Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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312 FXUS63 KOAX 132322 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 522 PM CST Fri Jan 13 2017 .SHORT TERM...
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(Tonight through Sunday) Issued at 312 PM CST Fri Jan 13 2017 ...The primary concern remains the winter storm which will impact the forecast area Sunday into Monday night... Manual 12z upper-air analysis and early afternoon water vapor imagery indicate a mid to upper-level cyclone off the southern CA coast with a downstream zone of confluent mid-level flow observed from the upper MS Valley into the Great Lakes. The confluent flow aloft was maintaining the presence of an anticyclone at the surface over MN/WI with the primary low-level baroclinic zone situated from southwest TX through the lower MS Valley as of 18z. Of note in 12z observed sounding data was a seasonably moist low- level air mass which extended from south TX into southwest MO. In the near term, there is little in the way of sensible weather concerns. The confluent mid-level flow to our northeast will maintain a surface ridge across the mid MO Valley, which coupled with persistent clouds, will support near or slightly below normal temperatures through Saturday. Saturday night into Sunday, the mid to upper-level low mentioned above will turn east across northwest Mexico, which will induce strengthening southerly low-level winds. This, in turn, will enhance the poleward flux of the warmer, more moist air mass to our south. This moistening process in conjunction with a broadening zone of warm advection will foster an expanding precipitation shield from south to north across the forecast area. Initial precipitation type will likely be a sleet-freezing rain mix which will transition to freezing rain as the warm advection continues atop the shallow, sub-freezing air mass. .LONG TERM...(Sunday night through Thursday) Issued at 312 PM CST Fri Jan 13 2017 Sunday night into Monday, we continue to see considerable spread amongst deterministic and ensemble model data in the track of the upper-air system through the central Plains into the mid and lower MO Valley. These differences have implications on the surface pattern, the stratification of the thermal profiles and resultant precipitation type. The ECMWF remains the warmest and farthest west solution, while the GFS is the coolest and farthest east, with a considerable departure noted from the previous (06z) forecast. As a result of this model variability, confidence in specific ice and snowfall accumulations remains lower than we would like at this juncture. The official forecast will indicate the swath of highest ice accumulations from near Fairbury, NE (0.50") into southwest IA (0.30-0.35"), with 0.30-0.40" possible along the I-80 corridor. The highest snowfall totals (i.e. 2-3") are expected to occur over northeast NE, mainly along and to the north of an Albion-Norfolk-Wayne line. We would like to stress that these snow and ice accumulations are likely to change between now and the onset of the weather event, as the models eventually come into better agreement. Due to the uncertainties mentioned above, we have elected to maintain the Winter Storm Watch, instead upgrade to a warning. A warning upgrade to some or all of the watch area is quite likely in the next 24 hours, once confidence in the weather scenario increases. Monday night into Tuesday morning, we will see a transition from rain or freezing rain to light snow as the cold air deepens on the backside of the departing cyclone. Snow amounts during that time frame should be relatively light. By the middle to latter part of next week, it appears that developing zonal flow aloft will induce downslope warming with afternoon temperatures rising into the 40s. Much of the precipitation that falls on Sunday and Monday will be runoff into area streams. This added volume coupled with ice melt from the warming temperatures could present some ice jam issues later next week.
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&& .AVIATION...
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(For the 00Z TAFS through 00Z Saturday evening) Issued at 520 PM CST Fri Jan 13 2017 Generally look for VFR conditions through the period. There are some MVFR ceilings din parts of southeast NE and southwest IA, but those are likely to stay south of the TAF sites. Winds should be mainly under 10 knots. Conditions should deteriorate late Saturday night.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...Winter Storm Watch from Sunday afternoon through late Monday night for NEZ011-012-015>018-030>034-042>045-050>053- 065>068. Winter Storm Watch from Sunday morning through late Monday night for NEZ078-088>093. IA...Winter Storm Watch from Sunday afternoon through late Monday night for IAZ043-055-056-069-079-080-090-091. && $$ SHORT TERM...Mead LONG TERM...Mead AVIATION...Miller

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