Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/19/17

Area Forecast Discussion...CORRECTED
National Weather Service Bismarck ND
939 PM CDT Tue Jul 18 2017 .UPDATE... Issued at 939 PM CDT Tue Jul 18 2017 Latest water vapor imagery shows multiple shortwaves across western Idaho on the nose of a 60kt 500mb jet, continuing to ride along the northern periphery of a broad upper level ridge. These shortwaves and jet will reach western ND late tonight/early Wednesday morning, followed by a more distinct 700mb-500mb shortwave Wednesday afternoon moving across southern ND. Soundings and latest CAM`s indicate increasing coverage of elevated thunderstorms late tonight/early Wednesday morning as a low level jet increases across western ND. This is then expected to morph quickly into a large area of showers and thunderstorms Wednesday morning, pushing quickly across central ND. Some severe weather is possible. Another round of possible severe weather would come in the afternoon with the aforementioned midlevel shortwave, mainly affecting locales along and south of Interstate 94. Convection will be rather messy in the morning, and that will play a role in how things evolve/destabilize in the afternoon, especially if cloud cover holds in. The latest 21z SREF calibrated severe thunderstorm has taken a noticeable uptick in the probability of severe thunderstorms in southern ND Wednesday. After collaborating with SPC, we will be mentioning some severe thunderstorm wording in the gridded data and text products. UPDATE Issued at 537 PM CDT Tue Jul 18 2017 Local/Regional radars indicative of a few supercells in southeast Montana at this time. The experimental HRRR seems to have some signal on what is occurring, with a couple splitting storms taking shape as they edge closer to our southwest border. Thus far, dime size hail being reported in southeast MT, along with gusty winds (sub severe at this time). Mixed layer cape sufficient between 1000 and 1500 J/Kg, with strong deep layer shear between 30kt and 50kt. DCAPE/Downdraft Cape on the order of 1200 J/Kg, so isolated damaging winds possible and will continue to monitor very closely. Adjusted pops based on current radar, movement, and forecast into southwest ND through 03z. Rest of forecast elements looked good. && .SHORT TERM...(This evening through Wednesday) Issued at 401 PM CDT Tue Jul 18 2017 Late this afternoon and this evening an isolated thunderstorm or two is possible in the southwest. The SPC day 1 convective outlook has the far southwest corner in a marginal risk for a severe storm. The current ECMWF/GFS/RAP are indicating ample 0-6 km bulk shear with values around 60 kts but the low/mid level lapse rates and CAPE values are not impressive. Any chance for severe thunderstorms in the southwest appear to be slight. The CAMS are scattered with only the HRRR hinting at something in the southwest around 22Z. As we get into Wednesday, an embedded pulse in the zonal flow aloft will result in chances for another round of showers and thunderstorms. SPC has most of the south in a marginal risk for severe storms. Severe weather ingredients look more promising for storms becoming strong to severe. Additionally, the current suite of ensemble and deterministic models are in good agreement on an area of QPF moving from the west to southeast through the day. The WPC day 2 QPF valid for Wednesday has between 0.10 and 0.25 inches of rain for much of western and central ND. West central and south central areas are painted with values between 0.25 and 0.75 inches of rain. Locally higher amounts are possible with thunderstorms. .LONG TERM...(Wednesday night through Tuesday) Issued at 401 PM CDT Tue Jul 18 2017 Most of the action for the extended will come Thursday evening through Friday, as a weak wave aloft will bring chances for showers and thunderstorms. The SPC day 3 convective outlook has most of western and central ND highlighted in a marginal risk for severe thunderstorms. The 12Z ECMWF/GFS convective parameters for Thursday are sufficient for the development of strong to severe storms. The outlook for the rest of the long term, a chance or two for a thunderstorm and near seasonal temperatures. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 537 PM CDT Tue Jul 18 2017 This Taf period, will be monitoring for a potential round of showers and thunderstorms, possibly heavy and/or severe, during the daylight hours Wednesday. Indications are that an area of thunderstorms couple develop over eastern Montana 09z-12z Wednesday, then quickly shift across western and central ND 12z- 21z Wednesday. Low confidence on timing and complete evolution of thunderstorms for any one terminal. Thus for now, have not carried any predominate mention of thunderstorms and/or intensity, but have mentioned a vcts during the expected timeframe. Will await the model guidance later this evening for better continuity and confidence. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...KS/AE SHORT TERM...AC LONG TERM...AC AVIATION...KS
Area Forecast Discussion
National Weather Service Cheyenne WY
414 PM MDT Tue Jul 18 2017 .SHORT TERM...(This evening through Thursday night) Issued at 300 PM MDT Tue Jul 18 2017 Forecast challenges deal with PoPs and chances for heavy rainfall through the short term. Latest water vapor imagery showing a dry slot moving into most of Wyoming this afternoon, which has really limited convection. Exception being down in the southern Nebraska Panhandle where we are seeing scattered convection developing. This band is moving at a pretty good clip and should be out of the Panhandle within the next hour or so. For this evening, most locations to remain dry as this dry slot remains over the area. HRRR guidance does show a cell developing across the northern Panhandle that could impact Alliance and Chadron. Does not look all that strong, so feel severe storms should hold off. PWATs on the increase for Wednesday. Counties west of Laramie Range increase from .5" this afternoon up to .75-.8" by Wednesday afternoon with the Panhandle increasing up to 1.3". Only trouble for tomorrow is there seems to be no forcing mechanism as the weak frontal boundary lifts northeast and lower elevation winds shift southwest. So we may not see much in the way of convection outside the mountains. GFS and ECMWF still in good agreement for Thursday as upper high remains well southeast of the area over eastern Kansas and monsoonal surge moves directly over the CWFA. PWATs well over an inch across much of the CWFA with near 1.3" in the Panhandle. Do have an upper shortwave moving through the monsoonal flow Thursday that should help develop convection. Greatest concentration of showers looks to be along the I-80 corridor from maybe Sidney to Arlington and in the mountains. HPC coordinated with us today for a Slight Risk area for Excessive Rainfall across our south central zones. That may need to be adjusted some more as the event draws closer. Looks like a good bet we will need some flash flood watches for some of our southern counties Thursday afternoon. .LONG TERM...(Friday through Tuesday) Issued at 300 PM MDT Tue Jul 18 2017 Friday...Relatively weak zonal flow aloft prevails. Deeper moisture will be limited to Colorado and to areas along our Colorado state line, thus will continue with isolated to scattered showers and thunderstorms over and near our southern mountains, dry elsewhere. Saturday...Drier air at low and mid levels will infiltrate our western and central counties in the wake of a cold front. There may be enough moisture left over our eastern counties for isolated late day showers and thunderstorms, primarily over the Nebraska panhandle. Sunday...The flow aloft backs to northwest with low level upslope winds helping to generate isolated showers and thunderstorms along our southern counties near the Colorado state line, with mostly dry conditions elsewhere. Monday...Low level upslope strengthens under ridging aloft. Looks like enough low and mid level moisture over our southern and eastern counties for isolated to scattered afternoon and evening showers and thunderstorms. Tuesday...Next shortwave trough aloft progged to move across during peak heating, helping to spark scattered showers and thunderstorms along and east of Interstate 25, and most numerous over western Nebraska. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 412 PM MDT Tue Jul 18 2017 Wyoming TAFS...VFR, with isolated thunderstorms near Cheyenne until 03Z. Gusts to 20 knots at Cheyenne and Rawlins after 18Z Wednesday. Nebraska TAFS...VFR. Gusts to 22 knots at Chadron and Sidney after 18Z Wednesday. && .FIRE WEATHER... Issued at 300 PM MDT Tue Jul 18 2017 Monsoonal moisture will remain over southeast Wyoming and Nebraska Panhandle for the next several days into next week. Result will be continued mountain showers and thunderstorms with a general increase in coverage each day. Expect fairly high afternoon humidity over the area. The exception being FWZs 301 and 303 where afternoon humidities fall into the mid teens both this afternoon and Wednesday. Look for fair to good overnight recoveries. Good chances for wetting rains in the mountains through Friday with best chances Thursday, where many lower lying areas stand to get wetting rains as well. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...GCC LONG TERM...RUBIN AVIATION...RUBIN FIRE WEATHER...GCC
Area Forecast Discussion
National Weather Service Flagstaff AZ
325 PM MST Tue Jul 18 2017 .SYNOPSIS...Deep moisture and an area of low pressure over western Texas moving west will bring numerous showers and thunderstorms to northern and central Arizona through mid-week. Heavy rainfall from the stronger storms will be capable of producing flash flooding at least through Wednesday evening. && .DISCUSSION...Very moist atmosphere and approaching easterly waves have produced numerous showers and thunderstorms across northern Arizona this afternoon. Heavy to very heavy rain and over an inch diameter hail has been observed (via radar). Very active afternoon! Deep moisture will remain over the area through Wednesday evening. The easterly flow across Texas and New Mexico will continue to bring instability over Arizona. Both the HRRR and NAM show the development of an MCS over Yavapai County or northwestern Coconino County tonight into Wednesday. While models have some timing and location differences concerning the actual placement of this event all operation models are leaning towards this solution; with the higher resolution models concurring that a mesoscale convective system is anticipated to develop and move across the high country in the overnight hours. Current Flash Flood Watch is out through Wednesday evening to cover this activity. On Thursday a slight decrease in moisture aloft is expected to move into the area allowing for a slightly less active day for convective thunderstorm development. Some storms are still expected to form, however they should be more widely scatter than their counterparts from the previous few days. This respite will not last long with models suggesting that a reinforcing surge of moisture will move back into the area from the New Mexico border Friday and lasting into next week. && .AVIATION...For the 00Z package...SHRA/TSRA will expand in coverage through the afternoon with widespread coverage expected through this evening. Storms will be moving east to west with areas of MVFR and isolated IFR in +RA. A few storms may produce severe wind and hail mostly south and west of a KGCN to KSOW line through around 03Z. Expect conditions to improve from east to west aft 07Z Wed. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Active monsoon conditions will continue with scattered to numerous showers and storms each day. Convective activity should continue overnight tonight as an upper level disturbance moves through northern Arizona. The threat for heavy rain will continue across all of Arizona through midweek. Expect near average temperatures. Friday through Sunday....An active monsoon pattern will continue with daily chances for rain showers and thunderstorms. No significant changes in the weather pattern are anticipated. && .FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch through Wednesday evening FOR AZZ004>018-037>040. && $$ PUBLIC...MAS AVIATION...MCT FIRE WEATHER...MCT For Northern Arizona weather information visit
Area Forecast Discussion
National Weather Service Hastings NE
742 PM CDT Tue Jul 18 2017 .SHORT TERM...(This evening through Wednesday) Issued at 417 PM CDT Tue Jul 18 2017 The main concern for this afternoon and tonight is the potential for thunderstorms as well as continuation of the heat advisory this evening. A solid layer of low to mid level cu formed late this morning and has persisted through much of the afternoon. This has held down temperatures across much of south central Nebraska. Highs have struggled to get up into the upper 80s and low 90s across the area. If this trend continues an early cancellation of the heat advisory may be possible, although southern portions are getting closer to criteria. Models have not been very consistent on thunderstorm chances for today. The NAM has kept things mainly dry for our area while the HRRR has had a line enter from our northwest with scattered showers and thunderstorms around through much of this evening through tonight into the early morning hours. Although any widespread precipitation is not expected, have kept some lower pops across much of the area to account for lingering showers. The best chances to see any severe weather remains across northwestern portions of the area. .LONG TERM...(Wednesday night through Tuesday) Issued at 417 PM CDT Tue Jul 18 2017 The stretch of hot weather really ramps up tomorrow through Friday with heat indices of 100 to 108 possible across the area. Have upgraded southeastern portions of the CWA to a heat warning to account for heat indices near or above 105 and low temperatures overnight only dropping to the mid 70s. Have the rest of the area in a heat advisory for tomorrow afternoon as the prolonged nature of the heat is a bit more uncertain in these areas, especially on Friday with an advancing cold front expected to start moving through the area. The upper level flow becomes more northwesterly as we head into the end of the week with multiple weak shortwaves providing us with slight chances for precipitation Thursday night through Monday. With a front expected to move through on Friday, cooler weather is expected into the weekend with highs back in the 80s to lower 90s. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Wednesday) Issued at 742 PM CDT Tue Jul 18 2017 At least for now, will officially advertise a very "quiet" period with no formal mention of thunderstorms and VFR ceiling/visibility, although this is by no means a guarantee and is subject to change. As for surface winds, they should be rather light (generally 6-7kt or less) from an easterly to southeasterly direction tonight, then picking up a bit from the south late in the period on Wednesday afternoon with gust potential to around 18kt. Will conclude with two of the primary/possible caveats to the going "quiet" forecast: 1) Although the chance of thunderstorms at either site appears low enough to no longer justify even a generic "vicinity" (VCTS) mention, this will need closely watched, especially if any of the ongoing activity over southwest Nebraska happens to hold together and start propagating east. 2) There are some hints that least brief, light haze/fog (perhaps MVFR visibility?) could materialize late tonight into Wednesday morning. For now expect "just enough" wind/mixing to preclude potentially more problematic visibility issues, but again, this bears watching in later forecasts. && .GID WATCHES/WARNINGS/ADVISORIES... NE...Excessive Heat Warning from 1 PM Wednesday to 8 PM CDT Friday for NEZ064-076-077-085>087. Heat Advisory from 1 PM to 8 PM CDT Wednesday for NEZ039>041- 046>049-060>063-072>075-082>084. Heat Advisory until 8 PM CDT this evening for NEZ082>087. KS...Excessive Heat Warning from 1 PM Wednesday to 8 PM CDT Friday for KSZ006-007-018-019. Heat Advisory from 1 PM to 8 PM CDT Wednesday for KSZ005-017. Heat Advisory until 8 PM CDT this evening for KSZ005>007-017>019. && $$ SHORT TERM...Petr LONG TERM...Petr AVIATION...Pfannkuch
Area Forecast Discussion
National Weather Service Goodland KS
714 PM MDT Tue Jul 18 2017 .UPDATE... Issued at 713 PM MDT Tue Jul 18 2017 Updated for the expiration of the heat advisory. UPDATE Issued at 624 PM MDT Tue Jul 18 2017 Cluster of thunderstorms currently over the northwest corner of the area. High resolution guidance having some difficulty in capturing latest trends although they do cluster around the best chance of thunderstorms over northern Yuma county. As a result of the latest trends and best performing high resolution guidance, am adjusting pops accordingly. && .SHORT TERM...(This afternoon through Wednesday) Issued at 208 PM MDT Tue Jul 18 2017 Large scale ridge extents from the southwest US, across the Central High Plains, and into the southern Mississippi River Valley. A plume of monsoonal moisture is shown on WV imagery to be rotating through the western extent of this ridge and into the Central Rockies. This afternoon-tonight: A front stalled over the Nebraska Panhandle may shift south slightly in response to a mid level shortwave associated with monsoonal flow riding the northern part of the ridge. This should remain north of our CWA, but the increased forcing may combine with weak convergence along surface trough in our northwest to kick off thunderstorm activity. CINh has already weakened in this region and a shallow CU field has developed. RAP analysis support ML CAPE in excess of 2000 J/KG and PWATs around 1-1.3" range. Shear is less impressive, so once again localized heavy rain and pulse thunderstorms are favored (hail/wind). Thunderstorm activity is shown by high res guidance to drift to the southeast which takes it away from better instability, but does raise the possibility for showers/thunderstorms further south and east than originally anticipated. I made adjustments to account for these trends. Wednesday: Ridge shifts just a little further north and we should see subsidence in place and a less favorable pattern for possible afternoon thunderstorm development. Guidance is in line with this shift in pattern, and keeps conditions dry over our CWA. Regarding Temperatures/Heat Advisory: We have yet to reach advisory criteria over most locations in advised area, but it is getting close and a few locations are just now starting to reach. There is an upward trend in temps in line with forecast, and Tds are remaining high in our east. No changes planned as heat index values 103-105 (a few higher) still appear likely across advised area. Overnight lows remain mild, but heat indices should decrease below 75 (may be close in our far east), so a decision was made not to extend advisory overnight. Tds may be a little lower on Wed, but temperatures will not be much different (upper 90s/lower 100s). Result should be 103-105 heat index values confined in our north and east, and I issued another Heat Advisory for Wed afternoon/early evening at favored locations. I am less confidence further west and south. .LONG TERM...(Wednesday night through Tuesday) Issued at 134 PM MDT Tue Jul 18 2017 High pressure aloft is expected to move east over the plains while a a short wave trough starts to move in behind the ridge. A few storms are possible during the evening, mainly over the northwestern sections of our area, due to a shift in the pattern. Thursday`s overnight low temperatures are expected to drop into middle to upper 60s over the western half and 70-75 over the eastern half of the forecast area. Over the weekend, the ridge will continue to flatten out and move towards the east on Friday. This will produce slightly cooler temperatures over the western half of our CWA while the eastern half is still expected to climb into the upper 90s to just over 100 degrees. A prefrontal boundary looks to push through the region from the northwest to southeast and serve as an axis for thunderstorm development Friday afternoon. Then a cold front will follow on Saturday producing another chance of thunderstorms across the region. This cold front looks to stall and weaken over the central Plains on Sunday. This will keep showers and thunderstorms in the forecast until the front weakens and eventually give way to another building high pressure from the west, decreasing rain chances Sunday night and early into Monday morning. As high pressure returns to the region during the first part of the week, weak troughs are expected to move through the region as well. with that said going to keep the chance of showers and thunderstorms that the builder is given for the end of. As for the period. As for temperatures, expect the highs to reach into the upper 80s. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 534 PM MDT Tue Jul 18 2017 Vfr conditions are expected through the period. For Kgld, a prefrontal trough that is currently near the site will move north later on this evening into the overnight hours. Late tomorrow morning the south winds will increase to near 17 knots with gusts to near 25 knots. For Kmck, thunderstorms will be in the area during the mid and late evening hours. However, current trends are not matching up well with high resolution/Cam output so have low confidence in what will happen. This is usually happens in weak flow aloft situations. So at this time chose to do vcts beginning at 03z and ending at 06z. For the first half of the period the winds will be less than 10 knots from the east or light and variable due to thunderstorm outflow winds. By late tomorrow morning/early tomorrow afternoon southerly winds will increase to near 15 knots with gusts to near 23 knots. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...Heat Advisory from 1 PM to 8 PM CDT Wednesday for KSZ002>004-015- 016. CO...NONE. NE...Heat Advisory from noon MDT /1 PM CDT/ to 7 PM MDT /8 PM CDT/ Wednesday for NEZ079>081. && $$ UPDATE...BULLER SHORT TERM...DR LONG TERM...BW AVIATION...BULLER
Area Forecast Discussion
National Weather Service Green Bay WI
1041 PM CDT Tue Jul 18 2017 Updated aviation portion for 06Z TAF issuance .SYNOPSIS... Issued at 210 PM CDT Tue Jul 18 2017 Warm and humid with periods of thunderstorms for the rest of the work week and into the upcoming weekend. A low amplitude band of westerlies will remain across the northern CONUS and southern Canada into the weekend. Amplification will begin during the weekend, and continue into next week. Though medium range models differ on the details of the pattern during that time, it seems likely that we`ll head back into what has been the favored pattern during the past several weeks. That would be a regime with a ridge over the intermountain West and a trough over the Great Lakes. The frontal boundary crossing the area tonight is likely to play a major role in our weather for the next several days, as it stalls and stretches out along the southern edge of the westerlies. At this point it seems unlikely to move far enough south to allow for any prolonged dry periods. The resulting numerous opportunities for precipitation are likely to result in above (north) to much above (south) normal precipitation amounts. Humid conditions and temperatures near to modestly above normal are expected through the weekend, though readings could be held back on any days with widespread clouds and precipitation. Drier conditions and temperatures returning close to seasonal normals are likely early next week as the upper flow begins to tilt northwest in response to the redevelopment of an eastern NOAM upper trough. && .SHORT TERM...Tonight and Wednesday Issued at 210 PM CDT Tue Jul 18 2017 The latest RAP analysis and satellite/radar imagery show a cold front moving southeast from southern South Dakota to far northwest Wisconsin early this afternoon. Showers and storms continue to develop ahead of the front with help from a old mcv as a result from convection over the Plains last night. The most widespread of storms have occurred over Vilas county, and its possible that the atmosphere may not have time to destabilize ahead of the front. The same cannot be said for further south and east where storms have been more isolated/short-lived and further destabilization is expected. ML capes approaching a 1000 j/kg over central and parts of far northeast WI where storms remain on track to develop in the 20-22z time period. 0-6km bulk shear of 25-30 kts will be sufficient for severe storms to develop. Damaging winds and large hail remain the primary threats through tonight. Tonight...As the mcv exits north-central WI by early this evening, a cold front will be moving southeast over central and northeast Wisconsin, and clearing east-central WI by midnight or shortly thereafter. Ahead of the front, mixed layer capes up to 1500 j/kg will be gradually diminishing through the evening. Therefore, the best chance of severe storms will occur for the first few hours of the evening over the southeast half of the forecast area. Some of the higher res models keep some precip around into the overnight hours, so kept a small chance going, but this may be too ambitious. High pressure will build in across northern WI in the wake of the front late tonight. Guidance is not excited about fog chances, and there may be just enough of a boundary layer wind to keep that from happening. Turning cooler and less humid behind the front, with lows ranging from the mid 50s north to mid 60s south. Wednesday...Will likely see some morning clouds over parts of central and east-central WI through mid-morning before drier air arrives with the southward moving surface high. With plenty of sun in the afternoon, raised temps a degree. Highs in the low to mid 80s. .LONG TERM...Wednesday Night Through Tuesday Issued at 210 PM CDT Tue Jul 18 2017 Confidence in forecast details beyond about 48 hours remains low due to the flat upper pattern. In addition to difficulties timing rain chances due to the low amplitude pattern, we are having major difficulties discerning the heavy rain/flooding potential associated with additional rounds of convection. Several days ago, heavy rainfall and flooding seemed like a realistic possibility given the proximity of the front. Then there was somewhat of a model consensus to shove the front just far enough south to keep the area safe from any flooding rains. The overall trend during the past 24 hours was to edge things north again, with much of the guidance suggesting a severe MCS will roll from southeast Minnesota, across southern Wisconsin late Wednesday night into Thursday. That may pose a risk of damaging winds in the area (though agree with the SPC Day 2 Convective Outlook that the greatest severe threat will probably be to our south). But at least central and east-central Wisconsin seem likely to be affected by the northeast flank of the MCS. With additional rain chances later this week and into the weekend, the possibility of a flooding threat evolving across the area looks higher than it did yesterday. Will attempt to detail the situation along with the uncertainty in the HWO. With little confidence in the forecast details, no significant changes were made the forecast initialization generated from a broad-based blend of guidance products. && .AVIATION...for 06Z TAF Issuance Issued at 1041 PM CDT Tue Jul 18 2017 Showers and thunderstorms have ended for the most part across the area tonight. In its wake some clearing skies and fog appears to be forming out to the west as the skies clear. Despite little to no fog on the MOS guidance, will put some in at the TAF sites overnight given the upstream observations. Will hit the western TAF sites the hardest given a sooner clearing out, with less fog out east where skies will clear later. Once the fog clears Wednesday morning conditions should return to VFR for the balance of the day. Another thunderstorm complex is forecast to move in over the western TAF sites at the end of the TAF period Wednesday evening. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS.......Skowronski SHORT TERM.....MPC LONG TERM......Skowronski AVIATION.......Kurimski
Area Forecast Discussion
National Weather Service Indianapolis IN
1003 PM EDT Tue Jul 18 2017 .UPDATE... The Aviation and Near Term Sections have been updated below. && .SYNOPSIS... Issued at 316 PM EDT Tue Jul 18 2017 The hottest and most humid air of the year is set to expand across the Ohio Valley and central Indiana for the second half of the week and into the weekend. Highs in the 90s and heat indices peaking above 100 degrees will be common. Chances for thunderstorms will gradually increase through the next several days as well...peaking over the weekend and into early next week. Cooler temperatures will arrive by early next week as well as the heat is shoved off to the south and west. && .NEAR TERM /Rest of Tonight/... Issued at 1003 PM EDT Tue Jul 18 2017 For the update...while subsidence is in place over the forecast area, a line of strong thunderstorms moving east across Illinois is causing some concern that ridging will not be strong enough to keep the western counties completely dry through the night as this complex approaches. HRRR and RAP have been trending in this direction for the last few runs, and while the system will have trouble maintaining itself the further east it comes, it may have just enough moisture and dynamics to keep from dissipating until after a shower or storm have moved into the northwestern counties. Given the strength of the subsidence only low confidence that this will occur, but enough of a chance that it deserves a slight chance mention starting at 9z. At this time will not add anything to the Wednesday morning (after 12z) portion of the forecast but rather continue to monitor how the system develops over the next several hours. Maintained mention of patchy fog with moist boundary layer, but lower confidence in this outcome especially west and northwest because of potential influence of mixing from aforementioned showers/storms. Going low temperatures in the upper 60s to low 70s look on track with current temperatures at 10 pm mainly in the low to mid 70s and dew points in the upper 60s. Relevant parts of previous discussion follow... Capping will become more prevalent across the entire forecast area this evening into the overnight with deeper subsidence overspreading the region under an expanding ridge aloft. Skies will become mostly clear tonight and with light flow and lingering low level moisture...anticipate patchy fog development once again in the predawn hours through daybreak Wednesday. Should see dewpoints fall back just a bit from current readings with the drier air aloft being drawn to the surface which will limit the humidity a bit. Temps...very likely looking at the last night with much of the area falling into the upper 60s until late weekend at the earliest. As mentioned above...a slight lowering of the dewpoints will take the edge off the mugginess tonight. Frankly tonight will feel pleasant compared to what is coming the next several days. && .SHORT TERM /Wednesday through Friday/... Issued at 316 PM EDT Tue Jul 18 2017 Forecast challenges focus first and foremost on heat and humidity expectations with the expanding heat ridge and the potential for parts of the forecast area to be impacted by the convective clusters that will ride around the periphery of the ridge. The growing heat ridge centered over the High Plains this afternoon will gradually shift E/SE through the short term...eventually centering over the Tennessee Valley by the beginning of the weekend. The position of the center of the ridge and expectation for mid level heights at 592-594dm to make it into central Indiana by Thursday and Friday support the likelihood of the hottest temperatures experienced yet this year to pay a visit to the region. Expectation for dewpoints remaining in the mid and even upper 70s at times by Thursday and Friday ensure oppressive levels of humidity and combined with the forecast temperatures...max heat indices rising to 100 to 105 degrees for much of the area by Thursday and Friday. It remains a bit premature to introduce any sort of headlines for the expected heat with the main impacts still at 36 hours away at earliest. The potential for a heat advisory is growing and will eventually need to be considered...especially over western/ southwestern parts of central Indiana. At this time...will continue to highlight heat stress dangers via the HWO and social media platforms. The other significant issue to consider in the short term is the potential for convection to impact parts of central Indiana... primarily from convective clusters riding through the northwest flow along the periphery of the ridge. While model guidance remains focused on the main path of storm cluster staying largely to our north from the upper Midwest southeast through the lower Great Lakes...cannot stress enough that if the mid level heights and ridge expansion are any weaker than currently progged...a greater potential would develop for these clusters to drift further south and impact parts of central Indiana. Taking that possibility into consideration will continue to keep a low chance pops running through the period...focused over the northern counties and during the afternoon and evenings. Additionally with so much moisture present in the low levels...cannot entirely rule out a stray shower or storm during peak heating any of the afternoons although presence of a modest cap should keep that largely at bay. As we experienced over the last few weeks...each convective clusters will have the potential to produce all forms of severe weather with damaging winds serving as the main threat. Heavy rain and flooding will also be possible with every cluster considering the high PWATs present. As it stands at this point...the northeast quadrant of the forecast area is likely most susceptible to be impacted by the southern fringes of a convective cluster with little to no threat for storms expected over the southwest counties in closer proximity to the core of the ridge aloft. Temps...after a day with upper 80s and low 90s Wednesday...the bulk of the hottest weather comes Thursday and Friday as 850mb temps surge above 21-22C and the highest mid level heights are realized. Taking this at face value...mid 90s could be argued for much of the area. However...there are a few reasons why think the only part of central Indiana that has a shot at the mid 90s either Thursday or Friday will be the lower Wabash Valley and areas predominantly southwest of a Terre Haute-Bedford line. These areas have been drier over the last 4-6 weeks and are much closer to the core of the ridge. Further northeast across the rest of the forecast area...the combination of high soil moisture content courtesy of all the recent rains and the high dewpoint air will limit full warming. Additionally...both afternoons the mixing level maxes out at only 4kft or so. Would really like to see that at 5-6kft to be able to tap into deeper warming. Right now...see Indy getting as warm as 92- 93 Thursday and Friday. Relief will be hard to come by at night as lows settle in the mid 70s in the muggy airmass. Forecast confidence is medium to high regarding the heat and humidity...and low with respect to thunderstorm timing...coverage and location of impacts. && .LONG TERM /Friday Night through Tuesday/... Issued at 236 PM EDT Tue Jul 18 2017 The long term period will be characterized by near constant low to middling chances for thunderstorms much of the area, and heat gradually returning closer to more seasonal levels, while humidity remains relatively high until late in the period. Large scale pattern will feature near zonal flow early in the period with the main storm track potentially in or near the area. As the period wears on, the ridge will again strengthen over the western US, allowing larger scale troughing to move into the Great Lakes. This will keep storm chances going across the area. As usual, the near constant storm chances are largely a result of significant uncertainty with respect to mesoscale evolution on longer time scales, and there will likely be lengthy periods of dry weather punctuated by multiple rounds of thunderstorm complexes. && .AVIATION /Discussion for 190300z TAF issuance/... Issued at 1003 PM EDT Tue Jul 18 2017 Updating current conditions only. May need to address line of storms moving east across Illinois for potential impact to KLAF, but at this point very low confidence that these will reach and directly impact KLAF so will leave out at this time. Previous discussion follows... Light winds and humid airmass will lead to fog development overnight. High confidence that at least some patchy fog will form at the sites starting around 7-9z, but low confidence on how low the visibilities will get. Will go with prevailing MVFR and tempo IFR until around 12-13z. The western sites have seen more subsidence and less cloud development during the day so may leave IFR out there or shorten the length of time. Will go most pessimistic at KBMG. After around 12-13z should see any visibility restrictions clear and then VFR for the rest of Wednesday. && .IND WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...Ryan NEAR TERM...Ryan/CP SHORT TERM...Ryan LONG TERM...NIELD AVIATION...CP
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
927 PM CDT Tue Jul 18 2017 .UPDATE... Issued at 914 PM CDT Tue Jul 18 2017 Thunderstorms are staying just northeast and south of the area at mid-evening. Still expect the rest of the night to remain dry as RAP is showing little forcing for showers and thunderstorms over the area overnight. Temperatures have slowly dropped the past few hours are now mainly in the 70s and lower 80s except in metro St. Louis where is still in the mid-upper 80s. Going lows still look good for now. Britt && .SHORT TERM... (Through Late Wednesday Afternoon) Issued at 255 PM CDT Tue Jul 18 2017 The synoptic pattern early this afternoon features a strong upper- level ridge anchored across the central Plains. This ridge will slowly meander eastward through the period, enhancing its influence over the Midwest which will help bring even warmer temperatures to the region on Wednesday. Main forecast concern will be the dangerous heat which has started across the area today and will only worsen on Wednesday. Latest air temperatures this hour sit in the low to mid 90s (STL at 97) which coupled with dewpoints in the upper 60s/70s have yielded heat index values from 95-105. As we head into Wednesday, the upper-level ridge building overhead should help push a weak boundary off to the northeast of the region. The further northward displacement of the front should enable dewpoints to mix out more efficiently than they have today. That being said, increasing 850mb temps and 1000-850mb thicknesses suggest temperatures will likely be warmer than today, with values in the mid 90s and into the 100s in the STL metro. This will translate to heat index values topping out near 105 in many areas (especially along/north of I-70). Given the heat is only expected to worsen Thursday into the upcoming weekend (see long term section below), have decided to upgrade portions of the Excessive Heat Watch to an Excessive Heat Warning in all areas but southeast MO and extreme southwest IL. In these areas, slightly lower dewpoints should limit heat index values to the 100-104 range. The other more minor forecast concern will be on convective chances this afternoon into this evening. Latest radar imagery depicts some very isolated showers along a weak front over southeast MO and along a differential heating zone over central MO. Given a fairly uncapped atmosphere, we will likely continue to see isolated shower/storm development in these regions through early this evening. Will have to keep an eye on an MCV/compact shortwave trough diving through the weak northwest flow aloft this evening. This mid-level forcing has been enough to force some showers and isolated storms over northwest MO, which could move into northeast MO and west-central IL through 2- 3Z (perhaps even lingering a bit later). Guidance has not handled this system well today so confidence in convective coverage associated with this feature is fairly low. KD .LONG TERM... (Wednesday Night through Next Tuesday) Issued at 255 PM CDT Tue Jul 18 2017 A widespread and significant heat wave will be ongoing at the start of the period with a strong upper level RIDGE dominating our region. Although the strength of this RIDGE will weaken some heading into Friday and Saturday, it is enough to maintain the going pattern and effects thru this time period, as it will have the effect of hanging a surface cold front to our north with southwest surface flow over our region and minimal chances for rain. Look for max air temps from the the mid 90s to the low 100s with heat index values from 105 to 114 each afternoon and early evening. The remnant Heat Watch will be converted to a Warning for all areas outside of southeast MO and far southern IL, with those areas being converted to an Advisory where the cooler effects of the Ozarks will place peak heat indices a bit more in check. All of the models develop, at some point, increasing NW flow aloft in response to a TROF settling into the Great Lakes region with this to continue into early next week. The point of contention remains just exactly when do they do it, which will directly impact on when this current heat wave ends. The GFS continues to suggest the need for an extension of heat headlines for many areas into Sunday, while the CMC and to a slightly lesser extent, the EC are showing much less of a need, especially in the northern CWA. We currently have a Heat Watch for our southeast MO and far southern IL counties thru early Sunday evening and this remains a plausible and valid time for that area given a decent consensus that the front will remain upstream. All other areas further north, the uncertainty increases and decided to keep the end of the heat headlines at early Saturday evening for now until we get a better handle on timing of the late weekend cold front. Models then come into better alignment by Monday, with NW flow aloft and a cold front thru and bring to an end this latest heat event with more seasonable temps, if not a little below average. What looks to be more dubious is the pcpn chances, and prefer to keep that at or below CLIMO values for now. TES && .AVIATION... (For the 00z TAFs through 00z Wednesday Evening) Issued at 619 PM CDT Tue Jul 18 2017 Isolated thunderstorm near Quincy is expected to move east of the terminal by 00Z. Otherwise, mainly dry and VFR conditions are expected through the period has a surface high currently over Illinois moves off to the east. Winds will remain light. SPECIFICS FOR KSTL: Dry and VFR conditions are expected through the period with light winds. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Heat Advisory from noon Wednesday to 8 PM CDT Sunday for Crawford MO-Iron MO-Madison MO-Reynolds MO-Saint Francois MO-Sainte Genevieve MO-Washington MO. Excessive Heat Warning until 8 PM CDT Saturday for Audrain MO- Boone MO-Callaway MO-Cole MO-Franklin MO-Gasconade MO- Jefferson MO-Lincoln MO-Marion MO-Moniteau MO-Monroe MO- Montgomery MO-Osage MO-Pike MO-Ralls MO-Saint Charles MO- Saint Louis City MO-Saint Louis MO-Shelby MO-Warren MO. Excessive Heat Warning from noon Wednesday to 8 PM CDT Saturday for Knox MO-Lewis MO. IL...Heat Advisory from noon Wednesday to 8 PM CDT Sunday for Randolph IL. Excessive Heat Warning until 8 PM CDT Saturday for Madison IL- Monroe IL-Saint Clair IL. Excessive Heat Warning from noon Wednesday to 8 PM CDT Saturday for Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-Marion IL-Montgomery IL- Pike IL-Washington IL. && $$ WFO LSX
Area Forecast Discussion
National Weather Service Nashville TN
733 PM CDT Tue Jul 18 2017 .UPDATE... FOR EVENING DISCUSSION. && .DISCUSSION... Radar this evening continues to show a few scattered showers and thunderstorms in far northwest zones as well as in far southeast zones. With loss of daytime heating underway, this activity should quickly diminish over the next couple of hours as HRRR also suggests. Will keep in a slight chance pop over northwest and southeast zones to account for this activity as well as adjust sky cover. Otherwise, forecast is on track with another warm humid night expected. && .AVIATION... 00Z TAF DISCUSSION. VFR. A few models are indicating potential for fog overnight, especially for KCKV and KCSV, but majority showing VFR conditions to prevail. Winds will be light and variable through mid morning before becoming more northerly/northwesterly for the late morning through the afternoon hours. && .OHX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION......Shamburger AVIATION........Barnwell
Area Forecast Discussion
National Weather Service Las Vegas NV
709 PM PDT Tue Jul 18 2017 .SYNOPSIS...A moist and unstable airmass will result in scattered to numerous thunderstorms and locally heavy rainfall across southern Nevada...Northwest Arizona...and far eastern California through the week. Drier conditions are expected across most of Inyo county where temperatures will remain hot and skies mostly sunny. A slight drying trend is possible by the end of the week. && .NEAR TERM...Current area of interest is small cluster of thunderstorms over eastern San Bernardino County...basically bounded by Nevada Highway 163 to the north...Highway 95 to the east and Interstate 40 to the south. Believe this area will continue to slowly build southward this evening so decided to expand the Flash Flood Watch to include eastern San Bernardino County and far southern Clark County. Earlier storms over the Lake Mead Natl Rec Area and Mohave County have dissipated for the time being. Cluster of storm moving west near Wickenburg AZ look as they will stay south of Mohave County/San Bernardino County. Secondary line of storms further east in Arizona could effect Mohave County later this evening/overnight and eventually Clark County around daybreak Wednesday. There is still quite a bit of uncertainty in this scenario as the HRRR has not been the most consistent today in its simulations. && .PREV DISCUSSION...239 PM PDT Tue Jul 18 2017 .DISCUSSION...High pressure over the southern U.S. will be the dominant feature at least through Saturday. This will keep east to southeast flow over our area, keeping the door open for monsoon moisture in much of the area, with the possible exception of the northwest corner of the area where drier southwest flow prevails. Precipitable water of 1.5 to 2 inches was present over the Flash Flood Watch area this afternoon. Storms were already beginning to pop over Mohave County, and more significant storms over Coconino and Yavapai Counties should roll west into Mohave County later in the evening due to easterly steering flow. Thus, the watch looks good, and made no changes to it. Day to day precip variations through the week will partly be driven by the previous day`s thunderstorm activity, which will stabilize the areas where it occurs, push moisture and outflow boundaries into nearby areas to help fuel storms the next day, and also leave differential heating boundaries around the edges of both the cloud shields and the rain footprints. Thus, made no significant changes to precip forecasts beyond Wednesday. Nudged temperatures up a bit the next two days as confidence has decreased in the idea of widespread cloud cover inhibiting heating. && .AVIATION...For McCarran...Through the rest of this afternoon and into the evening, there will be an increased chance of thunderstorm activity in and around the Las Vegas valley. Storms are likely to form along the higher terrain and are especially likely to form along the McCullough Range this afternoon and evening. Any storms that form in the valley or drift into the valley will likely bring variable erratic and gusty winds and lower visibilities. These conditions will likely be relatively short in duration. Besides thunderstorm influences, winds should be southerly varying from 150- 220 until diurnal southwest to westerly winds kick in overnight. SCT to BKN above 10 kft with occasional MVFR conditions with thunderstorm activity. For the rest of southern Nevada, northwest Arizona and southeast California...Scattered thunderstorms expected across most of Mohave, portions of Clark, Lincoln, and portions of southwest San Bernardino counties this afternoon through the forecast period. Any storms that form will cause variable erratic and gusty winds with low ceilings. Otherwise winds should be southerly and diurnal with ceilings above 10 kft. && .HYDROLOGY...Creeks, streams and rivers in northern Inyo County continue to run high and fast from snow melt. Some road closures continue in the area. Bishop Creek Bypass and Big Pine Creek Bypass continue to be utilized to minimize flows through Bishop and Big Pine. Isolated thunderstorms over the mountains may aid snowmelt runoff and keep some drainages elevated over the coming days as well. Remember, never drive through flooded roadways or around barricades. Also, pastureland or farmland adjacent to creeks, streams or rivers could experience areas of standing water. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && $$ Update...Pierce Morgan/Kryston For more forecast information...see us on our webpage: or follow us on Facebook and Twitter