National Weather Service
Area Forecast Discussion

307 AM EDT Mon Mar 25 2019
As low pressure moves east through the area this morning, a cold front will move south from the Great Lakes. While rain is expected today, drier conditions will move in behind the cold front, with high pressure building into the area through the middle of the week. This will allow for dry weather and a gradual warming trend through Thursday.

GOES-16 water vapor imagery is quite useful in depicting the larger-scale features affecting the weather early this morning. The well-defined swirl of a mid-level shortwave is currently located over Illinois, moving slowly to the east. Further north, a significant amount of drying can be seen moving south from the Great Lakes, in association with a cold front that is now crossing south of the MI/IN/OH border.

Although the wave is gradually dampening, and its associated surface low (tracking south of the ILN CWA) is also weakening, there is still appreciable forcing with this system. This is a result of the combination of low-level convergence, positive vorticity advection ahead of the wave, moisture transport on southwesterly flow ahead of the system, and even deformation on the north side of the surface low. Though the system has finally outrun what little instability was present (a few lightning strikes were observed southwest of Cincinnati) there is still some potential for steady moderate to even localized heavy rainfall. A swath of precipitation amounts around an inch should be possible, especially where deformation is maximized. One adjustment to the forecast was to bring this a little further north, where HRRR/WRF-ARW projections indicate that the deformation band may get into the Dayton and Columbus areas between 12Z-18Z.

A rapid decrease in precipitation coverage is expected after 18Z, once the axis of the wave is moving past the region, and drier air behind the surface cold front envelopes the region. A tight pressure gradient will lead to some northeasterly wind gusts of 20-25 knots this afternoon. The presence of the front will also have a role in the temperature forecast today, which is complicated -- there will be competing forces of cold advection and diurnal heating. Max temps are forecast to be in the lower to upper 40s, but this is a lower-than-normal confidence temperature forecast.

By 00Z tonight, the surface cold front will be completely through the forecast area, and precipitation should be done as well. This sets up a very quiet forecast through the rest of tonight and into Tuesday. An area of surface high pressure will move from the upper Midwest to the Great Lakes and Ohio Valley by Tuesday, with the air mass becoming very dry -- as an example, KILN precipitable water values are forecast to be under two tenths of an inch (NAM/GFS).

Though NNE winds will keep on blowing through the night, cold advection will allow temperatures to drop well below freezing, and mid to upper 20s are expected. Plentiful sun in a dry air mass on Tuesday will mean that temperatures should rise well on Tuesday, despite somewhat chilly conditions aloft. Not a lot of spread in GEFS projections for max temps on Tuesday, though SREF projections have a little more spread, as is typical. Nonetheless, owing to the dry air, this forecast will be on the higher end of the guidance envelope -- with expectations for highs in the mid 40s to around 50.

For Tuesday night into Wednesday, although the center of the sprawling high will move east to New England, then eventually off the New England coast, it will still extend westward into the Great Lakes and Ohio Valley. After a cold start in 25 TO 30 degree range, temperatures will begin to moderate with plenty of sunshine. Highs will range from the lower/mid 50s north to the upper 50s/lower 60s south.

A mid level ridge axis will move east across the region Wednesday night into Thursday. This ridge is now forecast to be a little more flat then previous model runs. In addition, models are now allowing a cold front to slowly push southeast into the Great Lakes during this period. Although WAA clouds will increase, the chances for rain will still remain low and relegated to the northern CWFA. After a chilly start, highs will warm nicely as southerly flow increases between the cold front to our northwest and the departing high to our east. Will continue to forecast highs from the lower 60s north (more clouds, slight chance of showers) to the upper 60s south (dry, more sunshine).

For Thursday night into Friday, models continue to struggle on how embedded energy coming off the California coast will phase or not phase with a large scale mid level trough slowly digging southeast toward the Great Lakes. Frontal boundary to our north will likely stall near our northern CWFA, while a wave of low pressure develops over the central Plains associated with aforementioned embedded energy. Clouds will certainly increase through the period as well as the threat for rain, but still remaining highest across the north near the frontal zone. Highs on Friday will range from the upper 50s north to the upper 60s south.

Best chance for precipitation is still forecast for the first part of the weekend as mentioned systems affect the region with an area of low pressure and a frontal boundary. Will maintain likely PoPs with showers. It will still remain mild on Saturday with highs in the mid 50s to the lower 60s.

Colder air will filter into the region Saturday night into Sunday in the wake of a cold front. Some snow may mix in across the north before pcpn tapers off. Will forecast highs from the mid 40s to the lower 50s. However, these may have to be trended downward depending on how much phasing and cold air pushes in from the northwest.

The main concern for the TAFs is the area of rain moving into the region as of now. This rain contains some embedded moderate to heavy rain, which may bring visibilities to MVFR or even IFR levels. In addition, there is a chance of thunder at the Cincinnati TAF sites over the next hour or two. It is less certain if thunder will be able to make it to the other airports.

Ceilings are expected to generally be in the MVFR category, though with some variations -- possibly to VFR, and possibly to IFR. The most likely chance for IFR ceilings will be at the Cincinnati airports between 12Z-16Z, and this may need to be added into the TAF if confidence increases.

Rain is expected to come to an end at the TAF sites during the late morning || early afternoon. Winds from the northeast will increase, with gusts into the 20-25 knot range. There should also be a fairly quick transition to clear skies and VFR conditions.


MVFR conditions are possible on Friday.

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