474 FXUS63 KLBF 082328 AAA AFDLBF Area Forecast Discussion...UPDATED National Weather Service North Platte NE 628 PM CDT Sun Oct 8 2017 .SYNOPSIS... Issued at 357 PM CDT Sun Oct 8 2017 H5 analysis this morning had a fairly low amplitude pattern across the CONUS. Two main features of note are a shortwave trough over the mid atlantic and a deepening trough of low pressure over the intermountain west. A third shortwave was noted over northern Manitoba. With respect to the western CONUS shortwave: Ht falls in association with this feature were running from 100 to 150 meters across southern Idaho, western Wyoming and northern Utah this morning. Further deepening of this feature is expected over the next 12 to 24 hours, as it is being fed by a 50 to 70 KT jet streak which is currently oriented from western British Columbia into western Oregon. Mid level cloud cover and precipitation in advance of the western CONUS feature was noted from swrn Wyoming into far western South Dakota this afternoon. This area of cloudiness was drifting slowly south and was approaching the northern Nebraska Panhandle as of mid afternoon. At the surface: Low pressure was located over southern Minnesota with a cold front extending ssw into sern Nebraska and swrn Kansas. North of this feature, winds were from the north or northeast and were gusting into the 20 to 25 MPH range across portions of central and southwestern Nebraska. Temperatures as of 3 PM CDT were in the mid 50s in the northwest, to the mid 60s south of Interstate 80. && .SHORT TERM...(This evening through Monday) Issued at 357 PM CDT Sun Oct 8 2017 Main forecast challenge through Monday afternoon deals with a potent mid level shortwave crossing the Rockies/Northern Plains and low that closes off over Kansas. Specifically, p-type will be tricky due to temps. Clouds will continue to thicken from northwest to southeast across the area as easterly H7-8 flow contributes to upslope flow ahead of the shortwave. Model consensus has slowed the start of the precip slightly, which agrees with current satellite and sfc ob trends. The best moisture aloft remains over central WY/far western SD per WV and IR imagery, and sfc dew point depressions around 25F remain at KAIA and KGRN as of 20z. Slowly work PoP in to cover areas west of Hwy 83 by 03z and Hwy 183 by 06z. Kept all precip as -RA through 05z, then begin to add RASN across the far NW. Initially used sfc temps of <37F to determine RASN and <34F for SN, then tweaked using forecast soundings. The NAM is the coolest model, suggesting a subfreezing layer as low as H85 and sfc wet bulb around 2C at KAIA, KCDR, and Merriman. RAP and GFS showing slightly warmer temp profiles, which will make a large difference in this scenario due to being near freezing. Brought RASN line east to Hwy 61 and north of Hwy 92, and all SN primarily invof the Pine Ridge. Went conservative on the snow amounts due to the amount of rain mixing in and warm sfc temps (4" soil readings in the 50s). Stayed near guidance for overnight lows with increasing cloud cover and precip, but trended toward the cooler solutions for Monday highs. The main concern of expanded area of RASN or SN is reliant on the magnitude of dynamic cooling. RAP and NAM agree with a couple deformation bands developing across the forecast area - one NW/panhandle and one central Sandhills to SW Neb. Cross section analysis suggests some slantwise instability, which could lead to enhanced precip rates and increased cooling in the temp profile. Can't rule out mixed precip as far east as KOGA to KVTN with the deformation band setting up in the pre-dawn hours. Even if a complete switch to snow occurs, little accumulation is expected. Stronger lift occurs H5-7, but the DGZ lies primarily H4-6. Regardless, SLRs are low, i.e. <10. .LONG TERM...(Monday night through Sunday) Issued at 357 PM CDT Sun Oct 8 2017 Monday night through Wednesday: The main forecast challenge deals with precipitation chances in the east with the exiting h5 trough Monday night, along with low temperatures Tuesday morning and the threat for widespread freezing conditions. For Monday Night with respect to the timing of the exiting h5 system and precipitation chances: The latest NAM12 soln has slowed somewhat, allowing deformation precipitation to back into sern portions of the forecast area Monday evening. The GFS is more progressive and leads to a dry fcst for the sern CWA Monday evening. With the NAM12 and the gfs to a lesser degree, indicating some lingering cloud cover in the sern forecast are late Monday night, will hold onto a freeze watch for Frontier, Custer, Garfield and Wheeler counties. Elsewhere, feel we will be clear enough overnight to reach the mid to upper 20s and will upgrade the freeze and hard freeze watches to warnings. Utilized a blend of the MET and MAV guidance temps for lows Monday night, which was below the superblend. On Tuesday, we should see clear skies across most of the forecast area but highs will remain cool with readings in the 50s. Warmer air will push into the region for Wednesday, thanks to the development of a low amplitude ridge across the high plains downstream of a deepening trough across the Pacific Northwest. Highs Wednesday will reach the mid to upper 60s. Wednesday night through Sunday: Dry conditions will continue through Friday with highs Thursday in the 70s. An upper level wave will cross southern Canada Thursday Night, forcing a cold front into western and north central Nebraska. ATTM, forcing for post frontal pcpn will remain north of the forecast area, so a dry forecast continues. Highs Friday will be upper 50s to lower 60s. A second upper level trough of low pressure will deepen across the intermountain west Saturday, inducing surface cyclogenesis across eastern Colorado. This will lift the front north as a warm front Friday night into Saturday with an increasing threat for showers, mainly in the eastern forecast area Saturday. A better chance for showers will arrive Saturday night into Sunday as the trough of low pressure aloft traverses the Central Plains. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 628 PM CDT Sun Oct 8 2017 Indications from the SREF suggest IFR/LIFR in SN/RA and low cigs/vsby will generally remain along and west of highway 61 tonight and Monday. MVFR/VFR will occur east of highway 61. VFR will become widspread along and north of I-80 by 00z Monday evening. && .LBF WATCHES/WARNINGS/ADVISORIES... Hard Freeze Warning from midnight CDT /11 PM MDT/ Monday night to 10 AM CDT /9 AM MDT/ Tuesday for NEZ004>006-008-009-022>027- 035>037-056>059-069-094. Freeze Warning from midnight Monday night to 10 AM CDT Tuesday for NEZ007-010-070. Freeze Watch from late Monday night through Tuesday morning for NEZ028-029-038-071. && $$ SYNOPSIS...Buttler SHORT TERM...Snively LONG TERM...Buttler AVIATION...CDC