Area Forecast Discussion
Issued by NWS Aberdeen, SD
Issued by NWS Aberdeen, SD
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928 FXUS63 KABR 020022 AAA AFDABR Area Forecast Discussion...UPDATED National Weather Service Aberdeen SD 722 PM CDT Wed May 1 2024 .KEY MESSAGES... - Rain showers over mainly south central SD will expand across the rest of central to northeastern SD this evening, before diminishing west to east Thursday. Rain totals through Thursday will range from a 0.05 to near 0.5"(highest over north central SD). - Active pattern continues in the extended period, with at least two systems affecting the region. The first (Friday afternoon and night) will quickly move through the southeast half of SD and bring generally light rainfall (0.1" or less). The next system will be larger and prolonged, lasting from Sunday night and potentially into Tuesday. Rainfall amounts may exceed 0.5" during that event (50% chance) and there may be a few thunderstorms on Monday (20% chance). - Near to below normal temperatures Friday and Saturday, warming to above normal Sunday and Monday. && .UPDATE... Issued at 713 PM CDT Wed May 1 2024 See below for an aviation forecast discussion for the 00Z TAFs. && .SHORT TERM /THIS EVENING THROUGH THURSDAY NIGHT/... Issued at 203 PM CDT Wed May 1 2024 The weather map early this afternoon shows the surface ridge that had dominated our area this morning shifting into western MN. There is a trough of low pressure extending from the main surface low over southeastern CO to another over western SD. A third low was moving in from Canada/northern MT. Winds out of the south are beginning to take hold across areas east of the MO River. Surface winds will shift out of the southeast tonight as the CO low moves to central KS/OK by 12Z Thursday and northern lows join forces over western ND Thursday morning into the early afternoon hours. Moisture pushing north into the area, and the assistance by embedded waves in the southwesterly flow at 500mb, will help bring a return of showers to mainly central SD. This moisture return is a bit faster than previously expected, with the main focus being across central SD this afternoon. There are 2 main areas of precipitation, over north central SD and our southeastern Counties, with not much in between (on the order of 0.02" through midnight). The trend is for the northern system to become more dominant across our area, with 0.l2-0.5" of rain over Dewey, Corson, and Campbell Counties (highest over western Corson County). Cooler air will remain in place, with 850mb temperatures staying in the single digits above 0C through at least 12Z Friday. A few readings just below 0C will be possible over north central SD right around 12Z Friday. Highs will remain in the mid 50s to low 60s, with lows mainly in the upper 30s to low 40s. Rain shower chances will continue to diminish Thursday afternoon into Thursday night as a cold front drags across the forecast area, extending from the surface low over southern Manitoba/far northeastern ND late Thursday night. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Issued at 203 PM CDT Wed May 1 2024 The start of the long term period (Friday) will continue the trend over the last couple of days, with a brief period of dry weather before another period of showers (Friday night). A surface low centered along the US/Canadian border of ND/MN at the start of the period will gradually lift northeast. Meanwhile, there will be upper jet support across southeast half of SD on Friday night, as a jet streak rounds the base of the upper ridge axis along the MT/ND/SD/WY border. This will also be supported by a nice area of mid-level warm air advection and q-vector convergence. All of these features come together over southeast SD and having rainfall chances of 30-50% to the southeast of Pierre/Aberdeen seems reasonable at this time. In addition, instability is extremely limited (MUCAPE values <100 J/kg), so we don`t expect any thunder at this time. With the best forcing to the southeast of our CWA, precipitation amounts look to be light where rain occurs and between a Trace and maybe 0.10" (only 30% probability of 0.1" from Watertown to Chamberlain). Behind the Friday night precipitation, the upper trough departs to the east on Saturday and high pressure builds over the area. That will quickly lead to the clouds departing and start a rain free weekend. While temps will warm up slightly on Saturday (60s), we`ll see a jump up on Sunday (into the 70s), as the upper ridge axis moves over the area and southeasterly winds increase ahead of the next developing surface low in the lee of the northern Rockies. Will need to keep an eye on wind gusts in central SD on Sunday afternoon, as they could be nearing advisory levels. The previously mentioned developing surface low is tied to a deep upper trough moving into the western CONUS on Saturday night. Ensemble clusters still showing a decent amount of variability on how they`re handling this upper trough as it moves into the northern Plains. This leads to increased uncertainty in the exact details, as it influences both the intensity and how long the upper wave lingers into early next week. Despite that, the main two takeaways are that measurable (0.01") rain chances remain high during this period (60- 80% values) and will continue to see gusty winds into Mon/Tues (NBM probabilities of gusts exceeding 34kts/39mph are 50-95% for both Mon/Tues). As for rainfall amounts, 24 hour probabilities of 0.5" or more are 35-55% for the Monday and Monday night period. Right now, any excessive rainfall amounts don`t seem too likely at this point, with 48hr rainfall probabilities of 1" of rain staying below 25%. That`s likely driven by the limited convection potential, even with the wrapped up low (somewhere in the 980-995mb range), as joint probabilities of sfc CAPE > 500 J/kg and 0-6km Shear > 30kts are between 5-30% depending on the cluster. That being said, there is some MUCAPE (500-1300 J/kg) on the leading phase of low/precip on Monday afternoon. That matches up with the elevated NBM CWASP values/percentiles at that time, although values are around rough Marginal risk values (50-64). Finally, this stronger and wrapped up low is what`s leading to the increased winds for early next week, although wind speed/direction for Tuesday depend on where the surface low is located. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 713 PM CDT Wed May 1 2024 Terminals KABR,KATY,KPIR,KMBG VFR conditions are forecast at KPIR/KABR and KATY through 06Z. KMBG may dip into MVFR conditions prior to 06Z. Between 06Z and 12Z, all four terminals should be down in MVFR or IFR cigs. Periods of rain are expected at all four terminals through 12Z. After 12Z Thursday, rain chances dwindle to just a few hours at KMBG and KABR. VFR visibility may dip to MVFR at times in rain overnight. Conditions are forecast to improve west (KPIR/KMBG back to VFR by 18Z) to east (KABR and KATY by 00Z) on Thursday. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...Dorn SHORT TERM...KF LONG TERM...SRF AVIATION...Dorn