Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
921 FXUS63 KFSD 041706 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1206 PM CDT Tue Jun 4 2024 .KEY MESSAGES... - Scattered showers & a few thunderstorms move across southeast SD this morning, with coverage of showers/storms increasing near and east of I-29 this afternoon. A few strong to severe storms are possible in northwest Iowa/southwest Minnesota. - Windy midweek, especially Wednesday as northwest winds may be briefly enhanced by scattered sprinkles. Lighter winds are expected Friday into the weekend, though afternoons may still be on the breezy side. - Precipitation chances Friday into early next week are low (at or below 30%). Neither severe weather nor heavy rain are expected. && .DISCUSSION... Issued at 317 AM CDT Tue Jun 4 2024 TODAY: Elongated area of showers and a few embedded thunderstorms pushing across our western counties early this morning, aided by low level jet/warm advection ahead of an approaching mid-upper level trough. Coverage of this activity may briefly wane near to shortly after daybreak as these features weaken, but anticipate increasing coverage again by mid-late morning as lead wave rotating through the base of the trough slides across the area. Limited instability prior to 18Z so would expect mainly an increase in showers with embedded non-severe thunderstorms. As the associated cold front approaches the I-29 corridor around 18Z, it will encounter an increasingly unstable air mass. Aided by moderate heating into the mid-upper 70s and dew points climbing into the mid to perhaps upper 60s, should see MLCAPE values up to 1500- 2000J/kg with an eroding cap allowing for rapid storm development. As we often see with cold frontal passages, instability is maximized ahead of the front, while favorable deep layer shear is displaced near/behind the boundary. The weak shear (generally <30kt) in place where instability is greater will likely lead to pulsy multicell activity capable of isolated quarter to half dollar size hail from the stronger cores. May also see isolated 50-60 mph wind gusts with collapsing cores as a secondary threat. While rainfall rates may be briefly heavy within a narrow corridor of precipitable water values near or above 1.5 inches, progressive storm movement should limit total rainfall amounts. However, still have to monitor for ponding water and additional rises on area rivers/streams, some of which are still holding near to above flood stage. TUESDAY NIGHT-WEDNESDAY: Upper trough and associated cold front push east of the forecast area by 05/00Z or shortly thereafter, leading to a comfortable night with light winds, clearing skies, and cooler temps as strong drying behind the cold front drops dew points into the 40s. Wednesday will see a trailing wave slide southeast through the region, along with a secondary cold front in the late morning and afternoon. Limited moisture should preclude measurable rain chances, but cannot rule out a few sprinkles. Main impact will be the potential for mixing stronger wind to the surface. In general, the cold advection will support gusts approaching advisory levels, mainly near/north of I-90. However, deeper post-frontal mixing may tap into 40-45+kt atop the mixed layer per forecast soundings, which could lead to isolated 50+ mph gusts, especially if sprinkles do materialize. Mixing of the westerly flow ahead of the boundary will allow for temperatures warming into mid 70s to lower 80s, though highs may be reached earlier than the typical diurnal timing with readings leveling off or falling back a bit during the mid-late afternoon. THURSDAY-MONDAY: Upper low digs into the Great Lakes through the latter part of this week while a modest ridge builds across the Rockies. This will maintain primarily dry northwest flow across our forecast area. Could see a few showers or storms with a subtle wave late Friday-Friday night, though moisture is sparse, so any rainfall would be light. Models diverge on the evolution of the upper low from Sunday onward, so confidence in temperatures and rain chances early next week is on the lower side. Could see scattered showers or storms by Monday if the upper low lags back across the western Great Lakes, but these chances would be lower if the upper low weakens and slides off to the east more quickly. Temperatures through Saturday should be close to seasonal normals. More uncertainty by early next week, again dependent on whether the upper low lingers in the west (cooler air for the northern Plains) or slides off to the east (seasonable temperatures are more favored). && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1202 PM CDT Tue Jun 4 2024 A progressive frontal boundary will slide eastward through the Tri-State area this afternoon. Ahead of the front, scattered showers and thunderstorms are likely to develop. A few strong storms are possible, mostly east of I-29. Brief periods of MVFR conditions are possible in convection. Skies will clear overnight as winds settle. Towards daybreak, scattered mid-lvl cloud field will arrive and could bring virga or scattered sprinkles to areas along and north of I-90. A front will then arrive in the afternoon, turning winds to the northwest and becoming rather gusty. Periods of 40 mph winds are possible through the afternoon. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...JH AVIATION...Dux