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
42
43
44
45
891 FXUS63 KIWX 191544 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 1144 AM EDT Thu Sep 19 2024 .KEY MESSAGES... - Remaining unseasonably warm (upper-80s) through at least Saturday. - Much needed rain enters the forecast as early as Friday for some (20-30% chance). - Not as warm next week with highs in the mid-70s. && .DISCUSSION... Issued at 343 AM EDT Thu Sep 19 2024 The primary forecast challenge is anticipating when the first raindrops will actually fall as this stagnant weather pattern comes to an end in the coming days. But first, dry once again today with any fog mixing out as the morning progresses. Fog is once again aided by a marine layer pushing in from Lake Erie. High cirrus this morning has had little impact on fog thus far, as fog continues to spread west through northwest Ohio. High pressure will remain in place over the eastern Great Lakes while a cold front, currently over central Nebraska, approaches the Mississippi River through the day. High resolution guidance is raising some concern for isolated severe storms Friday afternoon, which is somewhat curious but also within the realm of possibility. The parent low occludes over the Canadian Prairie which results in sheared-out forcing aloft locally by Friday. Moisture return is weak and generally shallow on Friday due to a strong ridge over Mexico extending through Oklahoma, along with high pressure to our east steering Atlantic moisture south of the Ohio River valley. Despite this, dew points in the low-60s are noted early this morning over far western Iowa and are forecast to advect east to our area by Friday. Forecast soundings otherwise depict adequate but not- uniform moisture through the column. No wonder, then, that box and whisker plots depict paltry rain amounts (if any) in Michiana Friday afternoon. With these miss-matched ingredients, I am skeptical of the high resolution guidance which might be over- convecting (perhaps due to erroneously high dew points impacting CAPE). Even with a modest adjustments to dew points closer to 60, low- level lapse rates would be adequate (7c/km) as would shear (30 knots). This is overall something to keep an eye on and I`ve increased POPs toward 30% as a result. Remaining warm both Friday and Saturday as 500-mb heights remain elevated along with continued balmy 850-mb temperatures. This ridge breaks down and our persistent eastern Great Lakes high gets kicked east as a trough over the Four Corners and trough over Manitoba buckles the jet stream. The result is some much needed rain in the Sunday through Tuesday time frame. Beyond this, scissors were deployed for POPs Wednesday and Thursday behind a departing low. Tried for a dry forecast Thursday, but some guidance and neighbors preferred the slight chance showers (15% chance). && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 1144 AM EDT Thu Sep 19 2024 VFR through the period. Low level moist axis extending downstream of lake Erie into ern IN yielded another round of dense fog overnight but expected to mix out this aftn and dissipate as flow veers srly into Fri morning. Thus do not expect a repeat of dense fog invof KFWA. Otherwise weak frontal zone will push across the terminals late Fri aftn with an uptick in mid lvl based cloud cover expected. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ DISCUSSION...Brown AVIATION...T