textproduct: Wilmington

SYNOPSIS

Brisk, cold, and mainly dry conditions will continue through today, with very cold temperatures continuing into tonight. A wintry mix of precipitation is likely Saturday into early Sunday as a system moves through the Ohio Valley, with the potential for some accumulating snow. Below normal temperatures are expected to continue into next week with another threat for winter precipitation on Tuesday.

NEAR TERM /THROUGH TONIGHT/

With the maintenance of a well-mixed BL and sufficient moisture within the cloud-bearing layer/DGZ, expansive cloud cover and scattered flurries will continue through daybreak through the morning before flurry activity tapers off from SW to NE by early afternoon. There is a signal for some SHSN activity to develop within a lake- effect corridor from NW OH through WC and central OH around sunrise, continuing through the morning. Have included a chance SHSN in these areas through this morning, with the potential for a trace or minor accumulations in the heaviest/most persistent activity. Otherwise, dry conditions will evolve area-wide into the afternoon with sfc high pressure moving in and the LL wind flow subsiding and becoming more westerly.

It is going to be another seasonably cold day, with highs again topping out in the lower/mid 30s. Some sunshine is expected from EC IN through the Tri-State into N KY by this afternoon, so some upper 30s cannot be ruled out in these areas.

SHORT TERM /SATURDAY/

Sfc high pressure will briefly drift into the region tonight before pulling off to the E quickly. Although skies will be clearing this evening, some mid/high clouds will overspread the OH Vly from the W into the predawn hours. Still, favorable radiational cooling conditions will allow for temps to dip into the upper teens/lower 20s tonight before plateauing late with the arrival of some better cloud cover toward daybreak and beyond.

After daybreak Saturday, attention will turn quickly to the approach of a system from IL/IN into late morning/early afternoon. Guidance has been trending a bit faster with the onset of pcpn, which may be as early as mid morning in parts of EC IN/WC OH. Although there is still some uncertainty regarding onset time and southward extent of the steadier snow, the latest data favors an initial band of snow pivoting into EC IN and WC OH by mid-morning owing to better WAA/isentropic lift nudging into the area during this time. The profile will saturate sufficiently to allow for SN to move into far W/NW parts of the area into the morning, with the band expected to drift to the NE into early/mid afternoon. Most of this initial activity will be focused from EC IN into WC OH, with locales near/S of I-71 likely remaining mostly dry into mid afternoon.

From an ensemble perspective, there has been a slight NW trend within the solution envelope across several datasets, with lends itself to questions regarding onset of mixed (RA/SN) pcpn near/SE oh I-71 into the evening hours as the steadier pcpn overspreads the region from the W. With this being said, the highest probabilities for at least 1"/2"/4" remain firmly NW of I-71 stretching from EC IN through WC OH, with probs for at least 1" ranging from less than 50% SE of I-71 to over 90% from EC IN into WC OH. The probs for at least 2" by Sunday morning are generally less than 25% near I-71 to over 75% from EC IN through WC OH. So the Winter Storm Watch is well-placed at this juncture as it relates to highlighting the area of greatest concern for several inches of snow. There is still some uncertainty whether warning-level criteria will be met in these areas, with only about 25% probability based on latest NBM output. But the watch is well- placed to highlight the greatest potential for at least 2-4" of snow, which seems reasonable given the latest data and the longer period of SN expected for these areas from Sat AM into late Sat night.

One item to mention is that ground temps and untreated surfaces will be very supportive for quick accumulation of SN at the onset as morning temps will generally be 10-12 degrees below the freezing mark, with afternoon temps topping out in the upper 20s in EC IN/WC OH to the mid 30s near/S of the OH Rvr.

The biggest challenge in this fcst remains the degree of BL warming during the daytime Saturday for locales near/S of I-71 and whether the initial depth of dry air can be enough for the profile to wet bulb and for near sfc temps to cool several degrees with the onset of pcpn. This would likely keep the pcpn snow a bit longer before an eventual transition to a RA/SN mix occurs toward midnight and beyond. And a lot of this will be impacted by how /soon/ the SN starts for the Tri-State into south-central OH as a later onset time into mid/late afternoon or the evening would allow for better BL warming and a shorter time for snow to accumulate. And this seems to be the most likely evolution at this juncture.

Nevertheless, do think that steady snow will overspread the entire CWA by early evening (and much earlier during the morning from EC IN through WC OH) as the column saturates. Fairly robust WAA will evolve later into the evening, aided by a strong 50+ knot LLJ. This will help transition p-types to a RA/SN mix and then to rain during Saturday overnight hours into Sunday progressively from S to N (which may help melt/compact some of the newly-fallen snow). As the system moves into the ern OH Vly and we get on the backside early Sunday morning, a brief transition back to RA/SN or snow will follow Sunday morning before pcpn tapers off from W to E area-wide by noon.

Although there is still quite a bit of uncertainty of where that RA/SN line will be, confidence in impactful accumulating snowfall is highest in EC IN into WC OH. An advisory will likely eventually be warranted for a larger part of the CWA than where the current watch is in effect, but confidence was just not high enough to move forward with WWA expansions/issuance at this time.

Stiff southerly winds will evolve late Saturday afternoon into the night, with SE winds of 15-20kts and gusts to 25kts expected before winds shift to more out of the W past 12z as the front moves through.

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/

Surface high pressure builds into the Ohio Valley Sunday night through Monday as a low pressure system pulls far off to the northeast. Dry and cold conditions prevail.

The next potentially impactful round of winter weather arrives Monday night and lasts through Tuesday. A shortwave upper level trough approaches from the west late on Monday and moves through the Ohio Valley on Tuesday. A surface low forms southeast of the Appalachians in response to the upper level shortwave trough Monday night/Tuesday morning. Snow is moderately likely to develop ahead of the upper level wave Monday night into Tuesday morning in the Ohio Valley. Some rain could end up mixing in southeast of I-71 on Tuesday deepening on temperatures. However, forecast uncertainty around the strength and position of the surface low greatly impacts snow amounts. A stronger low closer to the Ohio Valley could increase precipitation amounts (and impacts) as frontogenesis aloft (around 850 hPa) ramps up. However, a low further south limits forcing to the upper level wave without the aid of any lower level mesoscale banding. Precipitation eventually ends Tuesday afternoon behind the upper level trough. High pressure then brings cold, try conditions Tuesday night through Thursday. Precipitation chances increase late next week although the synoptic pattern remains highly uncertain.

AVIATION /13Z FRIDAY THROUGH TUESDAY/

High pressure will build east through the Ohio Valley today with primarily VFR conditions. A few patches of MVFR cloud and flurries may clip CMH or LCK this morning with skies clearing later. High cloud will be on the increase tonight ahead of a system moving from the southern Plains towards Chicago on Saturday.

Westerly winds will tend to be elevated towards Central Ohio with gusts to 20-25 knots this afternoon. Winds will be lighter towards CVG and will go variable overnight before developing out of the south Saturday morning.

OUTLOOK...MVFR/IFR CIGs and VSBY with wintry precipitation likely late Saturday into early Sunday. LIFR CIGs and VSBY will be possible during this time. Snow may bring additional reductions to CIGs and VSBY on Monday night into Tuesday as well.

ILN WATCHES/WARNINGS/ADVISORIES

OH...Winter Storm Watch from Saturday morning through Sunday morning for OHZ034-042. KY...None. IN...Winter Storm Watch from Saturday morning through Sunday morning for INZ050.