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FXUS63 KIND 021729 AFDIND

Area Forecast Discussion National Weather Service Indianapolis IN 1229 PM EST Sat Dec 2 2023

Key Messages

- Persistent overcast.

- More rain tonight into early Sunday.

- Additional rain chances with lighter amounts Sunday night and early Monday, and again Tuesday.

- Near normal temperatures trending warmer late next week.

Forecast Update
Issued at 945 AM EST Sat Dec 2 2023

Surface analysis this morning shows low pressure over western NY with a trough axis stretching SW across northern OH to Northern Indiana and Central IL. High pressure was found across Quebec and Ontario, spilling southwest into the western Great Lakes and the northern Mississippi River Valley. GOES16 shows extensive cloud cover across the region, with Mostly cloudy skies found across Indiana and the Ohio Valley. Surface Winds were from the west.
Aloft, water vapor showed a trough over the Rockies. Southwest flow ahead of the trough was resulting in a plume of tropical air flowing across eastern TX to Indiana and the Ohio Valley. Radar shows the nearest precipitation upstream of Indiana over Central TX.

Quiet weather is expected to persist today. 850mb surface shows a baroclinic zone across Indiana. This along with tropical plume of moisture aloft should lead to continued cloud cover through much of the day. Within the flow aloft, no forcing appears to arrive today, and forecast soundings and time heights fail to show a deeply saturated column as forcing is not available. Thus a cloudy afternoon is in store. Given the clouds but minimal temperature advection, highs in the upper 40s to lower 50s are expected.

Short Term
(Today and tonight)
Issued at 245 AM EST Sat Dec 2 2023

Subtle low-amplitude ridging within anomalously strong westerlies will help reinforce subsidence inversion and stagnant low-level moisture pattern. Thus, overcast will persist today. Drizzle/mist last night has ended as low-level convergence is shifting east with MSLP low center, and depth of moist layer has decreased. Temperature advection is negligible and with limited diabatic surface heating, nocturnal/diurnal min/max fluctuations will be dampened.
Temperatures will continue to be a few degrees above early December climo today.

Rain will return tonight with deeper synoptic scale ascent attendant to the next in a series of fast-moving shortwave perturbations. Top- down moistening is observed in model forecast soundings through the night and by the pre-dawn hours ascent and moisture will be sufficient for rain.

Long Term
(Sunday through Friday)
Issued at 245 AM EST Sat Dec 2 2023

Isentropic ascent magnitude and depth will peak from the pre-dawn hours Sunday through mid-late morning, before shifting east. Similar to yesterday's system, as the shortwave trough axis crosses, no displacement of residual low level moisture and weakly cyclonic flow will result in at least overcast conditions and perhaps some lingering drizzle/mist. Models that are steepest with low level lapse rates are more aggressive with precipitation signal the latter half of the day.

The next perturbation has displayed a slightly deeper and lower latitude track and passes through Indiana early Monday. Although spatial details are unclear given trends and slight model differences, some light precipitation may be possible somewhere across mainly the southern half of Indiana Monday morning. We have modest probabilities for now, tapering from higher south to lower north. In a reasonable worst case scenario, there appears to be a window for deformation banding north of midlevel closed low circulation that could enhance precipitation rates which may be an important consideration given the marginal thermal profile for rain/snow.

As this system departs, mean riding across the east breaks down and deeper moisture shifts further away. Thus, the next perturbation within trending northwesterly flow looks to produce a comparatively meager precipitation event on Tuesday.

Building central CONUS ridging will shift eastward causing a warming trend late next week into the following weekend. This should be a mostly dry period as stronger westerlies trend toward higher latitudes. At least a portion of Day 8-14 period looks above normal temperature wise with some precipitation chances, in a perturbed/progressive flow pattern.

Aviation
(18Z TAF Issuance)
Issued at 1229 PM EST Sat Dec 2 2023

Impacts:

- Mainly MVFR conditions will be expected.

Discussion:

A warm front will linger across Central Indiana this afternoon and tonight. Abundant lower levels clouds are expected to persist in the area, as seen on GOES16, across the TAF sites and through the region. This will result in continued MVFR Cigs.

Overnight a short wave will approach the TAF sites. This may result in some scattered showers across Central Indiana. Forecast soundings suggest some additional moisture within the column overnight, but they fail to become fully saturated. HRRR suggests best coverage will be found across the NW parts of Indiana, however confidence in timing and areal coverage is not high enough to include a prevailing RA mention. For now have used a large window of VCSH as showers will be possible at that time.

In the wake of the short wave on Sunday, winds are expected to shift to the west and wind gusts of 20-30 knts will be possible.

IND WATCHES/WARNINGS/ADVISORIES
None.

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