Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/20/19

See below for an aviation forecast discussion for the 00Z TAFs.

&& .DISCUSSION... Issued at 309 PM CDT Mon Aug 19 2019 A weak shortwave passes through parts of the Dakotas this evening. While a couple showers or thunderstorms may affect the northwestern CWA tonight off this wave of energy or via daytime heating alone, confidence has been decreasing that anything will develop. A better chance for precipitation occurs tonight as a low-level jet sets up over eastern South Dakota, but even then the best forcing looks to be mostly south of the CWA. Nevertheless, ensemble PWATS are about 1.25 standard deviations above climatological normals for eastern South Dakota as southerly winds help draw in low-level moisture. In addition, very good instability and moderate shear would indicate that if thunderstorms do develop, they would be able to sustain themselves and potentially become severe. High pressure builds into the region Tuesday and looks to keep things mostly dry through the day Thursday. Thursday night through the weekend will likely be more active. Models are in pretty good agreement and suggest a bit more potent shortwave working its way through the region Thursday night and through the day Friday followed by a second shortwave Sunday. High temperatures this week look to be seasonably cool overall with Tuesday being the warmest day besides this afternoon. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening) Issued at 655 PM CDT Mon Aug 19 2019 Probably looking at VFR conditions for the next 6 hours. However, there is a notably moist airmass advecting northward over the region right now, and some of it hasn`t mixed out completely. There could be some 3500 to 5000 ft agl bkn cigs at times through this evening at any of the four terminals, before cigs begin to lower. If KMBG sees a thunderstorm this evening, it`s mainly between 03Z and 05Z. If KATY sees a thunderstorm, it`s mainly between 09z and 13Z. RAP model guidance still supports sub-VFR stratus forming, mainly over the KABR/KATY terminals between 06Z and 12Z, and likely sticking around for a few hours on Tuesday until dry air advection and daytime heating have a chance to mix the lower cigs out. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...Dorn DISCUSSION...Telken AVIATION...Dorn
Area Forecast Discussion
National Weather Service La Crosse WI
1043 PM CDT Mon Aug 19 2019 .SHORT TERM...(Tonight through Tuesday) Issued at 150 PM CDT Mon Aug 19 2019 Upper level shortwave trough slides east across the northern plains this evening with the low level jet/850 mb moisture transport nosing into the shortwave by 09z as it shifts across northern IA. Convection should take off in earnest as this occurs, and meso models show just that with rapid development between 06-09z over northwest IA, dropping southeast into western IL toward 12z. Despite overnight timing, there looks to be some elevated instability to work on along with favorable shear, moreso in the 0-3 km layer. Expect some strong to severe storms across IA overnight. Current location would keep the bulk of this threat just southwest of the local forecast area. Certainly a scenario that bears a close watch, especially for northeast IA. As the MCS exits southeast, some models (esp RAP) hang an inverted trough/piece of upper level energy northwest of MCV. In those scenarios, enough low level saturation also hangs back, providing ingredients for cont shower/isold storm chances across the south into the afternoon. Don`t anticipate any strong/severe threat with any of this activity. Will hold small pops for now. Another bit of upper level energy looks to slip east/southeast across northern MN Tue morning, into northern WI by the evening. Differences in timing between the variety of models...with latest HRRR about 12 hours quicker on bringing in convection north of I-94 compared to the 12z NAM12. That said, many of the other models only produce a smattering of showers/storms. Going against the convection is no/little tap to gulf moisture (focused south with that exiting MCS), cloud cover across the south from the MCS (how extensive, thick), and bufkit soundings suggest capping that could/will need to be overcome (either warming or by the front/shortwave). What does get going will have some instability to work with - RAP suggests upwards of 2500 J/kg of SBCAPE over northern WI by 00z Wed and potentially +30 kts of effective shear. If that manifests, enough support for some stronger/isold severe storms. A lot of "ifs" though for Tue afternoon/evening...and confidence is not high at this time with how it will playout. .LONG TERM...(Wednesday through Monday) Issued at 150 PM CDT Mon Aug 19 2019 Models in good agreement with the overall, big picture for the last half of the week. Upper level shortwave trough slated to drop southeast across the great lakes Wed/Wed night. Little saturation to work on though - most of that will be cleared south/southeast with the Tue system. A sfc high then progged to build in from the west for Thu/Fri while the axis of an shortwave ridge a loft treks east across the northern plains. Should see a dry end to the work week, with temps likely a few degrees below the late Aug normals. The ridge quickly shifts east for the weekend, allowing for a shortwave trough to nudge in from the west. Showers/storm chances will accompany the trough and its associated sfc front. Should also see a bump up in temps as winds turn more southerly. && .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) Issued at 1043 PM CDT Mon Aug 19 2019 Patchy to areas of valley fog are possible at KLSE tonight then MVFR stratus could impact the TAF sites from mid Tuesday morning into Tuesday afternoon. Mid to high level clouds blowing off of thunderstorms over northwest and central Iowa will create increasing clouds at the TAF sites tonight and should keep the valley fog from going dense at KLSE. The storms then push southeast of the region Monday morning and stratus could develop along moist air pushing north into the area in the wake of the morning storms. A cold front then approaches the region from the northwest Tuesday afternoon and storms could develop along it and impact the TAF sites, especially KLSE, late Tuesday afternoon into Tuesday evening. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ SHORT TERM...Rieck LONG TERM....Rieck AVIATION...Wetenkamp
Area Forecast Discussion
National Weather Service Denver/Boulder CO
901 PM MDT Mon Aug 19 2019 .UPDATE... Issued at 848 PM MDT Mon Aug 19 2019 The forecast is generally on track. With dew points in the low 70s across the far northeast corner along with weak upslope flow, fog will likely develop after around 3am and continue into the mid morning hours. Therefore, fog was added to the grids over Morgan County and areas to the north and east. I wouldn`t be surprised if Denver made it into the upper 90s tomorrow so I bumped the high up a degree or two. && .SHORT TERM...(This evening through Tuesday) Issued at 237 PM MDT Mon Aug 19 2019 The record high of 97 has been broken with the max at 98 so far. There is still enough time to add another degree or two the record. If it reaches 100, that would be the latest for so late in the year. Generally light winds across the forecast area this evening. Too much of a mid level cap around 500 mb to produce thunderstorms, only chance could be over the far northeast corner with ML 100 CAPE around 1000 j/kg over the far northeast plains at 00z so will add isolated thunderstorms there until around 02z. Latest HRRR suggests the cap could be broken with the potential for one or two strong storms between 23-02z. The upper level ridge will bring another day of hot temperatures to the region on Tuesday. In the mountains, dry conditions will persist with rh values in the teens North and Middle Parks. Across the northeast plains, low level moisture will gradually increase from east to west as a weak front pushes into the urban corridor and northeast plains late in the afternoon. The forecast soundings keep much of the Front Range dry for most of the day with ML 100 mb CAPES around 200-300 j/kg. The instability will increase dramatically over the northeast plains with the NAM12 indicating ML 100 mb CAPES over 4200 j/kg with precipitable water values around 1.35 inches. SPC has the northeast corner under a slight risk, so strong to severe will be possible after 22z. .LONG TERM...(Tuesday night through Monday) Issued at 237 PM MDT Mon Aug 19 2019 The threat for storms will continue through Tuesday evening and even after midnight. Easterly low level flow behind the cold front will continue to transport moisture westward. A short wave trough will be tracking over the ridge and will help produce storms through the evening hours. Storms will likely survive after midnight as they slowly track east across the Colorado. Increasing easterly winds over northeast Colorado may result in enough shear for severe storms over northeast Colorado. Heavy rain, large hail, and strong winds will be possible with the storms over the northeast plains through the evening hours. Cooler airmass will be over the area Wednesday with highs in the 80s across northeast Colorado. Airmass will be moist with precipitable water values around an inch across northeast Colorado. Surface based CAPE climbs to 1200-2200 J/kg. Winds aloft will be weak, so there is uncertainty if there will be enough shear for severe storms. Heavy rainfall will be the main threat if there isn`t enough shear. Because of the weak winds aloft, storms will be slow moving. On Thursday and Friday, the upper level ridge will be over the Southern Rockies. This will result in a westerly flow aloft across Colorado. A lee side surface trough will act as a dry line. This is expected to be set up near the foothills on Thursday and keep the chance for thunderstorms in the forecast for much of northeast Colorado. The surface trough shifts eastward on Friday, reducing moisture over the and the chances for thunderstorms. For the weekend and next Monday, models still having issues resolving the large scale patterns. The GFS shows the upper level ridge remaining over the Central Rockies. The ridge retrogrades over the western U.S. if the ECMWF pans out. Will keep the forecast mainly dry with temperatures above normal. If the ridge retrogrades to the west, northwest flow could bring cooler air and low level moisture to eastern Colorado. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 848 PM MDT Mon Aug 19 2019 VFR conditions will continue through tomorrow. A weak boundary is pushing through DEN this evening which will turn the winds more northeasterly with a few stronger gusts possible. Once this boundary washes out, drainage is expected. Storms will develop to the east of the airports tomorrow afternoon/evening and may push an outflow boundary westward to the airports. With flow already being from the east, the boundary`s affect will probably be to increase wind speeds. && .FIRE WEATHER... Issued at 210 PM MDT Mon Aug 19 2019 On Tuesday, fire danger will remain elevated in the high country especially North and Middle Parks. RH values will drop below 15 percent but only light winds expected. Not as hot over the northeast plains but will still be in the low to mid 90s. Low level moisture however will improve from east to west in the afternoon behind a cold front that will start to push into forecast area late in the afternoon. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Danielson SHORT TERM...Cooper LONG TERM...Meier AVIATION...Danielson FIRE WEATHER...Cooper
Area Forecast Discussion
National Weather Service Cheyenne WY
1001 PM MDT Mon Aug 19 2019 .UPDATE... Issued at 916 PM MDT Mon Aug 19 2019 Though pretty dry right now...dewpoints are beginning to increase in the Panhandle this evening with southeast winds. Td at Alliance up to 66...Scottsbluff 62 and Sidney 64. Southeasterly winds continue this evening through Tuesday morning. HRRR and SREF hinting at low clouds and fog moving in after 09Z. Decided to add fog to the forecast tonight through 15Z Tuesday. UPDATE Issued at 803 PM MDT Mon Aug 19 2019 Area observations have been showing a down trend on wind speeds and a slow uptick in humidity this evening. Went ahead and let the Red Flag Warnings we had out...expire on time at 8 PM. Updates have been sent. && .SHORT TERM...(This afternoon through Tuesday night) Issued at 230 PM MDT Mon Aug 19 2019 A upper level ridge dominated the south-central CONUS with warm and dry zonal flow aloft. 700mb temperatures in the mid-upper teens Celsius and gusty downsloping westerly winds pushed the mercury into the 90s east of the Laramie Range. Cheyenne eclipsed its daily record high temperature of 92 degrees in 2001 with 95 degrees. Visible satellite imagery revealed a scattering of cumulus clouds across much of the Cowboy State. The combination of warm temperatures, gusty winds and low humidities was creating critical fire weather conditions across portions of south-central and southeast WY this afternoon. Dry and mild weather will prevail tonight under partly cloudy skies. A cold front poised just north of the Canadian/US border is forecast to progress southward into western NE and eastern WY plains Tuesday afternoon, shifting winds into the east. Low level easterly upslope flow will introduce cooler temperatures, increasing moisture and instability east of the Laramie Range during the afternoon and evening. NAM sounding profiles are progging MUCAPEs upwards of 3000-4000 j/kg with bulk shear values of 40-50 kt. The SPC Day2 Outlook includes much of the NE Panhandle in a Slight Risk for severe thunderstorms, with a Marginal Risk extending west to the I-25 corridor. The primary hazards will be hail (ping pong ball size or larger) and damaging downburst winds of 60-70 mph. With precipitable water values rising to 1.25 inches across the plains Tuesday evening, will also be concerned with locally heavy rainfall and minor flooding. Models have been consistent with convection lasting into the late night hours east of the Laramie Range. .LONG TERM...(Wednesday through Sunday night) Issued at 335 AM MDT Mon Aug 19 2019 Showers and thunderstorms will continue Wednesday and possibly Thursday ahead of a slow-moving Pacific system which will push east along the Canadian/US border through the middle of the week. Some stronger storms are possible Wednesday afternoon, but with the lack of decent 0-6km shear near the upper level ridge axis any concerns are limited at this time. Once this Pacific system moves east, drier air will filter into southeast Wyoming and western Nebraska for next weekend. Extended forecast then becomes uncertain into the last week of August as some models are hinting towards the first polar cold front of late summer moving southward out of Canada and into the northern Great Plains. The GFS and Canadian both show this cold front moving across the Front Range and bringing much cooler temperatures. but this feature is still 8 to 10 days out. && .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) Issued at 958 PM MDT Mon Aug 19 2019 Wyoming TAFS...VFR. Thunderstorms in the vicinity at Laramie and Cheyenne after 01Z. Wind gusts to 23 knots from 15Z to 01Z. Nebraska TAFS...VFR, except for IFR from 09Z to 15Z. Thunderstorms in the vicinity after 01Z. Wind gusts to 27 knots from 15Z to 01Z. && .FIRE WEATHER... Issued at 143 PM MDT Mon Aug 19 2019 Elevated to critical fire weather conditions will continue this afternoon across much of southeast Wyoming due to warm temperatures, gusty winds and low humidities. A cold front is forecast to move south across the plains Tuesday and stall along the Front Range through Thursday. Areas along and east of the Laramie Range can expect cooler temperatures with scattered showers and thunderstorms from Tuesday afternoon through Wednesday night. A few strong to severe thunderstorms will be possible. Areas west of the Laramie Range can expect mainly dry and warm conditions. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ UPDATE...GCC SHORT TERM...MAJ LONG TERM...TJT AVIATION...RUBIN FIRE WEATHER...MAJ
Area Forecast Discussion
National Weather Service Dodge City KS
806 PM CDT Mon Aug 19 2019 ...... .SHORT TERM...(This afternoon through Tuesday night) Issued at 1145 AM CDT Mon Aug 19 2019 Remaining stratus is burning off late this morning along the I-70 corridor, leaving behind scattered cirrus and rapidly building instability in a very moist boundary layer. Widespread dewpoints in the 60s currently, will only mix out to the upper 50s/lower 60s this afternoon. As SE winds increase to 15-25 mph this afternoon, convergence along the lee trough/dryline is expected to allow at least isolated convection to develop across the western/SW zones this afternoon. With limited forcing, coverage will not be widespread, and with instability/shear both far less than impressive, convective expectations through this evening are rather low. Marginal 5% wind probability from SPC basically west of US 283 is justified, given inverted-V soundings, a hot boundary layer, and well-mixed subcloud layers. It won`t take much to get a downburst wind gust of 50-60 mph, with the area most likely to see such activity along an Elkhart-Ashland line near the Oklahoma border, as shown by the latest several HRRR iterations. Any convection will dissipate rapidly with the loss of daytime heating, leading to a quiet warm night with an elevated south breeze near 10 mph. Most locations will hold easily in the lower 70s through Tuesday. With the loss of upslope flow, fog and/or stratus is not expected to redevelop through Tuesday morning. The heat will continue on Tuesday, with no change in airmass. Most locations will end up within a couple degrees of 100. Most of the daylight hours Tuesday will remain dry courtesy of strong upper level ridging aloft. That said, both 12z NAM/GFS generate scattered convective QPF late Tuesday afternoon/Tuesday evening across SW KS, apparently in response to weak shortwaves embedded in the anticyclonic circulation aloft. Wind shear will be weak to non-existent, with convective organization expected to struggle. Kept inherited 20-40% pop coverage for late Tuesday. Clearly, the more organized severe wind/hail threat Tuesday PM will remain focused on the frontal boundary well to the north of SW KS, mainly in Nebraska. .LONG TERM...(Wednesday through Monday) Issued at 217 PM CDT Mon Aug 19 2019 Stationary frontal boundary near the Kansas/Nebraska border early Wednesday is expected to receive a shove southward into SW KS and vicinity Wednesday night/early Thursday, in response to a strong upper trough swinging through the Great Lakes. 12z NAM depicts the cold front making steady southward progress through SW KS daylight Wednesday. The addition of the boundary will no doubt increase shower and thunderstorm coverage across Kansas late Wednesday through early Thursday, as the boundary acts as a trigger in a moist unstable airmass. While mesoscale placement/details are unknown, the NBM pop grids of 50-60% (into the likely category, which matches 12z MEX guidance) for late Wednesday/early Thursday were accepted in the grids. Locally heavy rainfall and strong storms are both possible, per SPC Day 3 marginal 5% wind/hail probabilities. One or two MCSs are expected in this type of pattern, but the locations in Kansas that receive them will be resolved in later forecasts. Convection will encourage the boundary further southward on Thursday, and this is the day when most of us have the best chance of remaining below 90 degrees. If cloud cover can hold north of the front stalled along the Kansas/Oklahoma border as 12z NAM suggests, then the going forecast temperatures for Thursday will be too warm. Northern counties may easily hold in the 70s for some free air conditioning. A warming trend through the 90s is expected each afternoon Friday through Sunday. Rain chances will dwindle over the weekend period, with most locations remaining dry. 12z ECMWF depicts a strong trough swinging through the northern and central plains next Monday, a sign that autumn is inevitably approaching. Strong convection is probable on the frontal boundary Monday afternoon/evening, followed by much cooler temperatures Tuesday Aug 27th. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 800 PM CDT Mon Aug 19 2019 Showers and thunderstorms at the beginning of this TAF period were on a weakening trend and only affecting the LBL terminal through the 01-02Z time frame. VFR flight category will prevail through this period. A warmer airmass in place late tonight and early Tuesday will prevent development of low level stratus and fog. South to southeast winds will prevail through this period as well with strongest winds 14 to 17 knots sustained mid to late afternoon. && .PRELIMINARY POINT TEMPS/POPS... DDC 74 101 71 93 / 10 10 30 30 GCK 71 100 67 95 / 10 10 30 30 EHA 70 99 68 95 / 10 10 20 20 LBL 71 100 68 96 / 30 10 30 20 HYS 72 98 68 89 / 10 10 40 40 P28 75 102 73 93 / 10 0 30 30 && .DDC WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Turner LONG TERM...Turner AVIATION...Umscheid
Area Forecast Discussion
National Weather Service Duluth MN
926 PM CDT Mon Aug 19 2019 .UPDATE... Issued at 843 PM CDT Mon Aug 19 2019 Due to the Day 1 severe weather outlook over the northwest corner of the forecast area being upgraded to a slight risk, have added some severe wording to the forecast. If any severe storms occur, they will be closer to 2 am at the earliest. Made some other minor adjustments, especially to cloud cover. && .SHORT TERM...(This evening through Tuesday night) Issued at 336 PM CDT Mon Aug 19 2019 A cold front will approach from the north tonight with scattered showers and storms developing along and ahead of the front, lingering through the day Tuesday. The cold front then exits from north to south on Tuesday afternoon leading to clear skies and below normal temperatures for Tuesday night. Total precipitation amounts will vary, and not all locations are expected to experience precipitation. There is a very low chance for a few strong to severe storms being possible in north-central Minnesota this evening, but generally storms are not anticipated to be severe. On the synoptic scale a fairly zonal flow pattern exists across the Canadian Prairie, the northern Great Plains, and the Upper Midwest. At low levels a weak cold front is moving south across southern Manitoba, tracking southeast towards the Northland tonight into Tuesday. While the area of high pressure behind the front will bring cool and dry air to the region, along and ahead of the front showers and storms are expected. Specifically, across the central and northern Great Plains rich low level moisture is surging northward, evident even in the visible satellite imagery as stratus advects across the Missouri River valley in south Dakota. While the mid/upper level is generally zonal, a weak mid-level impulse will move across southern Saskatchewan towards North Dakota this evening. The strong warm air advection combined with the weak approaching impulse will result in relatively strong broad-scale lift across the eastern Dakotas, with an elevated mixed layer with steep mid level lapse rates also advecting into this area. While capping should prevent any surface-based storms from developing this afternoon, this evening an increasing low level jet is expected to kick off scattered to widespread thunderstorms across the eastern Dakotas. These storms will then track eastward late tonight into early Tuesday morning, possibly in two clusters - one along the actual cold front near the international border and another cluster moving across central Minnesota. These storms could be capable of producing severe weather given around 2000 j/kg MUCAPE and 40-50 knots of deep- layer shear, mainly in the form of speed shear. The main threat from the strongest storms will be large hail given the elevated nature of the storms, with the best chance for severe storms across north- central Minnesota. As storms evolve east-southeastward and the cold front moves from north to south, showers and storms will linger into Tuesday morning. It is uncertain if storms will maintain their momentum after moving out of a better low level wind field on Tuesday morning, but there will remain both rich low level moisture and probably a decent EML to support convection if any is ongoing. The most likely scenario is that storms will fizzle out as they move into northeast Minnesota Tuesday morning and transition to more showers with embedded thunder as they get into northwest Wisconsin Tuesday afternoon, but there is a chance storms can sustain and remain strong, producing lightning and heavy rain across much of the Northland. This probability is low, but given the trends observed in both model guidance and current surface observations, the environment may support storms lasting well through the morning hours. On Tuesday afternoon, assuming the morning storms eventually fizzle out, there may be a second round of showers and storms that develop ahead of the cold front as it moves from north to south through northeast Minnesota and into northwest Wisconsin, resulting in isolated showers/storms through Tuesday afternoon in northwest Wisconsin. These storms would likely not be severe. Otherwise skiEs will already begin clearing out of north-central Minnesota by mid afternoon, clearing out across the rest of the Northland by the late evening hours. Highs Tuesday will range from the low 70s in north- central Minnesota to the upper 70s to near 80 in northwest Wisconsin. Lows Tuesday night in the 40s to low 50s. .LONG TERM...(Wednesday through Monday) Issued at 336 PM CDT Mon Aug 19 2019 Quiet conditions will be in place for the first part of the extended before turning more active for the weekend. High pressure will build in across the Upper Midwest for Wednesday and Thursday bringing clear skies and highs in the upper 60s and lower 70s. The high will then shift to the east on Friday setting up southerly flow across the Northland. This will bring in some warmer air along with an increase in moisture ahead of a shortwave trough moving into the Northern Plains. The ECMWF is much more organized with this trough with an upper low moving into eastern Saskatchewan and western Manitoba. Rainfall from this trough is expected to hold off until Friday night or early Saturday morning, mainly for western areas. This wave doesn`t look to move across the Northland as the upper level support weakens and leaves a boundary draped across the region. This will keep chances for showers and storms in place for Saturday and Sunday. Models diverge for the weekend with the GFS keeping zonal flow in place while the ECMWF transitions from northwest flow to southwest flow. With southwest flow persisting at the surface, this will keep the flow of moisture in place. Questions remain this far out as to the mesoscale and thermodynamic features that will be be in place for the weekend, but there are hints that some strong or severe storms may be possible at some point, especially if timing of energy aloft lines up favorably with daytime heating. Highs for the weekend will be in the 70s. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 716 PM CDT Mon Aug 19 2019 VFR conditions are expected through around 09Z. Clouds will start to move in from northwest to southeast late tonight as a cold front moves through Tuesday morning. This will bring showers and thunderstorms, which will bring terminals to MVFR and possibly IFR ceilings and visibilities. A brief period of fog is possible at HIB before clouds move in during the early morning, but it is possible that clouds could prevent it from forming. Winds are expected to become northwesterly through the afternoon, but should remain between 5 and 10 kt. There is a slight concern for some brief LLWS as the cold front moves through between 12Z to 15Z per NAM and RAP guidance, mainly at INL and HIB, but confidence is not high enough to mention it in the TAFs at this time. Clouds will gradually begin to clear out during the afternoon with most sites returning to VFR, possibly remaining MVFR for much of the afternoon at HYR. && .MARINE... Issued at 926 PM CDT Mon Aug 19 2019 A cold front will move through around midday that will bring showers and storms along with a wind shift to the northwest at 6 to 12 knots. A few of the storms may be strong, to near severe, with gusty winds and some hail, heavy rain and frequent lightning. Northwest winds will then continue on Wednesday at 6 to 12 knots with a few gusts to around 15 knots. Waves will be 2 feet or less through the period outside of any thunderstorms. && .PRELIMINARY POINT TEMPS/POPS... DLH 61 77 51 72 / 10 60 0 0 INL 57 72 44 68 / 80 90 0 0 BRD 62 78 50 74 / 10 60 0 0 HYR 57 79 50 74 / 0 50 30 0 ASX 59 80 54 74 / 0 40 30 0 && .DLH WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. LS...None. && $$ UPDATE...GSF SHORT TERM...JJM LONG TERM...BJH AVIATION...JS MARINE...GSF
Area Forecast Discussion
National Weather Service Des Moines IA
944 PM CDT Mon Aug 19 2019 .UPDATE... Issued at 942 PM CDT Mon Aug 19 2019 The active night still appears to be on target with little change from previous thinking. 4-5K j/kg MUCAPEs are present along the NE/IA border in the projected genesis area with 40-45kts of effective shear. The only concern may be slightly delayed timing and onset. 00z soundings and the latest model guidance do not depict the strongest low level jet with RAP 305K inflow into the base of the effective layer only 20kts or so. Nevertheless, once it goes it may go quickly with fresh 00z CAMs all still depicting a significant wind producing MCS NW-SE starting 06-09z and not exiting southeast sections until 12z or so. If this caliber of MCS develops as expected, it will be somewhat rare in magnitude reflecting the infrequency of overnight Enhanced Risks in IA. Possibly reminiscent of significant wind events in 2008 or 2010. && .DISCUSSION.../Tonight through Monday/ Issued at 309 PM CDT Mon Aug 19 2019 High pressure remains ridged into central Iowa this afternoon with return flow beginning to develop into far western Iowa and into Nebraska and Kansas. The return flow will increase this evening as the High departs to the east. The low level jet will form and increase to 35-40kts between 03-06z and will bring a strong push of theta-e advection into central Iowa. This combined with steepening mid-level lapse rates will lead to moderate to highly unstable environment with MUCAPEs exceeded 3500 J/kg. Expect thunderstorms to develop across portions of northwest to west central Iowa around midnight then roll southeast down the instability gradient. Severe weather and heavy rain fall will both be concerns with this activity overnight. Initial storms will be elevated with a few supercells capable of large hail possible. The initial cells should congeal into an MCS and propagate southeast with an attendant damaging wind threat into central and southeast Iowa. In addition, an isolated tornado or two may be possible given the amount of low level SRH if the 0-3 km shear vector can orient correct in time. This would be contingent on potential for increased mixing ahead of the line can help erode the low level inversion and allow for low level vortex stretching. A few areas of wind driven hail may occur given the maintaining instability and potential for cold pool development. The potential for heavy rainfall is increasing as the increasing instability within a moisture rich atmosphere with good warm cloud depths near 15 kft aiding in the efficient rain process. A rainfall band of 2 to 4 inches is possible and cannot discount a heavier localized band in excess of 5 inches. The intense rainfall amounts will cause significant ponding in urban areas. If a 5 inch band does develop, the threat may translate to a flash flooding threat given the rates and amounts. Warm advection following the the morning MCS will create a significant elevated mixed layer that will lead to a significant cap across the state. Convective debris looks like it will eventually clear out over parts of the state. The biggest challenge will be how much of the state will recover from the morning outflow. Have the warmest temperatures over central and western Iowa with high temperatures approaching 90 degrees and heat index values in the 100 to 105 degree range. Not anticipating any heat headlines at this point especially considering uncertainties given the recovering. Have lowered chances for thunderstorms Tuesday afternoon and evening. A greater threat for storms will late Tuesday night into Wednesday morning over as storms move east out of Nebraska. Little change to the remainder of the forecast with cooler temperatures Thursday through Saturday then a transition to more westerly flow by Sunday into early next week. This will lead to seasonal temperatures and a few more chances for precipitation. && .AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/ Issued at 637 PM CDT Mon Aug 19 2019 There is high confidence in VFR conditions into the evening, but also at least medium confidence that a significant thunderstorm complex will develop into portions of central IA during the early morning hours. Have VFR VCTS mention for now, but there will likely be a period of lower conditions for at least one of the TAF sites overnight. No mention until timing and location confidence increases however. Some lingering stratus is possible after the precip, but confidence is medium to high that VFR conditions will return by Tue afternoon. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Small DISCUSSION...Donavon AVIATION...Small
Area Forecast Discussion
National Weather Service Pueblo CO
255 PM MDT Mon Aug 19 2019 .SHORT TERM...(This evening through Tuesday) Issued at 245 PM MDT Mon Aug 19 2019 Area of isolated convection developing at mid-afternoon over the far southeast plains, where weak convergence along a rather diffuse surface trough was providing some modest lift near the wrn edge of the moist/unstable air mass near the KS border. Expect these storms to move into KS by late afternoon as trough drifts east, with HRRR suggesting all activity will be out of CO by 00z. Suppose there could be some briefly strong/gusty winds with storms given rather wide t/td spread, with perhaps a more organized outflow pushing westward across the plains this evening. Elsewhere across the region, dry and hot conditions persist, with record high already set at Pueblo (102f so far), while readings still a have couple more degf to go to break the the record (94f) at Colorado Springs. Overnight into Tue, upper level high pressure center remains just to our south, with weak sly flow bringing a modest influx of mid level moisture into the region by Tue afternoon. At the surface, pre- frontal trough turns winds on the plains ely through the day, while main cold front hangs back in nern CO until sometime Tue evening. Overall, most of the mountains should see a modest upturn in convection by Tue afternoon, though with dry low levels precip will be spotty and light. Activity on the the plains should stay fairly sparse, with perhaps a few cells along the NM border and up near the Palmer Divide. Max temps will continue on the unseasonably warm side Tue afternoon, with readings within a degf or two of Monday`s hot numbers. .LONG TERM...(Tuesday night through Monday) Issued at 245 PM MDT Mon Aug 19 2019 A boundary bringing in somewhat cooler air will arrive at the beginning of this long term period and bring relatively cooler air to the region (and a chance of storm) Wednesday and Thursday. Temperatures will warm up again and it will dry out from late in the week into Sunday. Cooler weather will likely return for the new workweek. An initial boundary will likely be on the Palmer Divide early Tuesday evening. This may spark a thunderstorm or two along the divide, otherwise it will remain dry over the region. Wednesday morning, a 2ndry surge of cooler air will backdoor into the region from the east and this will cool the plains down 10 degrees or so compared to Tuesdays max temps. With increasing upslope and a more unstable environment in place, the chance of showers and storms along the plains/mtns interface will increase, with a good chance of storms possible during the afternoon and evening time period. Given sufficient CAPE and marginal shear in place, a few marginally severe storms will be possible, and SPC has all of the plains in a marginal risk for severe storms for this day. Burn scar flooding may also be an issue on this day. For Thursday, upslope will continue although flow will be a bit more southerly and flow aloft will be a bit weaker (although still northwesterly). This should decrease the showers and storms over the plains this day, with the best chance over the mtns/plains interface and over the far se plains. Max temps should be a degree or two cooler than Wednesdays max temps. For Friday into the weekend, it will dry out area-wide with only isolated pops expected, and temps will return into the mid 90s/L100s across the plains. By late in the weekend into early next week another cool front should move into the region/ although long term guidance is not in good agreement when this front will move into the region. Looking a bit farther out, there is some agreement that a stronger cold front will move down the plains, and this could knock temps several degrees below normal by mid week next week. /Hodanish && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 245 PM MDT Mon Aug 19 2019 VFR conditions expected the next 24 hrs at all taf sites with usual overnight diurnal wind cycle. On Tue, slight increase in convection expected across the region, though with moisture still rather shallow, expect most activity to be weak, high based and tied mainly to the higher terrain. && .PUB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...PETERSEN LONG TERM...HODANISH AVIATION...PETERSEN