Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/26/20

Area Forecast Discussion
National Weather Service La Crosse WI
1033 PM CDT Sat Jul 25 2020 .UPDATE... Issued at 1030 PM CDT Sat Jul 25 2020 The 00Z MPX sounding had around 2.25 inches of precipitable water and surface based CAPE around 3000 J/kg. The NAEFS Precipitable water charts show that these values are around 4 standard deviations above normal with return values of 30 years and Maxed out through Sunday morning. The increasing low level jet will continue to feed moist, unstable air into southeast Minnesota and western Wisconsin overnight. Two to three inch rains per hour will be possible with the storms as they repeatedly move over the same area. MPX has had storm develop in their area and the moisture axis is from MPX into ARX`s cwa. Some of the guidance has the heavier rain staying north, while others develop it southward (ARW) As ouflows develop and storms develop, it seems like the ARX is catching on to this. The HREF has some locations picking up 3 to 6 inches. Flash flood guidance is generally in the 2 to 3 inch range and most locations can actually use 1 to 3 inches. The pattern calls for the potential for very heavy rain, however it will depend on how the bands of rain set up. For now will include a handful of counties in a flash flood watch to raise the awareness of the potential for flash flooding overnight. && .SHORT TERM...(This evening through Sunday) Issued at 201 PM CDT Sat Jul 25 2020 Currently observing scattered shower/isolated thunder activity across northern IA/southeast MN into northwest WI. This area was on the southeastern periphery of decent 850mb moisture transport and along a remnant MCV. Otherwise, temperatures across the local forecast area as of 1 pm were mostly in the 80s with a couple sites reporting lower 90s. Dew points were oppressive...well into the 70s with heat indices currently ranging from near 90 to 100. A Heat Advisory is in effect until 8 pm tonight for heat indices maxing out in the 100-105 range. For tonight will be watching for an uptick in showers/thunderstorms as a cold front slowly makes its way toward the region and as we are located on the southeast periphery of increasing low level 850mb jet/moisture transport. CAPE is ample in this very muggy airmass but shear is modest with RAP 0-3km in the 20-30kt range. 0-1km shear was fairly impressive though in the 25-35kt range. As such, will have to keep an eye on some stronger/possibly severe storms. Otherwise, overnight lows will only make it down into the low to mid 70s with those dewpoints in the a sticky/muggy night in store. The cold front will continue to push south into the area Sunday for increased shower/thunderstorm potential. Cloud cover will be the fly in the ointment as to how much CAPE can build during the day, NAM/GFS depicting some pockets of 4kJ/Kg but overall bulk shear values are modest. So, thinking we`ll see a few stronger/possibly severe mainly pulse type storms with a marginal threat for damaging winds. With expected shower/storm activity/cloud cover, will hold off on heat headlines as temperatures may be cooler than today. Also for consideration tonight into Sunday will be the potential for pockets of very heavy rainfall given high precipitable water values pushing 2.5 inches. .LONG TERM...(Sunday night through Saturday) Issued at 201 PM CDT Sat Jul 25 2020 The cold front finally pushes through the area Sunday night, taking the thunderstorms and uncomfortable heat with it. Monday will be markedly more pleasant with highs around 80 and dew points around 60. Upper pattern settles into northwest flow for the remainder of the forecast period. Result will be generally dry with seasonable temperatures. Surface ridging during the period will be weak, so could see some diurnal shower activity, especially later in the week as the surface ridging becomes more diffuse. Models diverge as we approach next weekend, although there are suggestions of a decent wave dropping down in the northwest flow that would bring the next notable chance of precipitation. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 646 PM CDT Sat Jul 25 2020 Isolated showers will continue to impact KRST and KLSE this evening. Thunderstorms are beginning to increase over southern Minnesota and expect this trend to continue with the low level jet increasing. Over time, the on and off storms will sag southeast toward KRST and KLSE. VFR conditions with MVFR/IFR ceilings and visibilities with occasional thunderstorms. South to southeast winds mostly 5 to 15kts will becoming northwest behind the front later Sunday 20 to 22Z. && .HYDROLOGY... Issued at 1030 PM CDT Sat Jul 25 2020 Most locations could use one to three inches of rainfall, however would not be able to take higher amounts or very high rainfall rates of two to three inches an hour without some flash flooding. Based on the rainfall forecasts rapid rises on rivers and streams are possible for parts of southeast Minnesota and west central Wisconsin as the water moves through the system or falls over the rivers and streams. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Flash Flood Watch until 8 AM CDT Sunday for WIZ032>034. MN...Flash Flood Watch until 8 AM CDT Sunday for MNZ079-086>088-094- 095. IA...None. && $$ UPDATE...Zapotocny SHORT TERM...DAS LONG TERM...DMD AVIATION...Zapotocny HYDROLOGY...Zapotocny
Area Forecast Discussion
National Weather Service Grand Junction CO
542 PM MDT Sat Jul 25 2020 .SHORT TERM...(Tonight through Sunday night) Issued at 326 PM MDT Sat Jul 25 2020 Deep layer moisture continues to stream into much of the forecast area today, thanks to the monsoon, and brought some widespread rainshowers to areas south this morning. However, northwest portions of the forecast area remained mostly clear and with the added daytime heating, showers and thunderstorms have fired. Upper level winds are fairly light and motion of this convection has been very slow so some locally heavy rainfall remains possible under the stronger, slower moving storms. Like yesterday, the extensive cloud cover has inhibited more widespread convection but visible satellite imagery does show breaks in the clouds down south. The question is will the clouds get thin enough to tap into the instability aloft. Both the HRRR and NAMNEST favor the convection getting going with the HRRR a bit more aggressive in its coverage while the NEST looks to place the stronger convection on the fringes of the cloud cover and clearer skies. CAPE values vary from about 300 to 500 J/kg up north, not much, and between 800 to 1000 J/kg for the San Juans and southern valleys so southern areas remain favored. Once heating ends, most convection will die down though a few showers can`t be ruled out for the San Juans. For tomorrow, high pressure remains to our east while a trough remains to the west and a wave well to our north will cause the plume of moisture to `tilt` more to the northeast. Models are picking up on this tilt with precip still expected for the San Juans but then shifting to the central mountains towards Vail Pass. On the backside of the wave, winds will bring in some drier air north of I- 70 which follows model solutions. Expect slow moving storms and showers again tomorrow so the risk remains for some heavy rainers. .LONG TERM...(Monday through Saturday) Issued at 326 PM MDT Sat Jul 25 2020 Deterministic and ensemble guidance remain in excellent agreement regarding the progression of the synoptic scale pattern over the long term period. A mid-level ridge of high pressure will retrograde west/southwest from the central Plains into the southern Four Corners Monday and Tuesday. While this will effectively cut-off the source of monsoonal moisture to our south, above normal moisture already in place (characterized by total precipitable water values of 0.5-1.5 standard deviations above the mean) will be trapped underneath and continually recycled through Tuesday. Additionally, a nearly stationary shortwave trough located over southern California will eject northeast over the Great Basin on Monday and then across eastern Utah and western Colorado on Tuesday. Given the enhanced dynamical lift associated with the shortwave trough, numerous to widespread showers and thunderstorms are likely, particularly on Tuesday. Gusty winds, frequent lightning and heavy rain will once again be the main threats, especially in the higher terrain. Changes then begin to take shape on Wednesday as the aforementioned shortwave rounds the northern periphery of the ridge and dives into the central Plains. In its wake, 500MB heights will rise and expand with the center of the ridge located directly over the Four Corners. Mid and upper level flow will turn more westerly and northwesterly in response, ushering in much drier air into the forecast area for the middle and latter part of the week. This will result in warmer temperatures (back to near or just above seasonal norms) and much lower chances for afternoon showers and storms. With that being said, weak, fast-moving disturbances moving through the west/northwesterly flow combined with diurnal heating and any leftover moisture may be just enough to touch off a few isolated orographic showers and storms each day, mainly in the higher terrain closest to the Continental Divide. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 541 PM MDT Sat Jul 25 2020 Scattered to broken skies, some overcast, will be common across the area through tonight as monsoonal moisture continues to pump into the region. Some convection is also likely overnight so included VCTS for many TAF sites. The main concern from storms will be some gusty outflow winds and visibilities dropping to below VFR conditions under moderate to heavy rain. ILS breakpoints will be met from time to time but do not anticipate this to occur for a prolonged period. Most convection will die down late this evening though some rain showers will persist over the San Juans. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...TGR LONG TERM...MDM AVIATION...TGJT
Area Forecast Discussion
National Weather Service Goodland KS
702 PM MDT Sat Jul 25 2020 .UPDATE... Issued at 659 PM MDT Sat Jul 25 2020 Cancelled the Heat Advisory over the northeast sections of the forecast area for today. && .SHORT TERM...(This evening through Sunday) Issued at 111 PM MDT Sat Jul 25 2020 Water vapor imagery and RAP analysis indicated CWA on western fringe of large H5 ridge centered over southeast Kansas. At the surface, weak convergent area noted across northwest CWA with towering CU developing along it. Another area of speed convergence was bisecting the CWA. Main forecast concerns will center around precip chances through the weekend and possible flooding impacts. Previously mentioned convergence zones will be likely focus for thunderstorm development this afternoon and early evening and with PWAT values around the 90th percentile of climatology and slow storm movement, heavy rain will once again be a threat. While storm motions will be more parallel to forcing across eastern CWA resulting in higher threat for heavy rainfall, confidence in this area initiating is somewhat low. Further north, while the storm motion may limit training of cells near the tri state border, area still recovering from very heavy rain that occurred on Thursday night and therefore remain especially vulnerable to flash flooding. For the time being, think flash flood watch will continue for this area. Given that storms are being driven more by surface heating and near surface features think there will be a strong diurnal trend with them. While increasing low level flow aloft may sustain storms near approaching front into the overnight hours, think the window for the GLD area will likely close by 05 UTC. For Sunday, cold front will sweep across the area resulting in nearly 20 degree temperature gradient from southeast to northwest. Guidance actually pretty consistent with placement of front and temperatures, but confidence in related precipitation threat somewhat low through the day. Best forcing will be immediately along front, which makes a quick exit from the CWA in the late afternoon. While there does appear to be forcing along H7 frontal zone late in the period, have concerns that available instability will be lacking. While a few models seem to be picking up on this potentially drier solution, consensus still looks like bulk of the area will see some meaningful rainfall Sunday. While there certainly will be hydro concerns, aforementioned concerns about precip placement keep confidence on the low side for any kind of watch. .LONG TERM...(Sunday night through Saturday) Issued at 210 PM MDT Sat Jul 25 2020 Sunday Night-Monday night: Broad cyclonic flow aloft over the Central/Northern Plains.. on the far southern periphery of an upper level low in Manitoba.. will transition to NW flow aloft on Mon as the aforementioned upper low progresses eastward into Ontario and a more-pronounced upper level ridge develops over the Intermountain West/Desert Southwest/Rockies. With the Tri-State area situated on the southern periphery of the westerlies /cyclonic flow aloft/ -- and a weakening /increasingly west-east oriented/ SFC-H85 trough progressing slowly southward from Nebraska into Kansas -- convection appears likely over the majority of the area Sunday evening into Monday morning, with activity gradually progressing south of I-70 during the day on Monday. Although brief severe downbursts are possible in assoc/w the strongest updrafts (mainly Sunday evening) -- heavy rainfall and isolated flash flooding appear to be the primary convective hazards -- particularly in areas hard-hit by recent heavy rain (i.e. Yuma/Dundy/Cheyenne counties). Tuesday-Saturday: Long range guidance suggests that an exceedingly complex synoptic pattern will evolve over the Central/Western CONUS in this period, lending *significant* uncertainty to forecast specifics -- particularly with regard to chances for precipitation/convection. With this in mind, the long range forecast will be steered toward climatology. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 553 PM MDT Sat Jul 25 2020 VFR conditions are expected at MCK and GLD through the 00Z TAF period. Thunderstorms are expected in the vicinity of both sites through about 05Z tonight. Thunderstorms are expected to develop across the area again on Sunday. With a cold front pushing through the area, thunderstorms coverage is expected to be more extensive and have introduced thunderstorms as a prevailing condition at both sites from about 21Z and beyond Sunday afternoon. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...Flash Flood Watch until 7 AM CDT Sunday for KSZ001. CO...Flash Flood Watch until 6 AM MDT Sunday for COZ090. NE...Flash Flood Watch until 6 AM MDT Sunday for NEZ079. && $$ UPDATE...LOCKHART SHORT TERM...JRM LONG TERM...VINCENT AVIATION...LOCKHART
Area Forecast Discussion
National Weather Service Lincoln IL
852 PM CDT Sat Jul 25 2020 .SYNOPSIS... Issued at 320 PM CDT Sat Jul 25 2020 A muggy night is on tap tonight, under mostly clear skies across central Illinois. Hot and humid conditions on Sunday will push heat index readings between 100 and 105 degrees. A cold front will trigger showers and storms later Sunday night and Monday. A few storms could be strong with gusty winds and locally heavy rain on Monday. && .UPDATE... Issued at 852 PM CDT Sat Jul 25 2020 No significant updates needed this evening. Although some shallow fog is possible overnight, sounding profile showing moisture dropping off quickly above the surface should promote dew over fog, while at least a light wind in many areas, especially the western half of the state, could help promote mixing and diminish fog possibility. Nevertheless, will continue to monitor for fog potential, mainly I-57 eastward, where combination of light wind and high surface moisture will be best. Otherwise, lows in the low 70s and mostly clear skies continue to look good for tonight. && .SHORT TERM...(This evening through Sunday) ISSUED AT 320 PM CDT Sat Jul 25 2020 The latest surface analysis shows high pressure centered over the Great Lakes with a ridge axis extending back across central Illinois. Southerly return flow around that high was pushing afternoon dewpoints up into the low to mid 70s in a majority of our CWA, with the highest readings generally west of I-55. Heat indices have remained below 100F so far, with Jacksonville at 99F at 230 pm. The HRRR and RAP continue to show a cluster of storms developing from Schuyler to Scott counties late this afternoon. Satellite pics show agitated CU closer to the Mississippi River, but not significantly towering at the moment. Shallow CU continued to bubble up in our counties. Still feeling the dry mid-level air will suppress storm chances in our counties, along with subsidence under the surface ridge axis. Therefore, will not add PoPs late this afternoon/early eve. The muggy air mass will help keep low temps in the lower 70s tonight, under mostly clear skies. There could be another round of late night shallow fog in our eastern counties, but confidence not high enough to include in the forecast. Sunday will be our hottest day of the next week, with dewpoints likely to climb into the mid to upper 70s, as high temps climb into the lower 90s. That will push heat index readings into the 100-105F range, just below our heat advisory criteria. Can`t rule out a couple locations possibly reaching 106F, but it is not expected to be widespread enough to trigger a headline for heat in our counties. Plus, some afternoon convection just northwest of our CWA could push a dense cirrus overcast into C IL, which would definitely limit high temps and lower the H.I. Will continue with an SPS for the heat. .LONG TERM...(Sunday night through Saturday) ISSUED AT 320 PM CDT Sat Jul 25 2020 A cold front will approach from the NW Sunday night, increasing PoPs to Likely in our NW counties after midnight. The front could even progress as far as a line from Rushville to Bloomington by 12z/7 am Monday, as suggested by the GFS. Still enough evidence in the consensus to keep the timing a little slower for now, which puts the bulk of the showers and storms in our counties on Monday. Have kept the categorical PoPs along and ahead of the front as it pushes southeast through C IL. PWAT values of 2-2.3" point toward heavy rainfall from the complex of storms. Model instability has dropped off from previous runs, with MUCAPEs now in the 2500-3200 range for areas east of I-55 and south of I-72. A Marginal Risk for severe storms extends only into our far eastern counties on Monday, while a Marginal Risk for excessive rainfall covers our entire CWA. A slower forward progression of the front in the latest models would tend to favor flooding as a higher concern for our area. The cold front is expected to advance to our far SE counties by 00z/7pm Monday, with rain/storm chances lingering mainly SE of I-70 overnight. A few showers could continue Tuesday morning along Highway 50, otherwise dry conditions are expected on Tuesday. Less humid air will help make the mid-week portion of the forecast more comfortable for late July. A few shortwaves are progged to trigger storms across the southern half of Illinois as early as Thursday, but there is quite of bit of uncertainty in the far extended forecast due to model differences. The 12Z ECMWF keeps our area dry for the Tues to Saturday time frame, save for a few storms in our far SE 3 counties on Thursday. Besides one warmer day on Wednesday (Highs in the mid to upper 80s), high temps for Tues to Saturday look to be in the 80 to 85 degree range with lows in the low to mid 60s. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 630 PM CDT Sat Jul 25 2020 VFR conditions expected to be predominant over the upcoming 24 hours at all central IL terminals. Patchy fog could affect terminals around 11-12Z, especially KDEC and KCMI, and isolated TSRA possible after 20Z, however probability of occurrence is too low for mention in current TAFs. Winds S 4-8 kts then becoming SSW around 10 kts with gusts around 15 kts after 17Z. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...37 SYNOPSIS...Shimon SHORT TERM...Shimon LONG TERM...Shimon AVIATION...37
National Weather Service Jackson KY
1100 PM EDT Sat Jul 25 2020 .UPDATE... Issued at 1100 PM EDT SAT JUL 25 2020 Sure enough just as soon as the pops were gone from the grids, a few showers started to show up on radar within the last couple of hours. These didn`t result to much, with only a flash or two of lightning, but a couple have persisted for quite some time and are finally dissipating at the end of the 2Z hour. Went ahead and increased pops again to isolated coverage across much of the CWA for the next couple of hours, at once point hopefully instability will have dissipated enough that no redevelopment will occur. was the case last night...may end up just having to watch the radar and update as warranted. Also loaded in the latest observations for temps and winds across the CWA. All updates have been published and sent to NDFD/web. A new set of zones and HWO have also been sent to reflect changes to the pops/weather. UPDATE Issued at 755 PM EDT SAT JUL 25 2020 Ended up reducing pops quite substantially from the afternoon package based on the current radar trends. There are still enough mesoscale boundaries around, and the instability is still high enough, that a few showers and thunderstorms can`t be ruled out throughout the rest of the evening, mainly south of Jackson. However, anything that develops has been diminishing almost as quickly as it forms, with maybe only a couple lightning strikes. This lowering of pops continued into the overnight and tomorrow morning, with a period of the overnight likely going dry based on the latest CAMS and neighboring offices as well. Pops should then ramp back up during the mid-morning hours. With conditions very similar to that of today, expect that coverage will generally be isolated to scattered. This is also in line with what the models are giving. Ended up lowering the pops from likely across the southern CWA back down to scattered as a result. This also lined up better with all of our neighboring offices. && .SHORT TERM...(This evening through Sunday night) Issued at 400 PM EDT SAT JUL 25 2020 Another warm afternoon out there today. Dewpoints are running a degree or two lower than the past few days in most areas, but still a good amount of moisture pooling across southern KY. Evidence all remains of the washed out boundary laying out east to west across the state. Slightly better moisture resides along and just to the south of the boundary. Convection today has been much weaker with updrafts not as sustained from what we have seen over the past few days. There are also a few rogue cells to the north. The threat for showers and a few storms will continue into this evening. Much like the past few nights, some weak moisture transport is forecast to develop again on the NAM and RAP and this could bring some shower activity to the area, especially late tonight. The RAP appears to the most aggressive, but given the fact we nearly had stuff all night last night under a similar pattern, opted to carry some slight and chance pops through much of the night. I wouldn`t rule out a very isolated storm, but for now will keep thunder limited through the overnight period. Sunday will feature more of the same as moisture remains pooled across southern and southeast Kentucky which should aid in more shower and storm development. Thunder should be more limited, similar to today, but a few storms cannot be ruled out given the instability in play. No shear will keep thunderstorm mode in the pulse category. Highs should again reach into the upper 80 to around 90. Sunday night, the better moisture transport should shift into West Virginia and this may allow for a lull in precipitation chances through the overnight hours. Some patchy fog may be possible in the river valleys assuming we clear out. .LONG TERM...(Monday through Saturday) Issued at 441 PM EDT SAT JUL 25 2020 Model agreement is good through day 4 but is fair to poor from days 5 through 7. Mid/upper level low over Ontario will track just south of Hudson Bay and eastward into Quebec by Dy5 Wed. Energy in the form of a positively tilted shortwave lobe ahead of additional upstream energy rotating through the base of the parent low will be driven south and eastward into the Ohio Valley by late Monday into Tuesday. Additional disturbances and/or at least one main short wave trough will roll into the lower to middle portions of the Ohio by the end of the period. A surface cold front associated with the initial system aloft will drop southeast close to the Ohio River by Late Tuesday is not sooner. There continues to be considerable differences with the operational runs in the timing and southward extent of this surface front. The ECMWF continues to be slower and stalls further north, just south of the Ohio river. However, the 12Z trend does appear to be slightly further south than previous runs. The GFS continues to take the front south of Kentucky, just south of the state line into the TN Valley. The Canadian, which is more often than not a compromise solution of the other two brings the front as far south as the Commonwealth, and with a west to east orientation effectively bisects our CWA before stalling out. Thus sought out ensemble solutions for some clues. GFS ensemble mean MSLP bisects eastern Kentucky as well. NAEFS and ECMWF ensemble H500 and H850 height anomalies of 1-2 standard deviations do reach well south of the Great Lakes and into the Ohio Valley, suggesting enough push to get the boundary at least into if not just south of our area. Interestingly the ECMWF ensemble anomalies reach further south than the NAEFS. Therefore ensembles support the idea of the frontal zone making it at least as far south as our forecast area by Tuesday night or Wednesday, which also matches up well with the NBM`s initialization. Sensible weather features a summer like, hot and muggy start to the extended on Monday with highs once again climbing to around 90 degrees. But a frontal boundary moving into the area combined with additional cloud cover and the increase in the threat of showers and thunderstorms will drop our afternoon highs from there into the 80s. Overnight lows will range from around 70 down into the mid 60s. Still could not rule out some lower 60s in some of our typically cooler locations should the front make it as far south as the Tennessee Valley. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) ISSUED AT 808 PM EDT SAT JUL 25 2020 VFR conditions should prevail at the TAF sites through the period. A few showers and a stray thunderstorm are still ongoing across eastern KY away from the TAF sites, however convection should continue diminishing as we head into the late evening/overnight hours with the loss of daytime instability. Valley fog is expected once more tonight, but should continue to trend lesser than the previous night. Since TAF sites really didn`t see much in the way of impact from this fog last night, went ahead and removed any mention of it for tonight`s forecast. That being said, can`t rule out a very brief lowering of VIS or CIG right around daybreak if valley fog is present and lifting near the TAF site. A very similar airmass and setup for convection to that of today will be in place tomorrow as well, so expect generally isolated to scattered convection across eastern KY during the afternoon hours. Best chances (SCT) will be in the south portion of the state, so did include some VCTS at KSME and KLOZ. However, with only isolated chances farther north, confidence was too low to mention in TAFS at this time. Winds should generally be light and variable, under 5 kts, through the period, outside of any thunderstorms that do occur. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JMW SHORT TERM...KAS LONG TERM...GEERTSON/RAY AVIATION...JMW
...Updated for 00Z Aviation Forecast Discussion...

.DISCUSSION... Issued at 307 PM CDT Sat Jul 25 2020 Heat index values at 3 pm were running 101 to 106 degrees, and thus no changes to the heat advisory that continues through 8 pm. Focus then shifts to potential convection overnight into Sunday night as a slow moving cold front moves through the region. There does appear to be a weak wave moving through the central Rockies. Scattered strong and possibly severe storms will likely develop across western and central NE within the area of the pre-frontal surface trough. This activity will be well west of the forecast area, so lowered the pops in northeast NE this evening. Believe the best scenario is for some nocturnal convection in our area after midnight, which would generally be along and north of I80, and that could linger into Sunday morning. While widespread severe storms aren`t expected, a storm or two could contain gusty winds and some small hail perhaps. The cold front will get a decent push into the area Sunday from a reinforcing upper wave coming out of the Rockies. We should see increasing areal coverage of thunderstorms as the front moves into the area during peak heating. This will result in cooler temps in the 80s behind the front, but still hot and oppressive ahead of the front, and southwest IA/southeast NE could again reach heat index criteria near 105. Thus may need another heat advisory south of I80 Sunday afternoon, but will let the night shift take a look with the later model runs. Secondary concern Sunday afternoon and evening will be potentially strong to severe thunderstorms along and south of the frontal boundary. There will a chance of damaging wind gusts, but the potential for heavy precip will also exist with 1-3" of rain still looking possible for southeast NE and southwest IA. While the storms will be moving, PW values will be quite high. 3-hour flash flood guidance values are running 2.25-3.0. WPC has placed much of the region in a slight risk for excessive heavy rainfall, but am optimistic we won`t have widespread flooding problems. Many areas need the rain badly. There may still be a few lingering showers south of I80 Monday, but overall, the heaviest rains by then should be pushing south into KS and MO. Much more comfortable weather expected with highs in the lower to mid 80s. The seasonable and even slightly below normal temps continue through the remainder of the week. Rain chances back into the forecast Wednesday through Saturday. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 620 PM CDT Sat Jul 25 2020 Latest thoughts are that thunderstorms could spread into parts of northeast NE by 11 pm to midnight, and these could possible affect the KOFK TAF by 05Z. Mid level clouds should increase over all of the area and recent runs of the ESRL HRRR 1 km radar reflectivity output seem reasonable, producing scattered precipitation spreading toward KOMA and KLNK 08Z-11Z. Will just include a VCSH group for that now. Mid level clouds are likely to linger much of Sunday, with TSRA developing and becoming more widespread. Tried to keep PROB30 groups into the main times where activity was likely. Could see MVFR or lower ceilings in TSRA and IFR visibilities. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...Heat Advisory until 8 PM CDT this evening for NEZ011-012-015>018- 030>034-042>045-050>053-065>068-078-088>090. IA...Heat Advisory until 8 PM CDT this evening for IAZ043-055-056-069- 079-080-090-091. && $$ DISCUSSION...DeWald AVIATION...Miller
Area Forecast Discussion
National Weather Service Phoenix AZ
450 PM MST Sat Jul 25 2020 .UPDATE... Updated Aviation && .SYNOPSIS... Chances for showers and thunderstorms will generally favor the higher terrain north and east of Phoenix this weekend. Southwestern Arizona and southeastern California will remain dry as the moisture remains farther east. High pressure will build across Arizona next week, resulting in a return to above normal temperatures and below normal precipitation chances. && .DISCUSSION... Latest water vapor imagery reveals a well-defined PVD across Sonora, with deeper moisture displaced north and east of the vort max across eastern Arizona. Further west, another closed low is evident across California. Ahead of this system, relatively dry Pacific air is being transported into southern California and western Arizona. Latest ACARS soundings confirm the drying around 850 mb, which is beginning to make its way to the surface across the lower deserts. Meanwhile, further aloft at 700 mb, the latest RAP streamline analysis depicts a weak anticyclonic flow, resulting in light north and northwesterly winds from Maricopa County eastward. General consensus amongst the HREF CAMs is that the best chance for showers and thunderstorms this afternoon will remain confined to the higher terrain of southern Gila County in the vicinity of the deeper moisture, and along the moisture gradient across northeastern Maricopa County. Main concern for today will be slow-moving cells that have the potential to produce heavy rain and perhaps even isolated flash flooding near the burn scars. With the aforementioned northerly component to the flow, storm motion will generally be southward towards the foothills and lower deserts. CAPE may be high enough for isolated storms to survive into the foothills, however the environment remains unfavorable for convection in the lower deserts with the warm layer near 450 mb yielding weak mid-level lapse rates. Even the most aggressive CAMs indicate little potential for outflows to reach the Valley and consequently PoPs remain below 5 percent for the Phoenix area. && .PREVIOUS DISCUSSION... The forecast for tomorrow looks conceptually similar to today but with slightly lower PoPs over the higher terrain and just minuscule chances for the lower desert as drier air continues to overtake more of the region. Guidance trends consistently support this evolution, but as always the case with convection, the outcomes from the previous day`s events can change the forecast from day-to-day. Drier conditions will eventually solidify by early next week confining most thunderstorm activity over the higher terrain well east of Phoenix, and over southeastern Arizona. The GEFS and EPS are both in pretty good agreement with the subtropical ridge re-centering over Arizona, which is not the most ideal location for monsoon rains. Given this, most ensemble members from both sets of guidance are very bearish regarding rain chances in Phoenix and most everywhere else in the forecast area beyond this weekend. If the guidance is off, and the ridge positions closer to the Four Corners area instead, we might be able to realize a more favorable monsoonal pattern. Another wrinkle to consider is the potential implications from Tropical Storm Hanna but confidence in any particular development is very low at this time. Otherwise, drier conditions combined with increasing atmospheric thickness underneath the ridge will support a warming trend. Forecast highs will approach 110 degrees Sunday/Monday, and remain in the 108-113 degree range for much of next week. As of now, no heat watches or warnings are planned but the increased heat risk will require monitoring. && .AVIATION...Updated at 2350Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: With SHRA/TS remaining well east of Phoenix through Sunday evening, identifying wind shifts will be the primary forecasting challenge. Storm outflows should be far less defined this evening versus previous days, and chances of distinct wind shifts are only remote. A wind shift to the traditional overnight easterly may be more delayed than usual, and a switch at KPHX may not occur until after sunrise Sunday, if at all. Otherwise, light westerly winds will settle over the region by early afternoon with a somewhat better chance of a more organized easterly outflow boundary later Sunday evening. Southeast California/Southwest Arizona including KIPL and KBLH: No substantial aviation issues will exist through Sunday night under clear skies. Trends in wind shifts will be similar to the past several days with directions oscillating between SE and SW, and in many cases variable for extended periods. && .FIRE WEATHER... Tuesday through Saturday: High pressure will build across Arizona, resulting in a return to above normal temperatures and below normal precipitation chances. Nevertheless, moisture will be sufficient for at least isolated storms each day, particularly across the higher terrain north and east of Phoenix. Min RHs will generally fall into the teens each afternoon. Meanwhile, winds will be light and diurnal each day, except in the vicinity of with thunderstorms. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Hirsch PREVIOUS DISCUSSION...Deems AVIATION...MO FIRE WEATHER...Hirsch