with some lower temperatures in areas with residual snow cover. Mon-Wed: Northwest flow at mid and upper levels will eventually transition to a more quasi-zonal to west-southwesterly flow by midweek. This should favor a gradual warming trend with highs in the upper 40s to lower 50s Mon rising 5-9 degrees above normal to the mid-upper 50s/low 60s by Wed. An 80-90 kt jet streak oriented northwest to southeast from the Great Lakes into western NC on Mon may promote orographic cirrus during the day and early afternoon, but otherwise quiet weather is forecast. At the surface, an approximately 1030 mb high pressure over SE Quebec will slowly move southeast over the North Atlantic by Wed. This will favor east- northeast flow becoming east-southeast by midweek. Thu: The latest deterministic model guidance is in relatively good agreement for our next weather system to approach the area during this period. The GFS/ECMWF show a deep mid-level shortwave trough on Wed over the southwest US that tracks east into the Midwest and Ohio Valley Wed night into Friday. Though timing differences are present, the surface pattern shows a 1045 mb arctic high over the Dakotas, with a cold front diving south into the Great Plains and Midwest Wed- Thu. The GFS/ECMWF/CMC develop a wave of low pressure along the arctic front, tracking up into the Great Lakes Thu night. Warm air ahead of the front will result in only rain showers with no ptype issues. A look at the latest ensemble guidance, the GEFS is slightly faster than the deterministic GFS/ECMWF on precipitation timing, while the NAEFS/EPS are slower, with the favored period being Thu- Fri as the arctic front approaches. Have trended toward the slower guidance, with the highest PoPs over the northwest Piedmont. The trend looks wet nonetheless with EPS mean precipitable water values around 1 inch Thu. Highs Thursday are expected to be in the low to upper 60s, with lows in the low to upper 40s, some 10-15 degrees above normal. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... As of 110 AM Friday... Periods of mid and high-level (VFR) ceilings will continue across cntl NC today, downstream of a vigorous upper level trough that will amplify across the MS and TN Valleys. Lift and a related band of precipitation accompanying that trough will pivot east across cntl NC tonight. The precipitation will likely begin as a brief period of MVFR rain at INT/GSO, then transition to moderate to heavy snow with LIFR conditions for a few hours after 00Z Sat. The precipitation band, initially rain then changing to snow --and sub-VFR conditions-- will then likely arrive at RDU and FAY around 06Z and RWI between 08- 12Z Sat. Lastly nwly surface winds will become strong and gusty into the 25-35 kt range with the passage of an Arctic cold front and following very cold/dry air and return to VFR conditions that will sweep east across the region overnight. Outlook: Once conditions improve to VFR from west to east late tonight into Saturday morning, VFR conditions are then expected to persist through Tue. && .RAH WATCHES/WARNINGS/ADVISORIES... None && $$ SYNOPSIS...MWS NEAR TERM...Hartfield/Swiggett SHORT TERM...CBL LONG TERM...Kren AVIATION...MWS