Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/07/19

Area Forecast Discussion
National Weather Service Denver/Boulder CO
914 PM MDT Fri Sep 6 2019 .UPDATE... Issued at 914 PM MDT Fri Sep 6 2019 Scattered showers continue moving over Elbert and Lincoln Counties with light to moderate rainfall. A few more showers are also moving over Grand and Summit Counties. These should dissipate over the next couple hours. No changes to tomorrow`s forecast. The airmass should be drier, so the threat of heavy rain will be diminished. Will still see isolated to scattered showers in the afternoon. Temperatures will be similar Friday`s highs. && .SHORT TERM...(This evening through Saturday) Issued at 300 PM MDT Fri Sep 6 2019 The Stratus has dissipated across the plains at this time. Convection is developed over the high country with one main storm now over Jefferson County. Models show an upper trough, mainly north of the CWA, to move east overnight and Saturday. The upper ridge flattens as a result. The flow aloft is west- southwesterly over night, then westerly on Saturday. There is weak upward motion on the QG Omega fields for the CWA tonight, then weak downward energy on Saturday. The low level winds should be pretty normal drainage patterns overnight. On Saturday, they are all over the place, but are generally weak upsloping by afternoon. For moisture, the precipitable water values are in 0.75 to 1.35 inches this evening. By Saturday, they dry out somewhat into the 0.50 to 1.00 inch range by Saturday afternoon. The dew point temperatures are in the 50s to lower 60s this evening, then they decrease into the 40s to lower 50s F by Saturday afternoon. The latest Acars soundings show CAPE values around 1500 J/kg with 85/59 F. For pops, will go with 20-50%s this evening, a bit linger overnight. On Saturday will drop pops somewhat across the CWA. For temperatures, Saturday highs look to be 1-3 C warmer than this afternoon`s highs. .LONG TERM...(Saturday night through Friday) Issued at 235 PM MDT Fri Sep 6 2019 A shortwave will pass north of Colorado Saturday night and Sunday with the associated lift and front late in the day Sunday. Low levels ahead of this trough will be fairly dry over most of the area Saturday evening, with soundings showing DCAPE values of 1,500 J/kg which indicates the potential for downbursts across the plains. Thunderstorms will dissipate as they move east Saturday evening into the drier more stable air. Moisture will increase Sunday as specific humidity levels will rise above 6.0 g/kg over the plains and precipitable water will reach 1.25 inches. Steady storm motion of at least 15 knots and the moving upper level trough driving the convection will limit the duration of storms and should keep the flooding threat low. However, a line of organized storms could produce a period of heavy rain as it passes. A shortwave trough will then rotate around the upper level low off the southwest Canadian coast, passing from the western U.S. across Colorado near midweek. On Monday drier air will move in from the southwest behind the ridge. Tuesday through Thursday there will be a slight increase in moisture leading to isolated storms Tuesday and a better chance of storms on Wednesday and possibly Thursday across the forecast area as the next trough approaches. A front is expected to move through Thursday afternoon bringing gusty winds to 25 mph on the northern plains. On Friday conditions will dry out again as a weak ridge brings more westerly flow. There`s some discrepancy in temperature forecasts this week, but highs should generally be in the 80s on the plains. Some solutions would have us creeping back into the 90s ahead of the midweek trough. It may cool into the 70s behind the trough if this system connects well with the cooler air to our north, but this varies from run to run. Humidities will also be low with some wind behind the trough on Monday, then it will still be dry with less wind on Tuesday. At this time it does not look like widespread Red Flag conditions, but we will be back to an environment where conditions are close to the criteria in the afternoons, especially over the mountain valleys. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 914 PM MDT Fri Sep 6 2019 No more aviation impacts overnight. Winds will remain out of the south overnight. Drier air will move over the Denver area Saturday, so coverage of showers will be much lower than earlier today. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Dankers SHORT TERM...RJK LONG TERM....Sullivan/Gimmestad AVIATION...Dankers
Area Forecast Discussion
National Weather Service Louisville KY
845 PM EDT Fri Sep 6 2019 .Forecast Update... Issued at 845 PM EDT Fri Sep 6 2019 A cold front is draped across central and southern KY at this hour, and will continue to work southward this evening. Seeing a few blips on radar with good convergence ahead of the front, but have yet to see any instances of actual rainfall, or even sprinkles for that matter. The latest AMDAR soundings still show a healthy inversion between H8-H7, and this should limit any deep convection in what would otherwise be a pretty unstable environment. The blips on radar are likely only to the depth of the inversion, and will not be able to develop deeper. So, will remove thunder from the forecast, but will keep the 20% chance of rain in the forecast for the next few hours. Overall, the threat of measurable rain is quite low. && .Short Term...(This evening through Saturday) Updated at 253 PM EDT Fri Sep 6 2019 A well defined cold front is showing up on surface observations this afternoon in central Illinois and Indiana. This cold front will slide into southern Indiana over the next few hours, and eventually central Kentucky this evening through the overnight hours. Models continue to show the development of isolated showers and storms ahead of the front, though they will have a strong cap to contend with. Recent AMDAR soundings from SDF have shown ~16C temperatures around 700mb, which would keep a lid on any convection... but model soundings show this cap slowly eroding as the front approaches, so it`s certainly plausible we could see an isolated shower or storm late this afternoon and evening in central Kentucky. As a result, will keep the mention of isolated PoPs in the forecast through the early overnight hours. The front should push through the region by midnight, leaving clear skies temporarily in its wake. There`s a pretty good post-frontal stratus signal for areas along and east of I-65 after 08-09z tomorrow morning, and it looks like the stratus could persist for a good portion of the morning and early afternoon hours. Some models also show fog developing, but given that drier air will be advecting in behind the front, and winds will remain light out of the north through the early morning hours, fog formation seems unlikely unless the stratus deck settles to the surface. Temperatures will be on the cooler side tomorrow behind the front, and may take a while to climb in areas that see extended cloud cover. Forecast highs will generally be in the upper 70s to low 80s. Dry conditions are expected. .Long Term...(Saturday night through Friday) Updated at 245 PM EDT Fri Sep 6 2019 Surface high over the Great Lakes will give us another pleasant day on Sunday, with low dewpoints and seasonable temperatures. By Sunday night a weak upper wave will pass to our north, and it appears the sharpening warm front will be just far enough north to keep any precip chances out of our area. Upper ridge over the southeast CONUS will expand into the Ohio Valley Mon-Tue, resulting in a warming trend. The hottest days will be Tuesday and Wednesday, with highs in the lower-mid 90s thanks to dry ground conditions. Dewpoints mainly in the mid/upper 60s will keep heat indices below 100. Ridge starts to break down late Wednesday, and more so Thu-Fri. Will continue with slight chance afternoon/evening POPs each day and keep temps above normal both day and night. && .Aviation...(00Z TAF Issuance) Updated at 751 PM EDT Fri Sep 6 2019 A cold front is pushing through the area at this evening, and is bringing an increase in cloud cover, along with an outside chance at a few isolated showers. Don`t have enough confidence that showers will impact the TAF sites to include mention, but did want to focus on the cloud cover in the short term, and in the early Saturday morning hours. Ceilings should be clearing at the northern TAF sites as of this writing, so will only mention Few around 3-4 K feet. BWG will hold onto the ceilings for a few more hours before clearing. Models are hinting at some fog toward dawn, but given steady N winds and drier air behind the front, think we will hold off on mention of fog, except at HNB were some brief MVFR vis is possible toward dawn. The other concern is for some stratus clouds to build into LEX in the pre-dawn hours and possibly SDF by mid morning. Will go ahead and forecast below fuel-alternate and some IFR at LEX, but stay optimistic at SDF between 14 and 18z. Otherwise, surface winds go northerly with the frontal passage, and should stay some sort of NW or N component through this forecast cycle. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...BJS Short Term...DM Long Term...RAS Aviation...BJS
Area Forecast Discussion
National Weather Service Phoenix AZ
553 PM MST Fri Sep 6 2019 .UPDATE... Updated Aviation section. && .SYNOPSIS... Seasonably hot weather will persist into the early part of the weekend before a significant cool down into next week. A weather system will move through the northern part of the region early Sunday bringing rain chances to mainly eastern Arizona, but also cooler conditions areawide. An unsettled weather pattern will persist through the first half of next week with shower and thunderstorm chances returning to much of Arizona while temperatures fall to below normal readings. && .DISCUSSION... Mid-upper level ridge extends from the Baja Peninsula northeastward into northern New Mexico, resulting in a light southwesterly steering flow. Meanwhile, conditions are seasonably moist with PWATs above 1.5 inches across the lower deserts. Latest ACARS soundings indicate two warm layers around 850 mb and 450 mb, which is resulting in considerable convective inhibition in the Phoenix area. However, along the periphery of the Valley, MLCAPEs have reached 500-1000 J/kg with less CIN. Latest local CAMs, HRRR and HREF are in good agreement and indicate isolated thunderstorms are likely in these areas, but will dissipate around sunset. Mean layer flow will become more westerly Saturday ahead of a weak short-wave trough across northwestern AZ and a deeper trough off the CA coast. Latest National Blend shows slight warming ahead of these systems, resulting in pockets of high Heat Risk across the Phoenix area. The day will start out quite warm, possibly breaking the record high min for the date of 87 degrees (set in 2011). Forecast high in Phoenix is 108 degrees, though 110 degrees is not out of the question. Latest long-range ensembles suggest this could also be the hottest day for the remainder of the year and an Excessive Heat Warning has been issued for the Phoenix area and Wickenburg. In addition to the heat, drier air will overspread the southwestern deserts, which will confine afternoon shower and thunderstorm activity to Gila County. && .PREVIOUS DISCUSSION... Moisture levels still look to be on the increase beginning Saturday, most likely Saturday night into Sunday as active monsoon conditions across northern Mexico should send moisture northward into Arizona. There is still some uncertainty for this weekend as any shift in the track of the shortwave may change our rain/storm chances. Models are at least in good agreement significant moisture will get pulled northward ahead of the advancing trough, but mostly show the moisture across eastern Arizona. The shallower depth of the trough also means we will likely see more of a westerly dry flow aloft. For now, best chances for rain fall across the eastern Arizona high terrain early Saturday night through Sunday, with at least a chance into the lower deserts later Sunday as a weak circulation across Sonora Mexico inches northward near the border. Model guidance diverges more for early next week with the European ensemble suite pointing toward best rain chances for south-central and eastern Arizona late Monday into early Tuesday whereas the GEFS mostly distributes QPF evenly Sunday night through Wednesday. Even though forecast confidence in the timing and positioning of any subtle disturbances early next week is quite low, it seems possible many locations from Phoenix eastward should see at least some rainfall at some point Monday through Wednesday. The potential storm severity and impacts look less impressive now that the shortwaves are more likely to pass farther to our north, but the increased winds aloft should at least keep a chance of some strong storms in the forecast early next week. Anticipated QPF amounts are just as hard to pin point, but with forecast low level mixing ratios near 12 g/kg this will at least bring some localized flooding potential across the eastern half of Arizona. As our long lasting high pressure ridge finally gives way to broad scale upper level troughing beginning Sunday, much cooler air will settle across the region. Forecast highs drop to between 100-105 on Sunday and bottom out in the middle 90s to around 100 degrees for Tuesday and Wednesday. Unfortunately, models agree the high pressure ridge will begin rebuilding late next week, eventually becoming centered over the Southwestern U.S. at some point the following weekend. The increasing heights aloft and drying conditions late next week will bring temperatures back to around or even a few degrees above normal at some point late next week. && .AVIATION...Updated at 0055Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: An isolated storm over northern portions of the metro (near/north of 101 Freeway) passing through the vicinity of DVT will cause enhanced gustiness for a brief time though it appears that it will dissipate before reaching SDL. Expect storms to remain outside of the vicinity of PHX and IWA. Couldn`t rule out outflow reaching PHX and causing a change to a crosswind but confidence in that is too low at this time to reflect in the TAF. Will continue to monitor. Otherwise, expect storms in the region to taper off with decreasing surface heating. Overall, westerly winds will prevail the rest of the evening with a slow trend toward downvalley/drainage patterns. Expect PHX will be the last of the TAF sites to lose the west wind tonight before light and variable toward morning. Also toward morning, anticipate isolated weak showers to pass by to the east possibly brushing IWA. Otherwise, anticipate the development of ceilings (bases AOA FL120) roughly between 10Z-16Z. Saturday`s storm activity is anticipated to remain well east of metro Phoenix. Anticipate a bit stronger southwest and west winds in the afternoon as well. Southeast California/Southwest Arizona including KIPL and KBLH: No pressing aviation concerns for the TAF sites though IPL is expected to have a modest sundowner this evening with a distinct change to westerly winds with some moderate gustiness early this evening. Expect west winds to continue at IPL through the period with some gustiness developing again Saturday in the afternoon. Meanwhile BLH will follow familiar diurnal trends with more noticeable gustiness Saturday afternoon. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Monday through Friday: Isolated to scattered showers and thunderstorms will continue each day on and off from Monday into Wednesday, especially from the S- central lower deserts to the higher terrain of east AZ. Max Ts will stay several degrees below seasonal normals through Thursday. Min RH will range from the teens over SE CA to above 20 percent elsewhere through Thursday before drying to the teens on Friday. Excellent overnight recovery through Tuesday night will fall to fair by Friday night. Winds will be light to seasonably breezy. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning from 10 AM to 8 PM MST Saturday for AZZ534-537-540>544-546-548>551. CA...None. && $$ DISCUSSION...Hirsch PREVIOUS DISCUSSION...Kuhlman AVIATION...AJ FIRE WEATHER...Sawtelle