Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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503 FXUS63 KOAX 222348 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 548 PM CST Thu Feb 22 2018 .SHORT TERM...(Tonight through Sunday) Issued at 315 PM CST Thu Feb 22 2018 Main forecast problems are two-fold this afternoon, ongoing mixed precipitation and potential for heavy snow Saturday into Saturday night. Main features noted from upper air charts this morning included the following. There was a 130 knot jet max at 300 mb over the TX panhandle, and another max of over 100 knots digging south right along the west coast of the US. At 500 mb, one area of height falls was lifting northeast from northern NM and southern CO, with a stronger area of falls (up to 120 meters) digging south from OR. There was a fairly tight baroclinic zone at 700 mb across the nations mid section. At 850 mb, the zero degree C isotherm stretched from parts of TX across western OK, most of KS and into northwest MO. Surface analysis early this afternoon had a ridge of high pressure extending from the Great Lakes bas into the central part of the Plains. Low pressure was back over CO and NM. Complex situation with precipitation type through the evening hours. Lift will be enhanced as a wave moves through the region. Forecast soundings show a warm layer aloft with not much ice present aloft, but any convective elements will be able to tap into ice aloft. Thus will keep mixed precipitation going. Some additional snow accumulations could be around 2 inches, with new ice accumulations up to around a tenth of an inch. This should be winding down by midnight but may linger a bit longer in western Iowa. Friday into Friday night should be a fairly quiet period as a system organizes to the west over CO. Models may be just a bit slow on precipitation development Saturday, so have some low POPs starting in our western and southern counties before 12z Saturday. Surface low should track from southwest KS at 12z Saturday into southwest IA by Saturday evening, and the low will be strengthening during that period. 12Z GFS model may be too high with its QPF, but did a blend of the GFS and ECMWF, since the ECMWF values seemed too low based on expected dynamics and available moisture amounts. Deformation zone should put highest snow amounts from central NE into northeast NE and then across northern IA. Specific humidity values in the 700-750 mb layer are around 3 g/kg in the watch area, so amounts around 6 inches are certainly possible. Will include the northern parts of the forecast area in a Winter Storm Watch from 6 am Sat to 9 pm Sat. That may need adjustment as we get closer. Winds should be strong enough for at least drifting snow and possibly some blowing snow. Then we are back to a dry forecast the rest of the short term period. In our southern counties, again it appears that we will have some warmer temperatures aloft for mixed precipitation and potential for some ice accumulation. Ice amounts at this time look to be a tenth of an inch or less, so no headlines for southern parts of the forecast area at this time. Dropped high temperatures a little on Saturday, ranging from mid and upper 20s north to mainly 30s south. .LONG TERM...(Sunday night through Thursday) Issued at 315 PM CST Thu Feb 22 2018 No significant precipitation is expected from Sunday night into Tuesday evening, but that may change by later Tuesday night. At that time, we will be in split flow with one shortwave trough over the southern Rockies and another moving toward the northern Plains. The GFS is wetter than the ECMWF Wednesday into Thursday. Confidence is not overly high but will include some chances for rain and snow. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 536 PM CST Thu Feb 22 2018 A wintry mix of snow, freezing drizzle, and possibly sleet will continue to bring deteriorating conditions to the region this evening. Expect IFR cigs across much of the area over the next several hours. Precip should move east of the area by around 06Z tonight, with cigs and visibilities improving through Friday morning. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...Winter Weather Advisory until midnight CST tonight for NEZ011- 012-015>018-030>034-042>045-050>053-065>068-078-088>093. Winter Storm Watch from Saturday morning through Saturday evening for NEZ011-012-015>018-030>034-042-043. IA...Winter Weather Advisory until midnight CST tonight for IAZ043- 055-056-069-079-080-090-091. Winter Storm Watch from Saturday morning through Saturday evening for IAZ043. && $$ SHORT TERM...Miller LONG TERM...Miller AVIATION...KG

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