Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 172118 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 418 PM EST Tue Jan 17 2017 .SYNOPSIS... A departing cold in the Ohio Valley combined with the passage of an upper level low will permit a few sprinkles over the region tonight. High pressure will build south of the region Wednesday and provide a brief dry period. This high will move east early Thursday, and the next chance of precipitation will occur with a warm frontal passage early on Friday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... H5 low and trough axis coming through with a good PV anomaly with deep enough low level moisture (1.5kft) to support an area of light rain and/or drizzle. Do not expect to have precip in any but my far southeast after 9Z given the h5 trough axis should be the deterministic factor in the occurrence of precip, regardless of how light or measurable it is. Overnight lows will be cooler but generally mild for this time of year, ranging from the mid 30s in the northwest to the lower 40s in the southeast CWA. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... The closed upper low will be situated over the OH/WV border at 12z and quickly exiting east. High pressure will build south of the area through the day, coupled with a slightly lagging upper level ridge. This ridge at both the surface and aloft will be over the region tonight but will likely not be strong enough to scour out the low level moisture trapped underneath a fairly strong temperature inversion. Was initially concerned about the potential for drizzle underneath this inversion but the depth of the saturated air appears to limit this potential, coupled with the absence of any strong upper level forcing due to a vort max or jet. Generally kept it cloudy and did not let the min temperatures drop much below the mid 30s given the expected cloud cover. On Thursday, the upper level ridge crosses and flow turns easterly at the surface. A warm frontal passage is slated to occur overnight, along with an increasing threat for rain. Kept the rain as stratiform and mentioned heavy potential where pops were likely or higher. Models are slowing the progress of the warm front in the Ohio Valley overnight Thursday. Believe that there may be enough slantwise convection along the occlusion to promote thunder late overnight, but did not include this in the forecast attm and kept the ptype as stratiform versus convective in nature. Temperatures will remain above normal. Forecast remains relatively unchanged with a general minor bump in both highs and lows. && .LONG TERM /FRIDAY THROUGH TUESDAY/... The long range will open up with a closed low ejecting northeast and taking on a negative tilt as it passes over the ILN forecast area. A slug of PV will rotate across the area Friday morning providing a strong source of lift. Omega values on the GFS also light up at this time. PWAT values rise to near 1.10". GFS forecast soundings do show the possibility of some thunder but for now have left the mention out as thunder looks marginal. Given the impressive lift, more than sufficient moisture, and instability have kept PoPs categorical. In the wake of Fridays closed low there will be a brief period of subsidence on the backside of the PV, but the main question is how quickly will the precipitation return. Overall ridging begins to setup across eastern Canada and the northeastern United States with an upper level trough over the western United States. The pattern will be messy though as multiple waves of mid-level energy can be found in the flow. The GFS is slightly further east with an upper level low pushing north on the western side of the mid-level ridge. As this occurs the ridge will slowly start to move east. The GFS is slightly stronger with this low Saturday and tries to bring in precip to the area Saturday afternoon across the western zones. The CMC looks similar to the GFS while the ECMWF is slightly weaker with the energy Saturday. Looking at forecast soundings on the GFS for Saturday shows dry air between 850 and 700 mb which would favor a later onset of precipitation. Given the above have trended the forecast towards the ECMWF solution and kept Saturday drier. Sunday, another stronger piece of energy will push east across the southern United States and wrap up into an upper level low. As this happens a wedge of PV will push northeast ahead of the low and move across the ILN forecast area. PWATs at this time again rise to around 1.00". Forecast soundings on the GFS show some dry air trying to remain in various levels of the sounding at this time so have kept PoPs at chance. Seeing how strong the upper level lift currently looks on the ECMWF and GFS Sunday, PoPs will probably have to be raised. Sunday into Monday the upper level low will drift overhead keeping the clouds and a chance of rain in the forecast. It should be noted that the low looks to be vertically stacked with dry air entrained. This means that a break in the precip will probably occur sometime on Monday (possibly in the morning) but given this is day 7 have just broad brushed the PoPs at this time. On Tuesday the upper level low will slowly drift east taking the rain and precipitation with it. && .AVIATION /21Z TUESDAY THROUGH SUNDAY/... Cdfnt is in the vicinity of I-71 at the start of the taf period. Some clear spots around the front have allowed the cigs to jump to VFR. However cigs are dropping back to MVFR behind the front. So have a tempo group for the first hour of the tafs to take care of this situation. Cigs will lower as the afternoon progresses and could reach IFR at some spots after 00Z. Meanwhile, an approaching H5 vort will increase the PVA aft 00Z and will give the chance of scattered SHRA. Carried a VCSH at the tafs between 00Z and 12Z. Tafs get into area of NVA tomorrow, so ended the VCSH around 12Z, but time sections are showing that low level moisture will be trapped, thus kept MVFR cigs. OUTLOOK...MVFR/IFR ceilings possible into Thursday. MVFR/ IFR ceilings are again possible Thursday night into Sunday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Franks NEAR TERM...Franks/Sites SHORT TERM...Franks LONG TERM...Haines AVIATION...Sites

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