Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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
790 FXUS63 KIWX 051850 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 250 PM EDT Sun May 5 2024 .KEY MESSAGES... - Primarily dry conditions will persist through Monday night but there is a low chance of rain south of US-30 late Monday. - Several rounds of thunderstorms are possible Tuesday through Wednesday night. Some of these storms may be capable of producing large hail and damaging winds. However, confidence in timing, placement, and strength remains low. - Cooler weather returns to end the week with periodic additional chances for light rain. && .DISCUSSION... Issued at 250 PM EDT Sun May 5 2024 Dry/tranquil weather will persist through Mon morning. Weak/diffuse cold front has largely cleared our area with stubborn postfrontal stratus deck holding in our northern counties. Can`t entirely rule out a sprinkle in our far E/SE but best chances remain outside of our area. Overnight cloud forecast is tricky with most guidance suggesting clearing by sunset. However, models have struggled with this cloud cover over the past 12 hours and confidence is not high. Will therefore hold with partly cloudy skies and lows generally around 50F. Cooler temps possible if clouds scatter entirely. Broad midlevel shortwave will lift into the Ohio Valley tomorrow but sharp midlevel ridging/AVA will maintain strong subsidence over the Great Lakes. Still some uncertainty exactly how far north showers survive tomorrow. General trend has been to keep precip just to our south given weak 850mb theta-e advection in our area. There are a few outliers though that suggest light showers sneaking to about the US-30 corridor. Have therefore stayed very close to inherited low PoP`s confined to our south. No impacts expected either way as profiles appear too stable to support thunder and any rain will be very light. Primary focus continues to be on Tue-Wed for potential severe weather and heavy rain concerns as deep western CONUS upper low lifts NE toward the Great Lakes. This will actually occur in piecemeal fashion as another strong Pacific jet/trough comes onshore Monday and forces the development of a very large upper low over the Northern Plains/Rockies that will also eject eastward in a piecemeal fashion later this week. Unsurprisingly models are struggling with exact details in this complicated pattern and confidence remains on the low side. Still expect the initial wave and associated warm front to lift through the area late morning-early afternoon Tue. Models have slowed this initial wave a bit which complicates the severe weather forecast. A later arrival could result in that being the primary "show" (which could itself feature large hail and damaging winds given steep midlevel lapse rates, moderate instability of 2000 J/kg SBCAPE, and a strongly sheared environment). Early arrival could limit the instability but if the slower trends continue that will increase the risk with round 1. If that is the case that will in turn limit our potential for a second round during the evening hours though with primary focus for severe storms well to our south. After a break Tue night into early Wed we will watch the potential for another round of storms Wed evening-overnight as the primary upper low finally releases east. All ingredients for severe weather and flooding remain favorable given ample moisture advection on strong LLJ, high instability, and very strong shear. The question for Wed will be where exactly these ingredients come together with track of surface low dependent on exact evolution of upper low and likely some mesoscale influences from the day before. It is possible the surface low and associated highest severe risks remain to our south as suggested by the 12Z deterministic GFS and reflected in the SWODY4. However several models suggest a further north track that would impact our CWA. Bottomline...the ingredients are in place for potentially several rounds of strong/severe storms but details regarding exact timing, placement, and strength remain low. Continue to monitor the forecast closely as we narrow down these details in the coming days. Negative height anomalies persist over eastern Canada for much of the Thu-Sat period. This will result in cooler temps with periodic chances for light rain. Better moisture and associated instability is shunted out of our region though. Chances for generic thunderstorms (let alone strong storms) appear very low. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 133 PM EDT Sun May 5 2024 Surface high pressure moving through today provides a reprieve from the rainfall for this TAF period. It moves in on the heels of an area of cold air advection that brought clouds to the area last night into this morning. This afternoon started with MVFR and IFR CIGs around, but they are expected to rise with the diurnal curve not too long into this TAF period. West winds today become more easterly overnight with the high pressure system to our north, and that is expected to provide more cloud cover into Monday. There is still quite a bit of variance in model output of CIG heights, but with the NBM having 30 to 40 percent chance of less than 3 kft CIGs will put a tempo group in there to indicate the possibility. Future shifts will want to continue to investigate this possibility further. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ DISCUSSION...AGD AVIATION...Roller