Area Forecast Discussion
Issued by NWS Wilmington, OH
Issued by NWS Wilmington, OH
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735 FXUS61 KILN 190551 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 151 AM EDT Thu Sep 19 2024 .SYNOPSIS... Slow moving upper level low pressure system over the Carolinas will continue to move slowly northeastward and redevelops off the Eastern Seaboard. Weak axis of high pressure from southeastern Canada into the Mississippi Valley will continue the warm dry weather over the Ohio Valley through Friday. A weak system pushing through the Great Lakes over the weekend may bring some limited or scattered rain showers particularly on Friday night or Saturday, but most areas will remain dry. A little more active and unsettled pattern will develop over the Ohio Valley from the early into middle portions of next week, with slightly better chances of showers and storms. It will remain warm through the period with highs well into the 80s. && .NEAR TERM /THROUGH TONIGHT/... Primary concern through sunrise is coverage/intensity of any fog overnight. Dewpoints in the lower 60s late today are hard pressed to be reached with overnight low temperatures. Warmer lows in the metro areas of CMH, CVG and to a lesser extent DAY will also detract from Td crossover temps being reached. More than a few models are showing lower temps tonight but also keep a warm metro area airmass. If temps drop below the already reasonably cool forecast, fog will play a more prominent role later tonight/early Thursday. Blended several models that were showing the lower end of temperatures for tonight`s lows and the 06Z temperature. This blend was a close proximity to the current forecast and was used to populate the T/Td overnight. One note here is that these models were a bit warmer on Td than current values. If this trend were to continue, the fog potential will be significantly lower and only reside in river valleys. Too much in play regarding T/Td hourly forecasts to indicate a change in course from this afternoon`s forecast. Unfortunately as with many nights with a fog potential, will have to be a bit more reactive to observations than proactive relying on more detail in humidity values. With the residual low level moisture that remains over the area, the background setup/support for at least a little fog formation is there. Light winds /easterly/, mostly clear skies, weak high pressure axis near the area, and longer September nights suggest valley fog should develop rather easily, and there are some signals /HREF probabilities of visibility <1SM/ of potential overland/areal fog to boot (see what happened this morning in NW Ohio and northern IN). For right now - given some uncertainty of coverage of this radiational event - have opted to mention patchy fog for now - but the potential exists for one or two areas of thicker/denser fog - and the likelihood of that seemingly centered in west-central or central Ohio. && .SHORT TERM /FRIDAY/... The mid/upper level low and trough axis will continue to open up and elongate as it shifts off the Eastern Seaboard on Thursday, leaving a rather nondescript/baggy/ill-defined surface pressure pattern over the local area. Underneath increasing upper ridging, a general axis of very weak high pressure and subsidence will remain over the area. The moisture pool in the boundary layer which pushed west into the ILN forecast area today, will begin mixing out amidst continued easterly flow, getting worked with plenty of sunshine and very dry soils. Dewpoints should once again mix down into the 50s during the afternoon as temperatures warm again in earnest into the middle and upper 80s in the afternoon. Clear skies will continue into Thursday. While a diminishing band of cirrus will cross the forecast area in the morning, more fair weather cumulus are again expected in the afternoon. Winds will remain light. Clear skies expected again Thursday night will likely again support valley fog formation, and lows will pull back toward 60F. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... This period will be characterized by an increasingly unsettled flow pattern that at least supports some chance of rain - better than what we`ve seen for a little while. Days 2 and 3 - An initial shortwave near Lake Winnipeg, with a southward-extending trough axis into the western Great Lakes on Friday morning, will largely pass northwest of the local area on Friday night into Saturday as it glances off mid level ridging centered over the Southern Plains. There is - and has been - a very low rain chance signal with this system for areas of west central Ohio in the 10%-20% range, but admittedly forecast soundings and background forcing signals are rather paltry, and will keep a dry forecast for now on Friday and night and Saturday as the remnants of this trough axis pass across the area. Some of the stronger solutions with this feature would drop a weak frontal boundary into the area on Saturday and renew a chance of showers developing in peak heating along the low level moisture axis, but in the presence of drought conditions and low level moisture being overforecast of late, will keep rain chances out of the forecast at this time period for right now, as the bulk of the ensemble membership remains dry under subtle height rises. Once again temperatures on both days will soar well into the 80s, with dewpoints mixing back each day into the 50s. Days 4-7 - Think Sunday remains largely warm and dry again as well, downstream of a rather potent shortwave trough moving through the Central Plains. This trough will be lifting northeast atop the persistent Southern Plains mid/upper level ridge, and may be in the process of being absorbed into larger scale northern stream troughing (GFS-based ensemble solutions) crossing central and southern Canada, or remaining separate and lagging behind on a slower/stronger solution (ECMWF-based ensemble solution). There is a rather decent forcing (and thus QPF) signal that develops as a result of these processes to our west on Sunday that become disparate between the forecast systems as the system shifts east Sunday night and into Monday/Tuesday. While the bulk of QPF should remain far enough west to guarantee yet another dry and warm day on Sunday, confidence breaks down on the specifics of the geometry, timing, moisture, and forcing quality as this mid/upper level trough sweeps through the Great Lakes Sunday night, Monday, and even into Tuesday as per the above. Moisture will definitely be on the increase as PWAT anomalies surge well above late September normals, and the presence of the shortwave trough and attendant frontal boundaries should be adequate for shower/storm chances Sunday night- Tuesday, but the timing and flow field differences right now amidst the ensemble members don`t allow for anything more than 25-40% chances during at particular time period. Will just need to wait for a better signal to emerge in the days ahead. Adding uncertainty during this time period is what looks to be a pattern in the Gulf of Mexico that may support potential of tropical / low pressure development, and if/when that occurs could have considerable impacts on ridge geometry over the south/east United States. Much uncertainty - the takeaway right now there are increasing signals for better rain chances - and the warmth will certainly continue. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... Areas of fog will be possible through daybreak and this could lead to some MVFR to locally IFR visibility restrictions, especially at KLUK. Otherwise, high level cirrus can be expected today along with few-sct afternoon cu. The cu will dissipate toward sunset with mainly clear skies expected through the remainder of the TAF period. OUTLOOK...No significant weather expected. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Binau NEAR TERM...Binau/Franks SHORT TERM...Binau LONG TERM...Binau AVIATION...JGL