textproduct: Wilmington

WHAT HAS CHANGED

Continue to adjust the snowfall forecast with locally higher amounts.

KEY MESSAGES

1) Accumulating snow across southeast Indiana, southern Ohio, and northern Kentucky today leading to impacts on the late morning and evening commutes.

2) Clipper moving across the area Friday with light snow accumulations possible and frigid temperatures to start the weekend.

DISCUSSION

KEY MESSAGE 1) Accumulating snow across southeast Indiana, southern Ohio, and northern Kentucky Tuesday into Tuesday evening leading to impacts on the evening commute.

Forecast update: Headlines remain the same across the area early this morning based on the latest guidance. While total snowfall amounts were still increased within the advisory area, there was not enough confidence to go with a localized warning at this time given several factors which could limit the higher end solutions (see below). The decision to upgrade to a warning may come later this morning if these negating factors are overcome.

Analysis: Latest regional radar is already showing signs of weak frontogenesis over Indiana and eastern Illinois ahead of the approaching low pressure system. These light radar signatures are ahead of the approaching shortwave, which is featured by a band of snow from Iowa to Illinois. Despite the signatures on the radar, ground observations do not indicate any of this is reaching the ground. The 00Z sounding from ILN revealed a fairly significant layer of dry air in the mid-levels. This may delay the onset of the heavier snow until mid to late morning, decreasing the potential for higher snowfall amounts.

As the shortwave pivots through the Ohio Valley today, frontogenesis in the lower levels of the atmosphere will combine with jet stream dynamics provided by the right-entrance region of the upper level jet. This will help to moisten the dry layer, allowing snow to reach the ground. Additionally, forecast soundings show lift occurring within the DGZ, producing large snowflakes. In the lower levels of the atmosphere where temperatures are close to melting, these large flakes are likely to stick together, resulting in effective accumulation despite any melting/compaction over time. Noted well in previous discussions, these combining factors will set up a scenario for locally heavy snowfall rates in bands throughout the late morning and afternoon. HREF guidance suggests snowfall rates of a half inch to three- quarters of an inch per hour at times. Despite surface temperatures near freezing and solar radiation, area roadways would likely struggle to remain wet in these higher rates. In locations where the rates are not as heavy, impacts to roadways may not be as enhanced.

Snow begins to end from northwest to southeast throughout the afternoon and early, pulling completely out of the area by late this evening. Temperatures continue to drop into the evening and overnight hours, which means some roads may remain hazardous into Wednesday morning.

Snowfall totals were put together using a mix of the more robust GFS and NBM/WPC. Have stuck with the generally 1-3" wording with a stretch of counties from northern Kentucky into southern Ohio having the best chances of reaching 3". If the localized banding can set up and remain robust, 4-5" amounts will be possible given the supporting items discussed above.

KEY MESSAGE 2) Clipper moving across the area Friday with light snow accumulations possible and frigid temperatures to start the weekend.

While a trend toward less snow has been mentioned in previous discussions regarding this system, recent guidance has trended stronger with the shortwave dropping through the Great Lakes Thursday night into Friday. Accumulating snow certainly remains on the table for much of the area, with the tri-state/Cincinnati metro seeing less snow compared to central parts of Ohio. A 2 to 3" snowfall event would be likely in this area if trends continue.

Another blast of frigid air would follow this system, with both days of the weekend seeing below zero wind chills. While confidence is fairly high on these frigid temperatures occurring, confidence is also fairly high that this would be a short-lived situation as deep layer ridging builds into the central CONUS early next week.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

MVFR CIGs continue this morning as the system begins to move in. Cannot rule out some breaks in the MVFR CIGs early, but as snowfall begins, these conditions should be more persistent. Confidence remains high on snowfall impacts to CVG/LUK/ILN, with lower confidence at DAY, and especially CMH/LCK. Overall, timing still looks good, but there could be some delayed onset due to dry air aloft. Expect IFR/LIFR restrictions in snow, with lingering MVFR CIGs into the evening and overnight hours. Conditions generally improve to VFR late in the period, but some lingering MVFR conditions are possible.

Winds are light and variable as the low pressure moves south of the area.

OUTLOOK...MVFR CIGs will linger into Wednesday.

ILN WATCHES/WARNINGS/ADVISORIES

OH...Winter Weather Advisory until 10 PM EST this evening for OHZ070>074- 077>082-088. KY...Winter Weather Advisory until 10 PM EST this evening for KYZ089>100. IN...Winter Weather Advisory until 10 PM EST this evening for INZ066- 073>075-080.