Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/01/19

Area Forecast Discussion
National Weather Service Des Moines IA
858 PM CDT Mon Sep 30 2019 .UPDATE... Issued at 858 PM CDT Mon Sep 30 2019 Forecast on track with rapid expansion of storms over Nebraska in ribbon of strengthening H850 low level jet and weak height falls suggesting first wave rippling northeast into KS/NE/MO now. Incredibly anomalous H850 moisture continues to funnel north into Iowa with H850 dew points of 15 to 17C continuing to be advected our way. Have continued FFA over same locations with recent update at 842 pm. PWATs continue to be forecast to 2 to 2.35 inches by 18 to 00z over the region Tuesday into Tuesday evening. This combined with warm cloud depths of 4 to 4.5km (12kft to 14kft) will yield very efficient rainfall processes. Added some wording to the FFA to include potential to affect traffic flow/speed and generally poor travel conditions during morning/afternoon commutes in bands or areas of heavy rainfall. Main wave still expected to arrive late tomorrow and tomorrow night which will bring the more widespread heavy rainfall to the region. /rev && .DISCUSSION.../Tonight through Monday/ Issued at 354 PM CDT Mon Sep 30 2019 The primary concern today remains significant convective trends overnight through Tuesday Night with heavy rains and at least some flooding likely. There is also an increasing severe weather potential southeast half late Tuesday, which is a change from recent runs. Secondary concerns also include low confidence frost potential north Thu Night north with below normal temperatures to end the week. Initially this afternoon Iowa is well into the warm sector with warm, humid conditions in brisk SSW winds. MLCAPEs are 1500-2500 j/kg but with little convergence or baroclinicity, and only small, minor CINH erosion along the approaching cold front in the Siouxland area, there will not likely be much development until the late evening hours. Water vapor imagery does not show much at the moment, but most models suggest QG forcing will overspread the Siouxland area by midnight aided by 850/700mb frontogenesis along and just behind the front. MUCAPEs will stay around 1500 j/kg, but with little effective shear the severe potential will be minimal. Heavy rains and flooding will be the primary threat. It would be difficult to produce a better environment in these regards with daily climatological record specific humidities and precipitable waters suggested by both recent EC ensemble and NAEFS runs, which would be atypical anytime of year. Compounding the concern will be the slow moving frontal boundary with mean winds parallel to the front suggesting training, and a steady fetch of strong, deep moisture transport. The 305K isent surface near the effective inflow base notes little baroclinicity, but a steady stream of 30-40kts of flow above the lower level frontal convergence with consistent trajectories from the Rio Grande Valley and TX tonight through Tue Night. Although not uniform across the entire forecast area due to the nature of convection, many locations may see one to three inch rainfall totals by early Wednesday with locally higher amounts expected. The HRW ARW run this morning suggests isolated max amounts may reach five to six inches with similar suggestions from the 12z HREF Local Probability Matched Mean somewhere across west central over northern Iowa. The severe potential cannot be overlooked southeast Tue afternoon and evening as well with those locations still in the warm sector and the long wave trough progression eventually increasing deep shear south and east of the frontal boundary, unlike expectations for this evening. This could result in supercells with recent HRRR and 4km NAM guidance suggesting that as well with enhanced updraft helicity tracks through central IA. There is not much backing ahead of the front, which may keep the low level shear, SRH and tornado threat down somewhat, but if a potent cell can track near the front a tornado is certainly not out of the question in a very locally enhanced near storm environment. LCLs should be quite low too. The front and heavy rain potential should be relegated to the IA/MO border Wed, but one recent model change has been a trend toward stronger forcing associated with long wave trough passage at this time. This has resulted in stronger synoptic lift and higher PoPs lingering longer into Wed with a stronger surface reflection now very briefly bringing the warm sector back into southeast IA. This may result in another burst of heavy rains for those locations late Wed before cooler, drier conditions are in place to end the work week. Strong subsidence should be in place Thursday with the attention turning toward frost potential Thursday Night as surface high pressure settles into the area. Favorable items for frost will be light winds and clear skies, but surface temps only dip into the upper 30s with dewpoints similar or only a few degrees below. Obviously decent uncertainty at this time range, but the low level moisture may be too high for vegetation temps to dip sufficiently resulting in a cold dew or fog rather than frost. Something to continue monitoring however. The next precip window appears to be around Saturday with deterministic and ensemble solutions in better agreement with mass fields and timing. This results in showers likely, and possibly a rumble of thunder, but overall return flow will not be sufficient for instability or severe potential. The depth and strength of the phased thermodynamic and kinematic forcing may still be sufficient for a short period of moderate rainfall however. After this, dry conditions and continued below normal temperatures are anticipated with fairly good model agreement for this time range with surface high pressure behind the passage of the long wave trough. && .AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/ Issued at 641 PM CDT Mon Sep 30 2019 Convection expected mainly northwest of area through 06z, then shra or VCTS working south and increasing in coverage through 12z north sites KFOD, KMCW, and KALO. Cigs will drop from VFR to MVFR between 08-12z north sites then further drop to IFR aft 12z over the same above sites. South site KOTM will remain VFR through entire period while KDSM expected to drop to mix of MVFR/VFR from 13z through end of period. Thunder risk again increases over most of area aft 12z with periods rain and sct thunder north sites...while KDSM more sct thunder. Heavy rain/lower vsby expected as well during period. Timing of worst conditions will need some adjustments through end of forecast aft 12z. /rev && .HYDROLOGY... Issued at 354 PM CDT Mon Sep 30 2019 Most models suggest conditions and forcing will be optimized Tue and/or Tue Night for the best heavy rain/flooding potential rather than overnight tonight so have expanded the Flash Flood Watch farther south and east to increase the likelihood of capturing heavy rains, and also better antecedent soil conditions south where recent heavy rains have fallen. Preliminary RFC river forecasts, based on 72 hours of QPF from the 12z forecast cycle, have resulted in specific River Flood Watches for minor flooding being issued for several locations in the Cedar, Des Moines and Raccoon River basins. Confidence in these river forecasts is low to medium however due to the extended range of forecast rainfall, and difficulty of pinning down the magnitude and locations of what can be very localized heavy rainfall maximums. Within bank rises and moderate flooding are still within the realm of possibility. && .DMX WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch from 7 AM CDT Tuesday through Wednesday morning for IAZ027-028-038-039-049-050-060-061-072>074-082>084- 093>095. Flash Flood Watch through Wednesday morning for IAZ004>007- 015>017-023>026-033>037-044>048-057>059-070-071-081-092. && $$ UPDATE...REV DISCUSSION...Small AVIATION...REV HYDROLOGY...Small
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
845 PM CDT Mon Sep 30 2019 .UPDATE... Updated for evening discussion. && .DISCUSSION... Another warmer than normal night can be expected with clear skies and lows near or at 70 degrees area wide. A few patches of ground fog is possible in the early morning for areas in the southeast. No major changes were made to the forecast./JNE/ Prior discussion below: Tonight and Tuesday: a persistence forecast with dry weather and record afternoon temperatures are expected again Tuesday. Mid afternoon satellite imagery and RAP analysis showed very suppressed cumulus clouds beneath a large 595dam high centered over northern Mississippi. Mid afternoon surface analysis had an >1018mb ridge nosing into our CWA from the northeast. These features will change little through Tuesday. Temperatures this afternoon were climbing into the mid 90s and are set to top out in the mid to upper 90s. This will tie and set new record highs at a few locations. Temperatures will top out in the mid to upper 90s again Tuesday. The sites at greatest risk of setting record highs Tuesday include Greenville, Greenwood, Vicksburg and Meridian. Tonight will be similar to the last few nights with mostly clear skies and a near calm winds with low in the upper 60s to lower 70s. Patchy light fog development will be possible in the south along the Highway 84 corridor but dense fog is not currently anticipated. /22/ Tuesday night through Thursday night...Strong high pressure at the surface and aloft will continue on Tuesday night into Wednesday, with lows falling into the lows 70s. The upper ridge will keep its grip over the region on Wednesday, with highs climbing into the mid/upper 90s once again. The ridge will weaken over the region on Thursday, out ahead of a cold front that will move into north Mississippi Thursday evening. The front will continue to move south across the area Thursday night into Friday, ushering in a drier airmass and slightly cooler temperatures. Highs on Friday will range from the mid 80s in the north to low 90s in the south. The main concern on Friday will be increasing fire weather conditions, with a combination of breezy winds and min Rh`s falling into the 30 percent range. This will have to be monitored for possible inclusion in the HWO/Graphicasts through the week. Saturday will continue to be dry, but the winds will decrease across the area as the surface gradient weakens. Rh`s will fall into the upper 20 to lower 30 percent range though, so will have to monitor for fire weather concerns once again on Saturday. The surface flow will swing back around to the south on Sunday and with afternoon heating, there will be a chance for isolated thunderstorms. All of the global models are in pretty good agreement of a stronger cold front moving across the area Monday or Monday night, although the models do not agree on the strength or the amount of precip associated with the boundary. Either way it does look like cooler and more seasonable weather will be on tap for next week./15/ && .AVIATION... 00Z TAF discussion: VFR conditions and light wind will prevail through the forecast period, but an expection is the potential for IFR/LIFR early morning fog in the HBG/PIB area given the persistent weather pattern. /EC/ && .PRELIMINARY POINT TEMPS/POPS... Jackson 69 96 72 96 / 0 0 0 1 Meridian 69 97 71 97 / 0 0 0 1 Vicksburg 69 97 72 97 / 0 0 0 1 Hattiesburg 68 95 71 94 / 0 2 0 2 Natchez 69 94 71 95 / 0 0 0 1 Greenville 69 97 72 97 / 0 0 0 0 Greenwood 70 96 72 96 / 0 0 0 0 && .JAN WATCHES/WARNINGS/ADVISORIES... MS...None. LA...None. AR...None. && $$ JNE
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
342 PM CDT Mon Sep 30 2019 .SHORT TERM...(This evening through Tuesday night) Issued at 338 PM CDT Mon Sep 30 2019 Main concerns this period are conditional severe weather threat this evening, and the heavy rainfall threat for tomorrow clipping our far south along I-90 (with Iowa, extreme SE MN, and Wisconsin more in the heart of the threat). As of this afternoon, the surface low was centered just west of Alexandria, with the warm front draped east across central MN. Temperatures south of the front have risen into the 80s with dew points commonly in the low 70s. Over 3,000 J/kg of CAPE is present in the warm sector, and hi-res guidance indicates some broken convection developing after 22Z along the approaching cold front which is now approaching the MN border from the Dakotas. The main question is the temperatures aloft, with +12C noted at 700mb based on RAP analysis. This warm air aloft reduces confidence in widespread convection, and explains why pops were limited to the 40- 50% range along the line. There will likely be thunderstorms, but just how widespread they will be is somewhat uncertain and dependent on overcoming the CAP. For storms that do initiate, supercells are possible given 40 knots of effective shear and ample instability. Large hail, damaging wind, and a few tornadoes could occur if storms become surface based, especially near the low/warm front. The cold front will move through our area overnight, cooling temperatures by nearly 30 degrees by morning. The frontal zone then becomes nearly stationary by tomorrow, oriented from Iowa toward northern WI. This will be the focus of additional shower and thunderstorm development through the day tomorrow and tomorrow night, which will likely be a long duration rainfall event for far southern MN. On the north side of the front, instability will be present, but weak. PWATs will remain high, and lapse rates modest at best. So, heavy rain is the primary threat with the severe threat shunted south of the frontal boundary. Could foresee 2-3" of rainfall or isolated higher amounts along I-90 and in collaboration with the Des Moines and La Crosse NWS offices, have issues a Flash Flood Watch for tomorrow and tomorrow night for along I-90 to the east of Fairmont. .LONG TERM...(Wednesday through Monday) Issued at 338 PM CDT Mon Sep 30 2019 The period will commence with an elongated E-W surface front stalled from the Central Plains through the northern Ohio Valley. Widespread rainfall will be ongoing in the vicinity of the front, mainly for southern MN into southwestern WI, where low level convergence and high moisture depth will be concentrated. While a few thunderstorms are possible, the main hazard will be heavy rain. This activity will gradually wane Wednesday night into Thursday as the front finally gets impetus to shift off to the southeast due to incoming modified western Canadian high pressure. This will produce a break from precipitation Thursday night through Friday evening. The main concern will be when the center of high pressure is directly overhead, allowing for clear skies and light winds, and this is expected early Friday morning. With the cold air advection expected into the area behind the departing cold front and with the incoming high pressure, temperatures for central MN will fall to the mid-30s which would be conducive to an early October frost. The next significant frontal system gets its start over MT/WY on Friday then progresses east across the Dakotas Saturday and moves into the Great Lakes on Sunday followed by high pressure once again early next week. This system will be the next rain-maker for the area, with the potential for some rain amounts in the 0.25-0.50" range for next weekend. As for temperatures, today`s one-day jump to summer-like temperatures, highs will drop to the mid 50s to mid 60s on Tuesday behind the front. Modest cold air advection will continue into late week, keeping highs in the low 50s to low 60s while lows generally remain in the mid 30s to upper 40s. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) Issued at 1239 PM CDT Mon Sep 30 2019 Warm front slowly lifting through the area today, with the surface low along the western MN border, moving NNE with time. Winds have turned SSW south of the front, and gusts over 20 knots can be expected to continue through the afternoon. Along and north of the front, plenty of low stratus is in place along with easterly winds. Some cu developed south of the front but should be mainly VFR through the afternoon. As the low lifts into northern MN this evening, the cold front will move west to east across the local area, with a chance for thunderstorms to develop along the front from about 22-03Z this evening. Coverage remains a big question mark with this setup, so continued to opt for VCSH wording in the TAF as confidence is too low at this time to commit to VCTS. KMSP...Thunderstorms are possible late afternoon-evening, but confidence too low to include VCTS at this time due to coverage being uncertain. /OUTLOOK FOR KMSP/ Wed...VFR/MVFR. Chance -RA. Wind NE 5-10 kts. Thu...VFR. Wind NW 5-10 kts. Fri...VFR. Wind SSE 5-10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...Flash Flood Watch from Tuesday morning through Wednesday morning for MNZ085-092-093. && $$ SHORT TERM...SPD LONG TERM...JPC AVIATION...SPD