Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 201729 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1129 AM CST Sat Jan 20 2018 .SHORT TERM...(Today through Monday) Issued at 329 AM CST Sat Jan 20 2018 Winter storm still on track to affect the Plains Sunday into Monday. And northeast Nebraska continues to be targeted for substantial snowfall, with a wintry mix expected in much of the rest of eastern Nebraska and southwest Iowa. Model forecasts continue to be in fairly decent agreement in regards to track of surface and upper low pressure centers, taking both through southwest Kansas Sunday afternoon into southeast Nebraska and southwest Iowa Monday morning, placing central through northeast Nebraska in favorable heavy snow quadrant of system. However there are discrepancies to the east and southeast on amount and timing of saturation of atmosphere, which will play a big role on precipitation types and amounts. Mid level storm system was moving onto the northern California coast this morning, and will track across Four Corners region tonight before swinging into the Plains Sunday and Monday. Increasing and diffluent flow ahead of it will deepen surface low in southwest Colorado today, leading to northward low level theta-e advection through eastern Kansas into southeast Nebraska and southwest Iowa. Already seeing low clouds expanding north in eastern Kansas, and expect arrival in our CWA later this morning. This increase in clouds will play havoc with temperature forecast today, however attendant moisture increase should push highs into the 40s despite cloud cover. Areas of drizzle are likely later today and tonight as low level moisture deepens under weak lift caused by mid level diffluent flow. Northward expansion of drizzle and surface temperatures at time of occurrence are tricky given competing influences of moisture advection from the south and low level northeast winds drawing cooler air into the area. We currently have temperatures just below freezing near and north of Interstate 80 where some freezing drizzle could occur for a time tonight before temperatures rise above freezing Sunday morning. Northeast Nebraska could see a slightly longer period of freezing drizzle as temperatures struggle to climb through the morning. However by afternoon expect temps above freezing so drizzle should be the predominant type until main storm system arrives late in the day. Strong frontogenetical forcing is expected to overspread northeast Nebraska by early Sunday evening when saturation of atmosphere will foster ice formation in dendritic temperature range. Once snow begins there, we should see a prolonged period of moderate snows as Q-vector forcing overrides the area into Monday. Specific humidity calculations in the 290-295K theta layer suggest snow amounts could easily top 6 inches overnight, with a few more inches possible during the day Monday, mainly northwest of a Columbus to Wayne line. Farther to the southeast things are not as clear given proximity to mid level low center and dry air wrapping into the system. The most likely scenario will be for periods of mid level saturation providing seeder ice crystals for occasional snow, interspersed with periods of drizzle or freezing drizzle when mid level dry air is predominant. Thus snow and ice accumulations will be difficult to nail down as we head toward I-80 in Nebraska and much of southwest Iowa. A gradual change to snow will occur as system drifts to the east on Monday and saturated trowal region of storm gives most areas some accumulating snows, but probably only on the order of an inch or two. Strong winds will also be impactful to travel with this system, and could create near-blizzard conditions, especially in northeast Nebraska where the heaviest snow is expected. North winds on the order of 25 to 35 mph are likely Sunday night in northeast Nebraska, then across all of eastern Nebraska and into southwest Iowa during the day Monday. Thus even with the lighter snow accumulations, blowing snow reducing visibilities can be expected. Will maintain our current configuration of the Winter Storm Watch, but have extended it through Monday afternoon as snow will be a bit slower to end and winds will remain an impact through the day. .LONG TERM...(Monday night through Friday) Issued at 329 AM CST Sat Jan 20 2018 After lingering light snow works through eastern Nebraska and southwest Iowa Monday night, the rest of the week offers a potential warming trend. Light snow on back side of exiting storm system will likely drop some minor accumulations in far eastern Nebraska and southwest Iowa Monday evening. But by Tuesday morning, we should see decreasing clouds. The coldest air will follow system to the east rather quickly, so no dramatic cooling is forecast for Tuesday. However amount of snow cover will certainly affect temperatures. Still expect highs to recover to the 30s except for the deepest expected snowpack in northeast Nebraska. Otherwise, upper level pattern will transition from northwesterly flow on Tuesday to a building ridge by Thursday, ahead of approaching storm system slated for Saturday arrival. Potential warming will be characterized by 850 temperatures rising above 0C by Wednesday evening, and approaching 5C or so by Thursday and Friday. Thus highs in the 40s by Thursday and Friday seem reasonable. && .AVIATION...
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(For the 18Z TAFS through 18Z Sunday afternoon) Issued at 1116 AM CST Sat Jan 20 2018 Conditions will gradually deteriorate throughout the period. Low level moisture will increase across the southern portion of the area this afternoon, bringing an area of MVFR and IFR cigs northward. Visibilities will begin to drop mainly after 00Z for KLNK and KOMA and after 06Z a KOFK. LIFR conditions will be possible at both KLNK and KOMA through Sunday morning.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...Winter Storm Watch from Sunday afternoon through Monday afternoon for NEZ011-012-015>018-030>033-042-043-050-065. IA...None. && $$ SHORT TERM...Dergan LONG TERM...Dergan AVIATION...KG

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