432 FXUS63 KGID 280000 AFDGID Area Forecast Discussion National Weather Service Hastings NE 700 PM CDT Mon May 27 2019 .SHORT TERM...(This evening through Tuesday) Issued at 456 PM CDT Mon May 27 2019 Main concern is potential for severe thunderstorms as well as additional heavy rain and the impact to ongoing flooding. Has been a fairly quiet day weather-wise, especially compared to 12-18hrs ago. Currently, temps are in the 70s to near 80 under p cldy skies. Looking regionally, last night's MCV/shortwave can be seen over E IA, with a trailing cold front/outflow extending to the SW to near OMA-HJH-HYS. S of this boundary, sfc Tds are in the mid to upper 60s. Scat intense convection has developed over the central High Plains in an area of upslope flow, weak-moderate instability, and strong deep layer shear. Strong to severe tstms still look like a possibility later this evening and overnight, though the exact placement and evolution still remains uncertain, even at this close of time range. I currently envision two most plausible scenarios (or a combination of the two) for our severe potential: Scenario 1) elevated convection developing after 03Z on the nose of 50-55kt LLJ near and north of a warm front. This activity would be fed by large reservoir of high theta-e airmass currently over KS/OK with steep mid-level lapse rates contributing to MUCAPE of 2000-3500 J/kg. Latest HRRR/RAP forecast soundings along with latest SREF indicate effective deep layer shear will be more than favorable for large hail potential, generally on the order of 40-60kt. There is some disagreement on location of the nose of LLJ/warm frontal placement and resultant QPF. Last several runs of HRRR as well as NAM suggest main area from Hwy 6 to I-80, but RAP has been along and just S of the state line. RAP appears to be a bit of an outlier attm. Individual cells would move SW to NE with the overall development zone shifting N with the LLJ overnight. Scenario 2) Convection developing over the High Plains moves E through W Nebraska this eve, then arrives in W CWA 03Z-06Z and is fed by developing LLJ. Several CAMs suggest this would arrive as linear features with perhaps embedded supercell structures near the boundary. In theory, this activity could have more of a damaging wind threat and perhaps a tornado or two as well, but the stabilizing boundary layer argues otherwise. Models keep this activity moving along a rather quick pace to the E, which would be good for hydro reasons. Overall, the shear/instability parameter space will likely be favorable for strong to severe storms tonight, whether it be from scenario 1 or 2, or a combination of the two. Hydro certainly remains a concern as well. Please reference the dedicated Hydrology section below for additional details. Activity should weaken and focus further E with time, coincident with a weakening and veering LLJ. There's potentially another round of severe convection in store for portions of the area Tuesday afternoon into early evening, though these details will largely depend on how activity unfolds tonight. In general, models have been trending further S with the sfc triple point and warm front and now track these features near and especially S of Hwy 6, potentially right along the state line. The 12Z NAM places the sfc low/triple point near Red Cloud, NE by 21Z. Areas along/S of warm front and E of trailing dry line would be most favorable for potential sfc based tstm development in the aftn. It is increasingly likely that areas along and N of I-80 remain in the cold sector of the system under the influence of moist, easterly upslope flow and thick low clds. However, a couple of the CAMs (namely the ARW) track what would likely be some slightly elevated supercells NE of the sfc low across the NE quadrant of the CWA. While not likely, this can not be completely discounted either. All of this depends on the speed of the upper system and current timing remains on track such that any risk for severe weather looks to remain largely confined to areas E of Hwy 281. It is possible most of the convection fires just E of the CWA altogether, but with several model solutions keeping the triple point in the SE CWA at 21Z, not ready to downplay svr potential attm. As far as severe threats: CAPE/shear once again looks favorable for supercell structures Tue PM. Large hail would be main concern for areas N of I-80 and E of Hwy 281. All modes of severe would be possible for SE quadrant of CWA, including a couple tornadoes, due to backed winds along warm front contributing to locally elevated 0-3km SRH values of 150-250 m2/s2. The main severe threat will quickly shift E Tue eve, but the upper low will remain in close proximity to continue at least a chc for shwrs/tstms into Tue night, esp for areas N of I-80. Finally, high temps on Tue are tricky. Continued trend of mid shift of decr highs, esp for areas from the Tri-Cities N and W, as low clds and E wind are more likely. Highs may still be too warm along Hwy 6 corridor, as current values are predicated on seeing a few hrs of sun in the aftn, which is uncertain. Right now, highs range from near 60 at Ord, to 82 near Beloit. .LONG TERM...(Tuesday night through Monday) Issued at 456 PM CDT Mon May 27 2019 With the main forecast concerns in the Short Term, not much time spent on the Long Term portion of the forecast. In general, though, expect a cooler, but still somewhat active, pattern for mid-week. Warmer temperatures are more zonal flow with low-end pcpn chances arrive late week and continue into next weekend. Models have trended slower and more strung out with the departing trough Tuesday night into Wednesday. In fact, nearly all the models now keep cyclonic mid to upper flow around through Thu. So what once looked like a few days of dry weather now look off an on wet, particularly for northern 1/2 to 2/3 of the CWA. Models differ on specifics, like how much QPF to expect, with GFS wetter compared to NAM/EC. Eventually, should see the low pressure weaken/move ENE and allow for shortwave ridging to move in for Fri, and perhaps Sat. General consensus is that upper pattern should become fairly zonal next weekend, with multiple small perturbations moving through. Low level moisture and instability should also increase, so off and on scat tstms will be possible. Zonal patterns don't lend much predictability for specifics, so far too soon to determine severe potential. Temperatures: combination of cool northerly flow, cld cover, and possible pcpn will keeps temps on the seasonably cool side Wed into Thu. Axis of high pressure shifts E on Fri, allowing for return to srly flow and warmer mid-level temps. Expect fairly seasonable temperatures next weekend. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday) Issued at 659 PM CDT Mon May 27 2019 Main issue will be lowering ceilings with time. Models are consistently forecast this, and feeling more confident of IFR ceilings by Tuesday morning. && .HYDROLOGY... Issued at 456 PM CDT Mon May 27 2019 Hydro remains a concern mainly tonight, and over the far SE on Tuesday. Have held off on issuing a Flash Flood Watch for now for a few reasons, some of which are uncertainty in location of tonight's tstms, faster storm motions, and lesser coverage. There is less upper forcing for widespread and continuous convection like last night, and latest CAMs keep storms moving along at a nice pace. Think areal average of 0.50-0.75" across south central NE is most appropriate attm. With that said, would not at all be surprised to have additional hydro issues tonight, on at least an isolated basis, as FFG values are low in areas that received hvy rn last night, mainly from Alma to Hastings to Aurora to Osceola. So some heavy cores passing over these areas could easily cause additional flooding or worse ongoing flooding. If confidence increases this eve on intensity and placement of strongest convection, then a Flash Flood Watch may be needed. Can't rule out some hydro concerns over the far SE Tue aftn, but the relatively small window for storms should keep the threat low/isolated. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ SHORT TERM...Thies LONG TERM...Thies AVIATION...Heinlein HYDROLOGY...Thies