####018005072#### FXUS65 KCYS 040847 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 247 AM MDT Sat May 4 2024 .KEY MESSAGES... - Mainly dry and warmer conditions are anticipated for the weekend. - Strong winds (60+ mph) return to southeast Wyoming and western Nebraska Monday with a prolonged period of elevated winds continuing for wind prone locations through midweek. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 247 AM MDT Sat May 4 2024 Today...Transitory shortwave ridging aloft will build overhead and with plenty of sunshine and 700 mb temperatures near 2 Celsius, maximum temperatures will reach the upper 50s to mid 60s, with south low level winds limiting the warmup. Tonight...Decent moderation in temperatures will occur as southwest flow aloft strengthens ahead of the approaching trough aloft over the Great Basin states, inducing increasing south winds and a thermal ridge over our counties, with low temperatures from the mid 30s to lower 40s. Sunday...Southwest flow aloft strengthens ahead of the approaching trough aloft over the Great Basin states, inducing a fairly significant surface trough along Interstate 25. Surface and low level gradients support a windy day with brisk south to southeast winds. Although the atmosphere will be relatively dry, it appears there will be enough low and mid level moisture to support isolated afternoon shower and thunderstorm coverage along the surface trough from Douglas to Laramie. 700 mb temperatures near 8 Celsius support maximum temperatures from the upper 60s to mid 70s. Sunday night...The negatively tilted shortwave trough aloft pivots into western Colorado, sending the leading edge of a potent Pacific origin cold front into our western counties. Looks like enough low and mid level moisture, combined with cold frontal lifting and dynamic forcing associated with the 500-300 mb and 700-500 mb quasigeostrophic forcing to produce scattered showers and isolated thunderstorms across our forecast area, with snow showers becoming widespread across our Snowy and Sierra Madre Ranges. && .LONG TERM /MONDAY THROUGH FRIDAY/... Issued at 247 AM MDT Sat May 4 2024 An upper level low will be traversing the region early next week with the trough axis of the initial wave passing through the CWA Monday. While severe storms are expected across the central plains farther east, strong winds are likely to be the local impact across southeast WY and western NE with this storm system. Strong cross barrier winds developing across the Laramie Range with impressive downward omega fields in the wake of the trough axis passage could lead to wind gusts 70-75 mph along the I-25 corridor. Latest NBM probabilities of 55+ mph wind gusts are quite high (>80%) for most wind-prone areas Monday across southeast WY with areas covered by 50% probabilities expanding outside of wind-prone locations onto adjacent foothills and plains. Additionally, in-house guidance continues to show high probabilities (60-80%) for high winds. There remains to be some uncertainty with the duration of this wind event with elevated to potential high winds continuing through Wednesday morning. However, guidance has been starting to suggest Monday is the most likely timing of the strongest winds across much of the area, while wind-prone locations could continue to see occasional gusts into midweek. 700mb flow climbing over 60 kt across southeast WY with strong ensemble support for high winds early next week as the latest NAEFS and EC are showing over climatological 99th percentile 700mb winds. Precipitation chances Monday will be best across Carbon Co as well as over east-central WY extending northward. Surface cyclogenesis with this upper low track appears more likely in southeast MT and western SD keeping much of the precipitation shield to the north. Additionally, this upper level low looks to stall out across the central CONUS with a potentially retrograding surface low leaving southeast WY and western NE under a general troughing pattern through the remainder of the week. This will lead to below average temperatures for early May with additional chances for light precipitation through the remainder of the week. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1120 PM MDT Fri May 3 2024 VFR conditions currently across area terminals as upper level clouds continue to move off towards the east, giving way to mostly clear skies. Latest GOES Nighttime Microphysics RGB does show lingering low clouds mainly near southeast WY terminals that could persist through the early morning hours. Gusty winds will return Saturday afternoon, generally out of the south. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...RUBIN LONG TERM...MB AVIATION...MB ####018007077#### FXUS63 KBIS 040847 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 347 AM CDT Sat May 4 2024 .KEY MESSAGES... - Low to medium chances (20 to 40 percent) for rain showers will diminish this morning across the far north central. More isolated showers (~20 percent chance) are possible this afternoon across the north central and northeast. - Expect warmer highs today through Monday before we cool back into normal to below normal categories for most of the work week. - Gusty southeast winds are likely Sunday through Monday. Sustained winds up to 35 mph will be possible with gusts to 50 mph. - Chances for rain return late Sunday evening and continue through the work week. The wettest period will be Monday through Tuesday when most of western and central North Dakota will see high chances (70 to 90 percent) of rain. && .DISCUSSION... Issued at 347 AM CDT Sat May 4 2024 At the mid to upper levels, a trough axis currently sits over central North Dakota and will continue to move east through the morning as a western ridge starts to approach. Given the upper level forcing of the trough, a few rain showers (20 to 40 percent chance) will remain possible across the far north central, mainly north of the Highway 2 corridor. Surface high pressure will move in today as the western ridge nudges closer. Clouds should diminish from southwest to northeast through the day and into the evening. We may see enough diurnal heating and synoptic forcing for a few more isolated showers across the north central and northeast this afternoon (~20 percent chance). This activity should diminish rather quickly around and after sunset given the loss of heating. Highs will be a bit warmer today than in previous days, ranging from the lower 50s to lower 60s. Areas that clear out earlier today may end up a touch warmer. The ridge axis then crosses the state on Sunday, which will lead to even warmer temperatures and a mostly sunny sky. Highs will range from the lower 60s around the Turtle Mountains, to the lower 70s southwest. That being said, the surface pressure gradient will tighten as a longwave trough approaches and a surface low deepens significantly over northern Wyoming. This gradient coupled with strong pressure falls and steep lapse rates will lead to gusty winds out of the southeast. The latest NAM/NAM Nest soundings have come in a bit stronger with winds at the top of the mixed layer Sunday and Sunday night. For now it appears that the strongest winds will be across the southwest and south central where forecast soundings suggest the potential for up to 50 knots at the top of the mixed layer. Elsewhere across the west, we could see 40 to 45 knots at the top of the mixed layer. All that being said, it certainly appears that we will see higher winds than we usually see in these southeasterly flow setups with some sustained values up to 35 mph and gusts up to 50 mph. Wind headlines will likely be needed in future shifts. As the longwave trough approaches Sunday night, the aforementioned surface low will move out of northern Wyoming and into eastern Montana. An initial shortwave impulse will overspread the low and we will see increasing chances of rain across the west by the late evening hours. Several waves will then move around the base of the potent trough and eject into the northern Plains through the day on Monday as it takes on a negative tilt. Another surface low moves into western South Dakota by mid to late Monday morning and then deepens (sub 985 mb?) as it lifts into western or central North Dakota by the late afternoon or early evening. By then, the system is forecast to become stacked and nearly stationary or even retrograde back into eastern Montana Tuesday into Wednesday. Cluster analysis suggests that two distinct scenarios have started to show themselves and at the moment it appears that each scenario has about a 50/50 chance of happening. One scenario would have the main low ending up in northeast Montana and the other would have the low ending up somewhere across southwest North Dakota. Scenario one would lead to the heaviest precipitation being mainly over eastern Montana with a more pronounced dry slot over central North Dakota. The second scenario would lead to some heavier rain across the west (especially the southwest) and maybe a less pronounced dry slot. No matter the scenario, it does appear that we will at least see some dry slotting somewhere across the central with the James River Valley and vicinity being the most likely area. Regarding thunderstorm potential on Monday, CSU Machine- Learning guidance still suggests low chances for severe weather in the afternoon and evening, but the signal continues to weaken given meager instability in the forecast. Shear will be strong and we could see some pockets of MUCAPE up to 500 J/kg or so. Thus, a few strong storms may not be out of the question but the severe threat continues to appear low. The upper low remains stalled out over the northern Plains through at least midweek before it washes out or moves out towards the end of the week (models are having a tough time deciding how this low predictability pattern evolves mid to late week). This will mean more highs in the normal to below normal categories (mainly in the lower 50s to lower 60s) Tuesday through the rest of the week and continued chances for rain. The period for heaviest rainfall will be Monday and Tuesday but the highest NBM probabilities for an inch or greater have shifted to the west, now maximized over portions of central and eastern Montana. That being said, 72-hour NBM probabilities (ending 12z Thursday) for an inch or greater still range from 40 to 60 percent across much of the west and central. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1243 AM CDT Sat May 4 2024 A few showers will continue overnight, mainly along the International Border across the north central and northeast. A band of MVFR to IFR stratus will move in from Canada overnight and sag into the northwest, north central, and perhaps to the northern fringes of the James River Valley. KMOT will likely see MVFR to IFR ceilings until late Saturday morning or early afternoon. Sites KXWA, KBIS, and KJMS will be right on the western and southern edges of this stratus band. Therefore, it isn't out of the question that some MVFR ceilings will occasionally impact these sites at times through Saturday morning. KDIK should remain in VFR conditions through the period. A few isolated showers may once again develop across the north central and northeast Saturday afternoon. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...ZH AVIATION...ZH ####018005971#### FXUS63 KJKL 040849 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 449 AM EDT Sat May 4 2024 .KEY MESSAGES... - A shower and thunderstorm potential lasts through the next 7 days. - Above normal temperatures are forecast through most of the next week. A cold front should pass late in the week and bring readings down to near or below normal. && .SHORT TERM...(Today through Sunday) Issued at 449 AM EDT SAT MAY 4 2024 Isolated rain showers were ongoing at time of forecast issuance early this morning, and were beginning to slowly increase in coverage, especially north of the Mountain Parkway. This trend is expected to continue through sunrise this morning. Once the sun is up, isolated to scattered showers are expected to fire across eastern Kentucky. The primary challenge in the short term portion of the forecast will be how widespread will showers and storms become today. To answer that question, the latest model data was consulted and revealed that in spite of ample moisture and instability being in place, the lack of a clear cut triggering mechanism will limit shower and storm coverage today. With several models all supporting this scenario, the HRRR, NAMNEST, and CAMS in particular, it made sense to go with much lower precip chances for today than previously forecast. The same scenario looks reasonable for Sunday as well. The 6Z analysis showed a stationary front in place from the eastern Great Lakes into southwestern Indiana and then across Missouri where it merged with a surface low situated over southeastern Nebraska. A weak trough of low pressure was also analyzed over central Kentucky, just south of the Ohio River, but due to the weakness of this feature, it appears it will not offer enough lift to spark widespread convection today. Instead, it looks like todays showers and storms will be diurnally driven, and will peak in coverage this afternoon into early this evening, before quickly tapering off after dark, when instability will also quickly wane. Another frontal boundary extended southwestward through Kansas into far western Oklahoma and then further west out to Nevada. A well defined dry line was also in place extended southward from a surface over the Oklahoma pan handle through eastern New Mexico and across extreme western Texas. This set of boundaries and surface lows will be the focus for severe weather across the southern Plains later today. Temperatures will continue to run above normal over the weekend, with todays highs maxing out in the upper 70s, and Sundays max readings in the upper 70s and lower 80s. Tonights lows should fall to around 60, with only minimal ridge valley differences due to extensive cloud cover and little radiational cooling expected. No significant weather concerns are expected at this time, with only garden variety thunderstorms on tap today and tomorrow. Winds should be generally from the south or southwest and 5 to 10kts today and tomorrow, and light and variable tonight. .LONG TERM...(Sunday night through Friday) Issued at 449 AM EDT SAT MAY 4 2024 The long term period continues to look wet. Prevailing large scale flow aloft will be persistent from the west southwest through at least Thursday, while low level flow is out of the southwest off the gulf. This pattern of warm/moist advection will favor precip whenever there are triggers/forcing mechanisms. A wavering frontal boundary will approach from the northwest at times, but being largely parallel to the upper level flow until near the end of the period it is not likely to make a forceful passage until then. This will leave us in a modestly humid air mass with surface dew points mainly in the lower to mid 60s. The main drivers for precip will be mid/upper level waves along with diurnal heating/destabilization cycles. The mid/upper level waves with the most agreement in the models are ones that would affect us on Monday, and also Wednesday night into Thursday, and these time frames contain the highest POP area wide at mainly 70%+. There are some model discrepancies in the Thursday-Friday time frame concerning timing of an eventual cold frontal passage. In the 00Z deterministic/operational runs, the GFS is faster than the ECMWF with the passage of the primary cold front, and this results in lower forecast confidence. The current forecast is a model blend, but temperatures are likely to end up being either warmer or colder, depending on timing of cold fropa. Also, a faster fropa would result in the POP dropping off faster, and a slower passage would allow precip to linger longer. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) ISSUED AT 135 AM EDT SAT MAY 4 2024 Scattered showers, and perhaps an isolated thunderstorm, will continue across the area through the night. The challenge will be determining whether or not a particular TAF site sees any showers or storms, so VCTS or VCSH were used to account for any such activity. We should see an uptick in showers and storms after the sun comes up, as heating begins to occur and instability increases. This will be especially true during the early afternoon through early evening hours on Saturday. In fact, widespread showers and at least scattered storms are expected from around 17Z today through around 2Z Saturday night. MVFR to IFR CIGs will be possible with any storm or intense shower, along with brief periods of MVFR VSBYs. Winds should be out of the south or southwest at less than 10kts during the day, but could be stronger and gusty with any storms that affect at TAF site. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...AR LONG TERM...HAL AVIATION...AR