Area Forecast Discussion
Issued by NWS Northern Indiana

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000 FXUS63 KIWX 141726 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 1226 PM EST Thu Dec 14 2017 .SYNOPSIS... Issued at 415 AM EST Thu Dec 14 2017 Other than some light lake effect snow showers today for NW Indiana and far SW Lower Michigan, weather will be dry. Partly mostly cloudy skies can be expected, with highs only reaching into the upper teens and low 20s north of US 30, and the mid-upper 20s south of US 30. Lows tonight will range from 12 to 22 degrees. Light snow is possible again on Friday into Saturday morning, though little to no accumulation is expected. Lake enhancement in west-northwest wind favored snowbelts could lead to snow totals up to two inches by Saturday morning. Highs Friday will be in the 20s and low 30s. && .SHORT TERM...(Today and Tonight) Issued at 415 AM EST Thu Dec 14 2017 With the eastward exit of our clipper system, the only feature of interest today is the eastward progression of a lake effect band from Lake Michigan this morning. Winds will shift from the NNE to the WSW by this afternoon-lightening significantly As it does, the lake effect band will drift eastward into LaPorte/Berrien Counties, though I expect it to fall apart and diminish no later than early afternoon under incoming surface high pressure, backing flow, and crashing inversion heights. It will be rather chilly today, with highs only reaching the upper teens in the far NE, and the mid-upper 20s across the southwest. Another wave aloft will approach the area overnight, causing flow to veer back to the west-northwest off the lake. With synoptic support and onshore flow, expect lake effect snow showers to develop in west wind favored snowbelts. Expect less than 1" of snow accumulation in these areas overnight. Lows tonight will bottom out between 12-22F. && .LONG TERM...(Friday through Wednesday) Issued at 415 AM EST Thu Dec 14 2017 The upper level wave will drift eastward through the day, leading to the spread of light snow inland from Lake Michigan, and continued lake effect snow in the westerly wind-favored regions. System snow would primarily impact areas along/north of US 30, though little to no snow accumulation is expected in these areas. For areas impacted by lake effect snow, expect as much as 1-2 inches by Saturday morning, mainly along/north of the toll road. Highs Friday will be in the upper 20s and low 30s, but by Saturday afternoon expect the arrival a warmer airmass as winds become southerly and a low pressure trough moves into the central CONUS. High temperatures will rise into the 30s and low 40s, warmest south of US 30. This will bring an end to our lake effect, and tighten the baroclinic zone just to our north, oriented from roughly WNW-ESE across Lower MI/WI, forcing it northward. Meanwhile, both the GFS/ECMWF have a surface low developing in the central plains by Saturday night in response to the digging trough aloft. The solutions diverge from there, but both models lift the low northeastward towards the Ohio Valley Sunday into Monday, with the low and return flow around a strong high over the Atlantic pumping up moisture from the gulf of mexico. The GFS pulls the low into southern Indiana beneath the phasing northern/southern stream of a coupled upper level jet, and then shunts it largely south of the IWX area, with a sharp cut off to precipitation on the north side. This isn`t totally out of the question, given we`ve seen where things develop well over IND`s area, and then that prevents the better moisture from reaching our area. However, the ECMWF has the phasing jets further northward, and a steeper secondary trough to our northwest, which brings that low north into our CWA Sunday. High temperatures will likely be in the upper 30s in the north half, and low-mid 40s further south, so it could be largely rain mixing in with some snow. Given the extreme discrepancies with the previous runs of the models at this time period, and the typical problems we see with phasing north/south streams of the jet, kept consensus blend for now with respect to pops. We`ll have to monitor this one, as it will certainly be interesting to see how it plays out. Finally, other than a few lake effect rain/snow showers Tue/Wed in WNW wind favored snowbelts, we`ll see relatively mild temps and quiet weather through Thursday. Highs on Thursday could rise into the low-mid 40s on Thursday afternoon south of US 30, but otherwise expect highs in the 30s through the remainder of the period. && .AVIATION...
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(For the 18Z TAFS through 18Z Friday Afternoon) Issued at 1226 PM EST Thu Dec 14 2017 Backing flow and increasing dry air entrainment has disrupted lake effect snow as expected this morning. KSBN could experience a few brief periods of MVFR early this afternoon but confidence in duration is too low for even a TEMPO mention given recent obs and radar/satellite trends. Primarily VFR expected to continue through tonight. Next clipper system arrives late tomorrow morning with another round of light lake effect snow and lower ceilings that could cause a period of MVFR conditions.
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&& .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...Small Craft Advisory until 4 PM EST this afternoon for LMZ043- 046. && $$ SYNOPSIS...MCD SHORT TERM...MCD LONG TERM...MCD AVIATION...AGD Visit us at www.weather.gov/iwx Follow us on Facebook...Twitter...and YouTube at: www.facebook.com/NWSNorthernIndiana www.twitter.com/nwsiwx www.youtube.com/NWSNorthernIndiana

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