243 FXUS63 KGID 200520 AFDGID AREA FORECAST DISCUSSION National Weather Service Hastings NE 1120 PM CST Thu Nov 19 2020 ...Aviation Update... .DISCUSSION...(This evening through Thursday) Issued at 254 PM CST Thu Nov 19 2020 Shaping up to be a really nice day today with highs well above average for this time of year. In fact, highs are actually over achieving in a few places so far, so adjustments were made as needed. The passage of a sfc trof along with a rather diffuse cold front this morning has turned our winds northerly for today with speeds generally less than 15 mph. Cooler, more seasonable weather is on its way back after today. Though we are expected to remain in rather zonal flow aloft the next couple of days, there will be a couple shortwave trofs that are expected to roll through over the next 7 days. Those two trofs and their associated precip chances is what I'd like to focus the rest of this discussion on. Shortwave 1, Saturday: This first wave has been increasingly becoming less of a concern for our area with each new model run it seems. A weak midlevel trof is expected to swing through on Saturday ahead of its upper level counterpart, and possibly bring a slight chance for some precip. Currently not too confident regarding PoPs Sat-Sun early morning. Overall there is not a whole lot of forcing or moisture. The GFS has pushed this system further south with each run, the ECMWF has some weak QPF signal Saturday night, and the European ensembles only have a few members showing measurable precip. Of the hi-res models, only the NAM and NAMNEST are run far enough out to capture Saturday at this point. The NAM keeps nearly all the QPF to our south, and the NAMNEST, unsurprisingly, has the strongest QPF signal for us. Wouldn't be surprised if the NBM decreases PoPs a good bit over the next several runs as the short term hi-res models make their way into the solution. Shortwave 2, Tuesday: Brief ridging aloft is expected Sunday night into Monday in the wake of the first wave mentioned above. Monday afternoon/evening a minor perturbation ahead of the next approaching trof looks to pass overhead, coinciding with the leading edge of the mid-level trof (ahead of the main upper level trof). As a sfc low develops just to the east of the Rockies expect to see a tightening of the sfc pressure gradient and therefore gusty southerly winds for Monday. PoPs will gradually begin to increase starting as early Monday afternoon, as the system as a whole moves east and the sfc low pushes off the Rockies. Currently the ECMWF has the upper level trof deepening as it crosses the Rockies and shows the sfc low deepening and centered over northern OK and into southern KS with a broad precip shield extending north and northeast. The GFS shows a faster and more progressive system with the upper level trof not deepening until over the Plains on Tuesday. With the upper level trof not deepening as early/further west, the associated sfc low ends up much farther north and is instead centered over central NE Monday night. These differences in progression lead to a wide disparity in both spacial and temporal coverage of precip. The ECMWF has the majority of QPF Tuesday afternoon into the overnight. The GFS on the other hand has the majority of QPF Monday evening and overnight into Tuesday morning. This could be a key difference to watch especially with regards to potential precip type. Once this second wave passes, we return to zonal flow aloft for a few days. && .AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Saturday) Issued at 1115 PM CST Thu Nov 19 2020 VFR conditions are expected through the TAF period. A cold front has just crossed KEAR and KGRI, bringing a wind shift to the northwest and an increase in wind speeds. Surface high pressure will build southeast from the Dakotas today/tonight with overall wind speeds relatively light. && .GID WATCHES/WARNINGS/ADVISORIES... NE...NONE. KS...NONE. && $$ DISCUSSION...Shawkey AVIATION...Fay