Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 050106 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 806 PM EST Sun Dec 4 2016 .SYNOPSIS... An upper level disturbance will move across the region today bringing mostly rain with snow possibly mixing in across the north. Drier conditions are expected on Monday, as high pressure moves into the area. On Tuesday, an area of surface low pressure is expected to move into the Ohio Valley, bringing rain to the area. Behind a cold front on Wednesday night, much colder conditions are expected through the end of the week. && .NEAR TERM /THROUGH MONDAY/... Starting to get reports of light rain across our northwestern zones (and sleet in Wayne County, IN). This is thanks widespread isentropic lift across the area along with a shortwave approaching from the west. Looking at the latest high res models confidence has built that rain will likely transition to a rain/snow mix and then transition to all snow possibly across our far northern counties (Mercer, Hardin, Auglaize). This transition will likely be driven by stronger upward motions and adiabatic expansion from lower pressures (dynamic cooling). The latest HRRR run shows these northern counties actually transitioning to all snow around 23z with some light accumulations on grassy surfaces possible. There may be some accumulations on roadways (esp. elevated surfaces) which could cause some slick spots but this should be transient. Have covered this in the HWO. All the three metro areas and south should stay all rain. The upper level shortwave will start to take on a negative tilt and eject northeast late this evening with precipitation coming to an end across the area around midnight. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... Monday morning a weak surface high pressure will move overhead behind the shortwave trough that moved through the area Sunday. Global models are showing some clearing Monday but there remains a sharp inversion in both GFS and NAM forecast soundings around 920 mb which could help trap some low level moisture. Looking at ECMWF, GFS, and NAM rh fields a potent surge of dry air is expected to move into the area and have allowed skies to clear a bit. High temperatures Monday will likely have trouble getting much above the mid 40s as 1000/ 850 mb thicknesses (~1305 m) support highs only in the mid 40s. Given the above mixing is only forecasted to be around 925mb so have backed off on high temperatures a bit for Monday. The weather pattern will be quick to change Monday night as an upper level low currently over northern Mexico (as of Sunday afternoon) will begin to head northeast Monday afternoon with a coastal low forming. This surface low will be near the Tennessee valley Tuesday morning and move just southeast of the area Tuesday afternoon. Current thermal profiles support rain across most of the area with the NAM and GFS trying to show a brief change over to snow across the far northern zones. Overall the GFS, ECMWF, and NAM are in pretty good agreement with the timing of the surface low which would still support non- diurnal temperatures. Have adjusted the timing of the precipitation onset a bit for Tuesday while also adding a brief period of rain/snow for our far northern counties. The surface low will also help bring deep gulf moisture northwards with PWATs on GFS/ NAM forecast soundings rising to above 1" Tuesday. These PWATs are also shown on the NAEFS which are 1 to 2 SDs above normal for this time. Given the above have kept PoPs categorical with storm total amounts of 0.50" - 1.00" of rain possible Tuesday. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... This period will be characterized moreso by temperature impacts rather than precipitation impacts - though the latter will still need to be watched on late Wednesday night/Thursday morning...and again later next weekend. Confidence assessment - there`s really pretty decent agreement in larger scale evolution of the flow into next weekend between higher resolution deterministic runs and parent ensemble means. There`s much higher confidence on temperature evolution Wed-Sun vs. precipitation...with the season`s first /well advertised/ cold spell centering on Friday with temp departures some 10-20 degrees below normal. Wednesday/Sunday can be viewed as transition days into /Wed/ and out of /Sun/ the thermal trough but this entire period will average out well below normal. Precipitation type/timing is much more problematic and of much lower confidence - with notably two decent changes at synoptic scale forcing/vertical motion. The first is with shortwave energy rippling along the advancing cold front Wednesday night/Thursday morning...the second is progressive shortwave energy across the Great Lakes next weekend. Very low confidence with the forecast next Sat/Sunday - as it is noted that ensemble plumes /GEFS and ECMWF/ get extremely noisy in Days 7-10 suggesting the pattern is of very low confidence with how the energy next weekend evolves. Both data show the deterministic runs trending away from their respective ensemble means by Day 8...suggesting caution in next weekend`s forecast. All that being said - however - Wednesday there is rather high confidence in a dry day downstream from approaching height falls moving through the Plains. Most recent /04.12z/ ECMWF has caught up in speed to GFS/GEFS which was a disagreement source early on. Advancing strong cold front and strengthening shortwave trough have had hints of developing a weak frontal wave as it approaches the area Wed night/Thursday morning...with deterministic ECMWF /04.00Z and 04.12Z/ consistent with a stripe of modest QPF enhancing on the cold side of the strong cold front which may be worthy of some light snow accumulations north of the Ohio River...but agreement in this scenario has less /GFS/ to much less /CMC/ agreement outside the ECMWF/ECMWF ens spectrum for anything more than mid-range snow chances at this time. Once this front/frontal wave passes...cold air blasts in but is progressive. -16C at 850mb is significant for mid-December on Thurs night and thus have no problem accepting mid/upper teens for lows and mid/upper 20s for highs Fri through this brief cold spell. Moderation begins on Saturday with temps back toward 30 on Saturday. Some cold advection flurries/snow showers are possible both Thursday/Friday...particularly across central Ohio in favorable trajectory off Lake Michigan...but coverage expected to be spotty. Per confidence assessment above - not a great deal of confidence how shortwave energy and associated rain/snow chances look for Sunday and this lingers beyond Day 7 depending how energy ejects within the upper trough. For right now have middle-range snow chances developing Sunday with transition from south to north given warm advection...but we`ll need to see more data before any potential impacts are. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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Rain associated with a trough of low pressure has overspread all TAF sites late this afternoon. Ceilings and visibilities have lowered into the MVFR category, with IFR ceilings likely and LIFR possible tonight as rain departs to the east. A period of Mixed snow in at kCMH and kLCK is possible late this evening prior to ending. Slow improvement to MVFR will occur Monday morning with lingering low level moisture. Clouds will clear from the southwest to northeast with VFR developing Monday afternoon. OUTLOOK...MVFR/IFR ceilings and MVFR visibilities expected Tuesday with rain. MVFR ceilings to linger Tuesday night into Wednesday morning.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Haines NEAR TERM...Haines SHORT TERM...Haines LONG TERM...Binau AVIATION...AR

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