Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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
44
45
46
47
48
49
50
330 FXUS63 KIND 221906 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 306 PM EDT Sat Jun 22 2024 .KEY MESSAGES... - Some showers and storms overnight into Sunday. Isolated strong to severe storms possible. - Tuesday likely to be warmest day of the week. - More thunderstorms possible Tuesday into Wednesday, with one or more rounds of strong to severe storms possible, though uncertain. - A brief respite from heat and humidity late in the week. && .SHORT TERM (This evening through Sunday)... Issued at 305 PM EDT Sat Jun 22 2024 The persistent mid-upper ridge is dampening quickly, but since we`re on the northwest side with enhanced southwesterly flow, 2-m temperatures are hot this afternoon (~+7 degree anomalies for mid- late June). With an upstream shortwave trough, the MSLP pattern has shifted and is providing a stronger breeze. This has kept wet bulb globe temperatures in the moderate category. As the aforementioned shortwave trough approaches, it will nudge a stationary front southward resulting in a diurnal blow-up of convection concentrated over Iowa. This is modeled to grow upscale and propagate into Illinois this evening. Despite it being on the southern periphery of stronger westerlies aloft, modest low-level jet will encourage east-southeastward propagation into Indiana late tonight. Although we will be approaching a diurnal minimum, a band of richer moisture through a deep layer will contribute to modest instability late into the night. This should support continued east- southeastward movement through our area during the morning, albeit in a weakened state. Intensity trends should mean only a low probability of strong to locally damaging winds across our northwest counties later tonight. The temperature forecast tomorrow has a higher degree of uncertainty than usual due to a substantial model spread (up to around 10 degrees of spread). This appears to be due to 1. remnant clouds from convection early and/or remnant PBL moisture, 2. over mixing and warm bias in ECMWF. We nudged lower to avoid the ECMWF, and generally near the mean of most other model guidance. Gradual infiltration of drier air mass and convergence displaced to the south by peak surface heating should preclude additional convection, once morning remnants moves out. && .LONG TERM (Sunday night through Saturday)... Issued at 305 PM EDT Sat Jun 22 2024 Continued warmth is expected throughout much of the long term forecast, with at least one day of widespread 90s expected Tuesday. The saving grace will be that some relief from the recent stifling humidity is expected on Monday, with slightly more sustained lower dewpoints late in the week. Additionally, a couple of opportunities for thunderstorms are expected, with some potential for organized severe thunderstorms late Tuesday into Wednesday, though uncertainty remains significant given guidance discrepancies and daily dependencies of convection on the influences of prior days` activity. The work week will begin with some slightly lower heat and humidity, and dry weather under the influence of surface high pressure. As we move into Tuesday and Wednesday, convection is likely to develop to our northwest along the tail end of a boundary extending from low pressure well to then north in a background environment of ample deep layer shear and strong to extreme instability within a prefrontal theta-e axis. This activity is likely to rapidly grow upscale into one or more QLCSs, then move steadily along the instability gradient late Tuesday into Wednesday. This is not unlike the traditional "ridge rider" scenario we often see around this time of year into the depth of the warm season, though there will be some contribution from frontal forcing as the boundary sags further south as well. However, if severe storms are to occur in central Indiana, it will be most likely be cold pool driven given far weaker deep layer shear this far south, with damaging winds the primary threat. Diurnal timing is not ideal, though late night severe is frequently seen this time of year via the aforementioned thermodynamically- driven scenarios. Additionally, reintensification or redevelopment of strong to severe storms will be possible Wednesday along the front or boundaries from prior convection, though degree of destabilization is more in question given the impacts of this prior activity on insolation and low level moisture advection. Overall, Tuesday into Wednesday will merit close monitoring for one or two windows of severe threat, primarily due to damaging wind potential, along with some heavy rain/localized flooding threat given fairly significant precipitable water values. Experimental machine learning guidance continues to support this potential. The latter portion of the work week will offer some relief in the form of quiet weather, slightly lower temps, and significantly lower dewpoints as high pressure traverses the region, though this may be short-lived as guidance indicates potential for the southwestern ridge to push back eastward and additional convective potential along the periphery as we get into next weekend, though model differences are significant with respect to ridge amplitude and location, and thus relatively low chances are forecast for the moment. Tuesday appears likely to be the hottest day of the week, though guidance clustering, as well as recent and longer-term NBM biases suggest the blend highs are a few degrees too warm. These were adjusted accordingly. Additionally, multiple potential influences from low level moisture, mixing potential, and convective influences present several ways that may impact ability to reach the hotter NBM numbers. The remainder of the week looks to see temps near to slightly above normal for the time of year. && .AVIATION (18Z TAF Issuance)... Issued at 107 PM EDT Sat Jun 22 2024 Impacts: - Wind gusts subside this evening - Showers and low probability of thunder late tonight - Brief MVFR stratus Sunday morning Discussion: As mixing decreases this evening, gusts are expected to end. Mid level cloud cover will slowly increase, but VFR conditions will prevail. Weakening convection will move east-southeast across Indiana later tonight, with some thunder possible, especially at KLAF. Otherwise rain showers may impact TAF sites in the time window indicated. Timing is fairly high confidence at this time. A band of stratus within the MVFR category is possible behind the convection during the morning, but confidence is low-moderate. Wind gusts will return with winds more west-northwesterly midday tomorrow. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ SHORT TERM...BRB LONG TERM...Nield AVIATION...BRB