Area Forecast Discussion
Issued by NWS Aberdeen, SD
Issued by NWS Aberdeen, SD
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095 FXUS63 KABR 200532 AAA AFDABR Area Forecast Discussion...UPDATED National Weather Service Aberdeen SD 1232 AM CDT Mon May 20 2024 .KEY MESSAGES... - Showers and thunderstorms are forecast to move over central and north central South Dakota late this afternoon through late this evening (30-65%), with a slight risk (2/5) of severe weather attached to them. The main threats include 1.00-1.50in hail and wind gusts to 60-70mph. A marginal risk (1/5) extends off into northeast South Dakota and west central Minnesota. - An active pattern continues next week with additional rounds of showers and thunderstorms for Tuesday-Friday. Near to slightly below normal temperatures are expected Tuesday-Friday as well. && .UPDATE... Issued at 1221 AM CDT Mon May 20 2024 Updated forecast for the 06Z TAFs below UPDATE Issued at 620 PM CDT Sun May 19 2024 Storms are ongoing mainly west of the Missouri River shortly after 23Z, in a favorable environment for large hail and strong winds. A line of additional storms will move into this same area from western SD in the next couple of hours. Expect additional storms to develop this evening and spread east, weakening as they near eastern SD into a less favorable environment. && .SHORT TERM /THIS EVENING THROUGH MONDAY NIGHT/... Issued at 210 PM CDT Sun May 19 2024 At 2 PM CDT, under a mix of sun and clouds, temperatures were noted warming into the 70s to low 80s throughout and west of the Missouri River valley, while mainly cloudy skies today have resulted in a slower warm up throughout and east of the James River valley where readings have only warmed into the 60s to low 70s. Southeast winds of 15 to 30 mph with gusts to 45 mph across western and central South Dakota is helping to draw moisture rich air up into the region (surface dewpoints increasing into the low to mid 50s over said area; +9C to +11C dewpoint air progged at 0.5km and 850hpa). These stronger southeast winds have yet to materialize out over the northeast corner of South Dakota and west central Minnesota. The set-up for late afternoon through late evening convection remains in place and, for the most part, relatively unchanged. The inverted surface trof/deepening surface low in the lee of the Black Hills in response to both daytime heating and the shortwave noted in water vapor moving over western South Dakota should provide the needed forcing and lift for convection. There is also a 90+knot upper level jet max in play over the region to lend support to strong convection potential. The instability component (higher octane air in the form of 50`s dewpoints) is in place as well. With deep layer shear of 40 to 50+knots and CAPE in exceedance of 1000J/kg, still thinking storm mode should come around to supercellular, with large hail and damaging winds the primary threat. Not sure the RAP13 is treating the boundary layer correctly. It is progging an increase in low level (0-1km) CAPE at Bowdle, SD this evening from <5J/kg at 00Z to ~110J/kg at 02Z, while increasing 0-1km shear from <10knots to ~20-25knots. This is also a position east or northeast of a surface low forecast to be in the vicinity. Perhaps the increase in low level shear is conflated by developing low level jet winds at 02Z. Could there end up being a localized and small time window risk area for tornado? Perhaps, but the pickens is awfully slim. Much higher threat potential exists for large hail/damaging straightline winds. With a general removal from needed unstable air the further east convection goes tonight, CAM guidance is still suggesting convection could eventually evolve into some sort of line or line segments that race off to the east into MN, decreasing in intensity as it does so. Most of Monday should be dry, but as the next upper low begins to take aim on the central plains, expecting rain chances to ramp up by Monday evening, as deformation-zone forcing starts to take hold of Nebraska and portions of South Dakota. The southwestern portion of the CWA (the area of central and south central South Dakota basically south of U.S. Highway 212) appears to be in a position to receive a goodly amount of deformation-supportive rainfall. This is noted in some of the ensemble-based 12 and 24 hour probabilities of 0.50in and 1.00in rainfall, respectively. Temp-wise, low level thermal progs and the ensemble-based 850hpa standardized anomalies tables indicate that the next 36 to 48 hours should hold temperatures generally near normal for this time of year. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Issued at 210 PM CDT Sun May 19 2024 The period will start of wet, windy and cool...essentially a continuation of the active pattern that`s been in place across the Northern Plains for several days and weeks. Lead s/w activity will kick off some showers, perhaps a thunderstorm or two Tuesday morning. This will be out ahead of the main upper trough that is progged to shift northeast out of the Central Plains into the Upper Midwest later Tuesday afternoon into Tuesday night. This system will aid in developing a Colorado sfc low that guidance progs to track northeast out of the Central Plains toward western IA during the daytime Tuesday before heading toward southern MN and western WI Tuesday night into early Wednesday. This system is going to spread a swath of precipitation northward across our forecast area on Tuesday. As our area will remain on the northwest side of the low pressure system, this will largely be a deformation zone or TROWAL type rainfall event...some of which is going to provide a decent dose of rainfall to parts of our CWA. The latest QPF forecast ranges still remain consistent from the previous fcst package in that they show mainly very little if nothing for rainfall across north central SD to more than 2 inches of potential rainfall for parts of northeast SD and west central MN. NBM ProbQPF values of reaching or exceeding 1 inch in 24 hrs ending at 1AM CDT Wednesday has highest values across those eastern zones of ours. Essentially from the James Valley east into west central MN has a 50 percent chance or greater of receiving an inch of rain. Highest probs are in the Watertown area with chances at 70-75 percent. Confidence if modestly high at this point that our eastern zones are in line for the greatest rainfall from this event. Backing this up is EC`s EFI output indicating a value of 0.8-0.9 across east central SD and and the Shift of Tails value of 1-2 across northeast SD and west central MN. This is basically telling us information about how extreme an event this potentially be in terms of rainfall and these values indicate that rainfall could be a high end event for those sections of our forecast area. It will be interesting to see if trends in these outputs chance over the next 24 hrs. This system will wind down toward Wednesday morning. Weak sfc high pressure will take over briefly giving us a break from the rainfall Wednesday into a portion of Thursday, although a follow-on upper trough working in behind the first, more robust one could maintain some shower activity to parts of the area on Wednesday. The next system is progged by guidance to shift out of the PacNW into the Northern High Plains and Northern Plains later Thursday through Friday. This will be our next good shot at more precip for our CWA. At this point in time, that system is progged to move out and leave us with a more drier conditions late in the period. Temperatures through the period will again maintain seasonal normals at times to slightly below normal values at other times between Tuesday-Sunday. The presence of clouds and rainfall will largely drive the days we see below normal temperatures. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1221 AM CDT Mon May 20 2024 Terminals KABR,KATY,KPIR,KMBG VFR conditions expected through the TAF period at all sites, besides KATY where MVFR cigs are forecasted between 10-18Z today. For KMBG/KPIR winds will be out of the northwest/north with gusts between 15-20kts this afternoon. Rain showers possible again this afternoon over south central SD and spreading northeastward through the evening with chances increasing overnight. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...MMM SHORT TERM...Dorn LONG TERM...Vipond AVIATION...MMM