Area Forecast Discussion
Issued by NWS Goodland, KS
Issued by NWS Goodland, KS
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960 FXUS63 KGLD 211906 AFDGLD Area Forecast Discussion National Weather Service Goodland KS 106 PM MDT Sat Sep 21 2024 .KEY MESSAGES... - Showers and thunderstorms will develop over majority of the Tri-State area this weekend. Both severe weather and flooding chances are very low (<5%). - Low temperatures in the mid to upper 30s are forecast for eastern Colorado by Monday morning. There is a concern for fog formation Monday morning, too. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 320 AM MDT Sat Sep 21 2024 This morning, the low pressure system that we have been monitoring for the past week will be near the Four Corners region and moving east-northeast. Over the past few days, guidance has been very gradually slowing this low, which is delaying the start of the precipitation. Another notable change over the previous 36-48 hours is that the low looks to be taking a more easterly path than previously thought. These two changes have broadened out the low, making it weaker, and has shifted it`s main path farther south, likely over the south-central CWA when it finally crosses. The broadening will push a the cold front into the area early this morning, likely crossing the entire CWA by 18Z. With this cold front, northerly winds sustained around 20-25 kts and gusts around 35 kts are expected this morning and mid-day. These winds will cause temperatures to remain cool, likely hitting maximum temperatures before noon. Temperatures today in the northwestern CWA will be in the low 70s, but the southeastern CWA will still warm into the low 80s before the cold front passes. This cold front coming earlier than previously thought, and the more southern track, has lowered total QPF for the northwestern half of the CWA. Guidance is showing the 500mb shortwave that will set off the precipitation will start forming showers and storms south of the CWA by 16-18Z. Over the following hours, this precipitation will move northeastward while new showers will form west of the already existing precipitation. No later than 21Z, we expect to see precipitation in the CWA. The best coverage of rain for will start around 0Z. From 0Z through 12Z, all of the CWA will have 50-75+ PoPs. After 12Z, PoPs taper off from the southwest as drier air moves in and pressure rises occur following the low. By 0Z Monday, all of the precipitation will have moved out of the area. For more information about the precipitation, see the hydrology discussion below. Severe convective weather seems extremely unlikely (<2% chance) due to a lack of instability. Temperatures overnight tonight will be a balancing act between the CAA and the clouds insulating us. Currently we expect lows to cool into the mid 40s in the west to low 50s in the east. However, if the northerly winds are stronger, expect cooler temperatures (~5 degrees cooler), but if the winds/CAA weaken, expect lows near 50 for the entire Tri-State area. Sunday`s high temperatures will be the coolest we`ve seen so far this season. The clouds and northerly winds will prevent majority of the day time heating. Temperatures are expected to remain in the low to mid 50s Sunday. As the low moves out of the area Sunday afternoon/evening, winds will weaken and the sky will clear out. This is creating an interesting setup overnight Sunday where two things could happen, or a mixture of both. Potential one is patchy to widespread fog; with clear skies, light winds, and recent precipitation, the environment is primed for fog formation, with a catch. The light winds that will exist will be westerly, downslope winds, which will work to prevent fog formation. Most likely scenario is valleys and locations sheltered from the light breezes will see fog form, but if the winds drop to 0, widespread fog could easily form. Potential two is frost formation, mainly in eastern Colorado. The same conditions that make fog possible/likely Sunday (minus the moisture) could allow for temperatures to drop into the mid 30s, allowing for light, patchy frost to form. The big unknown, and biggest limiting factor, for the frost potential is what the dew points will do Sunday evening/overnight. If dew points remain in the low 40s in eastern Colorado Sunday evening/night, the potential for frost is near 0. However, if the dew points are in the mid 30s, patchy frost becomes more likely. Confidence for "potential one," the fog, occurring is around 30% and could impact majority of the CWA. Confidence for "potential two," the frost, occurring is around 25%, but looks to be limited to our Colorado counties. As mentioned before, there is a chance (~20%) that both could occur; we could see fog in the eastern CWA and frost in the western CWA. We will be monitoring this closely over the next 36 hour. && .LONG TERM /MONDAY THROUGH SATURDAY/... Issued at 106 PM MDT Sat Sep 21 2024 Going into next week, the latest runs of the GFS/ECMWF continue to show an amplified 500mb ridge over the western portion of the country work eastward into the Rockies. The weak system that had been forecast the past couple of days to traverse the eastern side of this ridge Monday night into Tuesday has now weakened further. The two models are not consistent now with this system affecting the western portion of the CWA. With its passage now only Monday night, weak instability present to warrant only a mention of 15-20% chance for showers mainly from Highway 27 and points west into eastern Colorado. Dry conditions with near to above normal temperatures will ensue from Tuesday into the end of next week, aided in part by a persistent southerly surface flow beginning from late Tuesday onward. Both sets of guidance do show the potential for a cutoff upper low well east of the CWA to begin to retrograde Friday evening. Moisture pinwheeling around the system right now does work into eastern portions of Graham and Norton counties. Have kept in a 15% chance for a shower in those areas, but nothing major expected. For temps, looking for a slight increasing trend for highs across the area. Monday and Tuesday will see mainly 70s, with a few isolated 60s possible. By Wednesday mid to upper 70s expected with upper 70s to lower 80s for Thursday onward. Overall near to above normal numbers for highs from Wednesday onward, with slightly below normal for Monday and Tuesday. Overnight lows will range in the 40s area-wide through midweek, and then from Thursday night onward a range from the upper 40s west into the mid 50s east. Lows will range near to above normal. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1144 AM MDT Sat Sep 21 2024 For KGLD & KMCK... VFR conditions are forecast for a majority of the period, with MVFR and maybe some IFR ceilings near the end of the period. The front is through the area and winds are forecast to remain gusty until the cloud cover moves over and limits the mixing. Winds would still likely gusts near 20-25 kts through the evening and night. Rain is forecast to enter the area starting this afternoon, but dry air is forecast to keep the precipitation limited at both airports. So be alert for showers and storms starting around 21Z, but the main timeframe and higher chances is around 08-12Z as the upper wave moves over the area. Once this passes, the low levels are forecast to saturate and allow ceilings to drop to near 1000ft across most of the area. KMCK is more likely to stay VFR depending on how the dry air streak sets up over the area. && .HYDROLOGY... Issued at 320 AM MDT Sat Sep 21 2024 The 850mb LLJ has been moving moisture into the Great Plains overnight and will continue into Sunday, following the low as it moves east out of the area. Due to the more southerly path the low is expected to take and the early cold front, most of this moisture will not directly be moved into the CWA. The moisture will instead be moved into the area by the low as wrap-around moisture, as seen on 315K maps. Precipitation looks to start in the eastern CWA late Saturday morning/early afternoon, intensifying Saturday evening, and begin weakening Sunday morning/mid-day before moving out of the area by Sunday evening. Between 0Z-12Z Sunday, nearly the entire Tri-State area will see at least a few tenths of rain with the potential (20- 25%) of seeing 1+ inches in that timeframe. Concerns for flash flooding are low (<5%) with the potential for areal or river flooding being slightly higher at around 20%. Throughout the entire event, locations along and southeast of a line from Wallace, KS to Hill City, KS can expect to see .9-1.7 inches of rain, with pockets of 2.5+ inches being possible. Locations west and north of that line, but south of HWY 36 will receive around 0.4-1 inch of rain, with some pockets up to 1.75 inches. Areas north of HWY 36 will see the least amount of rain, generally ranging from around 0.25-.8 inches. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...None. CO...None. NE...None. && $$ SHORT TERM...CA LONG TERM...JN AVIATION...KAK HYDROLOGY...CA