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Displaying AFOS PIL: AFDIWX Received: 2018-01-13 05:42 UTC
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227 FXUS63 KIWX 130542 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 1242 AM EST Sat Jan 13 2018 .SYNOPSIS... Issued at 635 PM EST Fri Jan 12 2018 Dry air continues to stream in from the north tonight and clouds begin to break up away from the lake. Lake effect snow showers will develop in northwest Indiana and southwest Lower Michigan today. Minor accumulations are expected. Lows this morning will be in the single digits and teens. Highs today will be around 20. A clipper system will bring additional chances for accumulating snow Sunday night into Monday. Lake effect will return again Tuesday into Wednesday afternoon for north-northwest wind favored snowbelts. Drier and slightly warmer conditions are expected at the end of next week. && .SHORT TERM...(This Evening through Saturday) Issued at 339 PM EST Fri Jan 12 2018 ...Cold with Lake Effect Snow... I don't know how AFD readers feel, but I am definitely happy to NOT be writing much about today's wintry Mix. I believe this storm was a great lesson for everyone about hyping "big winter storms" too far in advance, with most areas ending up below 2" of snow accumulation (a few isolated 2.5 in reports as of 20z) and minor ice accumulation. Will let the advisory expire this evening once snow clears the area. The evening shift may be able to drop the remaining western counties (including Allen, IN) early. A few rivers have gone into minor flood stage this afternoon due to the snowmelt and rainfall we received, so monitor our AHPS page for any river flood warnings or statements. We're back to the snow and cold for the foreseeable future, and in the case of the short term-Lake effect snow showers. As mentioned in my earlier update, the beginnings of our post-system lake effect are underway. We see the first signs of lake effect snow bands on satellite/radar imagery, and a band over LOT's CWA. Expect this band to migrate slowly eastward this evening, especially once winds become more north-northwesterly around 9z and beyond. Delta theta-e's are decent and there is enough ambient synoptic support thanks to our upper level low, but drier air may serve to undermine any significant accumulations. We probably have more moisture than models indicate given the northerly fetch, but things are already off to a slower start than we had in the forecast previously. Things look to improve Saturday for snow accumulation as winds become northwesterly, and a shortwave pinwheels around the upper level trough, traversing our CWA through the day. Delta theta-e's are sufficient instability wise, and we have a little increase in the moisture content. Inversion heights at KSBN reach up to 6Kft by the afternoon, so thinking we'll see snow showers during this time associated with the eastward migrating band. As far as QPF goes, it looks to still be on the lower side but snow ratios might be pretty good for dendrite production. BUFKIT soundings at KSBN suggest that lift from the shortwave will be maximized in the DGZ around the 15-18z time frame especially, so have adjusted pops accordingly. Think we'll get some snow with the short wave further inland in the afternoon, but I am less confident in the extent. For now have some lower chances in the northwest. Lake effect snow accumulations look to be about 1-2 inches in favored regions, with less than half an inch further inland. High temperatures look to be around 19-20F, and lows tonight will drop into the single digits north and from 10-15F elsewhere. && .LONG TERM...(Saturday Night through Friday) Issued at 339 PM EST Fri Jan 12 2018 ...Clipper System & Lake Effect to Bring More Snow... High Pressure and Ending Lake Effect: Saturday Night-Sunday High pressure builds in and flow veers around to the west southwest by late Sunday morning, bringing our lake effect snow to a temporary end. Expect dry conditions, with highs again around 20F, and overnight lows Saturday/Sunday night in the single digits and teens. The pressure gradient begins to tighten by Sunday evening as another system approaches the area, leading to gustier southerly winds. Alberta Clipper: Sunday Night-Monday Late Sunday night into Monday we'll see our next chances for system snow as a clipper system develops ahead of another stronger, more potent shortwave trough aloft. The surface low will drop southeastward out of Alberta, and models generally agree on the path extending from WI/IL at 12z Monday through Lower Michigan by 12Z Tuesday. It will continue eastward into the lower Great Lakes by Tuesday afternoon as yet another 1048hPa high pressure sinks into the northern and central plains, ridging into our CWA. With good synoptic support and decent moisture, expect a widespread light to moderate snow over the CWA. Soundings suggest snow ratios initially around 12-15:1, rising to 17-20:1 by the late afternoon/evening hours. The prime DGZ initially looks to be located below 10Kft and the strongest/majority of the omega is above the DGZ. This would favor more of a 12-15:1 ratio versus the consensus blend's 20:1 (which has been overdone several times this season). Lowered the snow ratios to more what I would expect, as outlined above. This gives us around 1-3" of snow accumulation Monday. Expect we'll see some disruptions to travel for the Monday AM/PM Commutes. Lake Effect Returns: Tuesday into Wednesday Afternoon As winds veer around the surface low, we'll see north- northwesterly winds develop and strengthen. I've increased winds above the consensus blend for this time period (and Monday) as they seemed too light given the tighter pressure gradient. Moisture around the lingering low, in addition to a lake superior connection, and stronger delta theta-e's look to bring us our next lake effect event, specifically a "Type VI" event as mentioned in our previous AFD. Synoptic forcing will abound as a shortwave swings southwestward around the base of the upper level low pressure system, which at 18z Tuesday spans Lake Huron/Ontario/Quebec. Of course, with any lake effect confidence is not high in exact location of the band setting up. Have increased pops from consensus blend similarly to the previous shift, as models seem to agree on the general pattern (with some differences). We'll see the snow-it's just a matter of how much. High temperatures Tuesday will be downright cold, only reaching into the mid-upper teens. Lows Tuesday night will be in the single digits. We'll bounce back into the upper teens and low 20s Wednesday afternoon. Drying out and "Warming" Up: Wed Afternoon-Fri Night Yet another high pressure system builds into our area by Wednesday afternoon, and flow swings to the southwest. Additionally, models have a highly amplified ridge building in aloft. This will force our lake effect snow northeastward out of our CWA as they diminish under increasing subsidence, and bring in the dry air. It will also allow for some warmer temperatures to make it up to the Great Lakes. Temperatures will start out Thursday in the mid 20s, and then gradually rise into the low-mid 30s by Friday. && .AVIATION...(For the 06Z TAFS through 06Z Saturday Night) Issued at 1237 AM EST Sat Jan 13 2018 Strong northerly winds the main story for the early overnight on the backside of a low pressure system tracking into the Northeast US. Winds slacken some today, though cold/backing flow will allow lake effect plume and associated snow showers to work into KSBN later this morning/afternoon with periodic IFR/MVFR visibility restrictions and some light snow accumulations. Could even see a few snow showers or flurries briefly at KFWA later this afternoon/early this evening. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...Small Craft Advisory until 7 PM EST this evening for LMZ043-046. && $$ SYNOPSIS...MCD/Roller SHORT TERM...MCD LONG TERM...MCD AVIATION...Steinwedel 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