Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 280923 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 423 AM EST Tue Feb 28 2017 .SYNOPSIS...
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A warm front will lift northward across the area this morning providing a chance of showers and possibly a thunderstorm. Tonight an upper level disturbance will move over the region providing another chance of showers and thunderstorms. Some thunderstorms could be severe with locally heavy rain. During the afternoon Wednesday a cold front will sweep across the region with gusty winds possible behind the front. Colder conditions will be in store for the region through Saturday morning with a chance of snow early Friday morning.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Showers and isolated rumbles of thunder have started to move into Indiana this morning as strong low level WAA moves over the area. Looking at GFS isentropic surfaces also reveals the best lift and saturation further towards the north. GFS and NAM forecast soundings show a surface inversion across our area with weak elevated instability. The GFS is more restrained with the elevated instability while the NAM is slightly more robust. Overall thinking is in a slight decrease in lightning activity as storms move this way towards sunrise. Later this morning into afternoon showers and isolated thunderstorms from earlier will weaken across the central and northern zones with a warm front clearing the northern zones of the CWA before noon. As this occurs the surface inversion from this morning will slowly erode. Latest RAP, GFS, HRRR then show an upper level disturbance pushing northeast and clipping our southeastern zones. Also at the time an upper level jet streak will rotate north and east and approach the area. This is thanks to an upper level disturbance pushing east across AZ/ NM. The jet streak pulling north will likely translate into widespread showers and thunderstorms across KY/ TN this afternoon with the northern extent being around Interstate 71. Moisture wise PWATs around 1.20" (90th - 97.5th percentile for this time of year via NAEFS) will be easily found across the CWA with higher values preferred towards the south and east. Given the best lift, track of the upper level disturbance, and moisture values mentioned above have kept highest PoPs towards the southeastern zones this afternoon. Any storms that form this afternoon do have the potential to become severe as sfc- 3 km shear values will be mostly greater than 40 kts. The main inhibiting factor will be the lack of surface based instability. This means that the effective shear will still be impressive but less than mentioned above.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
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Tuesday evening will likely see a brief decrease in coverage as the weak disturbance from this afternoon exits. Coverage will remain light until the upper level disturbance that was over AZ/ NM rounds the base of the upper level trough axis and heads northeast. As this occurs vorticity will spill northeast towards the CWA with the upper level jet streak rotating northeast. A split in the upper level jet will occur across northern KY and southern OH with a surface low tracking northeast towards Chicago. As this happens many high res models show a complex of showers and thunderstorms pushing northeast towards the region. The ARW, NMM, WRF DART, and NCEP WRF all show this feature moving into southern OH around 6z. During this time forecast soundings destabilize across the region with PWATs approaching 1.30" on the NAM and GFS. SFC to 3 km shear is forecasted to between 40 and 50 kts with SFC - 3km SRH exceeding 300 m2/s2. Mean flow is also from the southwest at around 60 kts. Lapse rates will be around 7 degrees C/ km which coupled with ML CAPE values of 300 to 600 J/kg will support the possibility of some severe hail. Given the parameters above all threats appear to be in play. SPC has also highlighted the area in an enhanced possibility of severe weather for day 1. Day 2 enhanced also clips of southeastern zones. High res models show this complex of storms then moving east of the area between 9 and 12z. Towards our northwest though (northern IN/ IL) a squall line will likely form as precipitation from the upper level disturbance moves over our area. The main question will then be whether the squall line hold together as it dives southeast. High res models are mostly split on this. Given the strong upper level forcing think the squall line will hold together. The primary severe threat timing will be starting around 4z and continuing though Wednesday morning until the squall line clears the area. It should also be noted that heavy rain will also be possible with these storms. In particular where the first round of showers and thunderstorms moves over Wednesday morning. 6 hr FFG is generally greater than 1.80" across the area which is right on the border of expected rainfall totals. Overall guidance suggests that heaviest rainfall amounts will be across our southeastern zones which makes sense given the placement of the upper level lift. WPC also has the entire area in a marginal for excessive rainfall with the central and southern zones in a slight. Wednesday morning into afternoon the main upper level trough axis will push east with the best upper level lift heading east as well. A cold front will approach the western zones late Wednesday morning. Timing with the front appears to be in good general agreement with the GFS only being slightly faster. Some high res models have the squall line from earlier aligning more with the cold front while other models have the squall line racing ahead of the front. Given the placement of the upper level lift have trended forecast to show the squall line moving ahead of the front. As the cold front passes through the area Wednesday afternoon strong low level CAA will follow. PWATs will also plunge to around 0.30". As this happens lapse rates will steepen allowing strong low level winds to mix down to the surface. NAM forecast soundings are showing gusts around 35 mph possible with the GFS showing wind gusts of 40 to 45 mph possible. Overall have kept forecast trended towards the NAM. Given the above a wind advisory might be required for Wednesday afternoon.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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A clipper like system will drop out of southern Canada Wednesday night and into the upper Ohio Valley Thursday into Thursday night. This will be accompanied by an associated low level trough axis and a secondary shot of CAA. This will lead to an increasing chance of showers later Thursday afternoon into Thursday evening before tapering off later Thursday night as the system pushes off to the east. Initially, low level thermal fields are supporting mainly rain, but as we start to cool down, we should see a transition over to snow as we head into Thursday evening. The models are trying to latch on to some very weak short wave energy dropping quickly southeast across our area Friday night into Saturday. This could lead to a few snow showers, especially across northern portions of our area. We will then transition to more of a zonal pattern as we head through the weekend. Short wave energy will move across the Great Lakes region Sunday night into Monday, bringing the next chance of rain showers toward the end of the long term period. Highs on Thursday will be in the 40s, cooling into the mid 30s to lower 40s for Friday. Unseasonably warm temperatures will then return through the end of the period with highs by Sunday and Monday back up into the upper 50s to lower 60s.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/... Most TAF sites are VFR this morning with high pressure off to our east and low pressure off to our west. High and mid clouds are starting to move into the area but not before KLUK had a chance to fall to VLIFR. As the high and mid clouds have moved in from the west though visibilities have tried to recover a bit which isn`t surprising. Have gone ahead and shown this on the TAFs. This morning a warm front will lift north across the area with models showing a good swath of precip ahead of the warm front (mostly north of the TAF sites initially). Precipitation will likely then fill in south as the latest run of the RAP has a shortwave pushing through the area just after sunrise. Forecast soundings at this time show a surface inversion which will limit surface based instability but some of the high res and global models have enough elevated instability that thunder will be possible. Overall thinking for morning precipitation is that most of it will be shower based with some embedded thunder. During the afternoon hours as the warm front moves north of the area the surface inversion will erode. As this happens the chance of thunder will grow. The main inhibiting factor to development of precipitation in the afternoon will be the likely cirrus shield overhead from morning precipitation. Still though, the RAP is showing another shortwave moving across the southeastern zones Tuesday afternoon. The RAP, HRRR, ARW, NMM all hint at precipitation developing thanks to this lift. Tuesday evening as the shortwave exits the region there should be a brief break in the precipitation before the next round of showers and thunderstorms moves into the area from the southwest. This next batch of precipitation will likely move into the area around midnight Wednesday morning. The latest NMM, ARW, NCEP WRF all show this third round of precipitation moving in just with slightly different timing. Timing will likely have to be adjusted for future TAF packages. OUTLOOK...MVFR ceilings may linger Wednesday afternoon and night. In addition, wind gusts to 35 kt will be possible during that time. MVFR ceilings and visibilities will be possible again Thursday night into Friday morning. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Haines NEAR TERM...Haines SHORT TERM...Haines LONG TERM...JGL AVIATION...Haines

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