Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 220537 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1137 PM CST Tue Feb 21 2017 .SHORT TERM...(tonight through Friday) Issued at 253 PM CST Tue Feb 21 2017 Today likely is the peak of warm February conditions for most locations. Subjective 12Z upper-air analysis indicates a broad upper-level low centered over the Arklatex area. Another upper- level trough was digging in upstream off the Pacific coast. A 135kt upper-level jet extended into northern CA/northern NV, with smaller 130kt southwesterly jet streak across WI. Warm dome at 850mb continued, with 10C+ temperatures as far north as central SD to southeast MT and as far west as the NV/UT border. Surface low at 19Z was centered in north central SD, with a weaker surface low centered in northern AR, and a ridge axis extending between from southwest TX/western OK through eastern KS to southern and eastern IA. Main forecast concerns are temperatures tomorrow and winter weather system on Thursday-Friday. A weak and fast-moving shortwave will slide across the northern Plains tonight into Wednesday, dragging the first shot of cooler air into the central US. Surface to mid- level winds will turn northwesterly from morning through early afternoon across the CWA as the cold front slips into the area. Temperatures will still be quite warm, but in northeast NE where the airmass changes earlier, temperatures will likely remain in the lower 60s. The lower temperatures should hold RH values into the mid 20s or higher, keeping us just out of red flag territory, and will not issue a fire weather watch for tomorrow. By Thursday morning, a deeper western US trough will dig, with precipitation expanding from WY/CO into western NE/western SD. This area should expand eastward through the day as the western trough digs and closes into a low. Surface temperatures should remain above freezing across the CWA through the day, with model solutions having various speeds of dropping 850mb temperatures below 0C into the northwestern CWA. Given the warm surface layer, even if 850mb temps do fall below 0C, rain or a rain/snow mix would be likely through the day, with no accumulation. Temperatures in northeast NE should fall quickly after sunset, with slow progression of subfreezing temperatures from 850mb to the surface through the night. Even so, middle-of-the-road GFS and ECMWF solutions (between slower GEM and way-too-fast NAM) keep above-0C temperatures in western IA to southeast NE through around 12Z Friday. Above-freezing surface temperatures remain as far north as the I-80 corridor by 12Z in both solutions, with falling temperatures on Friday finally taking freezing temperatures across the rest of the CWA by around afternoon (ECMWF) to evening (GFS). All in all, the trend is toward a warmer solution in the south, while still cold and wet in the north. Not likely to be able to pin down the location of the heaviest snow band yet, but ECMWF/GFS solutions are fairly consistent in taking it across northern to northeastern Nebraska and then into SD/MN/northwest IA. ECMWF would have a broader swath of snowfall amounts of at least a few inches, while GFS has a tighter gradient on the south side of the band due to the warmer temperatures. Have reduced snowfall forecast in the southeastern CWA for now and nudged higher in the northwest. Solutions still look rather breezy on the back side of surface low pressure as it deepens and ejects across KS/southeast NE/IA, with winds switching from northeast to northwest as the inverted trough progresses eastward. Have opted to issue a winter storm watch for the northern five counties of northeast NE, where potential is highest for accumulating snowfall of 6 or more inches. .LONG TERM...(Friday night through Tuesday) Issued at 253 PM CST Tue Feb 21 2017 The late-week storm system will usher in a return to near-normal temperatures, along with a more active weather pattern. Upper-level flow will become zonal this weekend and turn more southwesterly through the week as another upper-level trough takes shape in the western US. Its depth and speed are still different among model solutions, but the pattern should favor gradual moderation and a progression of weak shortwaves that may generate brief, low-end precipitation. Saturday should remain cold and blustery behind the system, with temperatures lingering near or below freezing in northeast NE/northwest IA to the upper 30s elsewhere. Temperatures in areas with little or no snowpack should return to highs in the mid-40s into the work week, with slower but gradual warming in snowier areas. Have kept a slight chance of snow in the southern CWA on Saturday night/Sunday, as well as a small chance of precipitation on Monday. && .AVIATION...
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(For the 06Z TAFS through 06Z Wednesday night) Issued at 1136 PM CST Tue Feb 21 2017 VFR conditions are expected through the TAF cycle. Surface winds will become northwest Wednesday morning as a cold front pushes through the region. Some gusty winds to 25kts are possible in the afternoon but should subside by evening.
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NE...Winter Storm Watch from Thursday evening through Friday afternoon for NEZ011-012-016>018. IA...None.
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&& $$ SHORT TERM...Mayes LONG TERM...Mayes AVIATION...Kern is the U.S. government's official web portal to all federal, state and local government web resources and services.