Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/03/19

Area Forecast Discussion
National Weather Service Des Moines IA
633 PM CDT Sat Nov 2 2019 .DISCUSSION.../Tonight through Saturday/ Issued at 225 PM CDT Sat Nov 2 2019 .Overview...Temperatures through the period will remain at least 5 or more degrees below normal as cyclonic flow persists around an upper level low pressure over Hudson Bay. Overall, it will be dry, but there will be passing opportunities for precipitation including on Sunday/Sunday night, later Tuesday, and later Wednesday. Toward the end of the period, a quick shot of colder air will dive into the area followed by a temperature rebound by next weekend. .Details...GOES East imagery early this afternoon shows a split jet stream over the western CONUS with the streams merging to some degree over the eastern CONUS. Over the upper Midwest, northwest flow continues with the shortwave that brought the dreariness and drizzle/light rain on Friday exiting to the east. Heights will be rising slowly over the next 24 hours or so ahead of the next shortwave trough that will arrive later Sunday. This will likely lead to, on average, the warmest conditions over central Iowa for the next 7 days as temperatures peak in the middle 40s over northern Iowa to around 50 degrees over southern Iowa. Sunday will be overall cloudy with cross sections showing a layer of saturation that develops and deepens in the morning over southern Iowa and spreads northward through the day. With weak to moderate omega, expect there will be drizzle or light rain over southern Iowa later Sunday morning perhaps lingering into early afternoon. The 12z NAM Nest, WRF ARW and NMM cores, and recent runs of the RAP all show low chance PoPs so will continue to advertise this possibility. A better chance of precipitation will arrive later in the day into the night and be focused over the northern part of the state as the shortwave arrives with an area of weak low pressure passing well northeast of Iowa. Forecast soundings show that there is saturation within the ice introduction layer, but low levels are expected to be initially too warm for any snow. As temperatures lower in the evening, a transition to a rain snow mix and eventually all snow over northern Iowa is expected. Any accumulations will be confined to elevated and grassy surfaces and just a few tenths of an inch. With temperatures dipping to near freezing, elevated wet surfaces may become slick as they refreeze. Any lingering precipitation will end early Monday morning as high pressure slides into and through Iowa by early Tuesday. The remainder of the forecast is currently favoring dry conditions, though there are a few opportunities for precipitation to brush the state. As the high moves to the east Tuesday, return flow and weak warm air advection may foster a light rain snow mix to all snow late Tuesday afternoon into Tuesday night over northern Iowa. Another chance will come later Wednesday as an upper level low pressure currently off the California coast moves onto the southern Plains. The highest chance for precipitation will be south of Iowa, but it could brush southern Iowa with some light precipitation. As for temperatures, they will certainly be on the cool side for the first half of the week, but models show potential for a quick shot of colder air to end the week as a 1040mb-ish high drops down from the Canadian Rockies and over us Thursday. Looking at a randomly selected location in southern Iowa for temperatures on Wednesday, the distribution of guidance is relatively clustered tightly around a warmer solution compared to the previous forecast and recent run of the NBM, which fall outside of the IQR. The same is not true at a randomly selected location in northern Iowa. The distribution is relatively tightly clustered again, but the previous forecast and recent NBM are within the IQR and at or near the mean for the distribution. For Thursday and Friday, the distribution is more spread with the NBM near the mean over southern Iowa and near the lower end of the IQR over northern Iowa. Therefore, bumped temperatures a few degrees over the southern portion of the area tapering to initial guidance over the north on Wednesday and remained with initial guidance for Thursday and Friday. While the week may end with highs in the 30s, heights are expected to rise over the weekend with temperatures not as cold back into the 40s. && .AVIATION.../For the 00Z TAFS through 00Z Sunday evening/ Issued at 633 PM CDT Sat Nov 2 2019 Winds to become light and variable overnight and shift around to the south, before then shifting back to the southwest for much of Sunday. Sct-Bkn mid clouds overnight, then CIGS lowering to low VFR Sunday afternoon. Could see some gustiness at KOTM with the winds by Sunday afternoon. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ DISCUSSION...Ansorge AVIATION...Beerends
Area Forecast Discussion
National Weather Service Riverton WY
430 PM MDT Sat Nov 2 2019 .SHORT TERM...(Tonight through Monday) Issued at 353 PM MDT Sat Nov 2 2019 A shortwave in the northwest flow will quickly dive across northern/eastern Wyoming tonight, with some support from an upper level jet streak. Snow is expected to develop this evening, and expand in coverage through midnight over the northern mountains, along and east of the Divide. There will be a 3 to 6 hour period where the snow will be the heaviest (still light), as the main shortwave energy pulls across the area. As this occurs some snow could impact the adjacent foothills, but current thinking it would be mainly flurries if it did. In the wake of this shortwave, very light snow or flurries are expected to continue over the northern mountains, mainly over N. Bighorn Mountains Sunday in a moist northwest flow. Elsewhere through Sunday morning, dry conditions with variable mid-high level cloudiness. Another shortwave trough in the northwest flow will dive southeast into the N. Plains/Upper Midwest, sending a weak cold front south into the the area Sunday afternoon into Sunday night. At the same time, models in good agreement with a tightening baroclinic zone in the mid-levels across northern/northeastern parts of the forecast area. Snow is expected to gradually break out across N. Wyoming Sunday afternoon and expand in coverage Sunday evening with the best coverage over the Bighorn Mountains, Northern Bighorn Basin and N. Johnson County. Snow is expected to continue through Sunday night, but gradually decrease in coverage Monday morning as the main forcing shifts away and the area trends to the anti-cyclonic side of the upper jet. For now keeping the Bighorn Mts mainly at or below advisory amounts, with lower elevations an inch or less. One concern in the northwest flow is for the potential of banding of snowfall in the northern or eastern areas of the Bighorn Basin where snow totals are isolated higher by an inch or two. The HRRR and the 18Z NAM12 are hinting at this possibility. .LONG TERM...(Monday night through Saturday) Issued at 353 PM MDT Sat Nov 2 2019 The dominant northwest upper flow over the area will continue through the extended period. Warmer and dry Tuesday for most of the area. By late Tuesday night into Wednesday a cold front will begin pushing down from the north with increased chances of precip into northeastern Wyoming. While most of the precip should stay to the north, the Bighorns could see light snow with minor accumulations through Wednesday. As for temperatures: models disagree on how far the front will make it on Wednesday but highs east of the Divide will likely be 10 to 20 degrees cooler than on Tuesday. Cooler highs continue Thursday before a slight warm up on Friday. Models hint at a break down of the northwest flow by Friday which could usher in more active weather for the weekend. Low confidence for now but have kept higher precip chances across northwestern Wyoming Saturday into Sunday. && .AVIATION...For the 00Z TAFS through 00Z Monday East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals VFR conditions are expected at terminals through the period. A period of snow showers are expected in the northern mountains, especially the Bighorn Mts, between 03Z and 09Z Sunday. Showers will be hard pressed to push into the foothills. If they do, only flurries are expected with ceilings and visibility remaining VFR. Breezy to windy westerly flow will continue on lee side of mountain ranges into some foothills, as well as from Rock Springs to Casper. Will have low-level westerly wind shear for the KCOD terminal, as conditions look similar to what occurred Friday night. A weak cold front will push into northern Wyoming Sunday afternoon, with chances of snow increasing across the far north especially after 21Z Sunday. Ceilings will be lowering Sunday afternoon, but are expected to stay VFR in the lower elevations through 00Z Monday. West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals VFR conditions with variable high-level cloudiness. Wind will be light except breezy between Rock Springs and Casper, as well as over ridge tops. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued AT 353 PM MDT Sat Nov 2 2019 Periods of light snow over the north, mainly over the northern mountains tonight, and again Sunday night and Monday with the second system producing several inches of snow in the northern mountains, but little accumulation over the northern lower elevations. Smoke dispersal on Sunday will be generally poor in most areas, with the exception of areas of fair to good over the western mountains. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Murrell LONG TERM...Myers AVIATION...LaVoie FIRE WEATHER...Murrell