textproduct: Wilmington

WHAT HAS CHANGED

Increased coverage and amounts for snow, with some wintry mix likely, for Monday morning.

KEY MESSAGES

1) Mixed wintry precipitation expected Monday morning, with accumulating snow for some locations, particularly near, and just north of, the Ohio River. The Monday morning commute will be impacted by this wintry precipitation.

2) Warmer and wetter conditions expected from Tuesday through the rest of the week, leading to increased potential for areal and river flooding late weekend into the upcoming weekend.

DISCUSSION

KEY MESSAGE 1) Mixed wintry precipitation expected Monday morning, with accumulating snow for some locations, particularly near, and just north of, the Ohio River. The Monday morning commute will be impacted by this wintry precipitation.

Dry conditions have briefly settled into the region as a strong sfc high drifts to the SE through the Great Lakes region into the interior NE CONUS by tonight. Cooler and drier air will filter into the area through the daytime today, with all eyes on an the approach of a S/W into the OH Vly late tonight through Monday morning.

As we progress into tonight, an increase in lift/moisture will spread E through the region from the mid MS Rvr Vly into the OH Vly, with very dry BL air entrenched in the ILN FA ahead of the approaching system. This /very/ dry air will help the profile wet bulb as the moisture spreads E into the predawn hours, with pcpn falling into an initially warm/dry near-sfc layer. This will help the profile cool to near/below the freezing mark, supporting a narrow band of steady frontogenetically-forced SN from EC/SE IN through the Tri-State into nrn KY and SW OH into south-central OH, with some IP/FZRA rain favored just south of the primary band of SN. It is important to note that, even near/N of the OH Rvr where SN is the favored predominant p-type, a brief mix with FZRA/IP will be possible both near the onset and near the end of the primary pcpn band. Near the onset (~08z-10z), the column will be wet-bulbing and cooling, but may not entirely be below freezing as the pcpn initially reaches the ground. Near the end (~14z-16z), enough WAA into the H9-H8 layer, as well as a loss of moisture in the DGZ, may allow for some mixing with FZRA/IP. Far srn parts of the area from Carroll Co KY to Lewis Co KY may remain predominantly a mix of FZRA/IP/RA through the entirety of the event (with little/no SN) due to warmer BL conditions, but certainly a few hundredths of an inch of ice will be possible in these areas where prolonged FZRA is maintained. This will be especially the case on elevated surfaces, such as untreated bridges/overpasses and trees.

The high-res guidance continues to show a slightly more robust solution, particularly for the southern half of the ILN FA, with steadier pcpn and a slightly cooler BL (owing to drier antecedent BL conditions). The primary story here is that it is likely that a swath of wintry precipitation will work its way across the southern half of the ILN FA Monday morning, with a narrow W-E oriented band of 1-2" of snow likely somewhere near/N of the OH Rvr to just S of the I-70 corridor. Due to the orientation of this band and a sufficiently- cool BL profile, some lower-probability potential exists that banding could produce up to 3 inches in isolated locations. In addition to this, some brief mix with IP or FZRA also appears possible, even where the heaviest snow occurs. The surface will remain locked in ENE flow, but at 925mb-850mb, some southerly flow will bring overrunning theta-e advection, supporting the development of an elevated warm (above freezing) layer past 12z. Model soundings look favorable for at least a brief period of FZRA/IP to occur, particularly in northern KY and far southern OH by mid-morning as we lose some saturation in the DGZ. Confidence in where exactly the mix of p-types could set up is quite low, but has been included in the forecast for roughly the southern third of the ILN FA.

The concerning part of this setup is that it will be moving through right during the Monday AM commute. While the road temps may initially be above freezing, elevated surfaces, such as bridges and overpasses, will support some accumulation due to the steadier rates, with untreated road temps generally in the lower to mid 30s. The solar insolation will help conditions to improve by about 10 AM or so, but most of the steadiest wintry pcpn will be slowly tapering off by then anyway, with a transition to plain rain expected into early afternoon. This being said, it also appears possible that surface temps will not warm as fast as previously expected. If that occurs, some patchy light snow or mixed precipitation could continue into the early afternoon hours (mainly in nrn KY), but impacts should wane due to warming road temps. Due to the expectations for impacts for the Monday morning commute, a Winter Weather Advisory has been issued for areas where the 2" snow criteria exists for an advisory AND where the greatest impacts are expected due to accumulating snow and/or light ice accretion.

KEY MESSAGE 2) Warmer and wetter conditions expected from Tuesday through the rest of the week, leading to increased potential for areal and river flooding late weekend into the upcoming weekend.

A pronounced shift in the large-scale weather pattern is expected to begin Tuesday. On the wrn periphery of the Bermuda high, deep-layer S/SW flow will become established over the SE CONUS. A significant/prolonged feed of anomalous warmth and moisture is expected to develop from the Gulf through the deep south, the lower and mid MS Vly, and into the TN/OH Vlys. For the ILN CWA, BL flow is expected to switch to southerly at some point on Tuesday, and then more robustly in the warm sector by Wednesday. This theta-e advection will mark the start of both a warming and moistening trend. Max temps in the 50s to lower 60s are expected Tuesday, warming each day and getting into the lower to mid 70s by Friday, with temps well above normal for the foreseeable future.

On the periphery of the zone of higher theta-e, repeated rounds of rain are expected to develop. Initially on Tuesday, rain will be associated with the warm front moving N through the area. Rain/storm chances later in the week will be determined by the timing of additional waves moving E/NE through the mid MS Rvr Vly, OH Vly, and Great Lakes. Some embedded areas of heavy rain, and certainly some convection, will occur at times, although timing of the specific rounds of heaviest rain remains difficult to determine at this time. From a synoptic pattern standpoint, this is a setup that provides the potential for heavy rain and possible flooding -- focused to the W and SW of the ILN CWA, but extending into the ILN CWA to some degree as well. Still early to get into specifics about exactly where or when, but the overall potential would increase with additional rounds of rain going later in the week or even into next weekend. Ensemble guidance remains in good agreement with high (>70%) potential for total rainfall in excess of 2" for at least parts of the ILN FA Tuesday through Saturday, with certainly some potential for higher amounts depending on where the most prolonged training of convection develops.

It is not of the question that some strong storms could occur at some point late week, but still too early to look at when or where that may occur.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

A blanket of MVFR CIGs will continue to scatter out early in the period, with a clearing trend area-wide through the first few hours of the TAF period. However, some cirrus will begin to overspread the region from the W into this evening, with mid clouds arriving by 06z.

The thickening cloud cover will precede a band of wintry pcpn, which will overspread the local area between 08z-16z. Nevertheless, most of the pcpn should be SN for the local terminals, with the steadiest/heaviest expected for KCVG/KLUK/KILN between about 11z- 13z. Coinciding with this steady SN will be some IFR (or lower) VSBYs, along with some MVFR CIGs. The IFR VSBYs will quickly improve to VFR with the decrease in coverage of SN toward/beyond 14z-16z, but the MVFR CIGs will linger through the entirety of the TAF period, with increased coverage of RA expected toward 00z Tuesday and beyond. The most widespread MVFR CIGs and IFR VSBYs are expected for KCVG/KLUK/KILN.

NE flow around 10-15kts this afternoon will go more easterly around 10kts this evening, continuing through the daytime Monday.

OUTLOOK...Occasional MVFR conditions, perhaps with rain, will occur at times from late Monday through Friday.

ILN WATCHES/WARNINGS/ADVISORIES

OH...Winter Weather Advisory from 3 AM to 11 AM EST Monday for OHZ070>073-077>082-088. KY...Winter Weather Advisory from 3 AM to 11 AM EST Monday for KYZ089>100. IN...Winter Weather Advisory from 3 AM to 11 AM EST Monday for INZ066- 073>075-080.